Maximum test voltage Surge test

The determination of the test voltage at the surge tester is of great importance.

When training and using the surgetester, the question of what is the correct test voltage for low-voltage motors often arises.

For low-voltage motors, the desired (maximum) surge test voltage is not included in European standards. To give a guideline, see below an outline of experience values.

We would like to stress that the information below may be helpful to determine internally what (maximum) surge test voltage is desirable. In general, a distinction should be made between a new winding and one that has been in use.

The rated voltage of the electric motor serves as the basis for determining the maximum permissible test voltage.

For this, one can make a comparison with the basic rules of thumb, used to determine the maximum test voltage, in the AC high voltage test (Hipot AC).

The equation for an AC high voltage test is as follows:

Utest HVAC = 2x Unom+1000 V
Utest HVAC = maximum AC test voltage
Unom = rated voltage of the electric motor

To determine the maximum surge voltage, the calculated test voltage for the high-voltage AC test can be multiplied by a factor between one and two. This distinguishes whether the winding was produced recently or is an obsolete motor.

The test voltage for a recently produced winding may be higher than for an aged winding.

Calculation example

Based on this, the following are guidelines for the maximum surge test voltage:

Recently manufactured motor: Utest Surge max= Utest HVAC*2
Aging motor: Utest Surge max= Utest HVAC*1

Below is an example to determine the maximum test voltage of the surge test for a motor with a nominal voltage of 400 V. Using the equation for the high voltage test, test voltage of 2 x Unom + 1000V = 2 x 400 V + 1000 V = 1800 V.

New winding Utest Surge max = 1800 V x 2 = 3600 V
Old winding Utest Surge max = 1800 V x 1 = 1800 V

With ageing motors, it makes sense to slowly increase the voltage to the desired test voltage. Starting with an initial value (e.g. 500 V) up to the maximum test voltage. Under no circumstances should the voltage level be increased more when unstable surge graphs occur.

The Surgetest can be performed with different test systems:
MotorAnalyzer 3
MTC2 and MTC2-R7
Test system MTC3