Citation
Programmable logic controller applications in electric utility substations

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Title:
Programmable logic controller applications in electric utility substations
Creator:
Moreau, Brian Scott
Publication Date:
Language:
English
Physical Description:
vii, 144 leaves : illustrations ; 29 cm

Subjects

Subjects / Keywords:
Electric controllers -- Programming ( lcsh )
Electric substations ( lcsh )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references.
General Note:
Submitted in partial fulfillment of the requirements for the degree, Master of Science, Department of Electrical Engineering.
Statement of Responsibility:
by Brian Scott Moreau.

Record Information

Source Institution:
|University of Colorado Denver
Holding Location:
|Auraria Library
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
26787595 ( OCLC )
ocm26787595
Classification:
LD1190.E54 1992m .M67 ( lcc )

Full Text
PROGRAMMABLE LOGIC CONTROLLER APPLICATIONS
IN ELECTRIC UTILITY SUBSTATIONS
by
1 Brian Scott Moreau
B.S., University of Nebraska Lincoln, 1986
A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado at Denver
in partial fulfillment
of the requirements for the degree of
Master of Science
Electrical Engineering
1992
. > '
5 ft *


(c) 1992 by Brian Scott Moreau
All rights reserved.


This thesis for the Master of Science
degree by
Brian Scott Moreau
has been approved for the
Department of
i Electrical Engineering
by
William R. Roemish
}
> !
Date
,^/t 27 %


Moreau, Brian Scott (M.S., Electrical Engineering)
Programmable Logic Controller Applications
in Electric Utility Substations
Thesis directed by Associate Professor
William R. Roemish
ABSTRACT
Reduced capacity margins and increasing
customer (demands for quality power are requiring
utilities: to improve their substation control and
relaying systems, and obtain increased loading of
i
existing facilities. To meet these increased
demands with conventional means can be costly in
both engineering and equipment expenses.
The main purpose of this thesis is to discuss
the use of Programmable Logic Controllers for
substation control, metering, and protection
functions. Advantages and limitations of the
f
hardware and software are examined, and some trial
installations are reviewed.
A package of substation applications is
i '
developed and a cost analysis performed.


This abstract accurately represents the content of
the candidate's thesis. I recommend its
publication.
Signed
William R. Roemish


CONTENTS
CHAPTER V
I. INTRODUCTION ..............................
II. THE'TRANSMISSION AND DISTRIBUTION
SUBSTATION ...............................
The Role of Substations ................
Gbntrol, Monitoring, and Protection
Equipment ..............................
An Integrated Approach ........
III. THE PROGRAMMABLE LOGIC CONTROLLER ....
A Brief History ........................
Present Day Hardware ...................
Software ...............................
Why Use PLCs in Substations? .....
Concerns with PLCs in Substations .
i( ,
Risks and Failure Modes ................
,
I, 1
IV. SUBSTATION APPLICATIONS ...................
[v
Review of Recent Applications ....
Applications at Hypothetical Substation
i '
Discussion of Requirements . .
i 1 PLC Design Specification ....
M, Hardware Configuration .............
Ladder Logic Design ................
1
4
4
5
9
11
11
13
16
25
32
44
51
51
54
54
60
61
63


VI1
Cost Comparison at Hypothetical Substation 70
V. SUMMARY AND CONCLUSION....................... 72
APPENDIX
A. LADDER LOGIC FOR MULTI-SHOT RECLOSING RELAY 74
B. SINGLE SHOT, HIGH SPEED RECLOSING RELAY
AND BREAKER CONTROL.......................... 89
C. STATION MAIN PLC LADDER LOGIC PROGRAMMING
AND HARDWARE CONFIGURATION ................. 100
D. PLC vs. CONVENTIONAL EQUIPMENT
COST,COMPARISON ............................ 137
I
REFERENCES 139
BIBLIOGRAPHY .................................... 142


CHAPTER I
INTRODUCTION
Transmission and distribution substations are
called upbn to provide ever increasing services to
both the Customer and the utility itself. Today's
decreasing generating margin has made it more
difficult', for substations to provide continuous
power to allcustomers, with minimal outage times
and stricter limits on voltage, frequency variation,
and harmonic content. Planning engineers need more
i '
accurate load data to better forecast peaking
requirements. Overloaded transmission lines require
i" "
optimum power factor control to maximize energy
delivery over existing lines. Power quality concerns
may indicate ia need for measuring harmonics near
large industrial customers.
Since!substations are generally unmanned, and
often quite remote from the dispatch center, modern
i
information and control requirements are met with a
variety of automated systems including automatic
reclosing relays to restore temporarily faulted


2
feeders, Supervisory Control and Data Acquisition
(SCADA) terminals to control major equipment within
substations and to indicate to the master station
any alarms chosen by the utility. To meet these
automation requirements, utilities have gradually
improved the existing hard wired, manual control and
indication systems by adding SCADA, and bringing
back critical data in this way, with an operator at
the central station performing switching as
required. This thesis will examine the use of
Programmable Logic Controllers in substations as a
means to further automate transmission and
distribution substations to meet modern control and
i
information Requirements.
The substation's place in the power grid will be
discussed;, including purpose, control, metering, and
protection needs, and the operating and maintenance
philosophy regarding them.
The Programmable Logic Controller (PLC) will be
examined in length to develop an understanding of
its history, strengths, and shortcomings.


3
The jcase for using PLC's in substations will be
addressed, as well as possible concerns.
Applications that have been attempted will be
examined including:
Reclosing Relays
Breaker and MOD control
SCADA.interface
Local1 Station Annunciator
Indicating Metering, Telemetering
Remedial Action Scheme (automated switching)
Power Factor Control w/Capacitor Switching
Power Line Carrier Testing
Load Profile Data
System Harmonics data


CHAPTER II
THE TRANSMISSION AND DISTRIBUTION SUBSTATION
The Role of Substations
The primary focus of this thesis will be on
applications of PLC's to unmanned substations such
as bulk power transmission stations and distribution
substations. Since generator step-up stations are
generally manned sites with a different set of
operating and automation requirements, they will not
be considered here.
The Transmission substation's function is to
deliver large quantities of energy across long
distances, with transmission line voltages of 69kV
to 765kV commonly in use. The subtransmission
substation converts power from transmission voltages
to a voltage of 13.8 to 138kV for short runs between
distribution substations or large industrial
customers. The distribution substation transforms
power from a transmission or subtransmission voltage
to a final distribution voltage of 2.4 to 15kV that
is used to serve the majority of residential and
business loads [1].


5
There" are three major aspects to consider in the
design of substations in general and they are:[2]
Normal Operation,
Prevention of Electrical Failure, and Mitigation
of the effects of electrical failure.
Normal Operation would include transmission of
clean, reliable power to the load, study of the load
characteristics and future planning, metering for
both revenue and information, voltage and frequency
regulation, and system operation.
Control, 'Monitoring, and Protection Equipment
Conventional control & relaying equipment that
might be used for normal operation would include
regulating relays to operate load tap changers and
perform capacitor bank switching using voltage or
power factor! relaying, or protective relays such as
load shedding using underfrequency relays. Devices
that are used for studying the system are digital
fault recorders, oscillographs, and demand meters
that store several intervals of system data, or
i
transducers that transmit data to a control center
I
for later,study. Metering includes indicating


I
6
metering jfcio display instantaneous current, voltage,
MW or MVAR through any particular equipment,
accurate revenue metering to determine energy
consumption and charges, and demand metering to
record load profiles. Equipment used for system
1 i
operation,would consist of control devices such as
breaker and motor operated disconnect control
switches, local-remote transfer switches, manual
transformer tap changing control, reclosing cutoff
switches, maintenance tagging relays, and any remote
t
control of these items via a Remote Terminal Unit
(RTU).
Prevention of electrical failure is accomplished
primarily by the implementation of sound design
practices and would include such items as insulation
l;
coordination, lightning shielding, use of proper
electrical and operating clearances, and correct
operation and maintenance procedures.
The type of electrical failure that causes the
greatest Concern is a fault (short circuit). The
time it tjakes to remove the faulted segment from the
rest of the system has great effects on the overall


7
reliability and stability of the entire power
system. The faster a fault can be removed, the less
physical damage will occur to equipment, the less
the hazard to personnel, and the greater load the
system can supply without risking instability.
Mitigation techniques include:
1. Prompt removal of the faulted element from
the system.
2. Compensation for the loss of the element by
switching to alternate circuits, using reserve
capacity, and using automatic reclosing to
restore service once a momentary fault has been
cleared.
3. Providing the means to monitor and record the
system's operation during faults to evaluate its
performance.
Protective relaying is the primary weapon used to
mitigate the ;effects of failure.
t>
Present industry practice uses a combination of
electro-mechanical, solid state, and microprocessor
based relays based on economics, suitability to the
task, and real or perceived reliability. Since
electromechanical relays have performed very well
for 50 years or more, many utilities and engineers


8
are hesitant to abandon them for the newer solid
state or microprocessor types.
The quantities brought into and out of the
control house in order to control, monitor and
protect the substation, and transmission and
distribution' lines, include currents, voltages, and
equipment status and alarms in, and contact closures
out. In order to measure the high system voltages
and currents involved in energy transmission and
distribution, the monitoring and protection devices
use volta'ge and current transformers to convert the
power system quantities to values that are more
practical for measurement. These secondary
quantities are typically 120 Volts and 5 or 1 amps.
The majority of the control and protection
features used for normal operation and fault
mitigation are met by individual devices or systems,
each designed to perform a single function or series
of related functions, many using the same input
quantities as other devices and systems in the
control h'ipuse. This has come about in part due to
the evolution in the industry that gradually


9
required more and better control and protection
techniques. Another factor has been the hesitancy
to place too much reliance on any single piece of
hardware.
i An Integrated Approach
Many of the same input quantities are used by
several different control, metering and relaying
devices, and many control devices and protective
relays operate the same power circuit breaker(s) or
other circuit opening device(s). With the
proliferation of microprocessors, it should be
possible to integrate many of the substation
control, protection, and metering functions into a
single piece of hardware, and build the conventional
devices as logic in software. The hardware to be
l
examined is a Programmable Logic Controller (PLC).
The substation is a harsh environment both
mechanically and electrically. Control and relaying
equipment is subject to electromagnetic fields,
switching.surges, lightning surges, and ground
potential1-!rise during faults within or near to the
station. Since substations are generally unmanned,


I
10
the building that houses the relays may contain only
minimal auxiliary heating and cooling if any at all,
and relay;jcontacts, operating mechanisms and
electronic components will be exposed to airborne
:[.
particulates and widely varying levels of relative
humidity.'
While all controls and relays require some
maintenance, the electromechanical devices in use
for substation control and protection has operated
so reliably that often utilities increase
maintenance intervals as a cost saving measure.
For the vast majority of its lifetime, the
substation performs its primary function of
supplying power to load flawlessly and without
interruption. Certain controls or relays may not
operate for several years, and then be expected to
operate in milliseconds during a fault occurrence
[2]. Any "improvement" in substation controls and
protection must be evaluated against the reliability
,)1
standards^already established by electromechanical
Li
relays, and hardwired controls.


