How to use a megohmmeter to measure the quality of a motor

1. Use of megohmmeter (insulation resistance meter)

(1) Calibration. Before measuring, the megohmmeter should be subjected to an open circuit and short circuit test to check whether it is in good condition. Open the two connecting wires, shake the handle, and the pointer should point to "∞". Short-circuit the two connecting wires again, and the pointer should point to "0". If the above conditions are met, it is good, otherwise it cannot be used.

(2) The device under test is disconnected from the circuit, and large-capacitance devices must also be discharged.

(3) Select a megohmmeter that meets the voltage level.

(4) When measuring insulation resistance, generally only the "L" and "E" terminals are used. However, when measuring the insulation resistance of the cable to the ground or the leakage current of the device under test is serious, the "G" terminal should be used and connected to the shielding layer or the shell. After the line is connected, the crank can be turned clockwise. The speed of shaking should be from slow to fast. When the speed reaches about 120 revolutions per minute (ZC-25 model), keep the rotation at a constant speed and read the reading after 1 minute. The reading should be read while shaking, and it cannot be stopped to read.

(5) Discharge by removing the wires. After the readings are completed, slowly shake the meter while removing the wires, and then discharge the device under test. The discharge method is to remove the ground wire used during measurement from the megohmmeter and short-circuit it with the device under test (not megohmmeter discharge).

2. Measurement steps of megohmmeter (insulation resistance meter)

The use of the shake meter is divided into the following steps:

(1) Power off, test and discharge the equipment under test;

(2) Select a suitable megohmmeter according to the device under test;

(3) Check the megohmmeter, which can be divided into open circuit check and short circuit check. For open circuit, the two test leads are not in contact, the handle is turned at a constant speed, and the pointer points to infinity. For short circuit check, the handle is turned at a constant speed, the two test leads are in contact, and the pointer points to zero.

(4) First, connect section E to the ground, rotate the crank at a constant speed to 120 revolutions per minute, and then connect section L to the circuit;

(5) After measurement, discharge.

3. How to use a megohmmeter to measure the quality of a motor

First, measure the motor to ground, remove the connecting piece in the motor junction box (to ensure that each winding is independent), and connect one wire of the megohmmeter to the housing. Connect another wire to the three winding heads of the motor for measurement. It is normal if the resistance is greater than 1M. Then measure the insulation between the three windings, that is, connect one wire of the megohmmeter to one of the heads of the motor winding, and another wire to the head or tail of another winding (it is normal if the resistance is greater than 1M), then loosen one of the measuring wires of the megohmmeter, and connect it to the head or tail of the third group (unmeasured) of the motor for measurement (it is normal if the resistance is greater than 1M).

Cut off the power supply. Secondly, open the wiring and remove the terminal board connector. Third, connect the megger L to the head of any winding under the terminal board and set it as phase A, and connect E to the upper terminal. Gently shake the megger to find out the three phases ABC in turn. If there is any failure, the phase is broken. Fourth, measure the interphase insulation of the three phases ABC. The megger speed is 120 revolutions per minute. If the reading is above 0.5, it can be used. If it is less than 0.5, the insulation is damaged. Fifth, connect the first or last phase of the winding to L, and connect E to the shell. If the insulation resistance is above 0.5, it is good.

First, use a multimeter to measure the DC resistance of the three-phase winding. [In fact, the resistance of the winding is very small, and our ordinary meter can basically not tell the size, unless it is a very small motor, just check whether it is connected.]

Second, if the three-phase windings are all connected, use one wire of the megger to connect to the motor casing, and use the other wire to measure whether the resistance of the three-phase windings to the ground is normal. [The minimum resistance value must not be less than 0.5 megohms]

3. If the resistance of the three-phase winding to ground is normal, the last step is to measure the phase-to-phase insulation resistance. Connect one wire of the megohmmeter to the terminal of one phase winding, and the other wire to the other two terminals. [Note: do not connect two wires at the same time, connect them separately]. After the measurement, swap the megohmmeter wires to measure the other two phases of the winding. [During the phase-to-phase measurement, only the upper or lower three terminals need to be measured, and the resistance must not be lower than 0.5 megohms].

Clamp one of the two test leads of the megger on the terminal of the junction box and the other on the outer casing, shake the handle of the megger evenly, and the reading obtained is the insulation resistance of the motor to the ground, which is generally qualified at around 200K~2M. Clamp the two test leads of the megger on the terminals of different phases of the junction box respectively, shake the handle of the megger evenly, and the reading obtained is the insulation resistance between the phases of the motor. Generally, it is qualified when it is above 100K.