1

Power System Background

Originally, the model power system was constructed by Idaho Power, the main

Southern Idaho electrical utility, headquartered in Boise, Idaho. Idaho Power built the

system to test protection equipment such as relays and breakers. They also used the

model power system to model part of their own transmission system around the Midpoint

area in lower-central Idaho. In the mid-1990’s, Idaho Power donated the system to the

University of Idaho.

The University of Idaho has made several modifications to the system including

but not limited to (1) a fault matrix in which three faults can be placed on the system

either simultaneously or in an evolving manner (2) the ability to load impedance faults

onto the system and (3) incorporating SEL relays into the system.

Looking at each of the modifications in turn, the fault matrix is three sets of

thyristors controlled by three separate microcontrollers. Using a computer, a user can

program the microcontrollers to fire the thyristors for a specified period of time. While

the thyristors are being fired they act as a short circuit where the fault matrix is connected

to the system.

As a senior design project in 2001-2002, a group attempted to make it possible to

have impedance associated with a fault. At the writing of this guide this feature does not

yet function properly.

The SEL relays where donated to the University by Schweitzer Engineering Labs,

an industry leading relay design firm based out of Pullman, Washington. The relays are

microprocessor based and can be programmed for a variety of protection purposes. Some

protection purposes include, but are not limited to, overcurrent protection, under or over

voltage protection, and frequency protection. The relays also allow a user to piece

together logic blocks in which the relays will send a trip signal in the event of multiple

occurrences. Thanks to SEL, the University has been able to use the model power system

2

to enlighten students on the operation of relays, give students hands on experience with

actual power system configurations, research system designs, test relay settings, and

perform many other academic studies.

3

Main Parts of the Model Power System

The model power system consists of many different components. The following

components are listed here with an explanation because they are mentioned often in the

user guide.

(1) Transmission Lines

The power system consists of four separate transmission lines that can be connected

in any fashion the power system operator desires. Each transmission line is basically

a pi model consisting of a variable series impedance, a parallel capacitance to ground,

capacitance between the lines, and mutual inductances. The series impedance is

variable from .1+j*1 to 1+j*10 in .1+j*1 increments (Figure 1).

Figure 1: Variable Line Impedance

The parallel capacitance to ground and capacitance between lines is fixed at a

constant value of 470 µF. Series capacitors can also be switched in and out of the

system. For a more detailed view of the system look at the model power system AC

schematic taped to the wall in the power lab.

4

(2) Four Breakers

There are four three phase breakers connect to the system (Figure 2). Each of these

breakers is connected to a relay through a communication module located at the very

top of the model power system.

Figure 2: Six Single Phase Breakers (Two Lines)

The breakers closest to L1 and L3 are able to reclose if the “reclose switch” is on and

if given a specific command from the relays. All breakers have manual open and

close piston handles (Figure 3) connected to them, enabling the power system

operator to energize and de-energize the lines whenever desired.

Figure 3: Breaker Piston Handle

5

(3) SEL Relays

Each breaker on the system is connected to a specific relay. The breakers off of L1

and L3 are connected to SEL351S overcurrent relays and the breakers off of L2 and

L4 are connected to SEL321 distance relays. The overcurrent relays act like a fuse,

when the current running through them crosses a certain threshold, which is

programmed into the relay, the relay will send a trip command, after a specified

period of time, to the breaker and the breaker will open. The distance relays, rather

than using thresholds, use zones to determine the location of a fault. These zones are

specified in ohms. The relay will determine which zone the fault is located, by taking

voltage and current measurements, and trip according to elements set for that zone.

In the lab, the protection schemes are modified using Ewan Telnet, a program

installed on the computer closest to the South wall.

Figure 4: SEL 321 Distance Relay

(4) LEMs

The primary tool used to measure voltages and currents on the model power system

are voltage and current LEMs. The LEMs can be connected anywhere on the system

to measure voltages and currents. The LEMs sample the line to line voltages and

currents at discrete intervals and using the program GLGraphMain, installed on the

computer closest to the North wall, these readings can be acquired and seen on a

graph. In order to be able to view the values of the voltages and currents, the data

points stored on the computer must be converted into a readable graph in MatLAB.

The procedure to do this can be found on page 16 of the manual.

6

(5) Fault Matrix

There are three sets of thyristors connected to the fault matrix. Thyristors act like

diodes that require a firing signal before they can turn on. The firing signal comes

from the microcontroller connected to the thyristors. Using the program

GLGraphMain, the power system operator can program the thyristors to fire for a

specified period of time, thereby creating a virtual short on the system. This virtual

short created on the system is known as a fault. Using the microcontrollers, the user

can place single line to ground faults, line to line faults, double line to ground faults,

and three phase faults on the system for any amount of time, at up to three faults at a

time. There is also the option of having evolving faults, such as a fault beginning as a

single line to ground fault and then becoming a three phase fault.

