Megger | Working Principle Types History Uses of Megger 2023:

The device has been in use since 1889, increasing in popularity during the 1920s as the long back device is similar in its use and testing purpose, with some real improvements in design and quality of testers in recent years. . There are now high-quality options available that are easy to use and quite safe.


Insulation resistance IR quality of electrical systems degrades with time, environmental conditions, i.e. temperature, humidity, moisture and dust particles. It is also adversely affected by the presence of electrical and mechanical stress, so it has become very important to maintain the IR (insulation resistance) of the equipment to avoid any fatal or electric shock. Check periodically.

Uses of Megger:

This instrument enables us to measure the electrical leakage in the wire, the results are very reliable because we will be passing an electric current through the instrument while we are testing. This equipment is mainly used to verify the electrical insulation level of any device like motors, cables, generators, windings etc. This is a very popular test that has been done for a long time. It does not necessarily show us the exact area of electrical puncture but the leakage current and moisture level within the electrical equipment/winding/system.

Working Principle of Megger:

  • In the case of the hand-operated type, a battery is used for the electronic tester, the voltage produced by the hand-operated megger by rotation of the crank.
  • 500 volts DC is sufficient to test a range of equipment up to 440 volts.
  • 1000 V to 5000 V is used for testing high voltage electrical systems.
  • A deflecting coil or current coil is connected in series and allows the current taken by the circuit under test to flow.
  • A control coil also known as a pressure coil is connected throughout the circuit.
  • A current limiting resistor (CCR and PCR) is connected in series with the control and deflecting coil to prevent damage in case of very low resistance in the external circuit.
  • A hand-operated mager uses the electromagnetic induction effect to produce a test voltage i.e. the armature is arranged to move in a permanent magnetic field or vice versa.
  • Where an electronic type megger battery is used to generate the testing voltage.
  • As the voltage in the external circuit increases the deflection of the pointer increases and as the current increases the deflection of the pointer decreases.
  • Therefore, the resulting torque is directly proportional to the voltage and inversely proportional to the current.
  • When the electrical circuit under test is open, the torque due to the voltage coil will be maximum and the pointer will show ‘infinity’ meaning no short in the entire circuit and more within the circuit under test. has more resistance than
  • If there is a short circuit, the pointer shows ‘zero’, which means ‘NO’ resistance is being tested within the circuit.
  • Working philosophy based on ohm meter or ratio meter.
  • A deflection torque is developed with the Megger tester due to the magnetic field produced by the voltage and current, similar to ‘Ohm’s Law’.

Connection Diagram of Megger for Testing:

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