INSULATION RESISTANCE AND POLARIZATION INDEX TEST FOR TRANSFORMER BY MEGGER

Summary

The video script outlines a step-by-step procedure for testing insulation resistance and polarization index using a mega IR tester on a transformer. It involves injecting DC voltage, shorting the low voltage side, and connecting leads to the transformer's tank earth. The process includes checking insulation between low voltage winding and earth, core to earth, and high voltage side to earth, with the removal of air gap for core-earth insulation test.

Takeaways

• ⚡ The process begins with insulation, resistance, and polarization index tests for an auxiliary transformer.
• 🔌 A megger IR tester is used, which injects DC voltage to check the insulation.
• 🔧 The insulation between the low voltage side and the earth is checked by shorting the low voltage winding and connecting leads.
• 🛠️ The red lead is connected to the low voltage side and the blue lead is connected to the earth of the transformer tank.
• 📏 After testing the low voltage side, the earth connection of the core is removed to check the insulation between the core and earth.
• ⚙️ The process involves removing specific connections and testing insulation in different sections, like the core and winding.
• 🧲 The insulation between the high voltage side and the earth is also tested.
• 🔍 The focus is on checking insulation resistance and polarization index (IR and PI).
• 🛡️ The low voltage side is shorted during testing, while the insulation between low voltage winding and earth is verified.
• 📡 Lastly, the insulation between the transformer core and earth is checked by removing certain earth connections.

Q & A

What is the purpose of using a Mega IR tester in this process?

The Mega IR tester is used to inject DC voltage and check the insulation resistance of various components in the transformer, such as the low voltage winding and core, against earth.

Why is the low voltage side of the transformer shorted during testing?

The low voltage side is shorted to check the insulation between the low voltage winding and the earth effectively, ensuring no leakage paths or faults.

What is the role of the red and blue leads in the insulation test?

The red lead is connected to the component being tested (e.g., low voltage winding or transformer core), while the blue lead is connected to the earth to complete the circuit for insulation testing.

What is meant by 'insulation resistance' in this context?

Insulation resistance refers to the resistance offered by the insulation between the transformer components (such as the windings and core) and earth. It indicates the quality of insulation and the likelihood of current leakage.

What does the polarization index (PI) measure in transformer testing?

The polarization index (PI) is the ratio of insulation resistance measured after 10 minutes to the resistance measured after 1 minute. It is used to assess the condition of the insulation over time and detect issues like moisture or aging.

What is the significance of removing the earth connection from the transformer core during testing?

Removing the earth connection from the core allows for the insulation resistance between the core and earth to be checked independently. This ensures that the core is properly insulated from the earth.

What are the key transformer components tested for insulation resistance in this process?

The key components tested include the low voltage winding, transformer core, and high voltage winding, all checked against earth for proper insulation.

Why is it important to test insulation between the core and earth?

Testing the insulation between the core and earth ensures that the core is not in electrical contact with earth, which could lead to ground faults or other electrical problems.

How is the insulation resistance between the high voltage side and earth tested?

The high voltage side is shorted, and the red lead is connected to the high voltage terminal while the blue lead is connected to earth, similar to the low voltage test.

Why is it necessary to perform multiple insulation resistance tests on different parts of the transformer?

Multiple tests on different parts ensure that all components of the transformer are properly insulated and functioning safely, identifying any potential weaknesses or faults in the insulation.