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Transformer fault current charts

When service entrance facilities are within 25 feet of the transformer, contact LPC for 120 volt fault levels.

Single-phase overhead (120/240) worst-case short circuit for sizing secondary interrupting equipments

Transformer kVA
Z%
240 volt short circuit
25
1.3
8,000
37.5
1.3
12,000
50
1.3
16,000
75
1.3
24,000
100
1.3
32,000
167
1.6
43,000
250
1.7
61,000
333
1.5
93,000

Single-phase pad mount (120/240) worst-case short circuit for sizing secondary interrupting equipments

Transfer kVA
Z%
240 volt short circuit
25
1.2
9,000
50
1.2
17,000
75
1.0
31,000
100
1.0
42,000
167
1.4
50,000

Three-phase overhead banked: worst-case short circuit for sizing secondary interrupting equipments.

Bank kVA
Z%
1/Z pu
120/208 v short circuit
120/240 v short circuit
277/480 v short circuit
30
1.3
77
6,000
6,000
3,000
45
1.3
77
10,000
8,000
4,000
75
1.3
77
16,000
14,000
7,000
112.5
1.3
77
24,000
19,000
10,000
150
1.3
77
32,000
28,000
14,000
225
1.3
77
48,000
42,000
21,000
300
1.3
77
64,000
56,000
28,000
500
1.6
63
87,000
75,000
38,000
750
1.7
59
122,000
106,000
53,000
1000
1.5
67
185,000
160,000
80,000

Three-phase pad-mount: worst-case short circuit for sizing secondary interrupting equipments.

Transformer kVA
Z%
120/208 volt short circuit
277/480 v short circuit
75
1.0
21,000
9,000
112.5
1.6
20,000
8,000
150
1.4
30,000
13,000
225
1.6
39,000
17,000
300
1.5
56,000
24,000
500
2.6
53,000
23,000
750
5.75
36,000
16,000
1000
5.62
49,000
21,000
1500
5.62
74,000
32,000
2500
5.62
123,000
54,000

 

 

 

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