Electric Motor Checker is a very useful test equipment that can be used for detecting an electrical-fault (for example – short-circuit, open-circuit, damage of insulating material …… and many more) in case of motors/other 03 phase equipments in the fastest and easiest way. This Electric Motor Checker can, however, only be used for a motor which is stationary.
We should never use it on running motor. To ensure this, the supply input for the motor has to be cut-off prior starting the tests. It is not mandatory to remove the input cable. You can do it by just switching-off the input supply breaker also. You can take the reading at any convenient spot on the i/p supply of the motor.
Basic-test procedures :
This test may be carried out even if the phase winding is intact (not removed). But, before carrying out the tests, we should have knowledge of at least its basic fundamentals. Here we will talk about 3 phase equipments only. We can identify an electrical defect in it by carrying out :
- Insulation measurement with respect to ground.
- Measurement and comparison of the resistance between the three phases of the stator-winding.
- Measurement and comparison of the inductance between the three phases of the stator-winding.
Note : The Resistance/inductance value being measured/compared should be same or at least the variation between them must be inside the permissible tolerance-limit. s of each phase are measured and compared with each other. They should be equal or any between the values should be within acceptable tolerance limits.
It is therefore the purpose of the Electric Motor Checker is :
(i) Measuring insulation resistance.
(ii) Measuring and comparing the resistance of stator winding of an electric motor.
(iii) Measuring and comparing the inductance of stator winding and the effect of rotor position on electric motor.
Operation of Electric Motor Checker :
(A) MEASURING BATTERY CONDITION
(i) Select the function switch to battery
(ii) Now press to check button
(iii) The needle should deflect more than 70% to indicate good battery
(B) MEASURING INSULATION
(i) Now connect the test leads to the terminal marked insulation 500v
(ii) Connect one test lead to suitable point on the machine frame and other lead to one of the supply terminal. Press, “press to check button”. The insulation value in mohm is indicated in the blue scale.
(C) MEASURING RESITANCE/INDUCTANCE
(i) Check the battery first.
(ii) Set the function switch to resistance for taking motor winding resistance and put function switch to inductance for taking inductance of each winding.
(iii) Connect the test lead terminal marked resistance/ inductance.
(iv) On connected motor (star/ delta), connect the test clip to two of the supply terminals (RY, BY) and press the operating button.
(v) Observe the reading in % scale. Convert them to actual reading with the given measuring chart.
(vi) Now compare the reading for all three winding and look for any imbalance.
(i) Motor has to be isolated from its source of supply before conducting test
(ii) Insulation value obtained less than 1Mohm is dangerous for the motor to operate.