The process of testing 3-Phase motor starts with volt-ohommeter and some other supportive tools for normal testing whereas in advance testing some specialized tools are required. However, at the same time, in the testing process, there is needed to take some precautionary measures to avoid any uncertain situation. Some simple precautionary measures before start testing are; wear safety glasses and secondly make sure to shut all the connection to the motor (Rani, 2011).
At the following stage, the Votl Ohmmeter is switch to ohms and then each power connection is connected with the lead from motor. Subsequently, each reading gives OL or infinite ohms value on the ohmmeter. In case if the test does not show OL reading then it is the sign that the motor is not working effectively and its required to be replaced. Following are some other tests that are usually used to test a motor.
According to the writer it is said that in case if fault is found in multimeter testing but still it is recommended to make sure the condition with another test. For this aspect, a 3-Phase motor’s insulation could be effectively checked with use of megger. However, in this testing there is need to take care about the required volts and reading such as 1000v with minimum 2M Ohms or more is required for the testing of 480v motor. Moreover, there are two most common models are used in testing such as (Rani, 2011);
• Phase to Phase
• Phase to Ground
Threading Blance Check
At the following stage, with the help of evaluating the three phase currents, the threat balance check is conducted. However, in this process, there is needed to be very careful in maintaining voltage balance. Moreover, to make sure that the motor has same winding, the rough resistance test is also used.
Another goods way to test motor is to run it without any load but it requires little effort for splitting the coupling. This test is effective to check whether a motor is working in a good condition or required repairing because a bad motor does not work run well when it is offload.
Polarization Index Test
Polarization Index test is also known as IP test which takes 10 minutes to perform a test. In this process the voltage are kept lower than the IEEE43 prescribed voltage level. In this test, there is need to give around one minute to megohm reading and then it is repeated ten times. This practice of repeating meghom reading is helpful in finding the ground insulation flexibility. Following this, the ground insulation practices further found helpful while placing them in electric field. In case if the insulation is brittle or hard then there will be no polarization.
In the polarization index the ten minute insulation electrical resistance is compares while fractioning it to one minute reading. In this case, the PI value could be 2 or more than two when it is increased with same factor. However, if there is brittle insulation then the value possibly be less than 2 and on the base of this value it is decided that whether any polarization exist or not. Moreover, this test is somehow considering not much effective because it is only helpful for ground insulation whereas in turn to turn insulation it does not show any fault (Rani, 2011).
Surge test is another type of testing used for 3-Phase motor. Surge test is usually used to test the ending insulation condition. Interestingly, this test was introduced more than 80 years before and it is still used to test 480v motor’s performance. Interestingly, the surge test still have great importance because the faults such as coil-to-coil, phase to phase or turn to turn that cannot be detected from other techniques, can be easily detected by surge test. However, this test is greatly based on assumption such as the in stator it is not possible to distinguish all the three phase windings without the winding error. In this type of test usually it is required to look for shift through the waveform of testing towards left because it is helpful in the indication that the turn-to-turn insulation has produced to a grade below. Subsequently, at the same time the decision is made about the effectiveness of the motor (Rani, 2011).
However, motor testing is not considered as an important aspect but it has great importance to maintain the effectiveness and to improve the life of a motor. Considering this, motor testing should be done on regular basis to avoid any uncertain situation. Moreover, timely, diagnose of a fault and its fixing enables to avoid any big trouble that will require more time and more money.