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How to Use Insulation Resistance Tester (Megger)

by | Dec 21, 2020 | Industrial Equipements, Industrial supplier & distributor

An insulation resistance tester determines the total resistance between any two points separated by electrical insulation. Therefore, the test defines the efficacy of the dielectric insulation in resisting electrical current flow. These tests are useful not only when a product is first made but also when used to verify insulation consistency.

It can predict imminent insulation failures before they occur and avoid user injuries or expensive product repairs by conducting such tests regularly.

What is done during Megger Testing? 

We will test your circuits for the current connections and melted fault areas that may have happened during a fire incident. These results are then analyzed, and it is possible to isolate and repair individual circuits to ensure that the damaged circuits do not have any more issues. Talk to your Adjuster if you have had a fire and see if a megger insulation tester is needed. It is typically protected by insurance because one month after you can recover your house, the last thing they want to do is pay another claim.

How Do You Perform An Insulation Resistance Test?

Generally, you connect two leads through an insulation barrier (positive and negative). Your tester may or may not be available for a third lead that connects to a guard terminal. Whether it is, it may or may not have to be used by you. To remove the connecting part from the calculation, this guard terminal acts as a shunt. In other words, it enables you to be selective in assessing individual-specific pieces in a broad piece of electrical equipment.

Procedure for Measurement

There are typically four phases of an insulation resistance test: charge, dwell, measure, and discharge. The voltage is ramped from zero to the chosen voltage during the charge point, which provides stabilization time and restricts the inrush current to the DUT. If the voltage reaches the value chosen, the voltage may then be permitted to reside or hold at this voltage before measurements begin.

Dielectric Absorption

Dielectric absorption is a physical phenomenon in which, over time, the insulation absorbs and maintains an electrical charge slowly. This is illustrated by applying a voltage for a prolonged time to a capacitor and then discharging it rapidly to zero voltage. The meter reads a small voltage if the capacitor is left open-circuited for an extended time and attached to a voltmeter. This residual voltage is due to dielectric absorption. Electrolytic capacitors are generally associated with this phenomenon.

This effect causes the insulation resistance tester value to grow over time as you weigh different plastic materials. The inflated IR value is generated slowly over time by the material absorbing charge. This absorbed charge is leakage-like.

Charging Current

Because the essential characteristics of any insulated product are present, the voltage through the insulation allows a current to flow as the capacitor charges two conductors separated by a dielectric. Depending on the device’s capacitance, this current immediately increases to a high value when the voltage is applied. It then gradually decays exponentially to zero when the device becomes fully charged. Much faster than the dielectric absorption current, the charging current decays to zero.

Leakage Current

The leakage current is called the steady-state current that passes through the insulation. It is equal to the applied voltage divided by the resistance of the insulation. The object of the test is to measure insulation resistance. Apply the voltage, evaluate the steady-state leakage current after the dielectric absorption and charging currents have decayed to zero to determine the IR value, and then split the voltage by the current.

The test is successful if the insulation resistance reaches or exceeds the value expected. If not, you have failed the exam.