How To Judge The Quality Of The Motor By Measuring The Resistance Of The Three-phase Motor And The Single-phase Motor?

No matter whether the motor is in use or in failure, the quality of the motor should be measured before it can be powered on. How to judge the quality of a motor, there are mainly two parameters, one is to measure the resistance of the motor coil, and the other is to measure the insulation resistance of the coil and the casing. The three-phase motor and the single-phase motor measure the insulation resistance in the same way, but the method for judging the resistance of the coil is different.

three-phase motor

Three-phase asynchronous motors commonly used in work are composed of three sets of coils, and most of the coil connections are Y-connection or △-connection.

Motor Junction Box

To judge whether the coils of the three-phase motor are good or bad, it is necessary to measure whether the resistance between the three-phase windings is balanced. It is not necessary to know the actual resistance value of each group of coils of the motor with corresponding power, and it is not necessary to remove the connecting piece to measure the resistance values of the three groups of coils to judge whether the resistance values of the three-phase coil windings are balanced, which is rather troublesome.

Whether it is a Y-connected motor, a △-connected motor, or a two-speed motor. It can be used to measure the resistance between the U1, V1, and W1 terminals, and it can also be used to determine whether the three-phase resistance of the motor is balanced.

A multimeter is usually used to measure the resistance of the motor coil. The gear of the multimeter is selected in the resistance 200Ω range, and the red and black test pens are used to measure the resistance between the motors (U1, V1), (V1, W1), (U1, W1) respectively.

multimeter

When the mutual error between the measured resistance values is 2%, it can be judged that the resistance value of the motor is normal. When the error between the measured resistance values reaches more than 10%, it can be judged that the motor is bad.

When the error of the measured resistance value is 2%-10%, it is necessary to consider whether the coil of the motor is produced by the original factory, or whether the coil of the motor has been burned out and rewound in the later period, and the level of the maintenance personnel to replace the coil is the problem. The resistance value of the wound coil There is an error, when the error is not large, it can be used normally. When it is not accurate, you can use the inverter to drive the motor to check whether there is an alarm phenomenon to judge the quality of the motor.

When the resistance of the motor coil is three-phase balanced, it cannot be said that the motor is good, and the insulation resistance of the motor should also be measured. Generally, when the insulation resistance of the motor is lower than 0.58MΩ, it means that the motor insulation is not good and should not be used. When the insulation resistance of the motor is higher than 0.58MΩ, it means that the motor has good insulation and can be used normally.

When measuring the motor with a multimeter, the multimeter gear is in the resistance MΩ gear. One test lead is placed on any terminal of U1, V1, and W1, and the other test lead is placed on the motor casing. Be careful to place it in a place without paint. When the measured resistance value is greater than 0.58MΩ or fails, it can be judged that the motor insulation is normal. . When the measured resistance value is less than 0.58MΩ, the insulation is not good and should not be used. The insulation resistance of the motor measured by the multimeter is not necessarily accurate. When you feel that the insulation resistance value of the motor is different each time, it will affect your judgment. A megohmmeter can be used. The data measured by the multimeter is only of reference value, while the numerical accuracy measured by the megohmmeter is relatively high and can be regarded as real data.

Megohmmeter

The E and L terminals of the megohmmeter are connected to the wire rods. The measurement method of the two wire rods is the same as that of the multimeter test pen to measure the motor. The megohmmeter has no gear adjustment. Just shake the hand rocker at 120 revolutions per minute That's it.

single phase motor

A single-phase motor usually has only two sets of coils, the main winding and the secondary winding. The secondary winding starts and the primary winding runs. Inside the motor, the main winding and the secondary winding are in series relationship, and one wire is drawn from the connection, and three wires are generally drawn out of a single-phase motor, which can be represented by three wire ends ①②③.

Single-phase motor coils and wiring

Use the 200 ohm gear of the multimeter. When the motor power is small, the ohm gear of the multimeter can be increased.

Use a multimeter to measure the three wire ends of ①②③ of a single-phase motor, you can choose two-phase measurement, ①②, ②③, ③① to measure three groups of resistance values, the measured resistance values are normally 1 large and 2 small. When the sum of the two groups of small resistance values is not equal to the maximum resistance value, it proves that the motor is damaged, or when the measured resistance is infinite, it proves that the motor winding is broken and damaged. The main winding and the secondary winding are short-circuited together, and the short-circuit phenomenon of a group of windings is rare. When the sum of the two groups of small resistance values is the maximum resistance value, it proves that the motor coil winding is normal.

The single-phase motor also needs to measure the insulation resistance. The measurement method is the same as that of the three-phase motor. Please refer to the method for measuring the insulation resistance of the three-phase motor above. The insulation resistance higher than 0.58MΩ indicates that the insulation resistance of the motor is normal, and the insulation resistance lower than 0.58MΩ indicates that the motor is insulated. Not good for use. Generally, the resistance value with the smallest resistance value is the main winding, the second largest resistance value is the auxiliary winding, and the largest resistance value is the main and auxiliary winding series resistance.

The single-phase motor wiring is to measure the largest resistance value in parallel with the capacitor, and the smallest resistance value is connected to the single-phase voltage. When measuring the resistance value of a single-phase motor is 1 large and 2 small, when the two small measured resistance values are the same, it means that the resistance value of the main and auxiliary windings is the same. The motor is reversed. When the resistance values of the main and auxiliary windings are the same, it means that the single-phase motor has the function of forward and reverse rotation and can be used for forward and reverse rotation.