Test method: Before measurement, fully discharge to ground, pay attention to mechanical zero adjustment. During the test, except for the item under test, all other items should be grounded. Record the test time as
and the resistance value at 60s. After the test, calculate the absorption ratio, absorption ratio = R60/R15. The absorption ratio should be greater than 2, and the insulation resistance imbalance coefficient of each item should not be greater than 2 (the imbalance coefficient refers to the ratio of the maximum R60 to the minimum R60 among all items). 4.
N, 1.0UN, 1.5UN, 2.0UN, 2.5UN, 3.0UN, with a one-minute dwell time at each stage for the withstand voltage test, and record the current values at each voltage during the test. When testing each item, all other items must be grounded. Moreover, at the same voltage, the current values of each item should be relatively similar. Precautions:
After each test, it is necessary to fully discharge, otherwise accidents may occur. Special attention must be paid to the wiring of the temperature measurement coil. AC withstand voltage
(2) During the coil lowering process, the withstand voltage test should be performed every time about one coil is lowered. When testing coils, all other coils except the one under test must be grounded. The test voltage calculation formula is shown in the table below. (3) After the coil lowering is completed, for the withstand voltage test, when testing an item, other items should be grounded. The test voltage formula is shown in the table.
AC voltage and current generate a magnetic field in the stator core, while also producing eddy current and hysteresis losses, causing the core to heat up. By measuring the induced voltage obtained from the winding, the active power loss of the exciting current, and the temperature, the core loss per unit weight and temperature rise can be calculated (
(mm), number of ventilation ducts n, slot depth hc (mm), silicon steel sheet ampere-turns H0 (ampere-turns/cm), we take 2.4 here, slot type dimensions hc × slot width, fill factor K=0.95, select power frequency f=50 (Hz), select excitation voltage U, test magnetic flux density B=1T (theoretical value). Test parameter calculation: effective core height L=K×(h-n×b) (mm), stator core yoke cross-sectional area S=L×ha (cm2)
×Wl (turns), the measurement voltage is (V). Excitation coil cable cross-sectional area: selected according to per square millimeter (copper wire ampere selection, using copper core rubber insulated flexible cable.
Record once every 10 minutes; record excitation voltage, excitation current, induced voltage, iron loss, average core temperature, and average frame temperature respectively. Temperatures at various parts are measured using thermocouples, mainly at the core slot bottom, frame, core, and periphery. Fill in the corresponding tables respectively. For stator temperature processing, the temperature difference between upper, middle, and lower parts should not exceed 15°C, and the temperature difference between each segment and room temperature should not exceed 25°C.
The dielectric loss of stator coils is divided into normal state and hot state, and the test equipment is the same. Before the test, the coil should be pre-treated, that is, place the coil in an oven to bake at a temperature of 120
for about 8 hours. Then, before the coil test, wrap the coil with 0.05mm aluminum foil. To ensure full contact between the coil and the aluminum foil, wrap a layer of cloth tape on the outside, with half-lap wrapping, and the aluminum foil is also half-lap wrapped. The wrapping length of the coil is the low-resistance part plus the high-resistance part. At the high-resistance parts at both ends, the aluminum foil height is about 5mm lower, and the outer cloth tape is the same. Note that an electrode lead should be left at the middle wrapping point, and 0.5mm of aluminum foil should also be left at both ends for connecting the test leads. Normal state dielectric loss
N, 0.4UN, 0.6UN, 0.8UN, 1.0UN. Record the normal state dielectric loss tangent and resistance values, and then classify the coils according to the grading regulations. Hot state dielectric loss
N, 0.4UN, 0.6UN, 1.0UN. Record the normal state dielectric loss tangent and resistance values, and then classify the coils according to the grading regulations. The test temperatures are 50°C, 80°C, 120°C, and 155°C respectively. Precautions:
Test environment: Test at room temperature. Test tool: Turn-to-turn insulation tester. Test method: This test is performed on the stator coils of high-voltage motors. The test voltage selection formula is (2UN+2.5) kV, and the number of impulses is 3. For the use of the turn-to-turn insulation tester, refer to the corresponding instruction manual. During the test, pay attention to whether the waveforms on the oscilloscope are the same; only when the waveforms are the same can the coil be used. Part 2: Rotor Components 1.
DC resistance of individual coils Purpose: Through the DC resistance test of the magnetic pole coil, serious inter-turn short circuits in the magnetic pole coil can be detected.
Data processing: The test values of the magnetic pole coil should be processed as follows: (Imax-Imin)/Iaverage ≤ 2%
If the test data does not meet the above results, then the coil with the maximum or minimum resistance may have an inter-turn short circuit and should be treated before mounting. (2
) After the magnetic poles are mounted, DC resistance test of the rotor coil Purpose: Through the DC resistance test of the magnetic pole coil, it can be detected whether there are reasons such as deterioration of pole connection contact resistance.
