Contact resistance test of circuit breaker

A contact resistance test is a crucial test for circuit breakers to ensure their proper functioning and reliability. Here's an overview of the test:

What is contact resistance?

Contact resistance is the electrical resistance between the moving contacts of a circuit breaker, such as the main contacts, auxiliary contacts, and arcing contacts. This resistance can cause energy losses, heat generation, and even failure of the circuit breaker.

Why is contact resistance testing important?

Contact resistance testing is essential to:

  1. Ensure reliable operation: High contact resistance can lead to arcing, overheating, and premature failure of the circuit breaker.
  2. Prevent electrical shock: High contact resistance can cause electrical shock or even electrocution.
  3. Comply with safety standards: Many safety standards, such as IEC 60255 and IEEE C37.09, require contact resistance testing for circuit breakers.

Types of contact resistance tests

There are two main types of contact resistance tests:

  1. DC contact resistance test: This test applies a direct current (DC) voltage between the contacts and measures the resulting current. The test is typically performed at a voltage of 10-30 V DC.
  2. AC contact resistance test: This test applies an alternating current (AC) voltage between the contacts and measures the resulting current. The test is typically performed at a voltage of 50-60 Hz.

Test procedure

The test procedure typically involves the following steps:

  1. Connect the circuit breaker to a test setup, which includes a power source, a current measuring device, and a voltage measuring device.
  2. Apply the test voltage (DC or AC) between the contacts.
  3. Measure the resulting current using a current measuring device.
  4. Calculate the contact resistance using the measured current and voltage.
  5. Compare the measured contact resistance with the specified maximum value.

Acceptance criteria

The acceptance criteria for contact resistance testing typically include:

  1. Maximum contact resistance: The measured contact resistance should not exceed a specified maximum value, usually in the range of 10-100 mΩ.
  2. Contact resistance ratio: The measured contact resistance should not exceed a specified ratio of the maximum contact resistance, usually in the range of 1:1 to 1:10.

Conclusion

Contact resistance testing is a critical test for circuit breakers to ensure their reliable operation and safety. By performing regular contact resistance testing, you can identify potential issues and prevent failures, ensuring the reliability and safety of your electrical system.