I. Stator winding AC withstand voltage test wiring and method
    Figure 4-6 shows the wiring of the power frequency AC withstand voltage test of the stator winding of the generator. The head and tail of each phase of the stator winding of the generator should be short-circuited. The head of the test phase is connected to the tester, and the head and tail of the non-test phase are short-circuited. The rotor winding head and tail should be shorted to ground.
The test method is as follows:
    (1) The test shall be carried out after the shutdown and before the removal of the heat before the contamination. The standby unit can be operated in a cold state.
    (2) The AC withstand voltage test shall be carried out after other insulation tests have passed.
    (3) The test site shall be covered with signs, signs and guarded by special personnel.
    (4) Adjust the protective ball gap so that the discharge voltage is 105%~110% of the test voltage. There should be no significant difference between the three consecutive tests, and the reliability of the operation of the overcurrent protection device is checked.
    (5) After connecting the wiring according to the wiring diagram shown in Figure 4-6, it should be checked by a special person to confirm that it is correct.
    (6) The test shall be carried out in phases, the test phase shall be pressurized, the non-test phase shall be short-circuited to ground, and the rotor winding shall be short-circuited to ground .
    (7) The boost must start from zero, can not be impacted and closed, can be boosted at any speed before 75% of the test voltage, and then boosted evenly, and boosted at 2% test voltage per second.
    (8) In the process of boosting and withstand voltage, if abnormal conditions are found (such as the voltmeter pointer swings greatly, the ammeter increases sharply, the generator emits smoke, gas, burnt odor, flashover, burning or breakdown sound) When you stop, you should stop the boost and find out the cause after stepping down.
    (9) The general withstand voltage is 1 min.
    (10) The insulation resistance and absorption ratio of the generator should be measured before and after the test. There should be no significant difference between the two measurements.
    (11) For hydrogen-cooled generators, the test shall be carried out after the hydrogen purity after hydrogen charging is 96% or more or the hydrogen content after hydrogen discharge is 3% or less. It is strictly forbidden to test during the replacement process.
    It should be pointed out that there is no difference in principle between the AC withstand voltage test and the air-cooled generator of the water-cooled generator (the test wiring is shown in Figure 4-7). But should pay attention to the following points:
    (1) The AC withstand voltage test for water-cooled generators is divided into two modes: water-passing and non-water-passing tests. When the water is not tested, the water must be blown off to prevent the inner wall of the insulated water pipe from flashing and burning. In order to make the insulated water pipe together withstand voltage, the water pipe should be grounded to shield the current flowing through the water pipe. The mA meter reading is the capacitance current value of the sample. When passing the water test (the method generally used), the wiring is shown in Figure 4-7. However, the water pipe is not subjected to withstand pressure at this time, so it is necessary to perform a withstand voltage test on the water pipe separately.
    (2) The conditions of qualified water are: conductivity of 0.5μS/cm at 20 °C, pH value of 7~8, hardness >2 mix g/kg; total insulation resistance of each busbar is above 20~3OkΩ; The temperature of R60/R15 should be greater than 1.6 in the range of 10~30 °C; the insulation resistance value (interphase and ground) of each phase of the generator stator winding should not be less than 1000MΩ (1min value).
    (3) Short-circuit the connecting wire of the water-cooled motor temperature measuring component to the ground, and check the temperature measuring component itself, the insulation resistance value of the connecting wire to the ground or the winding conductor (measured by a 250V megger, not less than 1MΩ).
Second, the standard of AC withstand voltage test
    According to the requirements of the "pre-regulation", the test voltage of the AC withstand voltage test is divided into two cases:
    (1) The test voltage after all stator windings are replaced and repaired is: the capacity is less than 10000kw (or kVA), the rated voltage is above 36V, the test voltage (V) is 2UN+1000, but the minimum is 1500V; the capacity is 10000kw (or For kVA) and above, the test voltage is 20UN for rated voltages below 600oV; the rated voltage is 6000~18 000V, the test voltage is 2UN+3000(V); for rated voltages above 18000V, the test voltage is determined by special agreement. .
    (2) The test voltage after the overhaul or partial replacement of the stator windings and repairs is: for those running for 20 years or less, the test voltage is 1.5, and if the operation is more than 20 years, the test voltage is 1.5UN; operation 20 If the cable is not directly connected to the overhead line for more than one year, the test voltage is (1.3~1.5) UN.
Third, the analysis and judgment of test results
    (1) Determine the breakdown of the insulation. If the following phenomenon occurs during the test, the insulation may be broken down or broken down, and the cause must be found:
        1) The voltmeter pointer swings greatly or the voltage value decreases;
        2) The ammeter indication increases sharply;
        3) The insulation has a charred smell or smoke is found;
        4) There is a discharge sound inside the generator;
        5) Overcurrent protection trips.
