Select Page

How To Use A High Voltage Insulation Resistance Tester Correctly


An insulation resistance tester,also called a megger tester is an instrument used to measure insulation resistance in electrical equipment and power systems. It evaluates the goodness of insulation by applying a DC voltage to an insulated part of the equipment under test and measuring the current flowing through the insulating material. Testers are widely used in electric power, communications, manufacturing, petrochemical and other industries. The insulation resistance tester can detect whether the insulation material is damp, damaged, or aged, thereby finding equipment faults. Accuracy helps reduce risks during operation of electrical equipment.

Measuring insulation resistance can help operators identify where hazards exist in a line, especially where line equipment could leak current and cause problems.

In this article Push,China will introduce the problems that will arise if you do not conduct proper insulation resistance test and how to use the Insulation Resistance Tester correctly.

Common problems arising from poor megger test

1: When leakage current occurs in the line, the insulation layer is destroyed by the current and generates heat, which will cause insulation loss or damage and cause a fire accident.

2: Leakage current flows back and forth in all conductors, causing sudden leakage accidents and dangerous voltages that can hurt people.

3: Leakage current does not generate electrical energy for equipment production, power generation, etc., but consumes electrical energy and is wasted.

4: Leakage current will damage equipment with poor insulation, causing shutdown failure and tripping of protective devices.

Correct use of insulation resistance tester:

1. Before measurement, the power supply of the equipment under test must be cut off and the equipment must be short-circuited and discharged to ground. Never allow the equipment to be powered for measurement to ensure the safety of people and equipment. For equipment that may induce high voltage, this possibility must be eliminated before measurements can be made.

2. The surface of the object to be measured must be clean. Reduce contact resistance and ensure the accuracy of measurement results.

3. Before measurement, the megger tester should be tested for open circuit and short circuit, and the insulation resistance tester should be used to check whether the megger tester is in good condition. That is, before the megger is connected to the object being measured. Shake the handle to make the generator reach the rated speed (120r/min), and observe whether the pointer points to the “∞” position of the scale. Short-circuit the terminal “line (L) and ground (E)”, slowly shake the handle, and observe whether the pointer points to the “0” position of the scale. If the pointer cannot point to the position of the finger, it indicates that the megger tester is faulty. It should be inspected before use.

5. The wiring must be correct. There are generally three terminals on the megohmmeter, among which L is connected to the conductor part insulated between the object under test and the earth, and E is connected to the shell of the object under test or the earth. G is connected to the shield of the object under test or the part that does not need to be measured. When measuring insulation resistance, generally only the “L” and “E” terminals are used. However, when measuring the insulation resistance of the cable to the ground or the leakage current of the equipment under test is serious, the “G” end must be used and the “G” end should be connected to the shielding layer or shell. After the lines are connected, the insulation resistance tester can turn the handle clockwise. The shaking speed should be from slow to fast. When the rotation speed reaches about 120 revolutions per minute (ZC-25 model), keep rotating at a constant speed and take a reading after 1 minute. And it should be read while shaking. Can’t stop to take a reading.

6. Place the High Voltage Insulation Resistance Tester in a horizontal position during shake measurement, and do not allow a short circuit between the terminal buttons when the handle is rotated. The handle should be shaken slowly and gradually faster. If the pointer is found to be zero, it means that the insulation being measured may have a short circuit. At this time, the handle cannot be continued to be shaken. To prevent the coil inside the watch from heating and being damaged.

7. Reading completed. Discharge the device under test. The discharge method is to remove the ground wire from the High Voltage Insulation Resistance Tester and short-circuit it with the device under test (not to discharge the High Voltage Insulation Resistance Tester).