28
Main
Feeder circuit breakers
Fully rated or
Zone
selective
Selective
selective
Fully rated
Table 28.2
600 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
8700
10600
100
9600
11500
500
150
481
10000
11900
4.5%
Á
250
Â
(674)
10200
1900
12100
WPS-08
WPS-08
WPS-08
WPS-08
500
10500
12400
750
10500
12400
Unlimited
10700
12600
50
10000
12900
100
11100
14000
750
150
722
11500
14400
5.75%
250
Â
(1010)
11900
2900
14800
WPS-08
WPS-08
WPS-08
WPS-08
500
12200
15100
750
12300
15200
Unlimited
12600
15500
50
12400
16200
100
14300
18100
1000
150
962
15000
18800
5.75%
250
Â
(1347)
15600
3800
19400
WPS-16
WPS-08
WPS-08
WPS-08
500
16200
20000
750
16400
20200
Unlimited
16700
20500
50
16500
22300
100
19900
25700
1500
150
1443
21400
27200
WPS-08
WPS-08
WPS-08
5.75%
250
Â
(2021)
22700
5800
28500
WPS-16
500
23900
29700
750
24300
30100
WPH-08
WPH-08
WPH-08
Unlimited
25100
30900
50
19700
27400
WPS-08
WPS-08
WPS-08
100
24800
32500
2000
150
1925
27200
34900
5.75%
250
Â
(2694)
29400
7700
37100
WPS-20
WPH-08
WPH-08
WPH-08
500
31300
39000
750
32000
39700
Unlimited
33500
41200
50
22400
32000
100
29200
38800
WPH-08
WPH-08
WPH-08
2500
150
2406
32400
42000
5.75%
250
Â
(3368)
35600
9600
45200
WPS-32
500
38500
48100
WPX-08
WPX-08
WPX-08
750
39500
49100
Unlimited
41800
51400
WPH-16
WPH-16
WPH-16
50
24600
36100
WPH-08
WPH-08
WPH-08
100
33000
44500
WPX-08
WPX-08
WPX-08
3000
150
2887
37200
48700
5.75%
250
Â
(4041)
41500
11500
53000
WPS-32
500
45500
57000
WPH-16
WPH-16
WPH-16
750
46900
58400
Unlimited
50200
61700
50
27200
41600
WPH-08
WPH-08
WPH-08
100
38000
52400
3750
150
43700
58100
WPH-16
WPH-16
WPH-16
5.75%
250
3608
49800
14400
64200
WPS-40
500
Â
(5051)
55500
69900
750
57700
72100
WPH-32
WPH-32
WPH-32
Unlimited
62800
77200
50
30500
49700
WPX-08
WPX-08
WPX-08
100
44800
64000
WPH-16
WPH-16
WPH-16
5000
150
53000
72200
WPH-32
WPH-32
WPH-32
5.75%
250
4811
62100
19200
81300
WPS-50
500
71300
90500
750
Â
(6735)
75000
94200
Fused
Fused
Fused
Unlimited
83700
102900
breaker
breaker
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)
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
Distribution or motor control center
Table 28.1
Transformer forced cooled ratings
Fully rated
arrangement
Selectively
coordinated
arrangements