Megohmmeter test, which is very useful for testing internal cable resistance. This is one of the well-known methods for testing resistance. This test is designed to detect the condition of the internal winding of the instrument. By knowing the resistance value, we can choose appropriate safety precautions for the equipment to avoid damage.
What is a megohmmeter test?
Megohmmeter is also called insulation resistance megohmmeter, which is a device used to test the insulation resistance of cables. The test performed in this way to understand the insulation resistance value is called a megohmmeter test.
What is the purpose of insulation resistance?
The motor winding wound inside the motor must provide a certain insulation resistance. This insulation is provided to withstand large currents in the event of a short circuit. If the conductor has high insulation, its resistance to current will be higher. Similarly, if the insulation resistance provided is weak, the chance of large current flow damaging the equipment is greater. Therefore, in order to make any equipment work properly, it should have a high insulation resistance. Therefore, for this reason, a megohmmeter insulation resistance test was conducted.
The working principle of megohmmeter
It follows the principle of electromagnetic attraction. When the current-carrying primary coil is placed under the influence of a magnetic field, it will be subject to force. This force produces a torque which is used to deflect the pointer of the device to obtain a certain reading.
Insulation resistance test procedure
The process of testing the IR value of the motor winding involves the following steps. The winding of the motor is divided into red (R), blue (B) and yellow (Y), and the body (in the absence of neutral) or neutral (N). The figure below gives an idea of the appearance of a megohmmeter probe.
Plug the measuring cable with the probe into the port of the megohmmeter. It has two ports, one is a line and the other is a ground. In addition to these two, there is a button for insulation testing.
Connect one end of the probe of the megohmmeter to the line I, e (R), and the other end to ground. After connection, press the insulation test button. Then, if there is no problem, the megohmmeter should indicate an infinite IR value. If it represents zero, then we can conclude that IR cannot withstand large currents.
Repeat the process of connecting the probe to other lines I, e (B), and then connecting (Y). Check the IR value so that we know whether the IR of the winding is good.
What if the IR value is infinite or zero
When the probe of a megohmmeter is connected to two different windings, if the indicated IR value is infinite, the insulation resistance of the winding is sufficient to withstand large currents.
But in the case where the indicated IR value is zero, we can understand that the winding is short-circuited. In the case of a short circuit, due to the low resistance, the winding will not be able to withstand large currents and cannot compete with large currents.