26
Main
Feeder circuit breakers
Fully rated or
Zone
selective
Selective
selective
Fully rated
Table 26.2
240 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
À
short-time
inst.
inst.
50
14200
17100
100
15000
17900
300
150
15400
18300
4.5%
Á
250
722
15600
2900
18500
WPS-08
WPS-08
WPS-08
WPS-08
500
15800
18700
750
15900
18800
Unlimited
16000
18900
50
21900
26700
100
24100
28900
WPS-08
500
150
24900
29700
4.5%
Á
250
1203
25600
4800
30400
WPS-16
WPS-08
WPS-08
500
26100
30900
WPH-08
750
26300
31100
Unlimited
26700
31500
50
24900
32100
100
27800
35000
750
150
1804
28900
36100
5.75%
250
Â
(2526)
29800
7200
37000
WPS-20
WPH-08
WPS-08
WPS-08
500
30600
37800
750
30800
38000
Unlimited
31400
38600
50
31000
40600
WPH-08
WPS-08
WPS-08
100
35600
45200
1000
150
2406
37500
47100
WPH-08
WPH-08
5.75%
250
Â
(3368)
39100
9600
48700
WPS-32
WPX-08
500
40400
50000
750
40900
50500
WPX-08
WPX-08
Unlimited
41800
51400
50
41200
55600
WPX-08
WPX-08
WPX-08
100
49800
64200
1500
150
3608
53500
67900
5.75%
250
Â
(5052)
56800
14400
71200
WPS-40
500
59600
74000
WPH-32
WPS-32
WPS-32
750
60600
75000
Unlimited
62800
77200
50
49300
68500
WPH-32
WPS-32
WPS-32
100
62100
81300
2000
150
67900
87100
5.75%
250
4811
73500
19200
92700
WPS-50
500
78200
97400
WPX-32
WPH-32
WPH-32
750
Â
(6735)
80000
99200
Fused
Unlimited
83700
102900
breaker
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)
Table 26.1
Transformer forced cooled ratings
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
Fully rated
arrangement
Selectively
coordinated
arrangements
Distribution or motor control center