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AT WHAT VOLTAGE TO TEST WINDING OR A MOTOR?
The voltage test chart on the right gives a basic guiding formula for High Voltage insulation breakdown test and Surge Test as specified by the International standard organisations.
The formula used to calculate the
Test voltages is as follows:
AC/DC H.V Test Voltage = (2×E + 1000)
Surge Test Voltage = √2 × (2×E + 1000)
where "E" is the operating voltage of
the rotating machine

 
The table below indicates the test voltages required to test the rotating machines.

Operating Voltage of Rotating Machines AC/DC H.V Test Voltage Surge Test Voltage
120 V 1,240 V 1,800 V
240 V 1,480 V 2,200 V
440 V 1,880 V 3,000 V
660 V 2,320 V 3,500 V
2.3 KV 5,600 V 7,000 V
3.3 KV 7,600 V 10,000 V
6.6 KV 14,200 V 20,000 V
11 KV 23,000 V 30,000 V
23 KV 47,000 V 49,000 V
 

NOTE:
Many other formulas are also used to calculate the test voltages for AC form wound coils. These are generally based on experience and theoretical arguments about the distribution of voltage in a coil, and the entire winding. The formulas are difficult to apply because of great diversity of coil specification and charachteristics.
The other popular formula below also states the Min and Max test voltages:
MINIMUM TEST VOLTAGE = Number of Turns X 500
MAXIMUM TEST VOLTAGE = Operating Voltage X 1.5
  
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