The purpose of a short-circuit test is to determine the series branch parameters of the equivalent
circuit of a
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
.
Method
The test is conducted on the high-voltage (HV) side of the transformer where the low-voltage (LV) side (or the secondary) is
short-circuited. A
wattmeter
The wattmeter is an instrument for measuring the electric active power (or the average of the rate of flow of electrical energy) in watts of any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio ...
is connected to the primary side. An
ammeter
An ammeter (abbreviation of ''Ampere meter'') is an instrument used to measure the current in a circuit. Electric currents are measured in amperes (A), hence the name. For direct measurement, the ammeter is connected in series with the circuit ...
is connected
in series with the primary winding. A
voltmeter
A voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit. It is connected in parallel. It usually has a high resistance so that it takes negligible current from the circuit.
Ana ...
is optional since the applied voltage is the same as the voltmeter reading. Now with the help of
a variac, the applied voltage is slowly increased until the ammeter gives a reading equal to the rated current of the HV side. After reaching the rated current of the HV side, all three instruments reading (Voltmeter, Ammeter, and wattmeter readings) are recorded. The ammeter reading gives the primary equivalent of full load current I
L. As the voltage applied for full load current in short circuit test on transformer is quite small compared to the rated primary voltage of the transformer, the iron losses in the transformer can be taken as negligible here.
Calculations
is the full-load copper loss
is the applied voltage
is the rated current
is the resistance as viewed from the primary
is the total impedance as viewed from the primary
is the reactance as viewed from the primary
High-power tests
A short-circuit test for determination of transformer impedance and losses is carried out with relatively low power applied to the transformer, and with winding currents of the same magnitude as in operation. A different form of short-circuit testing is done to assess the mechanical strength of the transformer windings, and their ability to withstand the high forces produced if an energized transformer experiences a short-circuit fault. Currents during such events can be several times the normal rated current. The resultant forces can distort the windings or break internal connections. For large utility-scale power transformers, high-power test laboratories have facilities to apply the very high power levels representative of a fault on an interconnected grid system.
See also
*
Open-circuit test
The open-circuit test, or no-load test, is one of the methods used in electrical engineering to determine the no-load impedance in the excitation branch of a transformer.
The no load is represented by the open circuit, which is represented on th ...
*
Blocked rotor test A blocked rotor test is conducted on an induction motor. It is also known as short-circuit test (because it is the mechanical analogy of a transformer short-circuit test), locked rotor test or stalled torque test. From this test, short-circuit cur ...
*
Circle diagram
First conceived by A.heyland in 1894 and B.A. Behrend in 1895, the circle diagram is the graphical representation of the performance of the electrical machine drawn in terms of the locus of the machine's input voltage and current. The circle di ...
{{Electric transformers
Electric transformers