Figure 5: The Fault Matrix

(6) M/G Set

The M/G set is a 5kW, 120 Volt, synchronous machine. The M/G set is located in the

southwest corner of the lab however the controls for the M/G set are located on the

right side of the model power system. Using the controls on the model power system,

the power system operator can adjust the speed of the machine and the voltage at the

terminals of the machine. In order to run the machine in conjunction with the infinite

bus (Avista) there is a synchroscope to allow the power system operator to close the

7

breaker connecting the two at the correct time (in a fashion similar to the light bulbs

in the power lab).

8

Startup Procedures for the Model Power System

To ensure safety, because of the high voltage, two people must always be in the room

while running the power system.

1) Set Up

a) Ensure that the two mushroom head “Emergency Stop” buttons located near the

“System Power” and the “M/G Set” controls are pulled out.

Figure 6. Emergency Stop Button

b) Make sure that the shunt trip breaker on the south wall of the lab is reset (on).

c) Double check that the configuration patched together on the panel jacks is

electrically valid and safe. (i.e. Make sure the jumper cables to the M/G set are

disconnected if the M/G set is not to be used).

d) Ensure all four pistol grip breaker control handles show green (rotate the handles

to your left) indicating that they are open.

9

2) System Start

a) Remove the padlock and turn on the main breaker located on the south wall.

b) Flip on the “Communication and DC Control” switch located on the left side of

the power system to supply power to the relay control modules and the breakers.

c) Press the “System Power On” button to activate the system. The source light

should come on indicating there is a voltage on the line.

Figure 7. System Power Buttons and Source Light

3) M/G Set Operation (If the M/G Set is to be Used)

a) Look over the M/G Set equipment in the southwest corner of the lab for readiness

and safety.

b) Ensure that the circuit breakers where the M/G Set is to be patched into the

system are open (green). Before the M/G Set can be electrically connected into

the system it must be started up and synchronized with Avista.

10

c) Start the M/G Set and drive electronics by pressing the system on button. You

should hear the generator start up.

d) Before synchronizing, wait approximately 1 minute after starting for the

controller timer to engage the drive clutch. When the clutch engages, this will be

obvious from a sudden change in noise, the generator light on the right end of the

power system should illuminate.

Figure 8. M/G Set Panel Jacks and Light

e) Adjust the speed and voltage controls appropriately using the frequency,

synchroscope, and voltage meters. Adjust the voltage to 120 volts and adjust the

speed so that the frequency meter reads 60Hz and the rotation of the synchroscope

needle slows way down.

11

Figure 9. Frequency and Syncroscope Meters

f) The needle on the synchroscope should be rotating very slowly if close to

synchronous speed. Close the generator into the rest of the power system when

the synchroscope needle is pointing directly upward.

Note: To enhance understanding of the synchroscope, if the needle is pointing

directly downward and is not rotating, this is the point at which the M/G set is

exactly 180 degrees out of phase with the system.

4) System Stop

a) Only use the mushroom head “Emergency Stop” switch for emergencies (they

will trip the shunt trip breaker).

b) Return all pistol grips to the “green” (open) position before turning the system

power off to ensure that the breakers are actually reset (tripped open).

c) Press the “System Power Off” button to turn off everything (including the M/G

Set) except for the shunt trip breaker.

d) Turn off the main breaker and lock it if done with the system.

e) Turn off the Communication and DC Contol switch.

12

Initiating Faults onto the Model Power System

The model power system has the ability to have one, two or three faults

simultaneously occur on the system. These faults can be single line to ground, double

line to ground, line to line or three-phase. To initiate a fault on the system, follow the

instructions given below.

1) Connect the fault matrix to the system at the node where the fault is desired.

System X, Y, and Z are three different microcontrollers. This allows the user to

connect up to three faults at different locations on the system.

2) Go to the computer closest to the north wall in the lab and open a program called

“GL Graph Main”. There is a shortcut on the desktop for easy access.

Figure 10. Screen shot of the GL Graph Main program.

3) Click on the “Initialize” menu and select “Driver Linx”. It should be set on

Keithley KPCI-3100 Series, if it is click OK, if not then select it and click OK.

4) Click again on the “Initialize” menu and select “Subsystem”, then “Analog

Input”. This step is required to receive readings from the LEMs patched into the

system.