CHAPTER III
THE PROGRAMMABLE LOGIC CONTROLLER
A Brief History
The PLC was first implemented in 1970 at General
'I,
i' !
Motors' Hydramatic plant as an industrial relay
replacer [3]. Though originally, and sometimes
still, known as a PC for programmable controller,
the acronym of PLC has become the preferred
designation to avoid confusion with the IBM personal
computer. PLCs were designed to be easily
I
. I
reprogrammed without the need to make physical
wiring changes. As their acceptance grew, so did
i
the demands for increased I/O counts and types, more
functions, more memory, and the ability to
communicate with other control devices. Most
vendors responded to these demands by releasing new
models, but they were in general not compatible with
previous models, future models, or PLCs produced by
other venders. Programs were not interchangeable
from one mbdel to the next, nor were I/O modules.
In the mid1to late 80's, the market began to mature


12
and several important features began to take shape.
Manufacturers developed the "family" concept, which
allows for upgrading within that vendors product
line [4]. Common features among the family include
one programming language, identical I/O reference
numbers, one programming package, identical I/O
structure, programs that are transportable from one
module size to another, and identical options
available for each model. This allows for economies
by reducing spare parts inventories and training,
and by using familiar documentation. As
requirements change, the system can be expanded to
include new features without abandoning the
installed base.
Communication between PLCs of the same family on
a single site is generally accomplished over a
r1
proprietary Local Area Network (LAN), although there
is some movement to utilize available network
standards such as available from Ethernet [5].
Another important development was a move towards
compatibility between product lines. The two
leading standards are the VME bus standards (Virsa


13
Module Eurocard) developed in 1979 and the MAP
communication standard (Manufacturing Automation
Protocol) developed in the late 80's [5,6]. These
standards are supported by the major PLC suppliers.
VME allows third party vendors to design and build
modules that will work on any Manufacturers' PLC
without paying royalties or licensing fees. This
provides protection for the user in case any one
vendor goes out of business. MAP is a
communications standard designed to allow devices
from different vendors to communicate through
standard hardware and software interfaces.
Present Day Hardware
The PLC is a special purpose, industrial
i1
hardened computer that executes a series of
instructions (the program) based upon some measured
input quaritity, makes decisions, and controls
outputs [7]. It is comprised of a central
processing unit (CPU), input and output modules
(I/O), and interfacing equipment for communicating
with programming tools, other PLCs, or other


peripheral devices such as printers. It has a
built-in operating system/ generally referred to as
firmware, that enables it to recognize and carry out
the instructions input as the user program. This
firmware is stored on a PROM (Programmable Read Only
Memory) Integrated circuit (IC). This IC resides in
the backplane or on a separate module, and can be
l
replaced as a system upgrade.
r.
The user memory consists of several different
, l
types. The most common type is CMOS RAM
(Complementary Metal Oxide Semiconductor Random
Access Memory), which is easy to modify and
troubleshoot1 since it can be altered in real time.
RAM is a volatile storage medium, so batteries are
required to retain the program in the event of a
power failure. If this storage medium is used, a
battery maintenance schedule must be considered.
EPROM (Era!sable/Programmable Read Only Memory) or
EEPROM (Electrically Erasable/Programmable Read Only
Memory) chips are memory ICs that can be modified,
j.'1
but will retain their program on loss of power.
Many PLCs use RAM to run the program, but have a


15
socket for EPROM or EEPROM that stores the base
program. This allows for the development of a
scheme in,ureal time, which once debugged can be
saved to EEPROM. The EEPROM chip can then be
removed arid used to make EPROM copies for other
I..,
installations. This is the most secure method of
program control. Most Manufacturers provide some
method of, ^security access via password codes to
prevent unauthorized access or modifications to the
software. ;
PLCs operate sequentially in an infinite loop.
One pass through the loop is known as a sweep.
The basic! operation of all PLCs per sweep is as
follows:
1. Perfprm self-diagnostics and alarm faults.
Communicate with other devices.
2. Scan all inputs and place results in the
data register assigned to that input
3. Beginning with the first line, proceed step
by step through the program and execute the
given instructions based on the state of the
inputs previously scanned and place any
output quantities in the assigned data
register.
4. ' Using data stored in output data registers,
operate output relays to reflect results of
previous scan.


16
5. Go to step 1 (diagnostics)
Each complete sweep occurs in approximately 20
milliseconds depending on the size of the program
and the speed of the microprocessor.
While relatively new to the utility substation,
the PLC is a mature technology, with a proven
operating history in industrial applications over
the past 20 years. During the 70's, there were
dramatic changes with each new PLC, while today's
new models focus on enhanced communications and
better compatibility with past and future models and
even with other brands [8]. The maturity of the
market, trie great flexibility inherent in the PLC,
combined with the genuine need for more
sophisticated monitoring and control functions are
major reasons why electric utilities are now
beginning to consider the use of PLC's in their
substations.
Software
Though once requiring dedicated programming
stations, today's PLC programs are generally written


1
: 17
on an IBM compatible computer using proprietary
software. < By allowing programming to be performed
I
on a Personal Computer (PC), the vendors have
reduced the cost of support equipment, since most
users have, already purchased PCs for other uses and
will only have to purchase programming software.
User programs can be entered into the PLC either
directly from the PC via a communication cable, over
a network, or directly using a small hand held
programmer;. Most modern software packages are
extremely easy to use and provide help screens and
v
menu bars to assist the user [9]. The software
prohibits ;jithe designer from building rungs that can
not be realized by the PLC, thereby eliminating
r
I- . .
misoperation due to syntax errors.
;l 1
The programming device, either PC, dedicated
workstation, or hand held programmer, is used to
perform the initial configuration of the PLC (tell
it what modules are installed where), load the
software, and aid in testing. The programmer can
force contacts or place values in registers in real


18
time to observe the PLC's response. This is an
extremelyj,,1 important asset when debugging schemes.
There are currently three types of user programs
that can be run on PLCs based on the firmware.
The first, easiest to use, and most prevalent
method is called ladder logic programming. This is
a graphical system that lets the designer select
from a menu of available functions such as coils,
timers, counters, N.O. and N.C. contacts, and build
a schematic one "rung" at a time. The positive bus
is represented as a vertical line on the left, the
series and parallel combination of circuit elements
make up a horizontal rung, and the right side of the
screen is!the negative bus (generally no vertical
line is shown). This method of programming has been
around since the first PLC, is easy for anyone
familiar with conventional relay schematics to use
and follow, and allows PLCs to mimic any relay
scheme without a change in operating philosophy.
Ladder Logic programming is ideal for the design of
systems which once would have been implemented by
relays [10,11]. An example of ladder logic


19
programming documentation is shown in Figures 3.1
through 3:4.
(* (* (* (* (* (* , Program: MULTRCL PLC PROGRAM ENVIRONMENT HIGHEST REFERENCE USED *) *) *) *) *) *)
INPUT (XI) 512 INPUT: XI0021
(* I1 OUTPUT (XQ) 512 OUTPUT: XQ0016 *)
(* INTERNAL (XM) 1024 INTERNAL: XM0017 *)
(* GENIUS GLOBAL (XG) 1280 GENIUS GLOBAL: NONE *)
(* TEMPORARY (XT) 256 TEMPORARY: NONE *)
(* REGISTER (XR) 2048 REGISTER: XR0036 *)
(* ANALOG INPUT (XAI) 128 ANALOG INPUT: NONE *)
(* ANALOG OUTPUT (XAQ) 64 ANALOG OUTPUT: NONE *)
(* <* PROGRAM SIZE (BYTES): 512 *) *)
(* DECLARATIONS (ENTRIES): 39 *)
(* *)
Figure 3.1 PLC Hardware and Program data
Figure 3.1 lists hardware and software data. The
, I'
first column shows the allowable quantities of I/O,
internal relay coils, data registers, etc. The
second column reports on the highest reference of
each type that is used (there may be unused I/O's
and registers below this high value). The total
program size is given in bytes. This program size
can be used to calculate the approximate scan time
of the PLC.


20
Figure 3.2 demonstrates a convenient
documentation feature that allows the user to assign
descriptive labels to his schematics. The REFERENCE
column displays the variable that is recognized by
the hardware. The NICKNAME column is the user
i
' ! i" i
assigned variable. Once defined, the software will
treat entry of either the REFERENCE or NICKNAME
identically, and display either or both on the
documentation. The third column in this figure
allows a more complete description to be given.
i
This is analogous to a Legend or Notes column on a
conventional relaying schematic.
VARIABLE 1
REFERENCE NICKNAME
I, 1 I
DECLARATION TABLE
! REFERENCE DESCRIPTION
ZI000I,;
ZM0001
ZI0003
ZI0004
ZI0017
ZI0018
ZI0021
ZM0003 .
ZM0008'|
ZM0009 ,
ZM0010;'
ZQ0001 '
XQ0016
ZQ0003
ZQ0005'
ZQ0015
ZQ0002
ZM0002.1
ZM00041!
ZM0005
ZM0006
ZM0007
RC FAIL
RI_AUX
BLK_RCL
SYNC
TD1
TD2
TD3
PLC_ALM
TEST_PT
INST
CS_C
RESET
LO AUX
syjjind
PWRFAIL
CLOSE_l
CL0SE~2
RST_AUX
LO
PCB_A
PCB B
RI
RECLOSE INITIATE
RECLOSE INIT. AUX
BLOCK RECLOSE
SYNC CHECK SUPERVISORY CONTACT
52a CONTACT
52b CONTACT
52CS CLOSE CONTACT
RECLOSING RELAY RESET TIMER
LOCKOUT AUXILIARY RELAY
SYNC WINDOW TIMER
PLC POWER SUPPLY FAILURE
CLOSE OUTPUT #1
CLOSE OUTPUT #2
RESET TIMER ENABLED INDICATOR
RECLOSING RELAY LOCKED OUT
PLC TROUBLE ALARM
TRIP BKR SIMULATOR(TEST ONLY)
HIGH SPEED RECLOSE ATTEMPT
FIRST TIME DELAYED ATTEMPT
SECOND TIME DELAYED ATTEMPT
THIRD TIME DELAYED ATTEMPT
FAILED TO RECLOSE AFTER 4TH TRY
Figure 3.2 PLC Documentation I/O labeling


21
|BLK_RCL LO
+] [+--------+_....-........................ III
!RC_FAIL! | LO_AUX
+--] [-+ +..............................( )-
i i i
!SY_WIND! !
+-] [--+ 1
I I I
!PWRFAIL! !
+-]/[--+ ,, !
IZM0011 PCB_A PCB_B I
+--] [-----3/[-r1 [-+
! CS_C ' !
+~] [-----------*------+
#0041 LD ' 210003
#0042 OR ZM0007
#0043 OR Ih, l ZM0009
#0044 OR 1 NOT 2M0010
#0045 LD ' ZM0011
#0046 and NOT 210017
#0047 AN01' 210018
#0048 OR11 BLR
#0049 OR . 210021
#0050 SETM 2Q0005
#0051 OUT.1 2M0008
RUNG 18 STEP #0052
N0TE_8
(* COMMENT *)
! (* Go to Lockout (LO or Q5) If: Block reclose Input (13) Is received *)
! (* Palled on fourth reclose attempt *)
! (* Sync Window Timer times out *)
! (* Power to PLC has failed during cycle *)
I (* Breaker did not close within Is of attempt *)
! (* 1 <******** Breaker was closed by control switch *) **)
Figure 3.3 Relay logic Rung
Figure 3.3 shows a "rung" of ladder logic as
well as some 1 documentation features. The first coil
on the right end of the rung has an "SM" designation


22
that identifies it as a latching, maintained coil.
Maintained: means that if the PLC were to lose power,
the battety backup would hold the coil in whatever
state it was in prior to the failure. A non
maintained coil is shown directly beneath the SM
coil in Figure 3.3 and would reset upon loss of
power. Directly beneath the rung are the step by
step keystrokes that would be used to enter this
rung into the PLC using a hand held programmer.
Below this is an annotation that describes the
function of the rung above. Either of these last
two items are optional displays and can be hidden if
desired.
TD3
( )
!RI_AUX +------+. +------+
+ ] [ >DNCTR-t;,T---+ TMR +
10.10s
! RESET !
+-_] [---+R | CONST -+PV
+00200 |
+------
CONST -+PV | ZR0022
+00004 |
+------
ZR0019
Figure 3.4 Timer/Counter rung


23
The rung in Figure 3.4 shows two important
features Of the PLC, a counter and a timer. This
counter will count down from the constant value
entered into input PV for every positive change of
state on its input. In this case, PV = 4, and the
initial state on the input is 0, so the fourth time
that RI-AUX closes, the count will reach 0 and
positive will be applied to the input of the timer.
The Timer used here is a time delay on pick-up type
that will provide an output when positive is applied
for a given time. In this case, the increment is
set to 0.10 seconds, the PV is set to 200, so the
pick up time is 0.10 x 200 = 20 seconds. This
particular PLC allows two different timer
resolutions of 0.01 and 0.1 seconds, with the user
selecting' the largest increment that will meet his
needs in order to conserve memory.
The second method of programming is the use of
Boolean lpgic. This is mainly seen in process
control where PID (Proportional- Integral -
Derivative) type of feedback control schemes are
used, or where the designer wishes to simulate logic


24
gates or mathematical functions. For some control
schemes, this can result in a greater optimization
of the program code which results in shorter scan
times. This type of programming is more difficult
for the uninitiated to use and troubleshoot, and
would not be readily accepted by the personnel
responsible for operations and maintenance of
substations. For substation applications, this
method should only be used in designing complex
algorithms that are thoroughly checked and are not
expected to be modified, such as transmission line
protective relaying.
The third type of programming method is high
level assembler which is compiled program code. The
user designs the scheme with graphical function
blocks. This scheme is then compiled and the machine
language code is run on the PLC. This method is
completely foreign to the designer used to relay
schemes and is not widely accepted in America [12].


