Megohmmeters - Insulation Testers

Know More About Triplett Megohmmeters or Insulation Testers

What is insulation resistance testing?

The electric current that passes through a conductive wire must reach its destination. However, it may get lost due to various reasons. The conductive wires that carry this current are insulated with resistance sheathing to maintain conductivity. Some current will still leak despite this strong resistance sheathing. If the current escapes steadily, then it would damage the machinery and electrical circuits. This is where insulation resistance testing would help. It helps determine if the insulation in the wire or the circuits is performing as desired. If tested routinely it would help identify several operational issues and prevent equipment failures.

What are the uses of electrical insulation testers?

Electrical insulation testers or Megohmmeters are mainly used as a:

• Quality control measure during the manufacturing of an electrical equipment
• Commissioning tool to ensure the application is working properly and meets the operational specifications perfectly
• Tool for troubleshooting the current leakage
• Tool for preventive maintenance

How is insulation resistance testing done?

Insulation resistance testing is performed by taking the test equipment out of service. The apparatus is shut down and all switches are opened and the units are de-energized. The equipment is disconnected from all energized equipment. You will find positive, negative, and guard terminals on the insulation resistance tester. These need to be connected to the positive and negative terminals of the test equipment. Most equipment use these terminals; however, if you are testing the equipment at higher voltages then a third terminal called guard may be used. This means, if you are testing transformers or cables, you may be required to use guard terminals. You won’t find these terminals with most insulation resistance testers. However, they are present in our devices. 

How to choose the best Megohmmeters for your application?

We provide a broad range of insulation resistance testers to choose from. However, not all may be suitable for your applications. Here are certain things to keep in mind when buying them for your application.

• Application: How do you wish to use your insulation testing equipment? First, note down the applications that require insulation resistance testing. Next, focus on their nominal voltage. This value can be seen on the nameplate of the equipment on which you would perform tests later. Along with this, you need to focus on the number of tests that you plan to perform annually. Remember, the insulation resistance tester you choose must be able to withstand the challenges of application as well as demonstrate quality, reliability, durability, and convenience of use.
• Voltage Requirements: Our selection features digital insulation testers that can test insulation voltage up to 60 GΩ using test voltages 500V, 1000V, 2500V, and 5000V. Similarly, analog insulation testers can test insulation voltage up to 400MΩ using three test voltages 250V, 500V, and 1000V. Ensure the output test voltage applied to the equipment or application must meet these recommended test voltages.
• Operating Environment of Insulation Resistance Tester: Insulation resistance testers can be used for various applications other than preventive maintenance in shop environments or industrial plants. Depending on the features, these insulation resistance testers can be used to perform capacitance and voltage checks, insulation resistance tests, and temperature measurements. They can be used to check leakage and polarization current.

What are the safety precautions to keep in mind when using insulation resistance testers?

Insulation resistance testers produce high DC voltages, which can destroy energized electric circuits. Thus, they shouldn’t be connected to these circuits. Also, avoid using energized insulation testers to test electronic supplies such as VSDs, PLCs, battery chargers, and so on. Check the tester for applicable voltages, suitable environment, and ideal applications before using them. In addition to these, you need to focus on the self-discharge feature when choosing these insulation resistance testers. This is because these testers can hold high voltage for a long even after the testing has been completed and may take a long time to discharge. Many users ground these testers to check if the device has discharged completely.  

What does an insulation resistance test indicate?

During this testing, DC voltage is applied to the test equipment. Some current leaks out of the equipment under test and start charging the insulation. This current is referred to as capacitive charging current and it can be easily read from the digital interface. If the current leaks out of the test set, then the megaohm reading will be low. When the insulation gets charged, the meter will start showing high megaohm reading, which assures a good quality of insulation. If the insulation still shows a low value after getting charged, this is a sign of poor insulation. This often happens in the case of old insulations or the ones that are damaged. This is an indicator of immediate replacement or impending maintenance. Sometimes, the insulation resistance values may be affected by the temperature or other factors, too. Here are some pointers that may be helpful.

• Fair to high values: The insulation is working fine.
• Fair to high values, but the tendency to lean towards low values: The values may be affected by temperature or any other factor. Next, identify the cause and take a remedial measure.
• Low values, despite good conditions: This may be due to temperature or other factors. Check the cause and take remedial measures.
• Very low values: This may be due to poor insulation, else, you need to increase values.

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