13

5) Click on the “Options” menu and select “Channels/Gains”.

a. Click on the “Load” button on the top of the window

b. From the load window, click on “Root”, then select “SeniorDesign”, then

select the file “12channels.cgo”.

Figure 11. Screen shot of the “Channels/Gains” window.

6) This is an optional step. If the user wishes to alter the sampling rates of the

LEMs, click on the “Options” menu and select “Rates/#Samples”. To change the

values, simply click and retype the values according to the project.

Sampling Rate 18000 Hz

Sampling Period 5.55556e-00

Channel Sampling Rate 3000 Hz

Cycles 60

Samples (per Channel) 3000

Time 1 sec

Table 1. Default Values for the Rates/#Samples.

7) Click on the “Terminal” menu and select “Start”. This will bring up the Transient

Network Analysis window where the user can program a fault.

14

Figure 12. Screen shot of Transient Network Analysis window.

8) There are three microcontrollers that can be used. To access the first one type

“uC21” then enter. To gain access to the second type “uC22” and type “uC23” to

access the third.

Note: Nothing appears on the screen when attempting to access microcontrollers.

9) Once accessed, the name of the microcontroller, uC21, uC22, or uC23 will appear

on the left side of the screen. Hit “V” then enter to go into Verbose Mode. This

will allow explanation of how to enter a fault to later be brought up on the screen

10) Type “F” and return to enter Fault Mode. The program will want five values

entered to program a fault. The first number is the section, for all intents and

purposes use a “0” for this. The second number is the duration in cycles of the

fault to be put on the system. This value can be between 0-200 cycles. The third

number is the type of fault:

0 is no fault

1 is a line A to line C fault

2 is a line A to line B fault

3 is a line A to line B to line C fault

4 is a line A to ground fault

15

5 is a line A to line C to ground fault

6 is a line A to line B to ground fault

7 is a line A to line B to line C to ground fault

The fourth number is the initial fault degree, use a “90” for this value. And the

fifth number is the variable impedance degree, use a “0” for this value.

An example of a fault entry is:

0 60 7 90 0

This is a three-phase to ground fault for 60 cycles in segment zero with an initial

fault degree of 90. After the values are entered, press enter twice and the “uCxx”

will return on the left side.

11) After the “uCxx” returns, enter “X” then enter to exit the microcontroller. Close

the TNA window and press the “Acquire” button on the GL Graph Main window.

This will send the fault to the system.

12) After the fault has been sent, click on the display button and the waveforms from

the system will appear on the screen. These values however are unit-less and

need to be sent to a Matlab file to be converted.

13) The fault programmed will remain on the microcontroller until the user exits GL

Graph Main, the user re-enters the TNA Terminal window and programs a new

fault, or the user re-enters the TNA terminal accesses the microcontroller and

types “E” to erase the contents on that microcontroller.

16

Transferring Plots to Matlab

Unfortunately the sketches in the GLgraphMain program do not have scales along

the axis to allow accurate measurements to be read from the graphs. To create voltage

and current sketches with axis scales, one option is to transfer the data to Matlab.

1. In the “File” pull down menu of the GlgraphMain program select “save as” and save

the data as a dt file. (i.e. C:\seniordesign\sample.dt)

2. Next open up the file in “Notepad”. You should see columns of data. Each column

represents different measurements taken over time. The first three columns are the

three phases of current taken with LEM1. The next three columns are the line to line

voltage readings taken with LEM1. While the next three columns are the current

readings taken with LEM2. Etc.

3. To get this data into the right format for Matlab, delete the top row that includes only

two numbers as shown below.

12 3000 0.000056 Delete These Two Numbers-1.059570 3.784180 -2.583008 0.000000 -0.131836 0.102539 -1.748047 3.813477 -1.855469 -0.029297 0.131836 -0.087891

-1.899414 3.745117 -1.689453 0.034180 -0.136719 0.068359 -2.529297 3.715820 -0.957031 -0.063477 0.136719 -0.053711

-2.656250 3.598633 -0.786133 0.063477 -0.146484 0.048828 -3.183594 3.447266 -0.029297 -0.092773 0.141602 -0.034180

-3.291016 3.276367 0.166016 0.087891 -0.126953 0.019531 -3.598633 2.954102 0.859375 -0.107422 0.126953 -0.014648

-3.676758 2.783203 1.000977 0.102539 -0.117188 -0.004883 -3.676758 2.114258 1.748047 -0.112305 0.097656 0.043945

-3.720703 1.977539 1.835938 0.102539 -0.087891 -0.039063 -3.579102 1.191406 2.558594 -0.122070 0.068359 0.068359