Why Use PLCs in Substations?
All of the control, monitoring, and relaying
25
requirements mentioned previously can be met with
conventional methods. What then is the
justification for applying an industrial type device
that has seldom been applied in substations? The
major advantages to the application of PLCs in
substations are:
Hardware cost savings
Reduced engineering and commissioning cost
l |
Shortened project schedule
Flexibility of software design rather than
hardwire allows for easier, less expensive
modifications.
Self, diagnostic functions aid in maintenance
and troubleshooting, reducing down time.
Reduced field wiring since field contacts
can be multiplied in software.
Reduced panel space, smaller control house
Same hardware used at all voltage levels.
Minimized spare parts.


26
Schemes are transferrable. To change
vendors requires no scheme change, little if
any rewiring.
Can design & test on computer prior to field
installation.
Properly designed system can expand to
include additional functions with minimal
cost.
Cost savings realized by using PLCs is extremely
variable and depends a great deal on the functions
required. The actual savings will depend on the
degree of automated control and monitoring required,
and the size of the installation. The more
functions that are required, the more competitive
the PLC will :be since the majority of the "relays"
are in software. A small PLC may be able to
simulate the equivalent of 1000 relays, timers and
counters.,
By applying PLCs in place of conventional
equipment,, engineering costs will be reduced,
because an engineer can design his schemes and
troubleshoot them on the PC, concentrating on the


27
functions desired, rather than how to make any one
vendor's discrete relay or meter meet his
requirements. A good example of this is the
reclosing relay. There are at least eight
manufacturers of reclosing relays, each with several
different models designed for specific applications.
The mid range reclosing relay is comparable in price
to the small PLCs such as Modicon's Micro984 and the
GEFanuc Series 90-30. An engineer requiring a
reclosing relay, especially if purchased by
i1
competitive bid, would spend time in specification,
evaluation, and implementation of one of these many
relays. Since every utility has its own reclosing
philosophy, it is often quite time consuming
applying the relay to perform as desired. By
designing the scheme in software, virtually any
reclosing scheme can be implemented on any vendor's
PLC hardware. In the case of a reclosing relay,
software modules could be written that would allow
easy construction of all standard reclosing schemes
used by the owner utility. Once developed, future


28
applications could be quickly and inexpensively
implemented.
Once scheme design is decoupled from the
hardware, the project schedule can be shortened,
since engineering and panel manufacturing can occur
in parallel. In addition, since the scheme is
virtually hardware independent, the same design can
be transported from one vendor's equipment to
another's; allowing more flexibility in sourcing
equipment.
One of the most severe requirements of
substation control and protection equipment is that
it must sit idle for such a large percentage of its
installed lifetime. Since these systems are so
infrequently exercised, utilities use testing to
insure proper operation when called upon. Studies
indicate that the largest percentage of troubles are
caused by employee carelessness, so companies are
tending to increase testing intervals to 2 2 1/2
years [13]. This means that these systems could be
faulty for 2 years or more and no-one would know it
until they were called upon to operate and failed.


29
The ability to continuously monitor their health is
a major benefit that microprocessor based devices
bring to the substation. It is now quite common to
see the application of microprocessor based distance
relays in substations that provide "extras" such as
fault type and location information, self
monitoring, adaptive relaying, and remote
interrogation. The ability to identify and
annunciate faults within the CPU, I/O, and even
wiring, and to provide second contingency
protection* is a feature that some claim make
microprocessor designs statistically more reliable
than simple redundant electromechanical systems
[14].
Another area of cost savings that can be
realized is in cabling. A list of typical field
contacts required for control, annunciation, and
relaying includes:
Reclosing: l-52a, l-52b
Green light: l-52b
Breaker status to SCADA: l-52a
Target interrupts: 3-52a contacts
Breaker alarms: l-63a
MOD status: 3 contacts per line


30
These simple requirements would require 22
conductors: to be run from the control house to the
yard equipment. The number of times the PLC can
reference the same input address is limited only by
the available system memory, so only one contact of
each type need be brought into the control house.
This results in 12 wires instead of 22, or the
elimination of 1-10/c #12 control cable. At $2/ft,
the cable1 savings alone could pay for the PLC.
Further reduction in yard to control house cabling
could be realized with the use of distributed I/O.
A distributed I/O module acts as a rack mounted I/O,
with some intelligence of its own that can detect
wiring faults and opens and can annunciate these
problems. The remote module communicates with the
host PLC via a twisted pair, coax or fiber-optic
cable. The individual brand chosen should be
evaluated for expected environmental conditions
prior to selection. If mounted in outdoor power
circuit bieaker cabinets, factors to consider would
be seismic performance (during breaker operation),
humidity,,and temperature extremes. The PLC
I
I


31
manufacturers specifications should be consulted and
compared to the intended environment before applying
in outdoor equipment cabinets.
By integrating the functions typically performed
by several pieces of conventional equipment into a
single PLC> panel space requirements will be
reduced. The ultimate reduction in panel space, and
thereby control house size, must be evaluated on a
case by case basis depending on the degree of
integration achieved.
Since the PLC is, by design, a flexible relaying
and control platform, a system can be constructed
and installed by phases as confidence in the
application grows. As an example, a PLC-based
reclosing relay could be installed initially, with
the PLC chosen to ultimately allow the addition of a
Local Area Network (LAN) to communicate with other
PLCs and SCADA, and analog inputs could be added to
incorporate indicating metering and other functions.
After examining some of the limitations of PLCs,
and some applications, we will discuss how to select
a PLC to allow expansion into an ultimate design


32
that will enalble the user to add functions as
confidence in the system grows.
Concerns with PLCs in Substations
A review of the literature produced a very
curious unexpected result. While papers on
applications within the substation were a small
percentage; of the total available, they had the most
positive things to say. A normally conservative
industry appeared to be quite enthusiastic over the
! iii
success of PLC applications and the outlook for the
future. The industrial control journals presented a
more sober analysis, one balancing capabilities
against liabilities. One possible explanation is
that the industrial applications are much more
'i
complex than those being attempted in substations at
this time, and are therefor stretching the
boundaries,, whereas the relatively small amount of
I/O and processing requirements of the substation is
I
simple and easily implemented with existing PLC
technology. 'Another reason could be the greater
experience gained by industrial engineers through


33
twenty years of use. In any case, we will examine
the application considerations and concerns from the
standpoint of an electric utility substation user.
Reference [15] lists 365 different PLC models
from 87 different manufacturers and compares their
I/O capacities, programming methods, documentation,
communication interfaces, scan rate/lK of program
memory, maximum program memory size, Data memory
size, type of LAN, and country of origin. While
this is very useful as a one stop shop to compare
!''
features, anyone who has specified relay equipment
knows this is not the whole story. To the relay
engineer's relief, there are only 5 main vendors of
PLCs [4], with the rest being niche vendors. Most
of the 5 primary vendors have similar or identical
, I
capabilities, allowing the engineer to accept
competitive bids if desired. Some areas of concern
when developing a specification are:[4,5,8,9,16,17]
Power supply options
Speed (scan rate/IK)
Program storage memory type and security
Type of output solid state or contact
ratings, grouping of contacts


34
Maximum number of I/O and type (analog or
discrete)
LAN requirements, SCADA interface
Expansion capabilities, compatibility, open
architecture.
Noise immunity use of shielded twisted
pair, coaxial cable, or fiber-optic cable
Environmental requirements including
temperature range, humidity, seismic,
Special installation methods
Mounting and field wiring terminations
Programming methods, ease of use and
(documentation capabilities of development
software
Transient immunity surge protection
Stability of supplier
Availability of training and local support
From a utility standpoint, the PLC should be
suitable for application with standard substation
battery voltage ratings, generally 48 or 125 VDC.
This includes both power supply and I/O modules.
Most PLCs require 120 VAC or 24 VDC supplies, so
this requirement will quickly reduce the number of
acceptable vendors. While some utilities have
applied PLCs in substations and used dc/dc


35
converters, to obtain an acceptable supply voltage,
this does not address the I/O requirements and
introduces a weak link in the system [16]. At least
three major vendors support, or plan to support, 125
VDC applications.
The speed required of the processor or
processor/coprocessor system is dependent upon the
application. For small programs and non-critical
control functions, the scan rate is a minor
consideration. If protective functions are to be
incorporated, then speed becomes more critical.
The flexibility inherent in software
implementation of a relaying scheme can also be a
leading cause of reliability problems due to
accidental, unauthorized, or undocumented program
modification [17]. To insure against these hazards,
PLCs provide several features. Security codes can
be used to guard against unauthorized access or
modification to the ladder logic. Multilevel codes
are used to allow troubleshooting, and report
generating: without allowing program modification.
Higher level access codes are required in order to


36
change the; software. EEPROM is more secure than
battery backed RAM, since the program remains intact
upon power failure without relying on an on board
I
battery backup. It maintains full flexibility, but
is less secure than EPROM, since it can be modified
in the field. EPROM is the most secure since it is
a hardware codification of the scheme that can only
be written by an EPROM burner, and cannot be
modified. Combinations are available that use RAM
storage for normal program operation and
M
troubleshooting, with EEPROM or EPROM backup for
j
security. Once the system is debugged, the EEPROM
can be removed and used to program several EPROM
chips for permanent use and for use in other
installations,. The scheme can still be modified by
replacing the, EPROM chip or by loading a different
program ini RAM for trial use [18].
I
The type of output, solid state or dry contact,
should be examined closely. While dry contacts are
preferred by most relay engineers, the
manufacturer's data must be examined closely to
ensure proper ratings. Many PLCs use resistor-


37
capacitor snubbing networks across the output
contacts to increase the interrupting ratings.
While this is not a problem on DC circuits, AC
circuits may be affected by leakage currents in the
snubbing network [16]. Contact ratings are readily
available which are suitable for use with the X and
Y coils in power circuit breaker closing circuits,
but interposing relays should be used for directly
tripping or closing a power circuit breaker. The
engineer should use caution when specifying dry type
output contacts, since many vendors use groupings of
several contacts with a common node. This may cause
applicatibn problems where schemes must be isolated
. I
from one another.
It is1 recommended that PLC programs be kept
small and' simple, and that the number of functions
per PLC be kept to a few. An application philosophy
that follpws this recommendation and is consistent
with industry practice for conventional relay and
control panels, is to apply one PLC per line [19].
By applying one PLC for each line into or out of the
substation, the required I/O quantities will be


