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Page 1

ETAP TIP – No. 010
Transient Stability – Relay Controlled Actions

Applicable ETAP Versions: 5.5.0, 5.5.5, 5.5.6
(For lower versions, some of the descriptions and procedures below may differ in some ways)

As illustrated in ETAP TIP – No. 009, the “Events and Actions” method requires pre-determined action
times.

In power systems, many actions occur without any pre-acknowledgment, instead, they are controlled
by sensors and relays. For instance, a current relay (50/51) will trip off circuit breakers once the
measured current by relay exceeds a pre-set value. In another case, a voltage relay (27/59) can be
used to open or close circuit breakers based on its monitored voltage and comparison with an upper
and a lower setting. These types of actions do not have a definite time of happening and are solely
dependent on the system dynamic responses and relay settings. In ETAP, the actions of relays can
be integrated in the transient stability to resemble the true power system real operating conditions.

Illustration:

Using the “Example-ANSI.oti” sample project, suppose that Utility “CB1” tripped off. After this event,
generator “Gen1” will be islanded and will supply the balance power.

Utility

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Sub 3
4.16 kV

Bus1
0.48 kV

15/10/5 MVA

CB8

Sub3 Net

CB9

CAP1
450 kvar

CB18 CB19

T4

1.5 MVA

CB22

DC System

CB23

Bus1
0.48 kV

CB9

CB8

15/10/5 MVA

Sub 3
4.16 kV

CAP1
450 kvar

CB18

T4

1.5 MVA

DC System

CB19

CB22

CB23

Sub3 Net

Sub2B
13.8 kV Sub2A

13.8 kV

Main Bus
34.5 kV

Syn1
1250 HP

CB21

CB5

Mtr2
2500 HP

CB6

Gen1
7.5 MW

CB24

Sub2A-N

CB12

CB11

T2
10 MVA

T1

CB1

CB10CB2

CB4

1200 MVAsc

T2
10 MVA

Gen1
7.5 MW

1200 MVAsc

Syn1
1250 HP

CB10CB2

CB12

CB11
CB4

CB6

T1

Main Bus
34.5 kV

Sub2A
13.8 kV

13.8 kV

Sub2A-N

CB21 CB24

A decay of frequency at “Sub2B” bus will
manifest an overload to the generator “Gen1”.
Having a frequency relay (device 81) at this bus
will prevent such overload by shedding load(s)
immediately once the threshold is reached. Say
that if the frequency at “Sub2B” bus falls below
98.5% of the nominal frequency for a period of
0.5 sec, the “CB5” will be tripped off.

Tripped

In
te

rl
oc

k

Mtr2
2500 HP

Page 2

Procedure:

1. To incorporate the action of 81 relay in Transient stability simulation, it should be modeled first.

2. Activate the “Study View” one line diagram presentation by clicking its window (or you can go to
“project view” and double click “Study View” folder)

3. Switch to “Edit” mode by clicking the “Pencil” icon on the mode toolbar.







4. Model the Potential Transformer.
See Fig. 1 4.a

4.b 4.c

Fig. 1

a. On the “AC Instrumentation” toolbar,
click the “Potential Transformer” (PT)
icon.

b. Move the mouse under “Sub2B” bus

c. Connect the left terminal of the “PT” to
bus “Sub2B” by dragging the square
handle of the former towards the latter.













5. Model the Frequency Relay (Device 81).
See Fig. 2 5.a

5.b

5.c

Fig. 2

a. On the “AC Instrumentation” toolbar,
click the frequency relay “81” icon.

b. Move the mouse on the right side of the
PT.

c. Connect the device 81 relay to the right
terminal of the “PT” by drag and drop.



















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Page 3

6. Define the setting of the “81” relay. See
Fig. 3.

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a. Double-click the “81” relay symbol on
the One Line Diagram. The “Frequency
Relay Editor” dialog box will be
displayed.

b. Click on the “Setting” tab of the
“Frequency Relay Editor” dialog box.

c. On the “UnderFrequency Control
Interlock” frame, click on “Add...”
button. The “Frequency Relay Control
Interlock Editor” will be displayed.

d. On the “Frequency Relay Control
Interlock Editor”, enter the following:

Setting : 98.5%
Unit : %Hz
Circuit Breaker ID : CB5
Action : Open
Time Delay : 0.5 sec

6.a

6.c
6.b

Device 81 Relay Symbol

Fig. 3

Frequency Relay Editor

Frequency Relay Control Interlock Editor

6.d
6.e

6.f

e. Click the “OK” button on the
“Frequency Relay Control Interlock
Editor” dialog box.

f. Click the “OK” button on the
“Frequency Relay Editor” dialog box.