-3.583984 1.059570 2.602539 0.107422 -0.058594 -0.068359 -3.369141 0.258789 3.232422 -0.112305 0.048828 0.068359

-3.300781 0.073242 3.276367 0.122070 -0.029297 -0.097656 -2.973633 -0.664063 3.666992 -0.117188 -0.004883 0.117188

-2.861328 -0.810547 3.662109 0.112305 -0.009766 -0.112305 -2.246094 -1.567383 3.793945 -0.087891 -0.029297 0.122070

17

4. Next scroll down the file all the way to the bottom of the file until you see some data

similar to this shown below. Delete this block of data shown below.

Vxab 1 1 5.000000 0.000000 0.000000 1.000000 -1.000000

Vxbc 1 1 5.000000 0.000000 1.000000 0.000000 -1.000000

Vxca 1 1 5.000000 0.000000 1.000000 1.000000 -1.000000

Ixa 1 1 5.000000 1.000000 0.000000 0.000000 -1.000000

Ixb 1 1 5.000000 1.000000 0.000000 1.000000 -1.000000

Ixc 1 1 5.000000 1.000000 1.000000 0.000000 -1.000000

0 0 0.000000 1.000000 1.000000 1.000000 -1.000000

0 0 0.000000 1.000000 0.500000 0.000000 -1.000000

Vyab 1 1 -5.000000 0.443137 0.443137 0.776471 -1.000000

Vybc 1 1 -5.000000 0.443137 0.776471 0.443137 -1.000000

Vyca 1 1 -5.000000 0.219608 0.556863 0.556863 -1.000000

Iya 1 1 -5.000000 0.776471 0.443137 0.443137 -1.000000

Iyb 1 1 -5.000000 0.556863 0.219608 0.556863 -1.000000

Iyc 1 1 -5.000000 0.556863 0.556863 0.219608 -1.000000

c1 0 0 -2.000000 1.000000 1.000000 1.000000 -1.000000

c2 0 0 -2.000000 1.000000 0.854902 1.000000 -1.000000

Vzab 0 0 -5.000000 1.000000 0.141176 0.749020 -1.000000

Vzbc 0 0 -5.000000 0.749020 0.427451 0.749020 -1.000000

Vzca 0 0 -5.000000 0.498039 0.713726 0.749020 -1.000000

Iza 0 0 -5.000000 0.000000 0.713726 0.247059 -1.000000

Izb 0 0 -5.000000 1.000000 0.568627 0.247059 -1.000000

Izc 0 0 -5.000000 0.000000 0.854902 0.000000 -1.000000

0 0 0.000000 1.000000 1.000000 1.000000 -1.000000

5. Save the resulting notepad file as a .mat file. (i.e. C:\seniordesign\sample.mat)

6. Open up Matlab and create a file that includes the script on the next page. This file is

also already saved on the computer in the senior design directory under the name

plot_command.

18

plot_commmand script

clear all;

addpath c:/seniordesign;

load sample.mat -ascii;

time=(0:2999)*.00066666666; %Note: TNA is set to take 3000 samples

y1=sample(:,7); %Note: This takes three different columns (7,8,and 9) of data from % the output file (ex. sample.mat) and definesy2=sample(:,8); % the three different columns of data as three variables

y3=sample(:,9);

cf=10; %The current factor on the lems is 10

vf=81.4/sqrt(3); %The voltage factor on the lems is 81.4 line to line. The voltage is %divided by the square %root of three to make it a line to neutral voltage

figure(1);plot(time,y1*vf,time,y2*vf,time,y3*vf);grid;xlabel('Time');ylabel('Voltage');title('Longline Zone 1 Fault Voltage');

% end of program

You will most likely need to modify the matlab script so that the program will

plot the data you specify. Follow the steps below.

7. First after the “addpath” command, specify the directory that the file is in.

8. Next after the “load” command enter the .mat file name followed by “–ascii”.

9. Define the columns of data you want plotted into variables. In the example script

above three variables were defined. For example here is how a variable is defined

( i.e. variable name = filename(:,column number))

19

10. Next after the “plot” command, enter in the variables you want plotted. For each

variable to be plotted you will need to specify the x-axis, which is time.

11. For each variable in the plot command multiply by vf if it’s a voltage or cf if it’s a

current. These values are the voltage and current transform factors currently

configured for the LEMs.

12. Run the program. The program should give the currents and/or the line to neutral

peak voltages specified. (Note: For unblanced faults the voltage factor must be

changed. Dividing by the square root of 3 only works for balanced systems.)