38
minimal and easily met by most small PLCs. Possible
inputs would be breaker and MOD status and alarms
(discrete), and Line Volts, Amps, Megawatts, and
MegaVARS (analog). Other substation quantities
might be transformer tap position, power factor,
alarms, meteorological data, and harmonic content.
In order to integrate substation controls into a
complete system and to 'provide for a common
interface, the PLCs should be able to communicate
with each other and with SCADA, peripheral devices,
J 1 ,
operating terminals, and remote I/O. While it is
now possible to communicate between PLCs of
different manufacture, it is easier to apply if the
engineer determines a standard "family" on a per
station basis. If a "family" of PLCs of one
manufacturer are used exclusively at each or all of
an owners substations, the utility will reduce
training and spare parts costs, and will find
communication interfaces much more straightforward
than trying to use several different vendors. When
selecting PLCs, care should be taken to evaluate
methods of communicating with SCADA. Many


r
39
manufacturers are now supporting common SCADA
protocols. This capability would allow the
functions of the station RTU to be incorporated into
a station PLC, resulting in a further reduction in
station equipment. When evaluating communications,
[
be aware pf distance limits imposed by the various
protocols. RS-232C is most common for programming
and peripheral interfaces, but is limited to 90 ft
or less. RS-422 is used for longer distances up to
1500 ft, with some proprietary LANs rated for
[
operation at distances up to 7500 feet from the PLC
[18]. Communications to SCADA can be by a dedicated
leased line, or by a dial-up modem [20].
Proper planning is required in order to avoid
limiting oneself in future applications. By
applying PLCs on a line by line basis, the amount of
required planning should be minimal. The user
should strongly consider selecting a model out of a
"family" of PLCs in order to aid in communications,
compatibility with future models, and to retain
maximum flexibility in expansion options. By
choosing a family member, the programming skills and


40
training expenses will not be lost during future
upgrades. As a hedge against obsolescence, one
should consider a design that uses open architecture
such as VME. This isn't too great of a concern
i,
however, since most of the costs associated with PLC
applications are in the software, and a ladder logic
scheme can be implemented on any brand of PLC.
By using error checking and correction protocols
and standard shielded twisted pair cable, one
application has been tested for noise immunity in a
500 kV switching station with no misoperations of
the test ^program [20]. Care should be taken during
i 'i i
installation not to run the PLC bus cable in the
same raceway as CT, PT or other AC circuits. In
general, Shielded twisted pair cable is used for PLC
;i
communications. For excessively noisy environments,
or where high speed communications are required,
i
coaxial or fiber optic cable can be used. Coaxial
cable is jexp.ensive and difficult to install. Fiber
optic cable is virtually immune to noise, is
!1 i
extremely dubable, and is slightly less expensive
than coax, but requires special termination
i


41
techniques and is not widely supported by PLC
vendors. Fiber also has the limitation of requiring
equipment 'from one vendor only since there is no
standard for optical communications [5].
Environmental requirements such as temperature,
humidity, and seismic zone should be compared
against the manufacturers specifications to insure a
reliable application. In general, PLCs are more
rugged than many microprocessor based relays
currently in use in substations.
All microprocessors are susceptible to
electromagnetic interference and electrostatic
discharge. Proper grounding techniques and the use
of shielded cable are important tools used to
mitigate these effects. The current state of PLC
technology is well suited to most control house
applications, but may be unacceptable for use in
outdoor NEMA cabinets or breaker cabinets.
Temperature extremes present in external cabinets,
and vibrations present during breaker operation
could cause misoperation of a PLC.


42
,'i
t
'i
Physically, PLCs resemble projection mount
relays with a flat backplane onto which are fastened
the CPU, I/O Modules, and Communication Modules.
This is inconsistent with the semi-flush relay
j1'
panels currently in favor in the utility industry.
i', ' '
If mounted within a standard relay cabinet, the
front face could have a plexiglass door that would
provide access to the PLC mounted on a subpanel
behind the cabinet face. I/O terminations are
generallyjsmall and not suited to standard ring
type terminal lugs. External terminal blocks might
be used to allow more room for field and interpanel
terminations, with all available I/O factory wired
to these terminal blocks.
Since,!: the majority of the relaying will be
performed; in software, the tools available to
develop the ladder logic are of major importance to
i1'1
the overall acceptance by the utility user. The
software should be able to run on IBM compatible
computers1] to take advantage of the available
equipment1 and avoid purchasing a dedicated
il
programmer that could only be used for this one
li


43
task. The engineer should ask for a demonstration
package of the software prior to purchase, since
each package in general works only with a single
brand of PLC, and is therefor an important factor in
the evaluation of a PLC system. Important features
include oh or off line programming, cross
referencing to keep track of used addresses, cut &
paste capabilities, annotation, and the ability to
force I/O ; and monitor its effect on the rest of the
program. The package should be menu driven with on-
il
line help screens and strong editing features such
as global search and replace functions [9]. The
software package will be used to develop much of the
documentation and schematic diagrams, so it may be
advantageous to inquire about interfacing the files
to a graphics program such as AutoCAD.
Most [PLCs provide metal oxide varisters on their
I/O modules to protect against surge induced
i
transients. Check the vendor specifications in this
area and look for Surge Withstand ratings in
conformance with IEEE Standard 472-1974 and ANSI
C37.90A-1974 [21,22].


44
Important to the application of any device is
support services and supplier stability. The vendor
should be:evaluated based on experience and product
performance, and calls should be made to check on
customer satisfaction. Local support can be very
helpful, Especially for new products, where startup
expenses can be high while the user is learning the
new system. Most major suppliers provide training
seminars on the use of their equipment, either at
their location or at the users facilities.
Risks and Failure Modes
There! are four fundamental risks associated with
the use of PLCs:[17,23]
1. Influence of the environment
2. Randbm failure mode
3. Ease of program modification
4. Software Reliability
PLCs are generally acknowledged (by industrial
engineers) to be as reliable as electromechanical
relay schemes as long as proper installation
conditions are used. The manufacturers'


!
! 45
specifications should be followed closely, but in
;/. i
general a temperature range of 0 40 degrees
11
Celsius shlipuld be maintained, and dust, humidity,
and vibration should be held to the same values
I
required for any microprocessor based equipment.
Pickup voltage can be 60% of rated (105 VDC) with a
|]
current draw as low as 6 mA. An induced voltage
could easily be this high and could support such a
low current, so proper shielding and cable routing
lj
l<
techniques are extremely important. The two
classifications of induced transients are
i t !
differential and common mode. Common-mode surges
ir ,
produce equal voltages on a pair of wires with
respect to! ground and most often cause dielectric
i
failure. Differential-mode surges produce a voltage
difference between a pair of wires, similar to an
f
II
actual signal and can cause misoperation. Twisting
I ' ,
the signal and return leads minimize the effects of
differential mode coupling. Physical separation of
the PLC circuit from noisy circuits, or running the
PLC circuit perpendicular to the noise source are
routing methods that can be used to reduce the
I


46
effects of electrostatic and electromagnetic
induction. Twisting the signal and return lead, and
providing a metallic shield around these wires can
substantially reduce the effects of surges induced
from adjacent circuits.
Unlike conventional relay and control equipment,
for which failure modes can be predicted, solid
state components have a random failure mode. It can
not be determined whether the PLC will fail with an
open or close on its input or output contacts, or if
the program will "hang up" and cease to complete its
normal sweep procedure. There are several methods
that can be used to reduce the occurrence of random
failures affecting the application. All of these
schemes must be evaluated on a cost/benefit basis.
For output protection, some PLC modules can detect
and alarm for opens or shorts on their I/O modules
and field wiring. By using form a and form b
contact inputs from the same field device and
building a form C contact in logic, an error on one
of the input modules can be detected and alarmed,
and any output can be blocked on disagreement if so


47
desired. .Feedback from the controlled equipment can
be used to compare against the intended operation to
monitor for faulty outputs. Watchdog timers, both
internal and external, can be used to insure that
the CPU is; not "hung". The watchdogs are timers
that are reset during completion of each sweep. If
a sweep takes longer than a predetermined interval,
the PLC can be shut down and an alarm can be
r
sounded. In addition to these relatively
inexpensive methods, many forms of redundancy have
been applied. Completely redundant systems using
separate PLCs (or Hot Standbys), power supplies,
I/O, and cabling provide limited protection against
misoperation, since the failure mode is
indeterminant and either dependability or security
could be adversely affected. The most reliable PLC
system would be a triple redundant system using 2
out of 3 voting for decision making. This
introduces unreasonable expense and complexity for
most present substation functions but is used in
nuclear power plants and for critical process
controls.1
I


48
One of the most advantageous features of the
PLC, its flexibility, can also be one of its major
risks. Because it is easy to modify, technicians
may be tempted to alter the program code in the
field without complete testing and verification.
'h
This may result in misoperation during unforeseen
contingencies. Field modification can also result
in an installed scheme that is not properly
documented so that no one really knows what is
actually installed. Since programs can be modified
on-line, proper field isolation in terms of test
j
switches [Should be installed. Avoid using
maintained cbils that retain their state through a
power outage, since their output may cause
unexpected operation at such time that power is
restored.: I/O forcing is a useful debugging tool,
but care must be taken that all forced I/O are
cleared prior to commissioning the scheme. While
security access codes can be very effective, PROM or
EPROM memory for program storage are the only
guarantees against unauthorized program
modification.


49
Finally there is the risk of software bugs.
While hardware can be tested over time and its Mean
Time Between Failures measured and evaluated, the
reliability of software cannot be measured [23].
There are two types of software used, firmware
written by the manufacturer and installed in PROM,
and the user program written by the application
engineer, either of which can have errors. During
the development of firmware, quality control
techniques and extensive testing methods are used,
i
and any bugs found are fixed, but unrevealed bugs
may remain that will only appear upon the occurrence
of a particular set of conditions. Triple redundant
i
schemes using three different sets of firmware can
be used to reduce the risk of firmware failure, but
since programmers use similar methods, the benefit
of this approach is difficult to measure. Use of a
reputable vendor and interviews with other users is
probably the most effective method of quality
control the utility engineer can exercise in this
area. In the area of user developed programs,
current industry quality control techniques and


50
independent peer reviews of the ladder logic should
avoid misoperation of the scheme due to input
software. To avoid conflicting outputs, i.e. both
breaker trip and close outputs from occurring
simultaneously, use program modules such that the
act of picking up a coil resets the coil of the
previous rung [24].


