Tan delta test; loss angle test; dissipation factor test
Tan Delta Test (Loss Angle Test / Dissipation Factor Test) The Tan Delta Test is also known as the loss angle test or dissipation factor test . It is one of the most reliable methods to evaluate the health of insulation in electrical equipment such as power cables, transformer windings, CTs, PTs, and bushings . Principle of Tan Delta Test Any insulating material ideally behaves like a pure capacitor when connected across a power supply. In a pure capacitor, the charging current leads the applied voltage by exactly 90° . However, in reality, no insulation is perfect: With ageing, dirt, and moisture ingress , a resistive (leakage) current component appears in addition to the capacitive current. Therefore, the total current leads the voltage by slightly less than 90°. The loss angle (δ) is the angle between the total current and its ideal capacitive component. The tan delta (tan δ) is defined as: tan δ = I r I c = ( V / R ) V ⋅ 2 π f C = 1 2 π f C R \tan δ = \f...



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