Short circuit test
Encyclopedia
The purpose of a short circuit test is to determine the series branch parameters of the equivalent circuit
. As the name suggests, in this test primary applied voltage
, the current
and power input are measured keeping the secondary terminals short circuit
ed. Let these values be Vsc, Isc and Wsc respectively. The supply voltage required to circulate rated current through the transformer
is usually very small and is of the order of a few percent of the nominal voltage. The excitation current which is only 1% or less even at rated voltage becomes negligibly small during this test and hence is neglected. The shunt branch is thus assumed to be absent. Wsc is the sum of the copper
losses in primary and secondary put together. The reactive power consumed is that absorbed by the leakage reactance of the two windings.
is near to zero transformer windings are operational.
If neutral current is higher or equal to line current between LV phase one of the winding is open.
Electrical network
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...
. As the name suggests, in this test primary applied voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
, the current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
and power input are measured keeping the secondary terminals short circuit
Short circuit
A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....
ed. Let these values be Vsc, Isc and Wsc respectively. The supply voltage required to circulate rated current through the transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
is usually very small and is of the order of a few percent of the nominal voltage. The excitation current which is only 1% or less even at rated voltage becomes negligibly small during this test and hence is neglected. The shunt branch is thus assumed to be absent. Wsc is the sum of the copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
losses in primary and secondary put together. The reactive power consumed is that absorbed by the leakage reactance of the two windings.
Procedure
For carrying short circuit test on power transformer:- Isolate the power transformer from service.
- Remove HV/LV jumps and disconnect neutral from earth/ground.
- Short LV phases and connect these short circuited terminals to neutral
- Energise HV side by LV supply.
- Measure current in neutral, LV line voltages, HV voltage and HV line currents.
Analysis
If neutral currentNeutral current
Weak neutral current interactions are one of the ways in which subatomic particles can interact by means of the weak force. These interactions are mediated by the boson...
is near to zero transformer windings are operational.
If neutral current is higher or equal to line current between LV phase one of the winding is open.