27
Main
Feeder circuit breakers
Fully rated or
Zone
selective
Selective
selective
Fully rated
Table 27.2
480 volts, three phase
Transformer
rating 3-phase Max short-circuit
Full load
Short-circuit rating sym current (A)
kVA and
MVA available
continuous
Long-time inst.
Long-time
impedance
from primary
current
Transformer
100%
or long-time
Long-time
short-time
Long-time
percent
system
(amperes)
À Â
alone
Motor load
Combined
short-time ¿
short-time
inst.
inst.
50
10900
13300
100
12000
14400
500
150
12400
14800
4.5%
Á
250
601
12800
2400
15200
WPS-08
WPS-08
WPS-08
WPS-08
500
13100
15500
750
13200
15600
Unlimited
13400
15800
50
12400
16000
100
13900
17500
750
150
902
14400
18000
5.75%
250
Â
(1263)
14900
3600
18500
WPS-16
WPS-08
WPS-08
WPS-08
500
15300
18900
750
15400
19000
Unlimited
15700
19300
50
15500
20300
100
17800
22600
1000
150
1203
18700
23500
5.75%
250
Â
(1684)
19600
4800
24400
WPS-16
WPS-08
WPS-08
WPS-08
500
20200
25000
750
20400
25200
Unlimited
20900
25700
50
12000
16800
100
13400
18200
1000
150
1203
13900
18700
8%
250
Â
(1684)
14300
4800
19100
WPS-16
WPS-08
WPS-08
WPS-08
500
14700
19500
750
14800
19600
Unlimited
15000
19800
50
20600
27800
WPS-08
WPS-08
WPS-08
100
24900
32100
1500
150
1804
26700
33900
5.75%
250
Â
(2526)
28400
7200
35600
WPS-20
WPH-08
WPH-08
WPH-08
500
29800
37000
750
30300
37500
Unlimited
31400
38600
50
24700
34300
WPH-08
WPH-08
WPH-08
100
31000
40600
2000
150
2406
34000
43600
5.75%
250
Â
(3368)
36700
9600
46300
WPS-32
500
39100
48700
WPX-08
WPX-08
WPX-08
750
40000
49600
Unlimited
41800
51400
50
28000
40000
WPH-08
WPH-08
WPH-08
100
36400
48400
2500
150
3007
40500
52500
5.75%
250
Â
(4210)
44500
12000
56500
WPS-32
WPX-08
WPX-08
WPX-08
500
48100
60100
750
49400
61400
Unlimited
52300
64300
50
30700
45100
100
41200
55600
WPX-08
WPX-08
WPX-08
3000
150
3608
46600
61000
5.75%
250
Â
(5052)
51900
14400
66300
WPS-40
500
56800
71200
WPH-32
WPH-32
WPH-32
750
58700
73100
Unlimited
62800
77200
50
34000
52000
WPX-08
WPX-08
WPX-08
100
47500
65500
3750
150
54700
72700
WPH-32
WPH-32
WPH-32
5.75%
250
4511
62200
18000
80200
WPS-50
500
69400
87400
750
Â
(6315)
72200
90200
WPX-32
WPX-32
WPX-32
Unlimited
78400
96400
À
With transformer operating on base temperature rise, without fans. Larger frame size main
breaker may be required when dual temperature rise for forced cooled transformers are used.
Á
Minimum impedance.
Â
Maximum forced cooled rating indicated in parentheses.
L = Long-time delay trip (overload tripping)
S = Short-time delay trip (selective fault tripping)
I = Instantaneous trip (high fault current fast tripping)
Self-cooled
Transformer type
kVA
% increase with fans
Liquid filled: 65° C rise
750-2000
15%
2500-5000
25%
Liquid filled: 55/65° C rise
750-2000
15% (fans) + 12% (65° C)
2500-5000
25% (fans) + 12% (65° C)
Ventilated dry
750-2500
33%
Cast coil
500-2500
40%
3000-5000
25%
LS
LS
LSI
LI
LI
LI
Table 27.1
Transformer forced cooled ratings
Fully rated
arrangement
Selectively
coordinated
arrangements
Distribution or motor control center