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b) A 33 kV busbar having a short-circuit level of 4X0 MVA is connected to a 5 MVA 33/11 KV transformer as shown in Figure Q4.1. A three-phase fault on the 11 kV feeder produces a short circuit current of 12. XY KA. In the previous information, X and Y are the last two digits of your student number. 33 kV T CT 400/1 11 kV 33/11 KV о CB 5 MVA Relay CT 500/1 CB Relay Fault Figure Q4.1. Network for problem 4b). (i) Calculate the three-phase short circuit current for a fault on the 33 kV terminals of the transformer. (ii) What is the short circuit level of the 11 kV busbar? (iii) The 11 kV relay is a standard 2 A, IDMT over-current relay with a plug setting of 150% and a time multiplier setting of 0.75. Use the normally inverse curve characteristic shown in Figure Q4.2 to calculate the operating time for a three-phase fault on the 11 kV feeder. 30 10 TMS=1.0 Time (s) 1.0 2.0 3.0 5.0 10 20 Current as multiple of the relay setting (plug setting multiplier) Figure Q4.2. Normally inverse characteristic of a relay (time multiplier setting of 1.0).

b) A 33 kV busbar having a short-circuit level of 4X0 MVA is connected to a 5 MVA 33/11 KV transformer as shown in Figure Q4.1. A three-phase fault on the 11 kV feeder produces a short circuit current of 12. XY KA. In the previous information, X and Y are the last two digits of your student number. 33 kV T CT 400/1 11 kV 33/11 KV о CB 5 MVA Relay CT 500/1 CB Relay Fault Figure Q4.1. Network for problem 4b). (i) Calculate the three-phase short circuit current for a fault on the 33 kV terminals of the transformer. (ii) What is the short circuit level of the 11 kV busbar? (iii) The 11 kV relay is a standard 2 A, IDMT over-current relay with a plug setting of 150% and a time multiplier setting of 0.75. Use the normally inverse curve characteristic shown in Figure Q4.2 to calculate the operating time for a three-phase fault on the 11 kV feeder. 30 10 TMS=1.0 Time (s) 1.0 2.0 3.0 5.0 10 20 Current as multiple of the relay setting (plug setting multiplier) Figure Q4.2. Normally inverse characteristic of a relay (time multiplier setting of 1.0).

Introductory Circuit Analysis (13th Edition)
Introductory Circuit Analysis (13th Edition)
13th Edition
ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
Section: Chapter Questions
Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...
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b) A 33 kV busbar having a short-circuit level of 4X0 MVA is connected to a 5 MVA 33/11 KV transformer as shown in Figure Q4.1. A three-phase fault on the 11 kV feeder produces a short circuit current of 12. XY KA. In the previous information, X and Y are the last two digits of your student number. 33 kV T CT 400/1 11 kV 33/11 KV о CB 5 MVA Relay CT 500/1 CB Relay Fault Figure Q4.1. Network for problem 4b). (i) Calculate the three-phase short circuit current for a fault on the 33 kV terminals of the transformer. (ii) What is the short circuit level of the 11 kV busbar? (iii) The 11 kV relay is a standard 2 A, IDMT over-current relay with a plug setting of 150% and a time multiplier setting of 0.75. Use the normally inverse curve characteristic shown in Figure Q4.2 to calculate the operating time for a three-phase fault on the 11 kV feeder. 30 10 TMS=1.0 Time (s) 1.0 2.0 3.0 5.0 10 20 Current as multiple of the relay setting (plug setting multiplier) Figure Q4.2. Normally inverse characteristic of a relay (time multiplier setting of 1.0).
Transcribed Image Text:b) A 33 kV busbar having a short-circuit level of 4X0 MVA is connected to a 5 MVA 33/11 KV transformer as shown in Figure Q4.1. A three-phase fault on the 11 kV feeder produces a short circuit current of 12. XY KA. In the previous information, X and Y are the last two digits of your student number. 33 kV T CT 400/1 11 kV 33/11 KV о CB 5 MVA Relay CT 500/1 CB Relay Fault Figure Q4.1. Network for problem 4b). (i) Calculate the three-phase short circuit current for a fault on the 33 kV terminals of the transformer. (ii) What is the short circuit level of the 11 kV busbar? (iii) The 11 kV relay is a standard 2 A, IDMT over-current relay with a plug setting of 150% and a time multiplier setting of 0.75. Use the normally inverse curve characteristic shown in Figure Q4.2 to calculate the operating time for a three-phase fault on the 11 kV feeder. 30 10 TMS=1.0 Time (s) 1.0 2.0 3.0 5.0 10 20 Current as multiple of the relay setting (plug setting multiplier) Figure Q4.2. Normally inverse characteristic of a relay (time multiplier setting of 1.0).
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