Table 27.1 Transformer forced cooled ratings
Self-cooled
Transformer type
Liquid filled: 65° C rise
750-2000
2500-5000
Liquid filled: 55/65° C rise
750-2000
2500-5000
Ventilated dry
750-2500
Cast coil
500-2500
3000-5000
Table 27.2 480 volts, three phase
Transformer
rating 3-phase Max short-circuit
kVA and
MVA available
continuous
impedance
from primary
(amperes)
percent
system
50
100
150
4.5%
500
250
500
750
Unlimited
50
100
150
750
250
5.75%
500
750
Unlimited
50
100
150
(1684)
1000
250
5.75%
500
750
Unlimited
50
100
150
1000
250
8%
500
750
Unlimited
50
100
150
1500
250
5.75%
500
750
Unlimited
50
100
150
2000
250
5.75%
500
750
Unlimited
50
100
150
2500
250
5.75%
500
750
Unlimited
50
100
150
3000
250
5.75%
500
750
Unlimited
50
100
150
3750
250
5.75%
500
750
Unlimited
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.
Minimum impedance.
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)
kVA
% increase with fans
15%
25%
15% (fans) + 12% (65° C)
25% (fans) + 12% (65° C)
33%
40%
25%
Short-circuit rating sym current (A)
Full load
current
Transformer
100%
alone
Motor load
10900
12000
12400
601
12800
2400
13100
13200
13400
12400
13900
(1263)
902
14400
14900
3600
15300
15400
15700
15500
17800
1203
18700
19600
4800
20200
20400
20900
12000
13400
(1684)
1203
13900
14300
4800
14700
14800
15000
20600
24900
(2526)
1804
26700
28400
7200
29800
30300
31400
24700
31000
(3368)
2406
34000
36700
9600
39100
40000
41800
28000
36400
(4210)
3007
40500
44500
12000
48100
49400
52300
30700
41200
(5052)
3608
46600
51900
14400
56800
58700
62800
34000
47500
54700
4511
62200
18000
(6315)
69400
72200
78400
Main
Fully rated or
selective
Selective
Fully rated
arrangement
LI
LS
Selectively
coordinated
arrangements
Distribution or motor control center
Long-time inst.
or long-time
Long-time
Combined
short-time ¿
short-time
13300
14400
14800
15200
WPS-08
15500
15600
15800
16000
17500
18000
18500
WPS-16
WPS-08
18900
19000
19300
20300
22600
23500
24400
WPS-16
WPS-08
25000
25200
25700
16800
18200
18700
19100
WPS-16
WPS-08
19500
19600
19800
27800
WPS-08
32100
33900
35600
WPS-20
WPH-08
37000
37500
38600
34300
WPH-08
40600
43600
46300
WPS-32
48700
WPX-08
49600
51400
40000
WPH-08
48400
52500
56500
WPS-32
WPX-08
60100
61400
64300
45100
WPX-08
55600
61000
66300
WPS-40
71200
WPH-32
73100
77200
52000
WPX-08
65500
72700
WPH-32
80200
WPS-50
87400
90200
WPX-32
96400
Feeder circuit breakers
Zone
selective
Fully rated
LS
LSI
LI
Long-time
short-time
Long-time
inst.
inst.
WPS-08
WPS-08
WPS-08
WPS-08
WPS-08
WPS-08
WPS-08
WPS-08
WPS-08
WPS-08
WPS-08
WPH-08
WPH-08
WPH-08
WPH-08
WPX-08
WPX-08
WPH-08
WPH-08
WPX-08
WPX-08
WPX-08
WPX-08
WPH-32
WPH-32
WPX-08
WPX-08
WPH-32
WPH-32
WPX-32
WPX-32
LI
27