7. Switch to Transient Stability Analysis Mode by clicking the icon on the “Mode” toolbar.

Page 4

8. Create a new study case (by copying an existing one) by clicking the icon on the “Study Case”
toolbar




9. The “Duplicate Study Case” dialog box will be displayed
as shown in Fig. 4. 9.a

a. Select the existing study case to be copied i.e. “TS”.
9.b

b. Enter a unique name for the new study case. For
example, “Relay-Action” 9.c

c. Click “Ok” button




Fig. 4

10. Edit the study case “Relay-Action”. See Fig. 5

a. Select the study case
“Relay-Action”.

10.b
10.a

b. Click “Edit Study Case”
button




Fig. 5

11. The “Transient Stability Study Case” dialog
box will be displayed as shown in Fig. 6.
Click the “Events” Tab.

11























Fig. 6










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Page 5

12. In the “Events” tab, existing events and actions
will be seen that were inherited from the “TS”
study case copied in Step 9 (See Fig. 7). Delete
these and create a new event and action, i.e. trip
“CB1”.

12.a

a. Select “Even1” ID

b. Click “Delete” button

c. Do similar actions to delete “Event2”

d. Click “Add..” button. The “Event Editor”
dialog box will be displayed.







12.c 12.b

13. In the “Event Editor” dialog box shown in Fig.
8, do the following:

a. Type “E1” on the “Event ID” text box

b. Type “0.5” on the “Time” text box
Note: 0.5 is the time in second at which the event
occurs.

Fig. 7

c. Click the “OK” button



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14. With the Event ID “E1” active (selected) in
the “Events” Frame of the “Events” dialog
box, click the “Add” button at the “Actions”
frame (See Fig. 9). The “Action Editor”
dialog box will be displayed.


















13.a

13.b

Fig. 8
13.c Notice

14

Fig. 9

Page 6

15. Do the following in the “Action Editor” dialog box shown in Fig. 10:



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a. Select “Circuit Breaker”
on the “Device Type”.

b. Select “CB1” on the
“Device ID”.

c. Select “Open” on the
“Action.

15.a 15.c15.b

d. Click the “OK” button.





16. For this particular exercise, maintain the
existing setting on the “Solution Parameters”
frame.


17. Since the concern is to verify frequency at bus
“Sub2B” when “CB1” opens, instruct the
program to create plot profiles for the said bus.
See Fig. 11.

a. Click the “Plot” tab.

b. On the “Device Type”, select “Buses”.

c. On the “Plot Options” select “Sub2B”.

d. Click the “Plot & Tabulate” check box to
leave a check mark, or just click directly at
the “Plot/Tabulate” column adjacent to
“Sub2B”. Note: “X” mark means plots
will be created.

e. Click the “OK” button to close the study
case.







18. Now, run the simulation. On the “Study Case” toolbar, select “Prompt” from the “Output Report” pull
down box. The program will prompt for a filename of the output report for the study case “Relay-Action”
when the simulation is ran. See Fig. 12.

















Fig. 10

15.d

17.a 17.b

17.d

17.c

17.d

17.e

Fig. 11

18

Fig. 12

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19. On the “Transient Stability” toolbar, click “Run Transient Stability” button, see
Fig. 13.


19

20. The “Output Report Filename” dialog box will be displayed (due to Step 18) as
shown below. Type “R-RelayAction” and click the “OK” button. The program
will proceed with the calculation.











21. When the calculation is complete, the “Transient Stability Time-Slider” dialog
box will be displayed. This slider allows for animation of the result of simulation
at different points in time. See Fig. 14.

Fig. 13

a. Click the “Toggle Action
List” button to show the
“Action List”

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Fig. 15

22

b. Click and drag the “Slide
Pointer” towards right.

c. Notice the “Action List” is
populated with the events,
associated devices, and the
corresponding actions in
chronological order.


Notes for the Events:

i. Event “E1” is the Event
specified on the Study Case
with pre-determine action
time. See Step 13

ii. Event “Freq Relay” is the
event triggered by the relay 81
action where the action time
was determined by the system
dynamic response and relay
settings



22. To view the “Sub2B” bus profile, on the “Transient Stability” toolbar,
click the “Transient Stability Plots” button. See Fig. 15.















21.b 21.a

21.c

Fig. 14

Page 8

23. On the “Transient Stability Plot Selection” dialog box, do the following (See Fig. 16):

a. On the “Device Type”, select “Buses”

b. On the “Device ID”, select “Sub2B”.

c. There are 6 plots available for the Bus device.
But in this exercise, view only the
“Frequency”. Click the “Uncheck All”
button.

21.b

21.d

d. Check “Frequency”

e. Click the “OK” button.
21.a





















21.c

21.d

Fig. 16

24. The output plot is displayed in Fig. 17. When “CB1” tripped off, “Gen1” sustained overload as
manifested by the decay in frequency at bus “Sub2B.” When the decay reached the device 81 relay
threshold, it picked-up and after the time delay setting timed-out, it triggered “CB5.” “CB5” tripped at
1.245 sec. Aftewards, the frequency increased.



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