What is the working principle of megohmmeter?

In the case of manual mode, the battery is used in the electronic tester by shaking the instrument by hand and turning the crank to generate the test voltage; 500 volts DC is enough for testing in the range of equipment not exceeding 440 volts. 1000 V to 5000 V is used to test the high voltage electrical system. The deflection coil or current coil is connected in series to make the current absorbed by the circuit under test flow. The control coil (also called pressure coil) is connected at both ends of the circuit, and the current limiting resistors (CCR and PCR) are connected in series with the control and deflection coil to prevent the external circuit from being damaged when the resistance is very low.

In a manually operated megger, the electromagnetic induction effect is used to generate a test voltage, that is, the armature moves in a permanent magnetic field, and vice versa, just like in an electronic megger battery. With the increase of voltage in the external circuit, the deflection of the indicator increases, and with the increase of current, the deflection of the indicator decreases. Therefore, the resultant torque is proportional to the voltage and inversely proportional to the current.

When the circuit under test is disconnected, the torque generated by the voltage coil will reach the maximum value. And the pointer shows "infinity" (infinity) indicating that there is no short circuit in the whole circuit. And the resistance in the circuit under test is the largest. If there is a short circuit, the pointer shows "zero", indicating that the resistance in the circuit under test is "none".

Based on the working principle of ohmmeter or ratio meter. Due to the magnetic field generated by voltage and current, the megger tester will produce deflection torque, which is similar to ohm's law.

The torque of megohmmeter changes with the change of V/I (ohm's law: V = IR or R = V/I). The resistance to be measured is connected at both ends of the generator and connected in series with the deflection coil.

If current is supplied to the coil, the generated torque should be in the opposite direction.

1. High resistance = no current:-If the resistance is very high (that is, the infinite position of the pointer), no current is allowed to flow through the deflection coil.

2. Small resistance = large current:-If the circuit measures small resistance, large current is allowed to pass through the deflection coil, that is, the generated torque makes the pointer point to "zero".

3. Intermediate resistance = variable current:-If the measured resistance is intermediate, the generated torque will be calibrated or the pointer will be set in the range of "zero to initial".

Defendant: Huatian Electric Power