Withstand voltage testing is a crucial test for motor windings, but the applied voltage varies depending on the conditions, and there are several important points to note. Today, Ms. Can will categorize and share the test requirements for initial testing of new windings, repeated testing, and repair windings.
First test of the new winding
(1) The high voltage output terminal of the step-up transformer is connected to the winding under test, and the low voltage terminal is grounded.
(2) The casing (or core) of the motor under test and the windings without high voltage must be reliably grounded.
(3) The test pressurization time is divided into two types: 1 min and 1 s.
(4) For semi-finished motor stators and rotors, the test voltage should be increased compared to the overall machine voltage. The increase should be determined by the industry or enterprise.
(5) When using the 1-minute method, the voltage should be applied starting from no more than half of the test voltage, and then gradually increased to the full value evenly or in steps no more than 5% of the full value. The time taken for this process should be no less than 10 seconds. After the voltage reaches 1 minute, the voltage should be gradually reduced to half of the test voltage before the power supply is turned off.
(6) The 1s method is limited to mass-produced motors with a rated power ≤200kW (or kV.A) and a rated voltage ≤1kV, and the test voltage must be 20% higher than the value specified in the 1min method.
(7) For DC motors powered by static power converters, the voltage should be the higher of the motor's DC voltage or the effective value of the rated phase-to-phase voltage at the input terminal of the static power converter. If the static power converter includes an input transformer, the input voltage mentioned above refers to the transformer's output voltage.
(8) To prevent the stored charge in the test winding from discharging and injuring the test personnel, the test winding must be discharged to ground after the test is completed before the wiring can be disconnected. This is especially necessary for motors with larger capacity.
(9) During the test, non-test personnel are strictly prohibited from entering the test area; test personnel should have clear division of labor, unified command, and high concentration. All personnel should be more than 1 meter away from the test motor and face the test motor.
In addition to the test personnel who can cut off the power supply to control the test voltage, other power cut-off devices should be installed in other locations to deal with emergency situations.
Regulations for Repeated Tests
Because this test has a cumulative damage effect on insulating materials, it should generally not be repeated unless absolutely necessary.
If necessary (e.g., if strongly requested by the user or during certain acceptance checks), the applied voltage should be reduced to 80% of that used in the first test. Before the test, the insulation resistance of the motor should be checked. If the insulation resistance is low or the motor is damp, the motor should be dried. The test should only be conducted after the insulation resistance reaches the acceptable value.
Test specifications for the winding after repair
When a user and a repairman agree to conduct a withstand voltage test on partially rewound windings or a motor that has undergone major repairs, the following guidelines are recommended.
(1) For all rewound windings, the test voltage value is the same as that for new motors.
(2) For partially rewound windings, the test voltage value shall be 50% of the test voltage value of a new motor. Before the test, the old windings shall be carefully cleaned and dried.
(3) For motors that have undergone major repairs, after cleaning and drying, they should be able to withstand a test voltage of 1.5 times the rated voltage. If the rated voltage is 100V or above, the test voltage should be at least 1000V; if the rated voltage is below 100V, the test voltage should be at least 500V.
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