Megger Test

July 02, 2024 Post a Comment

Megger test

Detailed Solution. Megger: Megger is a portable instrument to measure high insulation resistances. It works on the principle of electromagnetic induction.

What is a good megger test result?

For a successful test, the insulation resistance measurement must be equal to or greater than 1 Gigaohm (1 Gigaohm = 1 G ohms = 1000 Mega ohms = 1000 M ohms). We recommend that you always check the megohmmeter instruction manual as each manufacturer can use different symbols or values for their testers.

Is megger test DC or AC?

The megger has a DC generator inside it. The DC generator may be of manual type of or electronic. It generates a high DC voltage. The positive lead of the megger has its connection with the current carrying part.

How do you test a cable with a megger?

Clamp the alligator clip on one of the megger probes to the wire or cable, touch the other probe to the exposed conductor and press the test button. The megger will generate a current between the probes, and the meter will record the resistance of the jacket to the flow of the current.

What is unit of megger?

A Megger consists of an EMF source and voltmeter. The scale of the voltmeter is calibrated in ohms (kilo-ohms or megohms, as the case may be). In measurements, the EMF of the self-contained source must be equal to that of the source used in calibration.

What is IR value?

An insulation resistance (IR) test measures the total resistance between any two points separated by electrical insulation. The test, therefore, determines how effective the dielectric (insulation) is in resisting the flow of electrical current.

What is a normal megger reading?

The rule may be stated: Insulation resistance should be approximately one megohm for each 1000 volts of operating voltage, with a minimum value of one megohm. For example, a motor rated at 2400 volts should have a minimum insulation resistance of 2.4 megohms.

What is megger value?

It gives an idea of an insulator's condition. It is measured using an instrument named Megger test capable of impressing D.C. voltage between its two probes, automatically calculating and then displaying the IR value. Megger test being so popular that “Insulation Resistance” and “Megger Test” are synonymously used.

What is the minimum megger value?

Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm.

How does megger work?

Megger works on the principle of electromagnetic attraction. When a primary coil that is carrying current is placed under the vicinity of a magnetic field it experiences a force. This kind of force generates a torque that is made to deflect the pointer of the device which gives some reading.

Why megger is DC not AC?

The accurate insulation resistance can be done if the DC voltage is applied to measure the megger value. That is why a megger has DC generator.

How is megger voltage calculated?

Test Voltage for Meggering: When AC Voltage is used, The Rule of Thumb is Test Voltage (A.C) = (2X Name Plate Voltage) +1000. When DC Voltage is used (Most used in All Megger), Test Voltage (D.C) = (2X Name Plate Voltage).

How do you megger a circuit?

If you are testing insulation resistance to ground, place the positive probe on the ground wire or the grounded metal junction box and the negative probe on the conductor or terminal. Energize the Megger for 1 minute. Read the value of the resistance at the end of the minute test and note it in your table.

How megger produce high voltage?

In hand operated megger electromagnetic induction effect is used to produce the test voltage i.e. armature arranges to move in permanent magnetic field or vice versa. Where as in electronic type megger battery are used to produce the testing voltage.

How do you calculate insulation resistance?

How is insulation resistance calculated and tested? We should all be familiar with Ohm's law. If we apply a voltage across a resistor and then measured the consequential current flow, we can then use the formula R=U/I, (where U=Voltage, I=Current and R=Resistance) to calculate the resistance of the insulation.

How many types of megger are there?

There are two types of meggers, manual and electrical megger. The main concept of megger is to measure insulation resistance and machine windings.

Why do we megger a motor?

This is an insulation test of motor windings, commonly referred to as megging, to megger, or to meg a motor. We are testing the motor's insulation, more specifically between the motor windings and the motor casing. If a fraction of current flows, it can be measured by these highly sensitive meters.

Why IR test is required?

Insulation resistance (IR) is a measurement of how good or bad your insulation is, which can help give you an overall assessment of your electrical equipment's health. By the way, no insulation is perfect—with infinite resistance—but good insulation has a relatively high resistance to current.

What is IR on megger test?

Insulation Resistance or IR Test is carried out by maintenance engineers to ensure the healthiness of the overall insulation system of electrical equipment. It reflects the presence or absence of harmful contamination, dirt, moisture, and gross degradation.

What is the maximum insulation resistance?

For many years, maintenance professionals have used the one-megohm rule to define the allowable lower limit for insulation resistance. The rule states that insulation resistance should be approximately one megohm for each 1000 volts of operating voltage, with a one megohm minimum.