20

Programming the SEL Relays

Before the user begins, the following settings must be known:

(1) Which relay do I want to read/change settings?

(2) In which group in this relay should I be operating?

If unsure about these questions first, please be sure not to permanently change any

setting in the relay (the program always asks to save settings, say NO) and second, find

out the answers by talking to Dr. Brain Johnson.

There is one relay for each of four breakers on the model power system. SEL 351S

relays are connected to the breakers closest to L1 and L3 and SEL 321 relays are

connected to the breakers closest to L2 and L4.

!IMPORTANT!

Current measurements into the SEL relays are scaled down by a factor of two. This is

important when creating current protection settings.

The four relays are also connected to ports on the SEL 2030 communication relay.

Using the computer closest to the South wall, the user can telnet into the SEL 2030

communication relay. Once the user has accessed the 2030, the user can use this relay

communicate with each of the other four relays to read/change settings.

This guide is not going to go into extreme depth to explain all the settings in the

two different types of relays due to the complexity associated with them, but it will go

over some basic changes that can be made. Everything explained, except for how to

navigate around Ewan Telnet, can also be found in the instruction manuals for these

relays.

21

To access a particular relay and read/change setting, follow the steps provided below:

1) Go to the computer closest to the South wall and open Ewan Telnet.

2) Once in Ewan Telnet, the first thing to do is gain Level 1 access to the SEL 2030

communication relay. To do this enter “ACC” and then enter the password

“OTTER”.

3) The next step is to gain Level 2 access. To do this enter “2AC” and then enter the

password “TAIL”.

4) To see a list of possible commands at this point type “WHAT”.

5) In order to begin changing settings in the relays the user must know which relays

are connected to which ports. Here is a list showing the relay connected to each

port. This can also be found by typing “WHO”

PORT 1: SEL 321 on L2

PORT 2: SEL 321 on L4

PORT 3: SEL 351S on L1

PORT 4: SEL 351S on L3

6) First, look at programming the SEL 321 on L2. Type in “PORT 1”.

7) Follow steps (2) and (3) once again to gain Level 2 access to the relay.

8) Now enter the group to read/change settings in by typing “GRO #” where # is the

number of the group desired. Each relay has six separate groups that are

unrelated, allowing for six completely different protection schemes for each relay.

9) Now, to view the settings in this group type in “SHO”. A list of acronyms will

stream down the window. Each one of these acronyms has a different meaning

22

which can be found in the Instruction Manual of the relay starting on page 5-25.

A few of the more important settings are listed below:

DIR1: This is the direction in which the relay is looking for its Zone 1

mode of protection. This is used in conjunction with many of the other

settings to determine whether or not the relay should trip. If the relay is

looking forward (F) and the fault is behind it, it will not "Zone 1 trip".

DIR2: This is the direction in which the relay is looking for is Zone 2

mode of protection.

Z1P: This is entered as in Ohms*sec. This is the impedance the relay

looks down the line for its Zone 1 mode of protection.

Z2P: This is the same as Z1P except Z2P is how far down the line the

relay looks for Zone 2. So, if the fault is within the distance specified in

Ohms*sec and is not in Zone 1, then the Zone 2 elements will pick up.

50PP1: This is the overcurrent entered in Amps*sec. If the current goes

above this value in Zone 1 (about 15 ohms down the line, depending on

the Z1P setting) then the relay will send a trip signal to the breaker it is

connected to.

50PP2: This is the same as 50PP1 except this overcurrent value is entered

for Zone 2 (30 ohms down the line). There will be more impedance

between the breaker and fault in this case so the value entered here is

generally smaller than the value entered for 50PP1.

10) Although many settings will stream down, these are not all of the settings

available to the relay. Setting at the end of the stream may or may not show up

based on settings at the beginning of the stream. For example, if there is no

Residual Time-Overcurrent element settings wanted then the user will enter “N”

under the E51P setting. When NO is entered under this setting, 51PC, 51 PP,

51PTD and many other settings will not show up because these extra settings are

only needed when E51P is enabled.

11) To be able to change/read all the settings in turn one at a time type “SET” and

23

then press return.

12) The user can now go through the settings one at a time by hitting enter. If the

user desires to change any of the settings simply enter the new value and proceed.

13) Once the user has went through all the settings a listing of all the settings will

once again be displayed with all the changes. At this point a save settings prompt

will appear and the user must decide whether to save these settings or not.

14) In order to go directly to one setting simply type “SET A” where A is the

acronym of the setting. This will take the user directly to that setting. If that is

the only change desired then type "END". At this point all the setting will once

again stream down the screen and the user will be prompted about whether to

save.

