Training Session

Question 1

Communication of Line Differential

Answer 1

Optical Fibre

Question 2

Communication of PWP

Answer 2

Metallic pilot wire cable

Question 3

Disadvantages of PWP

Answer 3

Length of the line (short or very long 20km) due to stabilization of looping resistance

Question 4

When does CB trip due to PWP faulty?

Answer 4

When enough current is flowing through the cable to reach the threshold limit of the CT in the PWP to trip the CB

Question 5

How is Guard Relay connected to PWP

Answer 5

Guard relay is connected in series with the PWP via NO/NC contacts

Question 6

Why does Source CB only trip when Guard Relay with PWP

Answer 6

Load end guard relay does not see the fault current, hence only the source trips

Question 7

Name and fault current rating of HRC fuse

Answer 7

Back up fuse, 3 times max load current

Question 8

11 kV feeder BCU/BCPU CT ratio and Accuracy classes

Answer 8

BCPU(5P15) + Metering ratio(0.2S-FS5): 400/1 A
BBD + BBC(PX): 3200/ 1 A

Question 9

How many CTs are connected in the secondary side of IDT in BMP stations

Answer 9

6

Question 10

What is the ratio of CTs connected in the secondary of IDT?

Answer 10

3200/1 A

Question 11

What is the new maximum short circuit current in the network?

Answer 11

31.2 kA/3s

Question 12

What is the current maximum short current in the busbar?

Answer 12

25kA/3s

Question 13

Will U/F protection operate when BCU fails?

Answer 13

U/F will not operate as it is within the BCU.

Question 14

Indication of negative sequence on relay

Answer 14

I2

Question 15

Type of CT used for EFI

Answer 15

Core balance CT

Question 16

Meaning of 50/51 in relaying

Answer 16

50(G/N) is instantaneous current(instantaneous E/F), 51(G/N) is inverse current(inverse E/F)

Question 17

Difference between IDT 11kV old and new philosophy

Answer 17

1 PX relay replaced by 1 5P20 (3200/1A)

Question 18

Difference between 11kV feeder old and new philosophy

Answer 18

3200/1 A PX in back up replaced by 400/1A 5P15