7.1.32 STRW - Stress Watts
The Stress Wattage test tests the transformer for breakdown of insulation by measurement of the energising power of a winding, usually the primary, with the remaining windings open circuit. This test applies the voltage, usually twice the normal operating voltage, and continually measures the power to determine any breakdown by changes in the measurement.
This test is suitable for sub-miniature line frequency, large line frequency bobbin wound and some HF transformers. It checks the integrity of interturn insulation, the magnetic material and joints.
A constant voltage source is applied to the winding under test. Both the rms voltage and the power are measured. If necessary, the voltage can is trimmed to the user specified value, and the measurement repeated. The measurement is repeated many times until the dwell time has elapsed. The result given is the measured power.
Usually, the energization is at twice the working voltage and frequency, and has the purpose of trying to create an inter-turn breakdown at a point of potential weakness in the wire enamel. This breakdown is detected by an increase in the measured power.