How to measure a motor with a multimeter
The good or bad of the motor with a multimeter can only do a preliminary judgment, that is, using a multimeter to detect the motor coil resistance. But whether the motor has abnormal ground insulation and phase-to-phase insulation still need to use the corresponding voltage level insulation shaking table to judge.
First of all, single-phase motor: using a multimeter to check the need to disengage the capacitor to check, that is to say, disengage the capacitor to check the single-phase motor's main winding and the secondary winding resistance, generally the resistance of the main winding is relatively small, the secondary winding resistance is relatively large, generally for the three terminals, you can measure the resistance value, under normal circumstances, you can get the three resistance value of the largest resistance value of the other two and the sum of the resistance value. Capacitors need to be checked separately (capacitors need to be discharged first), the multimeter will hit the capacitance file can be measured directly.
Three-phase motor: If it is a small three-phase motor with star connection, you can remove the short connecting piece first, and use the multimeter to measure the resistance of the three coils respectively, the resistance value is generally not very large, and the difference will not be very large, and between the phases and to the ground with the multimeter should be disconnected. If the resistance value is unstable when checking with the multimeter, it is better to use the corresponding insulation shaking table to confirm.
High-voltage motor: the inspection of high-voltage motor requires professional tools to check, using a multimeter to judge the easy accident.
Motor good or bad preliminary judgment measurement is an essential step, sometimes there is a failure can not immediately go to dismantle the motor, so the preliminary judgment is also easy to quickly find the crux.
Motor good or bad judgment
Smell the odor at the scene, if you smell the smell of burning is likely to be burned out of the motor. Three-phase motor three-phase ground insulation measurements have access phenomenon, may be in the detection point to the motor between the cable short circuit. It is also possible that a phase terminal of the motor terminal box is in contact with the shell. It is also possible that the internal insulation of the motor is in contact with the shell.
The cable of the motor may have a short circuit may also have a short circuit between the three-phase terminals as well as a series of short-circuit faults within the motor between the phases. Measurement of the motor three-phase motor insulation between the three phases is also infinite, may be measured to the point to the motor between the cable broken or motor three-phase terminals at the shedding, or the motor internal winding was burned off as well as the motor's neutral piece broken.
Measure the resistance between the three phases of the three-phase motor, such as ab, ac, bc, if the measured resistance between them is large, there is a three-phase imbalance in the motor, it is likely that the motor is burned out internally.
Measurement of the motor neutral piece and motor shell resistance, zero, then there is likely to be at least one phase of the insulation layer burned caused by contact with the motor shell to form a grounded short circuit. Remove the neutral piece of the motor to measure the motor phase and the other end of the motor corresponding to the neutral point, if the result is zero, the motor may be internally burned resulting in disconnection.
Many failures are unpredictable, maintenance personnel can only make a preliminary judgment, specific problems have to be specifically analyzed, it is inevitable that some of the words.
With a multimeter to measure motor insulation I personally think it is difficult to achieve the desired results. Because the ohm range of the multimeter is too small, the maximum range is only 10KΩ, and three-phase or single-phase motor phase insulation, insulation to the ground is not less than the absolute minimum of 0.5 megohm (MΩ) 10kΩ that is, 1OOOOO Ohm Ω while the 0.50 megohm (Ω) is 5 thousand million Ohm (Ω,) look at the measurement of the motor without the table insulation is really out of reach.
Measurement of 380 volts or single-phase motor insulation is the best choice of 500 volts (v) shaking table, in order to measure the three-phase (A, B, C) phase-to-phase insulation and the edge of the ground.
In the absence of a rocking meter, you can also use a multimeter to roughly measure, ohm 1 OK block are up to infinity can not be considered motor insulation is qualified. At this time you can turn on the power to try the machine, close the gate to close fast pull to fierce, close the gate to watch the size of the electric lone flower, listen to the sound of running is normal, there is no vibration, if they are normal with a test pen to measure the shell whether the leakage, everything is normal before being put into operation.
