A short-circuit test, also known as a "impedance test" or "low-voltage test," is a type of performance test conducted on a transformer to determine its parameters and characteristics. This test is typically performed on the low-voltage side of the transformer, while the high-voltage side is kept open. The primary purpose of the short-circuit test is to calculate the equivalent impedance, losses, and parameters of the transformer.
During the short-circuit test, the primary winding (high-voltage side) of the transformer is connected to a relatively low voltage source, and the secondary winding (low-voltage side) is short-circuited. This setup allows a small current to flow through the winding and the transformer's impedance, which can be measured using appropriate instruments.
The main objectives of the short-circuit test are:
Impedance Measurement: By measuring the current and voltage under short-circuit conditions, the impedance of the transformer can be calculated. Impedance is a critical parameter that affects the transformer's voltage regulation and fault current capability.
Losses Calculation: The test helps in determining the copper losses (IĀ²R losses) and core losses (hysteresis and eddy current losses) of the transformer. These losses are essential for assessing the transformer's overall efficiency and performance.
Voltage Regulation: The impedance value obtained from the short-circuit test is used to calculate the voltage regulation of the transformer under different load conditions. Voltage regulation indicates how well the transformer can maintain its output voltage within specified limits as the load varies.
The procedure for conducting a short-circuit test involves gradually increasing the primary voltage while keeping the secondary winding short-circuited until the rated current flows through the winding. The corresponding primary and secondary current and voltage values are then measured and used to calculate the various parameters.
Overall, the short-circuit test is an essential step in determining the characteristics and performance of a transformer, aiding in its proper design, rating, and operation within a power distribution system.