Tan Delta Tester (Dissipation Factor Tester)
A tan delta tester (also known as a dissipation factor tester, DF tester, or dielectric loss tester) is a high-precision electrical instrument used to assess the insulation condition of high-voltage electrical equipment.
Simple Explanation
Tan δ (tan delta) is the tangent of the loss angle. It measures how much energy a material dissipates as heat rather than storing it as an electric field. In good insulation, tan δ is very small, indicating low loss. In damp, aged, or damaged insulation, tan δ rises sharply.
Test Objects
Typical test objects include:
Power transformers
Bushings
Current transformers (CT) / Voltage transformers (VT)
Cables
Generators
Capacitors
Main Functions
Measures tan δ (dissipation factor)
Measures capacitance (C)
Often includes excitation current testing for transformers
Identifiable Issues
The tester helps identify insulation problems such as:
Moisture ingress
Thermal aging
Partial discharge damage
Contamination in insulation