CHAPTER IV
SUBSTATION APPLICATIONS
Review of Recent Applications
In developing substation applications for the
PLC, it is instructive to examine what has been
attempted to date, why the PLC was chosen, and what
success and or disappointments, have been realized.
Reclosing relays have been developed and
implemented by Duke Power [16] and Idaho Power [19].
As of 1991, Duke had installed 200 PLC based
reclosing relays, some of which are mounted directly
in the power circuit breaker cabinet. Automatic
Power Line Carrier testing schemes have been
implemented by Louisiana Power & Light [25], and
Duke Power [16]. Remote Terminal Units for SCADA
interfaces, and substation monitoring and control
schemes have also been successfully developed
[20,26]. Other applications described in the
l
literature are Automatic Station Switching schemes
[16], Substation Annunciators [19,26,27],
and a microprocessor based Metering & Control system
at LaPlata Electric Association [28]. One of the


52
most complex and critical PLC control schemes
applied in substations is the Triple Modular
Redundant Remedial Action Scheme developed by
Bonneville Power Administration that acts to
maintain system stability on the Western Power Grid.
By using specialized PLC hardware and implementing a
two out of three voting system, an availability of
99.9977% is achieved [29]. The reasoning used for
applying PLCS in these schemes varies, but common
factors include flexibility of off-line, software
I-
developed'schemes resulting in simple, standardized
installations, and the self testing ability of the
hardware,i.; which aids in maintenance and provides
I
increased availability over hardwired schemes. Once
installed, the schemes can be easily modified to
adapt to changing philosophies and system
conditions, and additional features can be added
with little extra cost.
111
i,
Substation capacitors are generally applied for
VAR support, with line capacitors placed along the
distribution feeders for voltage support on long
lines. A VAR or power factor controller could be


53
constructed within the PLC to control substation
capacitor bank switching. The setpoints chosen for
this type of controller must have sufficient
bandwidth to avoid pumping due to the system's
response to the presence or absence of capacitive
compensation. Since the application of a capacitor
bank tends to increase the voltage of the bus on
which it is connected, a voltage override function
must be included with this controller to prevent
placing a bank on line when the system voltage is
close to its upper operating limits.
Used in conjunction with microprocessor based
protective relays that can store several groups of
settings, the PLC could be used in an adaptive
relaying scheme that would automatically change the
relay settings based on the current station
configuration. By monitoring feeder data and
transformer loading, more accurate system planning
can be performed and planned transformer overloading
can be more accurately implemented.
PLC based schemes can be added one at a time,
expanding as confidence allows and requirements


54
demand. Careful advance planning is required when
purchasing PLCs to allow maximum flexibility for
future applications.
Applications at Hypothetical Substation
Discussion of Requirements
As an exercise in developing some substation
applications, a new substation will be examined
called Hypothetical Substation. System planning has
determined that a two bay breaker and a half 230 kv
station with three 230 kV lines, one 200 MVA
transformer, and four 12 kv feeders are required at
this time. A shunt capacitor bank will be placed on
the 12 kybus and switched on and off based on power
factor tq,improve loading on the transformer. A
switching one-line diagram is shown in Figure 4.1.
This will be an unmanned substation, so a SCADA
interface capable of remote monitoring and control
is required. Full metering of amps, volts, watts,
vars, and 12 kV bus power factor will be used. The
system should be expandable to allow for increased
I


55
trending data as the station reaches its maximum
present capacity.
LINE C LINE B LI NE A
LINE K
L I NE F
LINE E
L I NE D
Figure 4.1 Hypothetical Substation Switching One-
Line
Due to dependability concerns of PLC failure
modes (output can fail open or closed), and the
expense and complexity of providing two out of three
voting, PLC applications will be limited to control,
metering,, and annunciation functions, with
protective relaying being performed by


56
microprocessor based distance and overcurrent
relays.
As mentioned earlier, reclosing philosophies
vary widely within the industry, which makes the
application of PLCs to this task particularly
attractive due to its flexibility. A brief
discussion of reclosing practices is presented here
for background.
Utility experience has shown that up to 95% of
all line faults are transitory, and if cleared
quickly, the affected line can be returned to
service rapidly by the use of automatic reclosing
[30]. The majority of successful reclosures occur
on the first attempt after fault clearing, with
diminishing chances for success on each subsequent
attempt. A minimum dead time is required for any
reclose attempt to allow the fault arc to deionize.
An equation for this dead time has been developed
based on operating experience and is given in
equation 4.1, where kV is the rated line-to-line
voltage [30].


IcV
t = 10.5+------ cycles
34.5
57
(4.1)
Synchronism check relays are used to supervise
reclosing operations when there is a chance that the
sectionalized portions of the system could have
undergone a relative phase shift during the time the
breaker was open. The synchronism check relay
measures the phase angle difference between the
voltages on both sides of the breaker and by
I
supervising the reclosing relay, protects the
breaker contacts from overvoltage stresses and
minimizes shock to the system when it is forced back
together.
At transmission levels it is common to use a
single, high;speed, unchecked reclose attempt if
pilot relaying is in service. Reclosing is often
blocked if there is no pilot relaying since the
slower clearing time for faults near the end of the
line reduces the chance of a successful automatic
reclosure. When near generation, the first attempt


58
may be time delayed and supervised by sync check to
avoid generator shaft damage.
For distribution circuits, multi-shot reclosing
is often applied due to the impact of a line outage
on service continuity. In addition to lightning,
distribution lines have an increased likelihood of
tree limb induced faults which may be burned clear
by multiple reclose attempts. On radial feeders,
synchronism check is not needed, and up to four
reclose attempts are common. The first attempt is
generally high speed and can be initiated by an
overreaching instantaneous overcurrent element as
part of a fuse saving scheme. After the first
reclosure, the instantaneous overcurrent element is
blocked, and the time delayed pickup characteristic
will allow the fuse to blow if the fault is
downstream of the fuse. The remaining reclosing
shots may,;be called for to coordinate with
downstream line sectionalizers. The resulting
scheme provides a combination of minimum outage
areas for 'permanent faults, and service restoration
for temporary faults [30].


59
On distribution circuits with a source of fault
current on either end of the feeder, for example a
line feeding an industrial customer with a
cogenerator, one or two reclosing attempts may be
made. The first attempt could be high speed
unchecked, with the second attempt being time
delayed and supervised by either a check for
synchronism or that one of the sources is dead.
When applying multi-shot reclosing,
consideration must be given to the derating of the
breaker interrupting ratings.
Three reclosing schemes will be required at the
Hypothetical Substation. At 12 kV, the radial
feeders will use 1 high speed reclosing attempt with
3 time delayed shots, while one 12 kV looped feeder
will use 1 high speed reclose attempt plus one time
delayed attempt supervised by an external sync check
relay. At 230 kV a single high speed reclosing
attempt without synchronism check will be made with
the bus breaker, with the tie breaker reclosing only
after the relay has completed its reset time delay.


60
PLC Design Specification
The PLC selected should be capable of expansion
and easily networked with other PLCs. One
manufacturer shall be selected as a site standard,
to ease networking and minimize spare parts, but
open architecture and communication protocols will
be evaluated. The PLCs shall be a member of a
"family" of controllers to aid in future upgrading
and expandability. The system selected will have
provision 'for PROM or EPROM program storage to
provide security, and the power supply and I/O
modules will be suitable for use on a 125 VDC
station battery. Surge protection meeting the
requirements of ANSI C37.90A shall be provided.
Communication modules shall be available for use
with twisted pair, coaxial cable, or fiber optic
cables. IBM PC based programming software shall be
available capable of on and off line programming,
program storage, and testing. Proprietary Local
Area Networks are acceptable for station
communications, but an industry standard protocol


61
such as RTU must be available for communications
with SCADA.
Hardware Configuration
The substation controls, metering, and reclosing
functions;will be met with the distributed PLC
system shown in Figure 4.2. This installation will
use a small PLC for each line, and a larger Station
Main PLC will provide operator interface, station
! I
Annunciator,1 and Indicating Metering functions. The
i
main PLC will also provide the RTU interface to
SCADA. The system can be expanded to include local
data acquisition and trending by replacing the main
I 1
PLC with a more sophisticated model and replacing
; i
the operator'console with a PC based operating
station as future requirements dictate.
Discrete! I/O points to and from the substation
yard will land on the distributed PLCs. The analog
points will be wired directly to the main PLC.
Alarms and breaker status/control points will be
defined as Global Data, accessible by any PLC on the
network. One contact from each protective relay
I
lockout (Transformer & Bus Differential lockouts,
i


62
Figure 4.2 Distributed PLCs for Hypothetical
Substation
Breaker Failure lockouts) will be wired to the main
PLC and converted to global data, eliminating a
great amount of interlock wiring. Since the
communications bus will be contained entirely within
the control house, twisted, shielded cable will be


63
used for the network. Future remote I/O to the
yard, if used, shall be via Fiber Optic Cable to
eliminate.surge induced transients.
Ladder Logic Design
When designing a PLC based control scheme, some
method must still be retained to allow operation of
l
the Power,Circuit Breakers if the Main PLC is lost,
especially since the SCADA interface requires that
the main be on line. Emergency pushbuttons will be
installed for each breaker that will allow operation
of the breakers ONLY when the main PLC is out of
service.
While it is not economically feasible to
implement1 a two out of three redundancy scheme for
this application, the random failure mode must be
addressed. System security demands that a single
I'
random failure not result in a false trip or
unexpected close operation. To meet this
requirement, all trip and close outputs to the power
circuit breakers will consist of two output contacts
in series!. The PLC's self diagnostics will detect


64
any I/O failure as a logic disagreement (contact is
closed yet logic says it is open), and an alarm will
be annunciated. If the contact failed closed, the
process can proceed as normal until a repair can be
made. If the contact failed open, the process will
not work until repair is made, but no breaker
operation will have occurred.
To aid in the prevention of failed inputs, both
52a and 52b breaker status contacts will be used in
the logic in series to detect a disagreement. Any
t'
disagreement will be alarmed and the process will be
blocked.
The individual PLC configurations are shown in
Figure 4.3, with the main PLC configured as shown in
Figure 4.4.

HACK 0
IPS/CPU
IPWR323
I CPU 30
PROGRAMMED C0NPIGURATI0N
CMM301
GENCOM
MDL630IMDL630
|
I DC8 |I DC8
|
RefAdrIRefAdr
zioooiiziooi7
MDL940|
QRLY16|
RefAdr|
ZQ0001|
Figure 4.3 Distributed PLC configurations


65
+ 1 1 1 1 1 1 c t i < i p i i i i + -
i PS 1 !, 2 3 A RAMMED j CMM301IALG221 GENCOM!IALGIA | IRefAdr !ZAI001 5 6 | 7 configurat: 1 1 ALG221IALG221IALG221 j i IALGIA1IALGIA! IALGIA i i i RefAdr|RefAdr|RefAdr ZAI005|ZAI009!ZAI013 I 1 1 1 8 9 | 10 i
! PWR323 | CPU331IADC311 | 8 MHZ }ADC 1 i' ALG221 IALGIA RefAdr ZAI017 1 1 ALG221j CMM3111 i i IALGIA|CMM j i i RefAdr! [ ZAI021J [ i i i i
4--.. H 1 1 1 1 1 1 1 1 1 1 1 1 i i i i i i i t i i i t
+-----------------------------------------------------------------------------+
i ps : i 2 R 0 G ALG221 IALGIA RefAdr ZA1029 3 A | 5 RAMMED CONI 1 1 1 1 ALG221|ALG221|ALG221 IALGIAIIALGIA!IALGIA i i RefAdr|RefAdr!RefAdr ZAI033 SZAI037'ZAI0A1 i i 1 1 (. + + H 6 i 7 : 8 1 1 1 to 1 1 1 + 1 1 H | O 1 1 1
i i [PWR323[ALG221 i i [ [IALGIA [RefAdr [ [XAI025 i i i t 1 1 1 1 ALG221IALG221| | j IALGIA!IALGIA! i i RefAdr!RefAdr! ZAI0A5!ZAI0A9| 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 t 1 1 1 1 1 t 1 1 i 1
i i i i i i i i i i i 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
RACK 2 +----+-------+------+-
PS 1 2 R 0 G 3 A RAMMED 5 CONI 6 I G U
PWR323 MDL9A0 MDL9A0 MDL9A0JMDL9A0 MDL630 MDL630
QRLY16 QRLY16 QRLY16IQRLY16 I DC8 I DC8
RefAdr RefAdr RefAdr!RefAdr RefAdr RefAdr
ZQ0001 ZQ0017 ZQ0033[ZQ0049 ZI0001 ZI0009
8
RATION
10
Figure 4.4
Station Main PLC Hardware Configuration


