How do I measure a motor with a multimeter?
The good or bad of the motor with a multimeter can only do a preliminary judgement, that is, using a multimeter to detect the motor coil resistance. However, whether the motor has abnormal ground insulation and phase-to-phase insulation or need to use the corresponding voltage level insulation shaking table to judge.
First of all, single-phase motor: using the 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 largest of the three resistance value of the 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 shorting piece first, and use the multimeter to measure the resistance of the three coils with the resistance gear, the resistance value is generally not very large, and the difference is not very large, and the interphase and ground with the multimeter detection 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.
Judgement of good and bad motor
Smell the smell at the scene, if you smell the burnt smell is likely to motor burned out. 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 between the phases inside the motor. Measuring the insulation between the three phases of a three-phase motor is also infinite, the cable between the point of measurement and the motor may be broken or the three-phase terminals of the motor may be detached, or the internal winding of the motor may be burnt off and the neutral piece of the motor may be 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 motor neutral piece to measure the motor phase and the motor at the other end of the corresponding neutral point, if the result is zero, the motor may be burned out caused by internal disconnection.
Many failures are unpredictable, maintenance personnel can only make a preliminary judgement, specific problems have to be specifically analysed, it is inevitable that some of the words.
I personally think it is difficult to use a multimeter to measure the insulation of the motor 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 5,000,000 Ohm (Ω,) look at the measurement of the motor without the table insulation is really far 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 table, 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 normal operation, 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.
