As of my last update in September 2021, the term "transformer short-circuit test" refers to a common type of transformer test used to determine the impedance values of a transformer. The test is also known as the "short-circuit impedance test" or simply the "impedance test."
The purpose of this test is to determine the impedance of a transformer, which is an essential parameter for understanding its behavior and performance. Impedance is the opposition that a circuit offers to the flow of alternating current (AC), and it includes both resistance and reactance.
Here's how the transformer short-circuit test is typically performed:
Setup: The transformer is isolated from the system and all of its windings are disconnected. This means that the transformer is physically disconnected from the power source and load it would normally be connected to during operation.
Short-Circuiting: The low-voltage winding (usually the secondary winding) of the transformer is short-circuited, and the high-voltage winding (usually the primary winding) is supplied with a reduced voltage, typically 5% to 10% of its rated voltage.
Measurement: While the high-voltage winding is energized with the reduced voltage, the current flowing through the short-circuited winding is measured, as well as the voltage across the short-circuited winding.
Calculation: From the measured current and voltage values, the impedance of the transformer can be calculated. The impedance is given by the formula:
Impedance = Voltage / Current
It is important to note that during this test, the current flowing through the short-circuited winding is significantly higher than normal operating currents, so the test should be performed quickly to avoid overheating the transformer.
Relevance: The impedance value obtained from this test is typically referred to the high-voltage side (primary) of the transformer and is used for various purposes, such as protection coordination and voltage regulation.
The short-circuit test allows engineers and technicians to evaluate the equivalent impedance of the transformer, which helps in determining how the transformer will behave under different operating conditions, including fault conditions. It is an essential test for assessing the overall health and performance of a transformer. However, it's essential to follow safety precautions and guidelines when performing this test due to the high currents involved. Always consult the transformer's manufacturer documentation and safety guidelines before conducting any tests.