66
Global communications are implemented by
assigning ;unique references to each global I/O.
Each communications module is identified during
configuration with a specific bus address, with a
group of global registers assigned per address. The
CPU on the same rack as the communications module is
responsible for storing any data written to or read
from those registers. Any PLC on the bus can read
from or write to any global register.
The Operator Interface Terminal (OIT) is
i'L
configured with a separate software package than the
ladder logic programmer. It has backplane access to
its host PLC, and can access that PLC's I/O and
logic by addressing the appropriate data registers.
For example, if an A phase line current analog input
is wired to Analog Input 1, the OIT setup package
just refers to this address when designing a readout
screen, and the firmware handles the data transfer
automatically.
Appendices A, B, and C contain ladder logic
programs for the 12 kV line PLC, 230 kV line PLC,
and station Main PLC. These ladder diagrams were
l


67
developed on the GE Fanuc LogicMaster 90-30/20S
Programmed & Configuration Software Package, Version
2.04. The operation of the various schemes are
r
described with the built-in annotation feature of
the software.
The multi-shot reclosing scheme shown in
Appendix A has been tested on a GEFanuc model 90-30
PLC with a 311 CPU. The PLC was connected to a PCB
simulator and operation of all rungs of the ladder
logic prdgram were verified. The total scan time of
the program (with programmer on-line) was calculated
to be 11.iS msec, and was tested to be 10-11 msec.
Scan time is reduced by 3 msec, in the absence of
the hand held programmer.
The schemes in Appendix B and C have not been
tested, but a scan time of 10.1 msec can be
calculated for the 230 kV line PLC (w/o programmer).
The CPU used for the Station Main PLC is nearly
twice as fast as the distributed PLCs, but has more
I/O and communications tasks. Since no critical
functions are used on this PLC, a sweep time was not
calculated. The operating times found for the


68
reclosing, relays are fast enough for most
applications, since deionization delays exceed the
scan times by a factor of 20 or more.
Two possible operations console screens are
shown in Figure 4.5 and 4.6.
OPERATOR
INTERFACE
TERMINAL
Figure 4.5 230 kV One-Line Screen
Figure 4.5 is a screen showing a one-line of the
230 kV portion of the substation. Energized
components could be shown in red, de-energized


69
components in green. Overlays adjacent to the lines
show instantaneous Volts, Amps, Watts, and Vars,
with bus voltages shown next to the applicable bus.
XFMR LOW 01L XFMR l !o. XFMR TEMP
PCB A TROUBLE i ; PCP B TROUBLE PCB C TROUBLE PCB D TROUBLE PCB E TROUBLE
PCB F TROUBLE 'PCB G TROUBLE PCB H TROUBLE PCB J TROUBLE PCB K TROUBLE
PLC TROUBLE , I NTRUDER 'vm SWITCHER L TROUBLE
OPERATOR
INTERFACE
TERM INAL
I
Figure 4.6 Annunciator Screen
Figure 4.6 shows an annunciator screen with the
i
individual alarm cell flashing in a contrasting
color from the default hue.
i


70
Cost Comparison at Hypothetical Substation
A cost comparison between this PLC based system
and one implemented using conventional hardware can
be performed on several layers. The first and most
measurable quantity is hardware cost comparisons.
Secondly installation costs will be considered.
Project scheduling, engineering, maintenance and
support costs will be discussed briefly, but these
items are too nebulous to allow a simple cost
analysis.
Included in Appendix D is a spreadsheet
detailing the hardware and labor costs associated
with the installation at Hypothetical Substation.
The cost savings of 50% versus conventional
equipment are quite impressive. The largest savings
come in the elimination of the RTU and station
annunciator. Reclosing relays and metering cost
savings are less dramatic. As mentioned in chapter
2, the more features that can be incorporated, the
greater the savings.
The first installation of PLCs will require an
investment in training and support equipment, but


71
since these are one time expenses, they are not
included in the evaluation.
The self-checking capabilities of the PLC, along
with the standard building blocks of CPU's, Power
Supplies, and I/O modules will result in lower
maintenance, troubleshooting, and replacement costs.
Engineering time can be reduced through the use
of standard PLC configurations. The development of
new schemes can be tested off-line, and
modifications to existing schemes are easily
implemented in software. Since most of the control
logic is made up in software, panel wiring diagrams
will only be required for the relay panels, with the
control panels requiring interconnection diagrams
only. This will reduce the lead time for design,
shorten delivery of the control & relay panels, and
result in shorter commissioning schedules.


CHAPTER V
SUMMARY AND CONCLUSION
The functional requirements of modern utility-
substations was examined in light of control,
metering, and protection hardware. The need for
more sophisticated control and information gathering
functions was discussed.
The Programmable Logic Controller, once
considered strictly an industrial relay replacer,
was investigated for possible application to meet
modern substation requirements. With some cautious
use, the PLC can be an economical, flexible tool for
the substation engineer. Some factors to consider
are failure modes of the system, surge withstand
capabilities of the hardware, and the speed
requirements of the application. By examining these
factors, the engineer can evaluate whether a PLC is
suitable for application, and if so, can use the
criteria developed within this document to select
the specific hardware/software system.


73
Several utilities' applications were discussed
as reviewed in the literature. Though all
applications were fairly recent, preliminary results
were enthusiastically positive.
PLC based reclosing relays, breaker control
schemes, annunciation, and indicating metering
functions are all cost competitive with conventional
equipment.. The cost comparison was for hardware and
installation labor only and did not include
ancillary benefits of flexibility, modularity to
reduce inventories and reduce troubleshooting.
Three Ladder Logic programs were developed. One
scheme was,for a multi-shot reclosing relay, another
for a single shot reclosing relay with breaker
control functions, and the final scheme showed an
implementation of a station PLC that interfaces to
SCADA and a local CRT operator interface terminal.
In conclusion, the PLC was shown to be a useful
tool for the substation engineer to meet growing
demands on the electric utility system.


APPENDIX A
LADDER LOGIC FOR MULTI-SHOT RECLOSING RELAY


75
03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shot Reclosing Relay
Control, Alarm, and Global functions can be added later
GGGG EEEEE FFFFF AAA N N U U cccc
G E F A A 1 HU U c
G:GGG EEEE FFF AAAAA N N N U U c
G E F A A N NN U U c
GGG EEEEE F A A N N UUU cccc
AAA U U TTTTT 000 M M AAA TTTTT inn 000 N N
A A u. U T 0 0 MM MM A A T i 0 0 NN N
AAAAA U U T 0 0 M M M AAAAA T i 0 0 N N N
A A u. U T 0 0 M M A A T i 0 0 N NN
A A UUU T 000 M M A A T inn 000 N N
(*
(*
(*
(*
(*
<*
(*
(*
(*
(*
(*
(*
(*
(*
(*
(*
(*
Program: MULTRCL
PLC PROGRAM ENVIRONMENT HIGHEST REFERENCE USED
INPUT (ZI): 512
OUTPUT (ZQ): 512
INTERNAL (ZM): 1024
GENIUS GLOBAL (ZG): 1280
TEMPORARY (ZT): 256
REGISTER (ZR): 2048
ANALOG INPUT (ZAI): 128
ANALOG OUTPUT (ZAQ): 64
PROGRAM SIZE (BYTES):
DECLARATIONS (ENTRIES):
INPUT
OUTPUT
INTERNAL
GENIUS GLOBAL
TEMPORARY
REGISTER
ANALOG INPUT
ANALOG OUTPUT
512
39
ZI0021
ZQ0016
ZM0017
NONE
NONE
ZR0036
NONE
NONE
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
Program: MULTRCL
C:\LM90\MULTRCL


03-31-92
12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shot Reclosing Relay
Control, Alarm, and Global functions can be added later
[ START OF LD PROGRAM MULTRCL ]
t VARIABLE DECLARATIONS ]
VARIABLE DE
REFERENCE NICKNAME
210001 . RI
2M0001, RI AUX
210003 . BLK RCL
ZI0004 SYNC
210017 PCB A
210018 ' PCB B
210021 cs c
ZM0003 RESET
2M0008 ' LO AUX
2M0009 '' 1 SY WIND
2M0010 PWRFAIL
2Q0001, CLOSE 1
ZQ0016V CLOSE 2
2Q0003 RST AUX
2Q0005 LO
2Q0015 PLC_ALM
ZQ0002 TEST_PT
2M0002 INST
ZM0004 TD1
2M0005 TD2
2M0006 TD3
2M0007 RC_FAIL
I D E N T I
IDENTIFIER IDENTIFIER
MULTRCL,, NOTE 1 |i: PROGRAM COMMENT
N0TE_2 COMMENT
NOTE 3 . COMMENT
NOTE 4 , COMMENT
NOTE 5 COMMENT
NOTE 6 COMMENT
NOTE 7 COMMENT
NOTE 8 1 COMMENT
NOTE 9 COMMENT
NOTE_10' COMMENT
N0TE-11;:' COMMENT
N0TE_12 COMMENT
NOTE 13. COMMENT
NOTE 14'..- COMMENT
(*
CLARATION TABLE
REFERENCE DESCRIPTION
RECLOSE INITIATE
RECLOSE INIT. AUX
BLOCK RECLOSE
SYNC CHECK SUPERVISORY CONTACT
52a CONTACT
52b CONTACT
52CS CLOSE CONTACT
RECLOSING RELAY RESET TIMER
LOCKOUT AUXILIARY RELAY
SYNC WINDOW TIMER
PLC POWER SUPPLY FAILURE
CLOSE OUTPUT #1
CLOSE OUTPUT #2
RESET TIMER ENABLED INDICATOR
RECLOSING RELAY LOCKED OUT
PLC TROUBLE ALARM
TRIP BKR SIMULATOR(TEST ONLY)
HIGH SPEED RECLOSE ATTEMPT
FIRST TIME DELAYED ATTEMPT
SECOND TIME DELAYED ATTEMPT
THIRD TIME DELAYED ATTEMPT
FAILED TO RECLOSE AFTER ATE TRY
FIER TABLE
TYPE IDENTIFIER DESCRIPTION
Program: MULTRCL
C:\LM90\MULTRCL


03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shot Reclosing Relay
Control, Alarm, and Global functions can be added later
IDENTIFIER IDENTIFIER TYPE IDENTIFIER DESCRIPTION
NOTE 15 COMMENT
NOTE~16 COMMENT
[ START OF PROGRAM LOGIC ]
RUNG 3 STEP #0001
RI_AUX
( )--
TEST_PT
( )
#0001 LD ZI0001
#0002 AND ZI0017
#0003 AND NOT ZI0018
#0004 OUT ZM0001
#0005 OUT, ZQ0002
RUNG 4 STEP #0006
NOTE_l
(* COMMENT *)
I RI PCB A PCB B
+-] [--------] T-----3/T+
I I
I I
I I
I I
! +
(* RECLOSE INITIATE CONTACT INPUT, SUPERVISED BY POWER CIRCUIT BREAKER *)
(* STATUS CONTACTS (52a AND NOT 52b) TO INSURE THAT BREAKER WAS CLOSED *)
(* PRIOR TO RECEIPT OF INITIATE PULSE. *)
#0006 01 NOOP
RUNG 5 STEP #0007
|RI_AUX +-----+
+ ] [>DNCTR+.
S S *
! RESET | |
+-] [+R !
I I t
I i I
I I |
! CONST -+PV |
! +00001 | |
j +-----+
! ZR0001
+-----+
----i+ tmr +
!0.01s i
j I
CONST -+PV |
+00033 | !
+-----+
ZR0004
INST
-( )
#0007 LD ZM0001
#0008 LD ZM0003
IL TEXT FOR RUNG CONTINUED NEXT PAGE
Program: MULTRCL
C:\LM90\MULTRCL