15) Once the user has used the relay multiple times he/she may desire a faster process.

In this case, type "SET A TERSE". By typing TERSE the program will skip the

sep of listing out all the settings and go directly to the save prompt. This saves

quite a bit of tie when experimenting with different settings.

16) Now take a look at the SEL 351S. This relay is very similar to the 321 except the

351S is meant to be more of an overcurrent protection relay rather than a

directional relay. For this reason most of the acronyms are different. A few of

the more important acronyms are listed below:

E50P: This is where the user must specify how many levels of protection

are desired.

E32: Specifies whether or not directional control is desired.

E79: Specifies whether the relay will send one or more reclosing signals to

the breaker (Maximum of 4).

50P1P: This is the Level 1 phase instantaneous/definite time overcurrent

protection element on the relay. If the current ever exceeds this value the

24

breaker will trip instantaneously.

50P2P: This is the same as 50P1P except this is the Level 2 current

threshold.

67P2D: This is the time the relay waits to trip in the if currents exceed the

level 2 threshold. When this is set to zero, the relay will trip

instantaneously regardless of Level.

79OI1: Here a time is entered specifying how long the relay waits before it

sending a reclosing signal.

79OI2: This is how long the relay will wait before it tries reclosing a

second time.

17) Rather than work with zones like the 321, the 351 works with levels. In the most

basic sense this relay acts as a fuse. The relay will send trip signals based on the

threshold the current crosses , if the current goes above the Level 1 threshold it

will trip instantaneously whereas if the current goes above the Level 2 threshold it

rip based on the time delay specified (6P2D).

18) Navigating through Ewan telnet for the 351 is the same as the 321. See steps (8)-

(15) above.

25

Appendix

26

Appendix Table of Contents

Case Study 1 Long-Line 27

Case Study 2 Parallel-Line 34

Case Study 3 Time-Overcurrent 37

Case Study 4 Split-Line 41

Case Study 5 Reclosing 43

27

Case 1. Long-Line Study

The SEL 321 relay is a Phase and Ground Distance, Directional Overcurrent

Relay. This relay can be set to have different zones of protection. Zone 1, for example,

could be set to be 20 Ω down the line or any other value impedance value desired.

Generally, zone 1 is set to be about eighty percent of the line between breakers. Any

fault that the relay detects in zone 1 will trigger an instantaneous trip. Zone 2 could then

be set to be a hundred percent or more down the line. For any fault that occurs in zone 2

the relay would delay before tripping, waiting for another relay to respond or waiting for

some sort of communication telling it what to do. For this study use the group 5 settings.

The zone settings are shown in the table below.

Zone Impedance/Distance Time Delay Direction

1 13.91 ohms - F

2 30 ohms 20 cycles F

3 10 ohms 0 cycles R

Table A.1 Zone Settings for SEL-321 Relay (L2)

This study will explore the operation of the SEL 321 relay located at L2. Set up

the system so that the four lines on the system are in series like shown in the figure on the

next page. Set all four lines so they are at maximum impedance. (Note: For this study to

prevent the SEL-351s relay at L3 from tripping you may have to increase the Phase

Inst./Def.-Time Overcurrent Element Threshold 50P1P).

28

Figure A1. Long-Line Study Schematic

For the first part of this study place a three phase to ground fault outside of the

zone of protection of the relay at L2. Zone 2 protection for this relay reaches only part of

the way down L3. So place a fault between L3 and L1 and see what happens. The

setup of this fault is shown on the in Figure A2.

Figure A2. 3-Phase Fault out of SEL 321 Zone of Protection

29

The next two figures show the three-phase voltage and current at the fault point.

As expected no trip occurred because the fault was out the SEL 321s zones of protection.

So, while the fault occurred, there was a lag in voltage and spike in current.

Figure A3. Long-Line Fault Beyond Zone 2 Voltage

Figure A4. Long-Line Fault Beyond Zone 2 Current

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-150

-100

-50

0

50

100

150

Time

Vol

tage

Longline with Fault Beyond Zone 2

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-6

-4

-2

0

2

4

6

Time

Cur

rent

Longline with Fault Beyond Zone 2

30

Next for the second part of the study, place a fault between L4 and L3. This fault

is in the zone 2 region of protection for the relay at L2. If the test operates correctly then

the relay will delay for a set number of cycles to wait for another relay closer to the fault

to possibly respond, then when no other relays respond, the SEL 321 at L2 will trip its

breaker. Adjusting Z2PD sets this delay for zone 2. The set up for this part is shown

below.

