Question

Rework Example 10.5 for the following faults: (a) a three-phase, permanent fault on the load side of tap 3; (b) a single line-to-ground, permanent fault at bus 4 on the load side of the recloser; and (c) a three-phase, permanent fault at bus 4 on the source side of the recloser.

Bus	Maximum load current A	$\mathbf{3}\mathit{\varphi }$ fault current A	$\mathit{I}\mathit{L}\mathbf{·}\mathit{G}$fault current A
1	60	1000	850
2	95	1500	1300
3	95	2000	1700
4	250	3000	2600
5	250	4000	4050

Short answer

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Step-by-step solution

Write the given data from the question.

The system data is given as follows:

Bus	Maximum load current A	$3\varphi$fault current A	$IL·G$fault current A
1	60	1000	850
2	95	1500	1300
3	95	2000	1700
4	250	3000	2600
5	250	4000	4050

The operating system of the protective device for three phase, permanent fault on load side of tap 3.

(a)

From the given data, the value of the three-phase fault current at the bus 3 is 2000 A. By observing the given time-current characteristic curve, when the fault current is 2000 A, the fast recloser 560 A opens (first time) at 0.04 and recloses after 0.5 sec. After 0.04 sec, the fast recloser 560 A again opened and recloses into the fault after 2 s delay. During this time interval, the fuse 100 T cleared the fault and the delayed recloser, recloses 5 - 10 later restore the services to loads 1 and 2.

The operating system of the protective device for single line to ground fault, permanent fault at bus 4.

(b)

From the given data, the value of the single line to ground fault current at the bus 4 is 2600 A. By observing the given time-current characteristic curve, when the fault current is 2600 A, the fast recloser 280 A opens (first time) at 0.033 sec and recloses after 0.5 sec. After 0.033, the fast recloser 280 A again opened and recloses into the fault after 2 s delay. After the delay of 0.7 sec the recloser open again and recloses 5 - 10 s later. After this 280 A recloser open with the delay of 0.7 sec and permanently locked out.

The operating system of the protective device for three-phase, permanent fault at bus 4 on the source side of the recloser.

(c)

From the given data, the value of three phase permanent fault current at the bus 4 is 3000 A. By observing the given time-current characteristic curve, when the fault current is 2600 A, the phase over current relay got tripped and energize the coil of the circuit breaker to open.