I
78
03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shot Reclosing Relay
Control, Alarm, and Global functions can be added later
#0009 FUNC 16 DNCTR
PI: +00001
P2: ZR0001
#0010 FUNC 10 TMR
PI: 00001
. P2: +00033
' P3:' ZR0004
#0011 OUT ZM0002
RUNG 6
STEP #0012
N0TE_2
(* COMMENT *)
(* Cut & Paste 'the above rung as many times as required to develop a scheme *)
(* for a multi-shot,reclosing relay, increasing the DNCTR constant by 1 for *)
(* each successive shot, and entering the desired time delay for the TMR *)
(* constant. The first shot shown here is for a high speed reclosing *)
(* attempt with a 20 cycle deionization delay. *)
#0012 01 NOOP
RUNG 7 STEP #0013
|RI AUX + + + +
+__] [ >DNCTR+ + TMR +-
1 1 1 1 10.10s|
! RESET | 1 1 1 1
+--] t+R CONST -+PV :
1 1 1 1 +00050 | |
1 t 1 1 + +
! CONST -+PV ZR0010
: +00002 :
S +
! ZR0007
: #0013 LD ZM0001
: #0014 LD ZM0003
! #0015 FUNC '16 DNCTR
1 1 PI: +00002
1 1 P2: ZR0007
i #0016 FUNC 10 TMR
1 1 PI: 00010
1 1 P2: +00050
1 1 P3: ZR0010
i #0017 OUT ZM0004
Program: MULTRCL
C:\LM90\MULTRCL


03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shot Reclosing Relay
Control, Alarm, and Global functions can be added later
i RUNG 8 STEP #0018
I
jN0TE_3
!(* COMMENT *)
(* First Time-Delayed Reclose, set at 5 seconds
*)
#0018 01 NOOP
RUNG 9 STEP #0019
! RI_AUX +------+
+_.] [---->DNCTR+-
I I I
! RESET j j
+--] [+R !
I I I
I I I
S S !
! CONST -+PV j
I +00003 | 1
; +------+
! ZR0013
+------+
--------+ TMR +
|0.10s!
i t
CONST -+PV |
+00100 | |
+------+
ZR0016
TD2
( )
#0019 LD ZM0001
#0020 LD ZM0003
#0021 FUNC 16 DNCTR
Pis +00003
P2: ZR0013
#0022 FUNC 10 TMR
PI: 00010
P2: +00100
P3: ZR0016
#0023 OUT ZM0005
RUNG 10 STEP #0024
NOTE_4
(* COMMENT *)
(****************************************************************************)
(* Second Time-Delayed Reclose, set at 10 seconds *)
#0024 01 NOOP
Program: MULTRCL
C:\LM90\MULTRCL


03-31-92 12x34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
; Multi-Shoe Reclosing Relay
Control, Alarm, and Global functions can be added later
RUNG 11 STEP #0025
|RI AUX + + +


1 1 1 1 I 10.10s!
! RESET | 1 1 1 1 1
+ 1 1 1 1 1 £ ! CONST -+PV |
1 1 1 1 1 +00200 i :
1 1 1 1 i + +
| CONST -+PV i ZR0022
! +00004 | i
s +
! 'ZR0019 '
! #0025 LD ZM0001
i #0026 LD ZM0003
! #0027 FUNC 16 DNCTR
1 1 PI: +00004
1 1 P2: ZR0019
! #0028 FUNC 10 TMR
1 1 PI: 00010
1 1 P2: +00200
1 1 P3: ZR0022
! #0029 OUT ZM0006
RUNG 12 STEP #0030
NOTE_5
(* COMMENT *)
(* Third Time-Delayed Reclose, set at 20 seconds.
*)
#0030 01 NOOP
RUNG 13 STEP #0031
|RI_AUX +------+ RC_FAIL
+_.] [--->DNCTR+1........................................-......................( )
S S 1
|L0_AUX ! |
+_.] [+R |
I I I ,
! CONST -+PV |
! +00005 | |
+-----+
i ZR0025
#0031
#0032
#0033
LD
LD
FUNC 16
..PI*
ZM0001
ZM0008
DNCTR
+00005
----- IL TEXT FOR RUNG CONTINUED NEXT PAGE -----
Program: MULTRCL C:\LM90\MULTRCL


81
03-31-92 12:34 GE EANUC SERIES 90-30/90-20 DOCUMENTATION Multi-Shot Reclosing Relay
Control, Alarm, and Global functions can be added later
! , P2: ZR0025
| #0034 OUT ZM0007
I
I
! RUNG 14 STEP #0035
i
1NOTE_6
!(* COMMENT *)
(* After the 4th unsuccessful reclose attempt, send to Lockout.
*)
! #0035 01 N00P
I
! RUNG 15 STEP #0036
I
JZM0017 SYNC +-------+ SY_WIND
+] [-----]/[-+ TMR +.....................................................( )
i |0.10sj
! CONST -+PV !
: +00600 i i
! +---+
i ZR0028
#0036 LD ZM0017
#0037 AND NOT ZI0004
#0038 PUNC 10 TMR
PI: 00010
P2: +00600
;P3: ZR0028
#0039 0UT\' ZM0009
RUNG 16 STEP #0040
N0TE_7
(* COMMENT *)
(* Sync Window Timer set at 60 seconds. If a close output has been *)
(* attempted, but not completed due to failure to achieve permission *)
(* from the external Sync Check relay within the allotted time delay, *}
(* the relosing relay will go to Lockout. *}
#0040 01 !'NOOP
Program: MULTRCL
C:\LM90\MULTRCL


03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shot Redo sing Relay
Control, Alarm, and Global functions can be added later
RUNG 17 STEP #0041
I BIX RCL LO
+--] [..+------------------+--------------------------------------------------------(SM)-
I I I
I I I
!RC_PAIL| | LO_AUX
+] [+ + ( >
I I I
|SY WIND! !
+-T [--+ !
I I I
I I I
!PWRPAIL| 1 |
+-]/[-+ !
I I
IZM0011 PCB A PCB B |
+..] [------]/7----] T-+
I I
! cs_c !
+-] I............",......+
#0041 LD ZI0003
#0042 OR ZM0007
#0043 OR ZM0009
#0044 OR NOT , ZM0010
#0045 LD ZM0011
#0046 AND NOT ZI0017
#0047 AND Z10018
#0048 OR BIX
#0049 OR ZI0021
#0050 SEIM ZQ0005
#0051 OUT ZM0008
RUNG 18 STEP #0052
NOTE_8
(* COMMENT *)
(* Go to Lockout (LO or Q5) if: Block reclose input (13) is received *)
(* Failed on fourth reclose attempt *)
(* Sync Window Timer times out *)
(* Power to PLC has failed during cycle *)
(* Breaker did not close within Is of attempt *)
(* Breaker was closed by control switch *)
#0052 01 NOOP
Program: MULTRCL
C:\LM90\MULTRCL


83
03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shot Reclosing Relay
Control) Alarm, and Global functions can be added later
! RUNG 19 STEP #0053
! INST ZM0012 LO SYNC CLOSE 1
+--] E 1 1 [-+ 1 1 ( )__
1 1 TD1 ZM0013 | 1 1 1 1 1 ( CLOSE 2
+--] [ ]/[--+ J + ( )--
| TD2 ZM0014 ! 1 I 1 ZM0017
]/[--+ l'
1 1
1 1 TD3 ZM0015 1 1 1
+-_] [
: cs c , r i
+] [ +
1 #0053 LD ZM0002
! #0054 AND. NOT ZM0012
! #0055 LD ZM0004
: #0056 AND NOT ZM0013
! #0057 OR"" BLR
! #0058 LD ', , ZM0005
: #0059 AND' NOT ZM0014
i #0060 OR BLR
: #0061 LD i' ZM0006
: #0062 AND' NOT ZM0015
i #0063 OR,,' BLR
i #0064 AND NOT ZQ0005
! #0065 OR ZI0021
! #0066 LD BLR
! #0067 AND' ZI0004
! #0068 OUT, ZQ0001
! #0069 OUT ZQ0016
! #0070 OUT,, BLR
! #0071 OUT , ZM0017
RUNG 20 STEP #0072
N0TE_9 ,
(* COMMENT *')i
(* Breaker Close pulse initiated by INST, TD1, TD2, TD3 or 52CS, all *)
(* supervisediby the external SYNC check contact. Two output contacts are *)
(* used in series to provide security against a single output contact *)
(* failure resulting in an unexpected close operation. *)
#0072 01 NOOP
Program: MULTRCL
C:\LM90\MULTRCL


84
03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shot Reclosing Relay
Control, Alarm, and Global functions can be added later
| RUNG 21 STEP #0073
I
!CL0SE_1 +------+ ZM0011
+--] [----+ TMR + : ( )
! |0.10a|
i i
i i i
| CONST -+PV |
! +00010 i |
! +----+
I ZR0031
I
! #0073 LD XQ0001
! #0074 FUNC, 10 TMR
I PI: 00010
I P2: +00010
! P3: ZR0031
! #0075 OUT ZM0011
I
! RUNG 22 STEP #0076
I
|N0TE_10
!(* COMMENT
! (* Send to Lockout if breaker does not close within 1 second of the close *)
! (* outputs being made. *)
j #0076 01 NOOP
J
! RUNG 23 STEP #0077
!CLOSE 1 INST ZM0012
+--] [--+--] [.................................................................(SM)-
i i
I I
! ! TD1 ZM0013
I +-] [-.............................................................. 1 1 1
| ! TD2 ZM0014
! +-] [................................................................(SM)-
S I
! ! TD3 ZM0015
I + ] [................................................................(SM)-
I
I #0077 LD ZQ0001
! #0078 LD 1 BLR
! #0079 AND , ZM0002
i #0080 SETM ZM0012
i #0081 OUT. BLR
! #0082 LD ' BLR
! #0083 AND 1 ZM0004
: #0084 SETM ZM0013
! #0085 OUT BLR;
----- IL TEXT FOR RUNG CONTINUED NEXT PAGE --------
Program: MULTRCL C:\LM90\MULTRCL


85
03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shoe Reclosing Relay
Controli Alarm, and Global functions can be added later
#0086 LD | 1 BLK
#0087 AND ZM0005
#0088 SETM ZM0014
#0089 OUT,. |:BLK,
#0090 AND' , ZM0006
#0091 SETMi ZM0015
RUNG 24 STEP #0092
NOTE_ll
(* COMMENT *)
(* The M12,M13,M14,and M15 coils are used to keep the reclosing elements *)
(* from operating more than once in a cycle (a function of how the *)
(* downcounters work) *)
#0092 01 NOOP
RUNG 25 STEP #0093
!CL0SE_1 ZM0016
+] [--+--------i-'.............................................................(RM)-
I I
|L0_AUX |
+-] [+
I
I
! #0093 LD ZQ0001
! #0094 OR ZM0008
i #0095 RSTM ZM0016
RUNG 26 STEP #0096
N0TE_12
(* COMMENT *)
(* This rung is used to enable the reset timers. Necessary to keep timers *)
(* from runningj'after the relay has successfully reset. *)
#0096 01 .N0OP
RUNG 27 STEP #0097
LO AUX PCB A PCB B ZM0016
] [---]/[ ]/[
#0097 LD NOT ZM0008
#0098 AND ZI0017
#0099 AND NOT ZI0018
#0100 AND NOT ZM0016
#0101 OUT ZQ0003
RST_AUX
( >
Program: MULTRCL
C:\LM90\MULTRCL