Figure A5. 3-Phase Fault in SEL 321’s Zone 2 Protection

31

The next two figures show the three-phase voltage and current at the fault point.

The plots both indicate there was a delay before the relay tripped the breaker.

Figure A6. Long-Line Fault Zone 2 Voltage

Figure A7. Long-Line Fault Zone 2 Current

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

-150

-100

-50

0

50

100

150

Time

Vol

tage

Longline with Fault in Zone 2

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

-10

-5

0

5

10

Time

Cur

rent

Longline with Fault in Zone 2

32

Finally, for the last part of this study, place the fault between L2 and L4. This

fault will be within the relay’s zone 1 range of protection. For this fault the relay should

trip instantaneously. The setup for this part is shown below.

Figure A8. 3-Phase Fault in SEL 321’s Zone 1 Protection

The next two figures show the three-phase voltage and current at the fault point.

As you can see, the relay took about 3 cycles to respond to the fault. This is considered

an instantaneous trip.

Figure A9. Long-Line Fault Zone 1 Voltage

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

-150

-100

-50

0

50

100

150

Time

Vol

tage

Longline with Fault in Zone 1

33

Figure A10. Long-Line Fault Zone 1 Current

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

-10

-5

0

5

10

15

Time

Cur

rent

Longline with Fault in Zone 1

34

Case 2. Parallel Line Study

This setup will demonstrate the communication aided tripping between the SEL-

321 relays. The relays are set in group 5 to work under Permissive Overreaching

Transfer Trip Logic (POTT). This communication scheme allows the relays at L2 and

L4 to isolate a fault between the relays to allow current to continue to flow through the

other line and serve the load. Again set all four lines so that they are at their maximum

impedance. The setup for this study is shown below.

Figure A.11 Parallel Line

The fault between the relays at L2 and L4 is in both of their zones of protection.

For a normal setup, the relay at L2 would trip instantaneously, but then the current would

flow to the fault from the other direction through L4 and then the relay at L4 would trip

after a small delay. Rather than let this delay happen and inconvenience the load, a

communication scheme can be set up enabling the relays to trip at the same time in the

event of a fault between them. So, when a fault is place between L2 and L4, the SEL 321

at L2 will trip instantaneously while sending a signal to the SEL 321 at L4, telling it to

also trip instantaneously. The fault is then isolated from the rest of the system. The three

phase voltages and currents on the bottom branch at the breaker on L2 are shown in the

next two figures.

35

Figure A.12 Voltage at L2 Breaker

Figure A.13 Current at L2 Breaker

The next two figures show the voltages and currents of the other line, at the

breaker on L1, which was left online so that the load could be served, uninterrupted. The

0.05 0.1 0.15 0.2 0.25-20

-15

-10

-5

0

5

10

15

20

Time

Cur

rent

Parallel Line with Isolated Fault

0.05 0.1 0.15 0.2 0.25

-150

-100

-50

0

50

100

150

Time

Vol

tage

Parallel Line with Isolated Fault

36

voltage remained constant because measurements were taken at the infinite bus and as

expected, when the other line went down, all the current originally running through it was

forced through the top line. This causes more losses on the system, but more importantly,

the load is still served.

Figure A.14 Voltage at L1 Breaker

Figure A.15 Current at L1 Breaker

0.05 0.1 0.15 0.2

-150

-100

-50

0

50

100

150

Time

Vol

tage

Parallel Line with Isolated Fault

0.05 0.1 0.15 0.2 0.25

-6

-4

-2

0

2

4

6

8

Time

Cur

rent

Parallel Line with Isolated Fault

37

Case 3. Time-Overcurrent Study

This setting will demonstrate the levels of operation for the SEL-351s relay. The

Level 1 threshold current (50P1P) is set at 5 Amps and the Level 2 threshold current

(50P2P) is set at 2 Amps. There is no time delay associated with the Level 1 phase

instantaneous overcurrent element but for the Level 2 phase instantaneous overcurrent

element a 30 cycle time delay is set (67P2D).

If the configuration seen on Figure A.13 is placed on the system, the current

measured by the relay will exceed 5 Amps (don’t forget about the CT factor of 2 between

system and relay) and the relay will send and instantaneous trip signal to the breaker.

Figure A.16 Time-Overcurrent Study Setup For Level 1

38

The following two plots show the instantaneous trip for the level 1 threshold.

