| Three-phase asynchronous motor inspection test method | |
| 2020/11/13 | |
| 1. Three-phase asynchronous motor inspection test mainly includes: The measurement of the insulation resistance of the winding to the casing and the windings; the measurement of the DC resistance of the windings in the actual cold state; the no-load test; the insulation dielectric strength test of the windings to the casing and the windings; if necessary, the insulation between the windings Electric strength test. 2. Inspection and test method of three-phase asynchronous motor: a) Visual inspection: Check whether the shape is complete, the mark of the outlet end is correct, whether the screws, bolts and nuts are tightened, whether the rotor rotates flexibly, the radial deflection of the motor shaft extension and the vibration conditions, etc. For wound rotor motors, check the assembly quality of the brushes, brush holders and slip rings, and check whether the brushes and slip rings are in good contact. For enclosed self-fan-cooled motors, check the exhaust system; b) Measurement of insulation resistance: For the repaired motor, generally only the cold (normal temperature) insulation resistance of the winding phase to phase and relative to the ground should be measured. For the wound rotor motor, the insulation resistance of the rotor winding should also be measured. For motors with multi-speed windings, the insulation resistance of each winding should be measured one by one. Large motors can determine whether the windings are damp by measuring the insulation resistance. For motors with a rated voltage below 500V, a 500V megohmmeter is generally used for measurement, a 1000V megohmmeter for motors between 500 and 3000V; a 2500V megohmmeter for motors above 3000V. For motors below 500V, the insulation resistance should not be less than 0.5MΩ. All windings should not be less than 5MΩ; c) Measurement of DC resistance: The measurement of DC resistance of motor windings is generally carried out in cold state. The ratio of the error between the measured resistance values of each phase to the three-phase average value shall not be greater than 5%. If the resistance value difference is too large, it means that there is a short circuit, open circuit, poor welding or contact in the winding, or wrong winding turns, etc. If the three-phase resistance exceeds the specified range, it means that the winding wire is too thin; d) Withstand voltage test: motor After the stator winding phase and phase, phase and ground are insulated by insulating material, it can withstand a certain voltage without breakdown is called withstand voltage. Both AC withstand voltage and DC withstand voltage are withstand voltage tests, which are methods to identify the insulation strength of power equipment. DC withstand voltage test: The voltage is higher, which has a special effect on the discovery of some local defects of insulation, and can be carried out simultaneously with the leakage current test. Compared with the AC withstand voltage test, the DC withstand voltage test has the advantages of light test equipment, less damage to the insulation and easy to find local defects of the equipment. Compared with the AC withstand voltage test, the main disadvantage of the DC withstand voltage test is that due to the different voltage distributions inside the insulation under AC and DC, the DC withstand voltage test is not as close to reality as the AC withstand voltage test. AC withstand voltage test: The AC withstand voltage test is very strict to the test of insulation and can effectively find more dangerous concentrated defects. It is the most direct method to identify the insulation strength of electrical equipment. It is of decisive significance for judging whether the electrical equipment can be put into operation. It is also an important means to ensure the insulation level of the equipment and avoid insulation accidents. The AC withstand voltage test may sometimes make some weaknesses in the insulation more developed. Therefore, the test product must be tested for insulation resistance, absorption ratio, leakage current and dielectric loss before the test. The AC withstand voltage can only be carried out if the test result is qualified. test. 1) Stator winding: During the handover test, take 1 kV for those with a rated voltage of 0.4 kV and below, and 10 kV for those with a rated voltage of 6 kV; for a motor in operation, and for parts that have not been replaced or partially Motors that replace stator windings take 1.5 times the rated voltage, but not less than 1000 volts; all motors that replace stator windings take 2 times the rated voltage plus 1000 volts, but not less than 1500 volts; low-voltage motors that are less than 100 kilowatts are not important , The AC withstand voltage test can be tested with a 2500 volt megger; 2) Rotor winding: In the handover test, take 1.5 times the rated voltage for the irreversible rotor and 3 times the rated voltage for the reversible rotor. Note: For the AC withstand voltage test of the rotor coil of the synchronous motor, the test voltage is 7.5 times the excitation voltage, but it should not be lower than 1200V and not higher than 75% of the factory test voltage. e) Turn-to-turn insulation test: increase the power supply voltage to 130% of the rated voltage, and leave the motor idling for 5 minutes. There should be no short circuit. It is called the turn-to-turn insulation test. The purpose is to assess the insulation performance between turns; f) Measurement of rotor open circuit voltage: when measuring the rotor open circuit voltage, the rotor is stationary, the rotor winding is open, the starting varistor is disconnected, the rated voltage is applied to the stator winding, and the voltage between the lines is measured between the rotor collector rings, the rated voltage For motors above 500V, the voltage applied to the stator windings can be appropriately reduced; g) No-load test: The no-load test is to apply a three-phase balanced voltage to the stator windings of the motor to make the motor run without load. Its purpose is to determine the no-load current and no-load loss, and separate them from the no-load loss Iron loss and mechanical loss (including wind abrasion). During the no-load test, observe the motor's running condition, monitor whether there is any abnormal sound, whether the iron core is overheated, whether the temperature rise of the bearing and whether it is running normally, for the wound rotor motor, check the brush for sparks and overheating. For the repaired asynchronous motor, during the no-load test, usually only the no-load current is measured to check the quality of the repaired motor. Do no-load loss test only when necessary. 3. General inspection before DC motor test: a) Perform a general inspection of the assembly quality of the motor (such as whether the fasteners are tightened and the rotor is flexible); the brush holder should be firmly and accurately fixed on the brush holder, and the lower edge of the brush holder should be parallel to the surface of the commutator. The distance between the brush holders should be equal; the brush should be able to move up and down in the brush holder freely, but not too loose; the surface of the brush should be in good agreement with the commutator; the spring pressure at the top of the brush should be adjusted appropriately ; The surface of the commutator should be clean and smooth, and the mica pieces between the commutating segments should not be higher than the surface of the commutator, and the recessed depth is 1-1.5 mm; check whether the motor outlet is correct; b) Check the air gap under each magnetic pole on the circumference of the armature with a plug gauge, and measure it at both ends of the motor axis each time. The maximum allowable deviation of the air gap should not exceed ±10% of its arithmetic mean. The following tests are usually carried out on the repaired DC motor: a) Check the polarity of the motor winding and the correctness of its connection; check the correctness of the main magnetic pole and the commutating pole winding connection; check the correctness of the connection between the series-excited pair of shunt windings (or between the shunt windings) ; When measuring and measuring the insulation resistance of the winding to the casing and between the windings, in addition to measuring the insulation resistance of each winding to the casing and between each other, it also measures the wire hoop of the armature winding and the commutator The insulation resistance between the tightening ring of the device and the commutator and between the brush holder and the casing (the brush should be lifted at this time). The insulation resistance value should not be lower than the value calculated by the following formula, namely R=UN/(1000+PN/100), where R—insulation resistance (MΩ); UN—motor rated voltage (V); PN—motor rated power (KW); b) Measure the DC resistance of the winding, using a double-arm bridge. The measurement should be carried out three times, taking the arithmetic average value, and measuring the ambient temperature with a thermometer; when the windings of the motor are correctly wired, in order to ensure good performance of the motor, the brush of the motor must be placed at the position of the geometric neutral line; When changing windings, overhauling the commutator, etc., or in doubt about the winding insulation, conduct a withstand voltage test on the casing of each winding and commutator, and conduct a withstand voltage test between each winding; c) If the above tests are qualified, the motor can be energized for no-load test; d) The DC motor after general maintenance may not be subjected to load test. |
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