Surge tester for Electrical Motor

What is a surge test?

Surge voltage is a voltage pulse with which the test object is subjected to. A meaningful test is possible on stators, transformers and coils. A test on complete electric motors is only possible on pre-aligned permanent magnet motors, testing on squirrel cage motors is not useful.

How is the surge voltage generated?

After connecting a charged capacitor with high voltage, the energy stored in the capacitor discharges into the inductance of the test object winding and back into the capacitor. This results in a sinusoidal curve, which is produced by the damped oscillation. Each inductance to be tested has a specific frequency and a characteristic amplitude curve.

How is it measured?

The surge test is currently carried out on our products at a voltage of max. 6 kV. In practice, there are two methods of measurement: the master curve method and the double pulse method:

Double impulse: Used for 1-phase coils / windings. Two pulses are applied to the DUT one after the other and these are compared. Flashovers and insulation faults are detected by means of the two curves. Incorrect numbers of windings cannot be detected.

Master curve: Recording of a master curve with a sample DUT. Incorrect numbers of windings are detected and a comparison of several windings (e.g. with a 3-phase DUT) is possible. Flashovers and insulation faults are detected by means of the curves.

Show Figure 1 :If the DUT has a lower number of turns than the sample DUT, the oscillating circuit has a higher frequency. If there are too many windings, the opposite is true.

Show Figure 2 :The error pattern in the case of a short circuit of the windings is similar to that of a too low number of windings, but the curve is much more attenuated.

Show Figure 3 :When a wire breaks, the curve oscillates similar to the master curve, but is more damped and then stops abruptly.

Show Figure 4: Missing insulation from the housing

How can the result of the test be evaluated?

The evaluation methods "Defect area", "Differential defect area" and "Tolerance band" are available. Evaluations are possible both with the "master curve method" and with the "double pulse comparison method".

What are the advantages compared to hipot testing?

With the surge voltage test the windings can be tested among each other and the windings against ground / housing. Insulation faults within the windings can also be detected. With a mere hipot test, the windings are tested against earth / housing, but not the windings among each other.