Interturn

Interturn refers to the space or insulation between two adjacent turns of a coil in electrical windings, such as those found in transformers, inductors, or electric motors. The interturn insulation is essential to prevent current from leaking from one turn to another and to maintain the winding’s electrical and thermal performance.

Interturn faults are faults where the insulation between turns is damaged or degraded, creating an unintended short circuit across turns. Such faults can increase current, alter inductance, raise localized temperatures, and potentially lead to insulation failure or equipment damage if not detected and managed. They are a significant concern in high-voltage transformers and machine windings, where even small numbers of shorted turns can affect performance and reliability.

Causes of interturn faults include aging or moisture ingress in insulation, thermal cycling, mechanical vibration, manufacturing defects, and damage during handling or installation. Symptoms may include abnormal current draw, overheating, reduced efficiency, abnormal tap or leakage inductance, and, in some cases, nuisance tripping of protection systems.

Detection and monitoring methods for interturn faults vary. Routine tests such as insulation resistance, winding resistance, and hipot testing can indicate problems, but specialized techniques are often needed for early detection. These include surge comparison tests, partial discharge measurements, and condition-monitoring approaches like motor current signature analysis or frequency-domain techniques that can reveal interturn short circuits.

Prevention focuses on robust winding design, high-quality insulation and impregnation, proper moisture control, effective cooling, and regular maintenance and testing to identify deterioration before failure. Interturn faults are treated as a type of winding fault requiring both preventative design and ongoing diagnostic strategies.