86
03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
Multi-Shot Reclosing Relay
Controli Alarm, and Global functions can be added later
RUNG 28 STEP #0102
iN0TE_13 .1
i(* COMMENT *) '!
(****************************************************************************)
(* This rung is to provide a means to monitor whether or not the reset *)
(* has been initiated. Intended as a testing/troubleshooting auxiliary. *)
(**********iHHHHr*****ft***********W*iHfr***********************************W*)
#0102 01 N00P
RUNG 29 STEP #0103
RST_AUX ZM0016 ''+|+
+-_] [-----]/[--+ TMR ++
!0.10s
ZM0012
---(RM)-
C0NST -+PV ]
+00200 |
' +-1--+
. ZR0034 +
ZM0013
(RM)-
ZM0014
(RM)-
ZM0015
(RM)-
ZM0016
(SM)-
L0
(RM)-
RESET
( )-- i
#0103 LD 1 ZQ0003
#0104 AND NOT ZM0016
#0105 EUNC 101 TMR
: PI : 00010
P2: +00200
, P3 ZR0034
#0106 RSTM ZM0012
#0107 RSTM ZM0013
#0108 RSTM ZM0014
#0109 RSTM ZM0015
#0110 SETM ZM0016
#0111 RSTM ZQ0005
#0112 OUT ZM0003
i
I
Program: MULTRCL
C:\LM90\MULTRCL


03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION Multi-Shot Recloalng Relay
Control, Alarm, and Global functions can ba added later
I
| RUNG 30 STOP #0113
N0TE_14 !
(* COMMENT *)''
(* The above rung is the RESET timer, in this case set for 20 seconds *)
(* (testing), change to 43 seconds after checkout. If the breaker *)
(* remains dosed for 20 seconds and the BLK_RCL input is removed, reset *)
(* the reclose LO and redose count to zero, and enable the counter/timer *)
(* outputs. The M16 relay is used to clear the reset timer until the next *)
(* redosing cycle is initiated. *)
! #0113
i
! RUNG 31
1
!BLK_RCL
+--]/[-------
oi; noop
STEP #0114
PWRPAIL
( )--
#0114 LD NOT ZI0003
#0115 OUT | ZM0010
RUNG 32 STEP #0116
I
N0TE_15
(* COMMENT
*)
(* This circuit sends the relay to lockout when it wakes up after a power *)
(* failure. If the breaker is closed, the relay will automatically come *)
(* back on line, after the reset time delay, unless it was turned off *)
(* during the outage by enabling the BLK_RCL input (79CO for instance). *)
(****************W***********************************************************)
! #0116 1 01 NOOP
1 RUNG 33 STEP #[0117
i |SY FLT +--] [--+ 1
!10 FLT +-] [--+ ' j
|HRD FLT! +] [--+
!SFT FLt! +-] [-+ !
1 #0117 LD ZSC010
IL TEXT FOR RUNG CONTINUED NEXT PAGE
PLC_ALM
< )
Program: MULTRCL
C:\LM90\MULTRCL


03-31-92 12:34 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
| Multi-Shot Reclosing Relay
Control, Alarm, and Global functions can be added later
i #0118 OR , ZSC011
j #0119 OR ZSC014
! #0120 OR : ZSC015
j #0121 OUT : ZQ0015
! RUNG 34 STEP #0122 i
JNOTE 16
!(* COMMENT *)
(* This rung Is toiannunciate PLC troubles detected by self-monitoring *)
(* devices. The faults annunciated for include: System Fault, 1/0 Fault, *)
(* Hardware Fault, and Software Fault. Other fault types can be used if *)
(* desired. *)
(* *)
('kifit'k'kick1c1rkit,k1ek,k-ki(4t1tit1t'k/rk1rk,k4tirkkikic'kkk'kkitk1t1c'k,k,k4c,k,k1tit'k1e1t1t1rk'k1t1rk4t'kiit'k'k,kilrk4t'ie1c1t4t1eiek)
#0122 01 NOOP
[ END OF PROGRAM LOGIC ]
#0123 END OF PROGRAM
Program: MULTRCL
C:\LM90\MULTRCL


APPENDIX B
SINGLE!SHOT, HIGH SPEED RECLOSING RELAY
1 AND BREAKER CONTROL


90
03-31-92 12:29 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
I One Shot High Speed Reclosing Relay
Control, Alarm, and Global functions are added
GGGGjEEEEE FFPFF AAA N N U U cccc
G 'E F A A NN N U u c
G GGGiEEEE FFF AAAAA N N N U u c
G GlE F A A N NN U u c
GGG EEEEE F A A N N UUU cccc
i
AAA U Uj TTTTT OOO M M AAA TTTTT IIIII OOO N N
A AD Ul T 0 0 MM MM A A T I 0 0 NN N
AAAAA U U' T 0 0 M M M AAAAA T I 0 0 N N N
A A U U, T 0 0 M M A A T I 0 0 N NN
A A UUU T OOO M M A A T IIIII OOO N N
i
(* <* (* l* Program: PLC PROGRAM ENVIRONMENT RCL230 HIGHEST REFERENCE USED
(* INPUT (ZI): 512 INPUT: ZI0014
(* ! OUTPUT (ZQ): 512 OUTPUT: ZQ0015
(* INTERNAL (ZM): 1024 INTERNAL: ZM0013
(* GENIUS GLOBAL (ZG): 1280 GENIUS GLOBAL: ZG0040
(* TEMPORARY (ZT): 256 TEMPORARY: NONE
(* REGISTER (ZR): 512 REGISTER: ZR0024
(* ANALOG INPUT (ZAI): 64 ANALOG INPUT: NONE
(* ANALOG OUTPUT (ZAQ): 32 ANALOG OUTPUT: NONE
(*
(*
(*
(*
PROGRAM SIZE (BYTES): 480
j DECLARATIONS (ENTRIES): 63
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
*)
!
Program: RCL230
C:\LM90\RCL230
i
i
i
l


03-31-92 12i29 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
j One Shoe High Speed Reclosing Relay
Control, Alarm, and Global functions are added
]
![ START OF LD PROGRAM RCL230 ] (*
i
![ VARIABLE DECLARATIONS ]
VAR ij ABLE DECLARATION TABLE
REFERENCE j NICKNAME REFERENCE DESCRIPTION
ZI0001 A52A BREAKER A 32a CONTACT
ZI0002 A52B BREAKER A 52b CONTACT
ZI0003 SYNC SYNC CHECK PERMISSIVE CONTACT
ZI0004 ! RI RECLOSE INITIATE
ZI0005 BLK-RCL BLOCK RECLOSE INPUT
ZI0006 B52A . BREAKER B 52a CONTACT
Z10007 ; B52B BREAKER B 52b CONTACT
ZI0008 A 63A BREAKER A ALARM
ZI0009 B_63A BREAKER B ALARM
ZI0010 C PB A EMERGENCY CLOSE PUSH BUTTON A
ZI0011 LO MAIN LOSS OF MAIN PLC
ZI0012 C PB B EMERGENCY CLOSE PUSH BUTTON B
ZI0013 T_PB A EMERGENCY TRIP PUSH BUTTON A
ZI0014 T PB B EMERGENCY TRIP PUSH BUTTON B
ZQ0001 TRIP_A1 TRIP1 OUTPUT TO BREAKER A
ZQ0002 TRIP A2 TRIP2 OUTPUT TO BREAKER A
ZQ0003 TRIP B1 TRIP1 TO PCB B
XQ0004 TRIP B2 TRIP2 TO PCB B
ZQ0005 CLOSE1A CLOSE1 TO BREAKER A
ZQ0006 CLOSE2A CLOSE2 TO PCB A
ZQ0007 CLOSEIB CLOSE1 TO PCB B
ZQ0008, CLOSE2B CLOSE2 TO PCB B
ZQ0015 PLC_ALM PLC TROUBLE ALARM
ZG0001 A79CO 79CO RECLOSE CUTOFF A
ZG0002 B79CO 79CO RECLOSE CUTOFF B
ZG0033 A52CS T OPERATOR CONSOLE TRIP A
ZG0035 B52CS T OPERATOR CONSOLE TRIP B
ZG0034 A52CS C OPERATOR CONSOLE CLOSE A
ZG0036 B32CS C OPERATOR CONSOLE CLOSE B
ZG0016 LO 86NB NORTH BUS DIFFERENTIAL LOCKOUT
ZG0020- A_86BF BREAKER FAILURE LOCKOUT A
ZG0021 B 86BF BREAKER FAILURE LOCKOUT B
ZG0022 C_86BF BREAKER FAILURE LOCKOUT C
ZG0023 ! D 86BF BREAKER FAILURE LOCKOUT D
ZG0018 j LO 86T TRANSFORMER LOCKOUT
ZQ0009 ; LO RECLOSE LOCKOUT
ZM0002 | INST HIGH SPEED RECLOSE ATTEMPT
ZM0003 ! RESET RECLOSE RESET TIMER
ZM0004 LO AUX RECLOSE LOCKOUT AUXILIARY
ZM0006 RC FAIL FAILED TO RECLOSE AFTER 1ST TRY
ZM0007 PWRFAIL PLC POWER SUPPLY FAILURE
ZG0037 A 52A BREAKER A STATUS
ZG0038 | B 52A BREAKER B STATUS
ZG0039 j A ALARM BREAKER A ALARM
ZG0040 1 B ALARM BREAKER B ALARM
Program: RCL230 C:\LM90\RCL230


I
92
03-31-92 12:29 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.0A)
! | One Shot High Speed Recloslng Relay
Control, Alarm, and Global functions are added
! IDENTIFIER TABLE
IDENTIFIER
RCL230
N0TE_1
NOTE_9
NOTE_10
NOTE_A'
NOTE 6
NOTE~7
NOTE 8
NOTE^IA
NOTE_13
N0TE_15
N0TE_11
NOTE_20
N0TE_16
N0TE_18
N0TE_19
N0TE_21
N0TE_22
[ START OF PI
IDENTIFIER TYPE
PROGRAM
COMMENT
COMMENT
COMMENT
LABEL
COMMENT
COMMENT
COMMENT
COMMENT
COMMENT
COMMENT
COMMENT
COMMENT
COMMENT
COMMENT
COMMENT
COMMENT
COMMENT
LOGIC ]
IDENTIFIER DESCRIPTION
RUNG 3 STEP #0001
! A52A AS2B Rl! +---+
+__] [--]/[--!] j[>DNCTR+
I .It
I III
! RESET ! |
+~] [..........-+R !
i t i
i i i
i ii
{ CONST -+PV !
I , +06001 i
! 1 +---+
: | zroooi
+------+
--------+ tmr +
!0.01s i
I I
CONST -+PV |
+00033 | j
+
ZR000A
INST
-< )
RUNG A STEP #0008
NOTE_l
(* COMMENT *)
(* If breaker A was closed and received a reclose initiate signal
(* indicating a redosable fault type, then this rung enables the
(* 1st reclose shot, with a 20 cycle deionization delay
*)
*)
*)
I
Program: RCL230
C:\LM90\RCL230


93
03-31-92 12:29 GE FANUC SERIES 90-30/90-20 DOCUMENTATION (v2.04)
,| One Shoe High Speed Reclosing Relay
Controlt Alarm, and Global functions are added
| RUNG 5 STEP #0009
i RI +-----+, RC_FA1L
+__] [->DNCTR+................................................-T )
i IS'
|L0_AUX : i , !
+] [--+R i j
| i ;
I CONST -+PV j
I +00002 | |
J ++
I XR0007 ;
! I
! RUNG 6 STEP #0013
N0TE_6
(* COMMENT *)
(* If 1st Reclose Attempt is unsuccessful, send to lockout
RUNG 7 STEP #0014
!BLK-RCL LO
+--] [+---+.................................(SM)-
ii ii ,i
|RC_EAIL| j | LO_AUX
+] [-+ | +--------------------------- (M)~
ii 1 i
i i ii
jPWREAILj !' |
+]/[+ !
j j
IIM0008 A52A A52B |
+..] [-----3/1. ].[--+
*
i i
j A79CO I |
+--] [.........-[----+
! i !
'A52CS_C !
+--] I---------------- +
RUNG 8 STEP #0025
NOTE_10
(* COMMENT *)
i
i l
Program: RCL230
C:\LM90\RCL230
l