    (2) Voltage or current resonance may occur during the test, and it is necessary to prevent misjudgment. During the boosting process, the voltage resonance occurs due to the change of the parameters (that is, the voltage rises slightly, the current increases sharply), that is, the series resonance. Generally, the leakage resistance of the test transformer is small, and voltage resonance is less likely to occur. During the boosting process, the voltage is slightly boosted, and the current is instead reduced. This is the current resonance, also known as parallel resonance. When the pressure is regulated, the output voltage of the test transformer is increased due to the greatly reduced voltage drop across the varistor, which jeopardizes the insulation of the generator. To this end, the following conditions shall be checked, ie C x >1.3S N /U N *10 6 (C x a test capacitor, pF; S N a test transformer rated capacity, kVA; U N - test transformer rated voltage, kV).
Fourth, ultra low frequency withstand voltage test
    As the capacity of the motor increases, the electric capacity of the generator winding to the ground is also increasing. Especially for the hydro-generator, the capacity of the AC withstand voltage test is larger, which brings difficulties to the test. Since the frequency of using 0.1Hz is reduced by 500 times compared with the frequency of 50HZ, this solves the problem of the capacity of the test equipment. It is stated in the "pre-regulation" that when the condition is met, the 0.1Hz (ultra-low frequency) withstand voltage can be used, and the test voltage It is 1.2 times the peak value of the power frequency withstand voltage test voltage and has a duration of 1 min. The advantages are as follows:
    (1) The capacity of the test device is greatly reduced, which is close to the capacity required for the DC test.
    (2) The dielectric loss caused by the interlayer insulation is small, so the accumulation effect of the insulation aging is small when the high voltage test is repeated.
    (3) The insulation of the stator winding end of the generator is subjected to a higher voltage, and it is easier to detect the insulation defect at the end than the AC withstand voltage of 50 Hz.
    (4) The capacitance current is smaller than 50 Hz, so the energy generated during the flash discharge is small, and the damage to the semiconductor antihalation layer at the end of the stator winding is small.
    Figure 4-8~4-10 are several principle wirings of the 0.1Hz high voltage generating device, which are respectively amplitude modulation mechanical rectification type 0.1Hz high voltage generating device; amplitude modulation silicon rectifying type 0.1Hz high voltage generating device and electronic type 0.1 Hz high voltage generating device.
    The principle of action is briefly described as follows:
    (1) The operating principle of the amplitude modulation mechanical rectification type 0.1 Hz high voltage generator. The electric amplitude modulation regulator (3kVA, 0~200V) changes the amplitude of the sinusoidal voltage into an amplitude-modulated sinusoidal AC voltage; the test transformer raises the amplitude modulation voltage to the required voltage. The high voltage divider is used to separate the 0.1 Hz voltage waveform.
    (2) The principle of operation of the amplitude modulation silicon rectifier type 0.1 Hz high voltage generator. The output of the electric voltage regulator is 0.1Hz sinusoidal voltage, which is rectified by the test transformer and the high voltage silicon reactor, and then added to the tested generator.
    (3) The operating principle of the electronic 0.1Hz high voltage generator. It uses thyristor to control the amplitude of 50Hz voltage, and is boosted by the test transformer. It is equipped with high-voltage test transformers with different voltage and capacity to obtain different output voltages and currents. Because there are no mechanical moving parts, it is technically advanced.
V. Rotor winding AC withstand voltage test
    Rotor winding AC withstand voltage test method and AC winding withstand test method for stator winding
    Similarly, since the rated voltage of the rotor winding is low, the test voltage is also low. The test voltage requirements are as follows:
    (1) After the mains and the hidden pole rotors are all replaced and repaired: the rated excitation voltage is 500V or less, the test voltage is 10UN, but not less than 1500V; those above 500V are 2UN+400V.
    (2) When the pole-type rotor is overhauled and the winding is partially replaced and repaired, the test voltage is 5UN, but not less than 1000V and not more than 2000V.
    (3) After the inner part of the hidden pole rotor is insulated and partially replaced and repaired, the test voltage is 5, but not less than 1000V, not more than 2000V.
    Pay attention to the test:
    (1) When the hidden pole rotor removal ferrule is only used to repair the end insulation, it can be replaced by a 2500V megohmmeter insulation resistance.
    (2) If the hidden pole rotor has an aluminum saddle at the end, the voltage resistance test of the winding to the aluminum saddle is performed after the ferrule is removed. During the test, the rotor winding was connected to the shaft, and 2000 V was applied to the aluminum saddle.
    (3) The water-cooled rotor shall be tested under water conditions.
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