Result determination: If the total DC resistance of the entire coil does not match the sum of the DC resistances of individual coils, then there may be reasons such as deterioration of pole connection contact resistance, and treatment should be given. 2. Rotor insulation resistance test (
Individual coil insulation resistance test Purpose: By testing the rotor insulation resistance, check whether there are reasons such as inter-turn short circuits in the rotor coil. Test environment: Insulation resistance test is generally performed in a cold state.
Before the insulation resistance test, it is best to conduct an appearance inspection and comprehensive cleaning. Preferably, use dry compressed air to blow off dirt around the magnetic poles, and then measure with a megger. Precautions:
During the test, pay attention to turning off the meter after the test to prevent electric shock. After the test, discharge should be performed, and the discharge time depends on the specific situation. Measurement method:
During measurement, the voltage should be applied between the magnetic pole coil and the magnetic pole core. Note: The pointer of the megger should be connected to the coil. Data processing: The insulation resistance value of a single magnetic pole coil should not be less than 5M
Ω. There should not be a significant difference in insulation resistance values between each magnetic pole. The insulation resistance value of the pole ring should also not be less than 5 M
Result determination: For insulation resistance that does not meet the requirements, drying treatment should be performed. When drying by passing DC current through the winding, it should be carried out at 60%~70% of the rated current. For the selection of power supply and precautions, refer to the corresponding content. The winding surface temperature should be controlled not to exceed 80°C. Rotor winding heating and drying can be combined with rotor pole hot keying. (2
Purpose: By testing the rotor insulation resistance, check whether there are reasons such as inter-turn short circuits in the rotor coil. Test environment: Insulation resistance test is generally performed in a cold state.
For rotor rated voltage above 200V, use a 2500V megger for measurement. Pre-test preparation: Before the insulation resistance test, it is best to conduct an appearance inspection and comprehensive cleaning. Preferably, use dry compressed air to blow off dirt around the magnetic poles, and then measure with a megger.
The pointer of the megger should be connected to the coil. Data processing: The insulation resistance value of the entire rotor winding should generally not be less than 0.5 MΩ
Result determination: For insulation resistance that does not meet the requirements, drying treatment should be performed. When drying by passing DC current through the winding, it should be carried out at 60%~70%
of the rated current. For the selection of power supply and precautions, refer to the corresponding content. The winding surface temperature should be controlled not to exceed 80°C.
Purpose: The purpose of the AC withstand voltage test for the rotor coil is to check insulation defects in the rotor winding. Test environment: AC withstand voltage test is generally performed in a cold state.
Test tool: A set of withstand voltage test equipment. Precautions: Since the AC withstand voltage test is a high-voltage test, attention should be paid to safety during the test. The test area should be enclosed with protective barriers to prevent others from entering the test area, causing safety hazards.
In addition, since the capacitance to ground of a single magnetic pole winding is very small, and the test voltage is much lower than the stator withstand voltage, the capacitive current is very small. Therefore, the test transformer used for the test does not need to be very large. For specific precautions, refer to the precautions of the corresponding test. Test method: Before or after mounting, as well as for collector rings, leads, brush holders, etc., the withstand voltage test standards are all
Precautions: Since the AC withstand voltage test is a high-voltage test, attention should be paid to safety during the test. The test area should be enclosed with protective barriers to prevent others from entering the test area, causing safety hazards. In addition, since the capacitance to ground of the entire rotor winding is very small, and the test voltage is much lower than the stator withstand voltage, the capacitive current is very small. Therefore, the test transformer used for the test does not need to be very large. For specific precautions, refer to the precautions of the corresponding test.
Test method: After the rotor is fully assembled. Before being lowered into the stator bore, the test voltage is 10 times the rated excitation voltage, but not less than 1500V. After the rotor is lowered into the stator bore, the test voltage during handover is 7.5 times the rated excitation voltage, but not less than 1200V. The pressurization time is 1 minute for both.
Test environment: Cold state, room temperature. Test tool: Test transformer. Precautions: Pay attention to safety during the test to prevent electric shock.
Test method: The AC impedance test of a single coil should be performed under the pressure of a hydraulic press, with the pressure being the centrifugal force of the coil at the runaway speed of the motor. Test conclusion: Umax-Umin/Uaverage ≤ 5%
Test method: During the test, each coil is tested at a voltage of 1000V. Before the test, first estimate the total voltage, and then test the voltage of each coil separately.
The testing of low-voltage units is similar to that of high-voltage units in many aspects, but the items inspected are more than those for high-voltage units. The test items for low-voltage units are as follows: Stator part:
1. Magnetic pole coil DC resistance (same as high voltage) 2. Magnetic pole coil insulation resistance (same as high voltage) 3. Magnetic pole AC impedance (same as high voltage)
Disclaimer: This article only represents the author's personal views. Sohu is an information release platform, and Sohu only provides information storage space services.
Network port withstand voltage test
