7/29/2019 Short Circuit Defintion

1/1AMTED300014EN_001_01Schneider Electric Gamme

0Short-circuit power

We have to calculate each of the Isc currents.

Introduction# The short-circuit power depends directly on the network configurationand the impedance of its components:

lines, cables, transformers, motors... through which the short-circuit

current passes.

# It is the maximum power that the network can provide to an installation

during a fault, expressed in MVA or in kA rms for a given operating

voltage.

U : operating voltage (kV)

Isc : short-circuit current (kA rms.) Ref: following pages

The short-circuit power can be assimilated to an apparent power.

# The customer generally imposes the value of short-circuit power on us

because we rarely have the information required to calculate it.Determination of the short-circuit power requires analysis of the power

flows feeding the short-circuit in the worst possible case.

Possible sources are:# Network incomer via power transformers.

# Generator incomer.

# Power feedback due to rotary sets (motors, etc);

or via MV/LV transformaters.

Zcc

Icc

LA

U Zs

R

B

E

Ssc U Isc=

Exam p le 1 :

25 kA at an operati ng voltage of 11 kV

Ex am p le 2 :

# Feedback vi a LV I sc5 is only

possible if the transformer ( T4)

is powered by another source.

# Three sources are flowing in the

switchboard (T1-A-T 2)

5 ci rcu i t breaker D 1( s/c at A)I sc1 + Isc2 + I sc3 + Isc4 + I sc5

5 c i rcu i t b reaker D 2( c/c at B)I sc1 + Isc2 + I sc3 + Isc4 + I sc5

5 c i rcu i t b reaker D 3( c/c at C)I sc1 + Isc2 + I sc3 + Isc4 + I sc5

63 kV

T1A

T2

A B C

D1

D6

MT

BT

D4 D5 D7

D2 D3

10 kV

T3M

BT MT

T4

Icc4Icc5

Icc1 Icc2 Icc3

Design rules