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Tutorial 1 :- To study current transformer models and fault simulation

Objectives :-

Understanding models related to fault simulation. Comparing different CT models.

Procedure :-

T1.1 Create a new case by using either the MenuorToolbar. A new case should appear in theWorkspace setti ngsentitled noname [psc]. Right-click on this Workspace settings entry andselect Save As and give the case a name.

NOTE: Do not use any spaces in the name!

Create a folder called c:/PscadTraining/Faults. Save the case as case01.psc

T1.2 Open the main page of your new case. The single line diagram shown below is a part of a

substation feeding a shunt reactor. The reactor is modeled in two parts to enable a fault at pointB, inside the turns. The component data is as shown. (make the transformer losses zero to limitthe number of nodes if using the student version)

You may use the wire mode to connect different components.

Station 115 kV

bus

Station 13.8 kV

bus

RL RRL

0.0125

Short line

EL

IL

Ea

Ir1Ir2

0.0125 AB

REACTORS

0.005 0.1

#1 #2

115 kV,50 Hz Source

Z+ = 1.1Ohms / 88 deg

Z0 = 2 Ohms / 86 degY-D Transformer

Z = 8%

Full load loss = 0.3%

No load loss = 0.5%

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T1.3 Build the case in PSCAD and enter the component data.

T1.4 Plot the current IL and the voltage EL.

T1.5Use the fault component to simulate a phase A to ground fault at location A at 0.1s.

T1.6 Observe the fault curent, IL. What is the reason for the presence of the initial DCexponential component?

T1.7 What affects the rate of decay of the DC components. Change the resistance of the short

line to 1 Ohm and observe the results.

TimedFaultLogic

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T1.8 Does the instant of the fault inception have an effect on the DC offset.?

T1.9 What negative impacts can the DC offset have on the system protection.?

T1.10 Connect the phase A line current at point A to the CT model as shown below. The CTratio is 5:400. The CT burden is 0.15 Ohms in series with 0.8mH. Plot the secondary current and

the flux density.

T1.11 Increase the burden resistance to 4 Ohms and observe the results. Note the half cycle

saturation effects due to the dc offset in the primary current.

IL1

Burden resistance

1 and 0.1 Ohms

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T1.12 The reactor is protected by a differential relay scheme. Use the 2-CT model in PSCAD to

connect one phase of the reactor protection scheme.

T1.13 Verify the burden current in the differential CT connection for faults at A and B.

T1.14 Does the impedance of the connection leads have an effect on the results.? How is thisimpedance accounted for.?

T1.15 Open the case ftdiff.psc. Check the performance of the differential relay during

transformer energization.

Ir1

Ir2

1

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