Your task is to study the operation of the directional elements of a 132 kV tran
ID: 2079230 • Letter: Y
Question
Your task is to study the operation of the directional elements of a 132 kV transmission line protection scheme with the 90-degree connection as shown in class. The phase elements have a MTA of 45 degrees (current leading) and the ground element has a MTA of 60 degrees (current lagging). Two faults were simulated with the following results for the phase voltages and currents "seen" by the relays: For each case, determine which of the four directional relay elements will operate. Use graphical and analytical methods. Use CTR=250/5, VTR = PTR = (132000/squareroot 3)/67 Determine the operation time in each case for the directional overcurrent phase and ground relays if the overcurrent element settings are: Phase relays: I_pu=4.5 A, TD=2.5 and t=TD(5.95/(M^2-l)+0.18); INST=infinity Ground relay: I_pu=0.5 A, TD=2.5 and t=TD(5.95/(M^2-l)+0.18); INST=infinityExplanation / Answer
CASE A :
PHASE A CURRENT = 4389 AMPERES WITH AN ANGLE 0F -80 DEGREE . THE LINE DRAWS A HIGLY LAGGING FAULT CURENT IN THE CASE A . THE HIGHLY LAGGING CURRENT WILL INITIATE THE GROUND RELAY WITH MAXIMUM TORQUE ANGLE OF 60 DEGREE LAGGING .
CASE B;
PHASE A CURRENT = 1238 AMPERES WITH AN ANGLE 0F 98 DEGREE . THE LINE DRAWS A LEADING FAULT CURENT IN THE CASE B. THE HIGHLY LEADING CURRENT WILL INITIATE THE PHASE A RELAY WITH MAXIMUM TORQUE ANGLE OF 45 DEGREE LEADING .
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