Applying a DC voltage to the handbag insulation at the end of the generator stator winding can detect faults in the handbag insulation at the generator end when the leakage current of the three-phase coil of the generator is seriously unbalanced. the stator seal burning method can be avoided. Finding local faults without damaging the stator structure can be found;
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 requirementwhen the water temperature is 20°C: for open water systems it does not have 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 when the water collection pipe of the unit is directly grounded, make sure that the water diversion pipe is strictly blown ; 3.5 After handling the insulation, the insulation should be dried before measurement; 3.6 Lighting installations (including incidental lighting) must meet operating requirements
3.7 Safety measures for high voltage; the work must be adopted during the test, and the operator must wear insulating gloves and insulation
3.8 After the test is completed, the high-voltage wire must be completely discharged before work can begin; the stator and steam excitation ends must be monitored;
3.10 Uneafter the test is completed, when removing the aluminum foil attached to the insulating surface of the handbag, it must be cleaned and there must be no residue; When removing the aluminum foil, discharge should also be carried out to avoid possible dangers caused by a small amount of residual charge.
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 fTin 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 be 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:
Resultstests are generally not higher than Column values:
Hand-packed insulated wire connector, turbine side phase insulated connector: 20 μA; voltage drop across 100 MΩ resistor: 2000 V end connector (including water pipe cone insulation) and transition wire parallel block: 30 μA; ; the voltage drop across the 100 MΩ resistor is 3,000 V.
This sentence applies to generators whose cooling method is the water-hydrogen-hydrogen method, that is- i.e. water passes through the hollow conductor inside the stator winding and the water carries away the heat generated during operation. of the generator to achieve the cooling effect. There are ventilation channels inside the stator core and rotor windings, which are cooled by hydrogen.
If the temperature of the internal cooling water of the stator winding of the generatornerator is higher than the temperature of the hydrogen outside the winding, condensation will form on the outer surface of the stator winding, i.e. the insulation surface. of the stator winding will become very wet, which will damage the insulation of the stator winding. As a result, the stator winding will be partially discharged and will no longer be able to function.