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12
EXAMPLE TO WORK OUT PSC
TRF
=
500 Kva
I
=
650 Amp
SCC
=
4.5%
Supply cable to M-DB
Size
=
4 Core Cu x 630mm
2
L
=
55 meters
NB:
Get the rated current first, this could be determined in the SANS 10142-1
Table 6.8 Pg 114
NB:
Resistance (R) & Reactance (X)
These values could be obtained in the SANS 10142-1
Table E.1 Pg 307
V
= 400 volts (declared voltage)
P
= Transformer Power in KVa
Z%
= Transformer Impedance from rating plate
Z
= Transformer Impedance in Ohm (
Ω
)
A
Z (TRF)
=
Z (TRF)
=
Z (TRF)
= 0,0144
V
2
PX10
3
Z%
100%
x
Ω
400
2
P x 10
3
4.5%
100%
x
=
400 x 400
500 x 10
3
0,045
x
=
160 000
500 000
0,045
x
Ω
C The PSCC of complete system
A + B
= Z (TRF) + Z (conductor)
= Z Total
Isc
=
= A
=
Isc
=
Isc
= 12 136.829 A
Isc
= 12,36829 kA
The circuit breaker for this system must be the next size:
15 kA will be OK!
400
0,0326882
V
3 x Z Total
400
3 x (0,0144 + 0,0044716049)
Z conductor
= Cable impedance in Ohm
L
= The length of cable in meters
See table E.1
= Conductor Resistance in Ohm/Km
Page 307
= Conductor Resistance in Ohm/Km
SANS 10142-2
B Z conductor =
Z (TRF)
=
=
=
Z conductor =
Z conductor =
L r
2
+ x
2
10
3
Ω
55 0,043
2
+ 0,069
2
10
3
55 x 0,0813019
10
3
.4,4716049 x 10¯
3
0,0044716049
55 6,61
2
10¯
3
10
3
Ω
{
Summary of Contents for ACADEMY T419
Page 1: ......
