Introduction to DC Withstand Voltage Testing of Stator Windings and Leakage Current Testing

Introduction Introduction to stator winding DC withstand voltage test and leakage current test 1. The test voltage is 3 times the motor rated voltage. 2. The test voltage is increased in steps according to 0.5 times the rated voltage for each level.

Introduction to DC Withstand Voltage Testing of Stator Windings and Leakage Current Testing

1. The test voltage is 3 times the motor rated voltage.

2. The test voltage is increased in steps of 0.5 times the rated voltage in each step, staying for 1 MIN in each step and recording the leakage current under the specified test voltage

2. p>leakage current should comply with the following regulations: 1. The leakage current difference of each phase should not be greater than 50% of the minimum value when the maximum leakage current is lower. 20ΜA, the difference between each phase should not be obvious from the factory test value; 2. Leakage current should not increase with time

; be found and eliminated. 3. When the leakage current increases significantly and disproportionately to the voltage, it should be analyzed in time.

3. Hydrogen cooled engines must be tested before hydrogen charging or after hydrogen dischargeogen and when the hydrogen content is less than 3%. Testing during the hydrogen replacement process is strictly prohibited.

4. When testing water-cooled motors, the low-voltage shielding method should be used.

In the original "Preventive Testing Procedures for Electrical Equipment", only DC withstand voltages and leakage current measurement has been specified; in the new 1996 version this item is described as a stator winding leakage current test and a DC withstand voltage test. Leakage current is listed separately and advanced to emphasize the importance of measuring leakage current to assess the insulation condition of the. generator.

The test wiring and measurement methods of leakage current and DC withstand voltage are the same, and the applied voltage is also the same. However, the purpose of the two assessments is different. evaluate priMainly the resistance of the generator insulation, for example whether there is insulation or not. Air gaps or damage, etc. The leakage current mainly indicates whether all the insulation of the wire rod has been affected by moisture and deteriorated. can also reflect the cleanliness of the surface at the end of the wire rod. It can be judged more accurately by changes in leakage current.

By applying DC voltage to the purse insulation at the end of the generator stator winding , defects in the insulation of the handbag at the end of the generator may be noted; When the leakage current of the three-phase coil of the generator is seriously unbalanced, the use of hot opening can be avoided. The stator seal method can detect local faults without damaging the stator structure; hidden leakage risks caused by welding and the quality of copper wiresRe hollows at the stator seals may be discovered.

Test conditions and precautions

3.1 The generator is in maintenance condition and the end covers on both sides of the steam generator have been opened

3.2 Before; the test, all internal generator The temperature measuring element must be shorted to ground to avoid damage during pressurization.

3.3 When testing under water flow conditions, the quality of the cooling water should be transparent and pure, without mechanical impurities. The conductivity requirement when the water temperature is 20°C: For open water systems it does not need to be. greater than 5.0×102μS/m; The independent closed circulating water system is 1.5×102μS/m;

3.4 When testing without water and the unit's water collection pipe is directly grounded, make sure the water diversion pipe isst strictly blown; 3.5 After handling the insulation, measurement should be carried out after the insulation is dry; 3.6 Lighting installations (including incidental lighting) must meet operational requirements;

3.7 Safety measures for high-voltage live work must be adopted during the test. The operator must wear insulating gloves and boots and be supervised by a dedicated person

3.8 Once the test is completed, the high voltage wire must be completely discharged. 3.9 During the testing process, the stator and steam ends should be monitored.

3.10 After the test is completed, when removing the aluminum foil attached to the insulation; surface of the handbag, it must be cleaned and must not leave residue; discharge should also be carried out when removing the tin foil to avoid possible dangers caused by the small amount of residual chargee.

4 Test Steps and Judgment Standards

4.1 Number the end bars at both ends of the steam excitation, either according to the manufacturer's number or from the first slot below the horizontal position on the left Start dialing counterclockwise.

4.2 Generally, the test is carried out before cleaning the end joints. The tested joints are hand wrapped with a layer of aluminum foil with a thickness of 0.01mm to 0.02mm for the insulated lead joints and transition wire. parallel blocks. Due to the irregular geometric shape of the coil root, the tin foil is not easy to adhere, so be sure to stuff it as tightly as possible and try to stuff it into as many parts as possible. 4.3 In case of water flow or no water flow, the test wiring generally adopts the positive wiring method. The reverse wiring method must bebe used without water.

4.4 Apply DC twice the rated voltage Un from the generator to the stator coil. One end of the test rod contacts the tin foil wrapped end connector and the other end is grounded via a microammeter. per point and record the voltage value and current value, when the data exceeds the standard, the testing personnel should find the specific parts in the sections.

4.5 After testing, before removing the wiring, fully discharge the high voltage cables when removing the tin foil; 4.6 Judgment criteria:

Test results are generally not higher than the following values:

Insulated wire connector in handbag, turbine side phase insulation connector : 20μA; The 100MΩ resistor is 2000V; the external connector of the terminal (including the insulation of the water pipe cone) and the parallel block of the ftransition il: 30 μA; the voltage drop across the 100 MΩ resistor is 3000 V.

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