Figure A.17 Level 1 Instantaneous Trip Voltage

Figure A.18 Level 1 Instantaneous Trip Current

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

-10

-5

0

5

10

15

Time

Cur

rent

Level 1 Instantaneous Trip

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

-150

-100

-50

0

50

100

150

Time

Vol

tage

Level 1 Instantaneous Trip

39

If the configuration of Figure A.15 is used, the current will not exceed 5 Amps

however it will exceed the 2 Amps Level 2 threshold. In this case, the relay will still

send a trip command but it will wait the time specified by the 67P2D setting, which is 30

cycles in this case.

Figure A.19 Time Overcurrent Study Setup for Level 2

Again, the following two figures show the voltage and current readings at L1 for

this kind of trip.

Figure A.20 Level 2 30 Cycles Delayed Trip Voltage

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

-150

-100

-50

0

50

100

150

Time

Vol

tage

Level 2 30 Cycle Delay Trip

40

Figure A.21 Level 2 30 Cycles Delayed Trip Current

The last two plots show the relay acted properly by delaying 30 cycles before the

trip. As mentioned earlier, the threshold for level 2 can be adjusted by changing 50P2P.

The time delay for level 2 can be adjusted by varying 67P2D.

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

-10

-5

0

5

10

Time

Cur

rent

Level 2 30 Cycle Delay Trip

41

Case 4. Split-line Study

This case represents a simple secondary protection scheme. A load is being

served off of L3 but there is a fault on L4. Ideally, the SEL 321 should trip

instantaneously allowing the load to still be served by Avista.

Figure A.22 Split-Line Study Schematic

A problem that might present itself in a system like this is incorrect settings for

the relays. If for example Level 1 of the relay is set to be too sensitive, both the SEL 351

on L1 and the SEL 321 on L4 will trip instantaneously. Now, the load can not be served

by Avista, this is not our ideal case. Also, if 67P2D, the phase instantaneous overcurrent

level 2 delay, is set to zero, the same problem presents itself. So, one way to fix this

problem would be to set the phase instantaneous overcurrent thresholds of the SEL 351

on L1 extremely high. In this case, however, the user gives up secondary protection (and

you have a relay doing nothing but taking measurements). If the SEL 321 on L4 does not

operate correctly, or is set incorrectly, then a fault will remain on the system indefinitely

and the load will suffer. So, the best way to set up the power system protection for this

case is the following:

42

SEL 351 on L1:

50P1P: 5.8 Amps

50P2P: 2 Amps

67P2D: 20 cycles

SEL 321 on L4:

50PP1: 2 Amps

For the settings above, the SEL 321 on L4 will trip instantaneously but the SEL 351 will

see a level 2 fault. If for some reason the SEL 321 does not trip, the SEL 351 will trip

after a 20 cycle delay, giving the first relay plenty of time to do its job before the

secondary protection kicks in.

43

Case 5. Reclosing Study

This study explores the reclosing capability of the SEL-351s relay. The group 5

settings have reclosure settings enabled for both the 351 relays. Each of the relays is set

to have 2 reclosure attempts otherwise known as shots. For each shot, the user can

specify the delay in cycles before the breaker is reclosed. These time delays are specified

under the settings 790I1 and 790I2 for the first and second reclosures respectively.

Other settings associated with reclosure are the 79RSD and 79RSLD settings.

79RSD is the reset time from the reclose cycle state. For example if the relay was able to

successfully reclose the breaker into the fault on the first shot than the relay would wait

the specified 79RSD time before resetting.

79RSLD is the reset time from the lockout state. When the relay is in its lockout

state reclosure is no longer possible. The relay will reset from lockout after the time

interval 79RSLD has passed.

The figure below from the SEL-351s manual shows the different states for

reclosure logic.

Figure A.23 Figure of Reclosing Sequence

44

To begin working with a reclosing relay use the configuration in Figure A.17

below.

Figure A.24 Schematic For Reclosing Study

The following two figures show the voltage and current for a double reclosure.

After the first reclose, the fault was still present on the system, so the breaker reopened.

Next, after another specified time delay, the breaker reclosed into the system again. The

fault by that time was gone so no trip after the second reclose was necessary.

Figure A.24 Double Reclose Voltage

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-300

-200

-100

0

100

200

Time

Vol

tage

Double Reclose Voltage

45

Figure A.25 Double Reclose Current

To further understand reclosing and the different sequences of reclosures try

different lengths of faults and different reclosure time settings. Also watch the LED

lights on the front panel of the SEL-351s. You can watch the relay cycle through

different reclose sequence states (i.e. lockout to reset, or cycle to reset, etc.).

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

-20

-15

-10

-5

0

5

10

15

20

Time

Cur

rent

Double Reclose Current