Please see how to identify three phase windings for proper winding identification. If any particular phase fails the continuity test, your motor is probably burnt. Using a multimeter, check the continuity of motor winding from phase to phase ( U to V, V to W, W to U ).Each phase to phase must have a continuity if winding is OK. For three phase motors, connection type is either Star (Y) or Delta Check the connection bar for terminal (U, V, and W). Ensure the terminal for power supply is in good condition. Check that the correct voltage is applied to the motor using a multimeter.

Further troubleshooting maybe requiredįor three phase motors, the expected voltage for a 230/400V system is 230V phase to neutral and 400V between each of the three phase supply lines. Any value greater 0.5 ohms indicate trouble with the motor. A good motor should read less than 0.5 ohms. With a multimeter, measure the resistance between motor frame (body) and earth. Examine the name plate thoroughly and compare values of running amps test (see below) with name plate value (3) As with all testing and inspections, the motor name plate provides valuable information that will help to ascertain the true health of the motor.

If shaft rotation is free and smooth, bearing is possibly in good condition, otherwise consider replacing, repair or carry out further diagnosis. Look out for smooth and free shaft rotation. (2) Manually rotate motor shaft to examine bearing condition.

Check for burnt, damage to body or cooling fan or shaft. Therefore, it is recommended that for all three-phase transformers, regardless of their capacity, only the unbalance rate limit of the DC line resistance can be specified as 2%.The basic steps in ascertaining the health of a three-phase AC motor are given below:įor the three-phase motor, do the following: 6MVA or above, the phase resistance unbalance rate should not exceed 2%, the winding without neutral point, the line resistance unbalance rate should not exceed 1% the capacity of 1.6MVA and below Transformer, the phase resistance unbalance rate is generally not more than 4%, and the line resistance unbalance rate is generally not more than 2%.įrom the engineering practical point of view, it can be considered that the line resistance imbalance is half of the phase resistance unbalance rate. Unbalance: It means that the three-phase current (or voltage) amplitude is inconsistent in the power system, and the amplitude difference exceeds the specified range.Īccording to the power transformer with the specified capacity of 1. How to calculate the transformer DC resistance imbalance of the transformer?Dividing the maximum number of three-phase subtracted by the three-phase average is the unbalance rate.ĭC resistance unbalance rate = (OB-OC) / ((OA + OA + OC) / 3) = (5.772-5.758) / ((5.761 + 5.772 + 5.758) / 3) = 0.014 / 5.7636667 = 0.002429 * 100% =0.2429

Motor winding resistance imbalance