What is the tan delta test on a transformer?
The tan delta test on a transformer, also known as the Dielectric Dissipation or Loss Angle test, is a method
used to assess the quality and condition of the
transformer's insulation system. This test is crucial for determining the health of the transformer and
identifying potential insulation faults or aging issues.
The test involves applying a low-frequency test voltage to the transformer's components, such as windings,
current transformers, potential transformers, transformer bushings, and cables.
The goal is to measure the dissipation factor, often referred to as tan delta, which indicates the quality of
the insulation.
Here's how the tan delta test works:
1. Isolation: The component to be tested is isolated from the system.
2. Low-Frequency Voltage: A low-frequency test voltage is applied to the equipment.
3. Incremental Voltage: The test begins with a normal voltage. If the tan delta values are satisfactory,
the voltage is then increased to 1.5 to 2 times the normal voltage.
4. Measurement: A tan delta controller unit measures the tan delta values, while a loss angle analyzer
compares these values at normal voltage and higher voltages to analyze the results.
The primary purpose of the tan delta test is to ensure the secure and reliable operation of the transformer. By
calculating the dissipation factor and capacitance values, this test provides insights into the insulation condition of the transformer, including bushings and windings. Changes in
capacitance values can indicate partial breakdowns in bushings and shifting of windings,
while the dissipation factor quantifies losses due to factors like insulation aging and increased energy levels,
which are transformed into heat.
In summary, the tan delta test is a critical diagnostic tool that helps assess the insulation's quality and predict
potential issues in transformers, ultimately ensuring their safe and efficient operation.
