What is Megger? How to Test a Motor using Megger?

 What is Megger?

A Megger is a portable electronic instrument used to measure the insulation resistance of electrical equipment such as cables, transformers, motors, and generators. It is also commonly referred to as an insulation tester.

The Megger applies a high voltage DC (direct current) voltage to the insulation being tested and measures the current flowing through the insulation. The instrument then calculates the insulation resistance by dividing the applied voltage by the measured current.

Megger tests are used to ensure that the insulation of electrical equipment is functioning properly and to identify potential problems such as deteriorated insulation, moisture, or other contaminants that can affect the performance and safety of electrical equipment.

In addition to measuring insulation resistance, some modern Meggers can also perform other tests, such as polarization index (PI) testing, which involves measuring the ratio of insulation resistance at 10 minutes to that at 1 minute, and dielectric absorption (DA) testing, which measures the rate at which the insulation absorbs charge after being discharged.

Overall, Megger testing is an essential part of electrical equipment maintenance and safety programs and is commonly used in a variety of industries, including power generation, industrial manufacturing, and telecommunications.

The purpose of measurement of insulation resistance

The purpose of measuring insulation resistance is to ensure the safety and reliability of electrical equipment. Insulation resistance is the ability of the insulation material to resist the flow of electrical current through it. If the insulation resistance is too low, electrical current can leak through the insulation, leading to various problems such as equipment failure, fire, electric shock, and injury to personnel.

By measuring the insulation resistance, it is possible to determine the condition of the insulation and identify any potential problems that may arise. Insulation resistance measurements can also be used to verify that newly installed equipment meets the required specifications and standards.

In addition, insulation resistance measurements are used to:

1. Identify damaged or deteriorated insulation that may need to be repaired or replaced.
2. Check for moisture, dirt, or other contaminants that may be affecting the performance of the insulation.
3. Verify that the insulation is suitable for the voltage and operating conditions of the equipment.
4. Ensure that electrical equipment is safe to use and complies with relevant safety standards and regulations.

Overall, measuring insulation resistance is an important part of electrical equipment maintenance and safety programs and is necessary to ensure that equipment operates safely and reliably.

Steps in testing a Motor using Megger?

Testing a motor using a Megger involves the following steps:

1. Disconnect the motor from the power supply and make sure it is de-energized.
2. Remove any covers or access panels from the motor to expose the insulation.
3. Clean the insulation surface to remove any dirt, dust, or moisture that may affect the accuracy of the test.
4. Connect the Megger to the motor, following the manufacturer's instructions. Typically, one lead is connected to the motor's ground, and the other lead is connected to the motor winding being tested.
5. Set the Megger to the appropriate voltage range, based on the motor's rating and the insulation type.
6. Apply the test voltage and allow it to stabilize.
7. Record the insulation resistance value displayed on the Megger. Repeat the test for each winding and compare the results to the manufacturer's recommended values or previous test results.
8. Interpret the results of the test. If the insulation resistance is lower than expected, this may indicate a problem with the insulation, such as contamination, moisture, or damage. Further tests or inspections may be necessary to determine the cause of the problem and the appropriate course of action.
9. Disconnect the Megger from the motor and reconnect the motor to the power supply.

It is important to follow safety procedures when testing a motor with a Megger, such as wearing appropriate personal protective equipment and ensuring that the motor is de-energized and properly grounded. Additionally, it is recommended to refer to the manufacturer's instructions for specific guidance on using the Megger for testing motors.