AC high voltage motor stator forming coil test
The most cumbersome and most critical aspect of high-voltage motor manufacturing is the coil manufacturing of the motor. The turn-to-turn and withstand voltage tests are essential in the coil manufacturing process. Some motor manufacturers use the sampling inspection method for the coil, and many motor manufacturers use the coil-by-coil inspection method to ensure the electrical performance of the high-voltage motor.
For motors with rated voltages of 3000V-15000V, the surge voltage level is obtained according to the standard formula, and the value is rounded. It is divided into two types: specified lightning surge voltage and specified steep wavefront surge voltage; usually rated voltage level ( 3, 3.15, 3.3, 4, 6, ..., 13.8, 15) The motor, the standard gives the specific value of the specified surge voltage level and the power frequency resistance (effective value) and its formula, and specifies the lightning impulse voltage. There are three cases of anti-steep wavefront surge voltage and power frequency resistance.
Standard lightning surge voltage
The lightning impulse voltage is the ability to verify the electrical equipment's insulation withstand lightning impulse voltage by manually simulating the lightning current waveform and peak value. According to the measured results of the lightning discharge, the lightning wave waveform is considered to be a unipolar double exponential curve with a wave head length of several microseconds and a wave tail length of several tens of microseconds. Most of the lightning is negative polarity, and the national lightning standards of the countries all standardize the standard lightning shock wave as: the apparent wave head time T1=1.2μs, also known as the wave head time; the apparent half-wave peak time T2=50μs, also known as the wave tail time. The peak value of the voltage generated by the actual test device and the allowable deviation between the waveform and the standard wave are: peak value, ±3%; wave head time, ±30%; half-wave peak time, ±20%; the standard lightning waveform is usually expressed as 1.2 /50μs.
When the standard specifies the lightning impulse voltage, the applied surge voltage is calculated according to formula (1) and rounded to thousands.
UPL=4UN+5............(1)
In formula (1):
UPL------- applied surge voltage, kV;
UN-------The rated voltage of the motor to which the test coil belongs, kV.
Steep wavefront surge voltage
The level is determined according to the apparent wavefront 0.2μs. When the steep wavefront surge voltage is specified, the applied surge voltage is calculated and rounded according to equation (2).
UPD=0.65×(4UN+5)=0.65UPL............(2)
In formula (2):
UPD - the applied surge voltage, kV;
UN - the rated voltage of the motor to which the coil under test is, kV.
Power frequency withstand voltage test
When the power frequency withstand voltage is specified, the applied surge voltage is calculated and rounded according to equation (3). This method is the most commonly used test method for motor manufacturers.
US=2UN+1............(3)
In equation (3)
Us——the applied surge voltage, kV;
UN - the rated voltage of the motor to which the coil under test is, kV.
Coil turn-to-turn and main insulation withstand voltage test method
●Dual test
A surge voltage was applied 5 times between the two terminals of the coil using a day meter. The peak value of the applied surge voltage is obtained by the equation (2).
●Main insulation withstand voltage test
Test the impact resistance level of the main insulation using the power frequency voltage or the impulse voltage. During the test, the coil under test is embedded in the groove or wrapped with a grounded conductive tape on a straight portion of the winding. In order to facilitate the operation, many motor manufacturers use the steel ball method, that is, the straight side of the coil is embedded in the steel ball with a diameter of not more than 1 mm.
(1) Power frequency voltage test Apply a power frequency voltage (2UN+1) kV between the lead terminal of the coil and the ground. After 1 minute, the voltage is increased at a rate of 1 kV/s to reach 2 (2UN+1). kV, then immediately lower the voltage to zero at a rate of at least 1 kV/s. No breakdown occurred during the test to meet the requirements.
(2) Impact voltage test A surge voltage is applied between the lead end of the coil and the ground. The wave front time of the surge voltage was 1.2 μs, and the number of impacts was 5 times. The peak value of the test voltage is calculated by the equation (1).
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