Electrical

# What is a megger and how is it used

#### What is a megger and what does it do

A megger is an electrical measuring instrument, it can be used to measure the insulation resistance. A megger has a DC generator and an ohmmeter in it. A normal ohm meter cannot be used to measure high resistance values, so in that case, we can use a megger or megohmmeter. With the help of a megger, we can measure the electrical leakage of a wire and it is done by passing an electric current through the wire for a certain period of time. It can be used to check the electrical insulation of devices such as electric cables or a motor. The megger must be calibrated before any testing, for conducting test a megger with a range of 500V/1000V must be used. In order to do a wire testing, a megger that has 500V range is used, and to do a cable testing, a 1000V range megger is used. So by testing an electrical device by using a megger we can make sure of electrical safety.

#### What are the factors that must be considered while meggering

• The equipment which is under test must be disconnected and isolated
• Meggering shall only be done to conductors and insulators that are clean and dry
• Before meggering we must make sure that all the connections in the test circuit are complete

#### Can a megger shock you

A megger must be handled by a person who knows how to operate it and how to0 do the measurement otherwise, it can hurt the person or damage the equipment. Certain factors to be considered while using a megger they are

• A megger must be used for high resistance measurements, like insulation resistance.
• We must not touch the test lead if the handle is cranked.
• Before connecting a megger, we must de-energize and discharge the circuit completely.
• Before connecting a component to a megger for checking it must be disconnected from other circuitry.

#### How to construct a megger and what are its parts? How does a megger work

Deflection and control coil

These coils are connected parallel to a generator and they are placed right angle to each other and they create torque in the opposite direction.

Permanent magnets

It would create a magnetic field, to deflect the pointer with north-south pole magnet.

Pointer

One end of the pointer is connected to the coil and the other end deflects on a scale from infinity to zero.

Scale

We can see a scale in the megger which is used to measure the value.

DC generator/Battery

The voltage that is required for testing is provided by a DC generator for a manually operated megger. For an electronic megger, an electronic voltage charger or battery is used for this.

Pressure and current coil resistance

This will protect the device from any damage due to the low external electrical resistance under test

A generating voltage is required to start a megger in a hand-operated megger it can be done manually, while in the electronic type it has a battery. One terminal of the megger is connected to the insulation part and another terminal is connected to the body of the equipment that is being tested.

Electrical continuity test

The megger leads are connected to the conductor that is to be measured and it would apply a high DC voltage to it. So while doing the electrical continuity test or any test the leads must be connected and the megger must be switched ON for test so while switching ON the megger the reading must be zero otherwise it is an open circuit.

Working principle of a megger

A megger works on the principle of electromagnetic attraction, so when a conductor that carries current is placed in an electric field then it would experience a force. This force creates torque and it is used to do the measurement.

#### What are the types of megger

1. Electronic type
2. Manual type

There are two types of megger electronic megger or automatic megger and a hand-operated megger. A hand-operated megger doesn’t use any battery or it can also be said that it won’t use an external source. In this type, a hand crank is provided and it is rotated to generate a voltage. This type of megger has an analog display.

The automatic megger has a battery to generate voltage and it is very compact, it has a digital display and selection switches and we can select different parameter range by this and it has many indicators.

#### How can we do the inspection of a megger

• Check if the megger has a loose connection
• The meter and pointer can be checked for damage
• Carrying case must be checked for corrosion
• Battery level must be checked for digital megger
• Check all the indicators of the megger

#### What are the advantages of a megger

• Electrical safety
• It can detect leakage in a wire
• It can check the insulation level of any electrical device
• Hand operated megger is very cheaper
• A hand-operated megger doesn’t need any external source to operate
• A megger can measure high resistance
• Accuracy is very high for electronic type megger and is also safe
• Electronic type megger can be used in congested space
• Easy to operate and carry
• Cheaper

#### What are the applications of a megger

• Primary current injection testing of protective systems
• Testing of circuit breaker
• Motor and alternator testing
• Testing of generator and transformer
• Heat runs
• Safety ground device can be tested
• Ground grids can be tested
• Protective relays can be tested
• It can measure the electrical resistance of insulators
• Installations for winding
• Earth ground connection can be tested