What Is an Insulation Resistance Tester?
An insulation resistance tester is a device used to diagnose insulation conditions. Insulation resistance testers that can apply a high voltage of about 1,000 VDC according to the voltage of the power system are also available.
It is very important for equipment that uses electricity to be insulated. If the insulation condition deteriorates, it can cause electrical leakage, fire, or electric shock. To prevent the above accidents from occurring, it is necessary to periodically evaluate insulation performance with an insulation resistance tester.
Uses of Insulation Resistance Testers
Insulation resistance testers are used to quantify insulation capability. It is rarely seen in ordinary households.
In production, they are used for final testing of electrical products at the factory where they are shipped. In addition, maintenance personnel of electrical equipment often have it as a measuring instrument for maintenance.
Resistance measurement involves the application of a voltage, and the applied voltage varies according to the system voltage. For example, insulation resistance testers that apply a voltage of 25 to 50 V are used to measure the insulation of telephone lines, while 125 VDC is used for home appliances. A voltage of 1,000 VDC is applied to high-voltage distribution lines and power plants.
Principle of Insulation Resistance Testers
An insulation resistance tester consists of a wiring terminal, a switch, a DC power supply, an ammeter, and a current protection element.
The wiring terminal uses two terminals, called the ground terminal and the line terminal. The ground terminal is grounded, and the line terminal is connected to the measuring section for measurement.
By pressing the switch, a DC voltage created by a DC power supply is applied. The minute current flowing to the ground is called leakage current, and insulation resistance tester is obtained by measuring the leakage current when the voltage is applied with an ammeter.
Since a high-voltage voltage is applied, the impedance is increased with a current protection element to prevent overcurrents from flowing in the circuit. Due to the current protection element, the internal impedance of the insulation resistance tester is designed to be very high.
The higher the insulation resistance value, the better the insulation performance. If an insulation breakdown occurs, the insulation resistance will be extremely low.
Other Information on Insulation Resistance Testers
1. Purpose of Using an Insulation Resistance Tester
Insulation resistance testers are used to measure the insulation condition of electric lines and electrical components installed in factories and homes.
Causes of insulation defects may include poor installation of electrical circuits, poor insulation between charging and non-charging parts, deterioration over time, deterioration of internal wiring, damage due to shorts in parts used, and damage to the housing. If left unchecked, these problems can lead to electrical leakage fires and electrocution, which are extremely dangerous.
To prevent such problems, shut off the power supply system and measure the insulation resistance as soon as the “leakage breaker tripped” or “electric shock occurred during operation” appears. 2.
2. Measurement Method
To measure the insulation resistance tester, follow the procedure below.
- Connect the ground terminal of the insulation resistance tester to a grounded metal point (if possible, a terminal connected to the grounding pole).
- Select the applied voltage with the knob according to the system voltage.
- Press the line terminal against a grounded point other than the ground terminal and press the measurement button.
- Confirm that 0.00MΩ is displayed. (Zero check).
- Remove your hand from the measurement button and press the line terminal against the measurement point.
- Press the measurement button and check the insulation resistance.
If the circuit length is long, it may take time for the electric charge to accumulate, and the insulation resistance display may not be stable. In this case, continue to apply voltage until the display stabilizes.
Also, when a high voltage such as 1,000 VDC is applied, a large amount of residual charge will accumulate. Touching the circuit with bare hands may cause an electric shock, so it is necessary to ensure that discharge measures are taken.
The technical standard for electrical equipment specifies insulation resistance values for voltage system categories. This is the standard for judging the measurement results.
- Ground voltage of 150 V or less → Insulation resistance of 0.1 MΩ or more
- Ground voltage of 150V or more but less than 300V → Insulation resistance of 0.2MΩ or more
- Low-voltage circuits with a ground voltage of 300 V or more → Insulation resistance of 0.4 MΩ or more
In the event of an actual insulation failure, measuring the insulation resistance of electrical circuits and electrical equipment separately will lead to the early detection of the deteriorated part. The early detection of insulation defects is a testament to the skill of electrical equipment maintenance personnel.