How to perform diagnostic testing of HV circuit breakers

Filed diagnostic testing

Understanding diagnostic testing of HV Circuit Breakers is essential. When diagnostic tests are performed on HV Circuit Breakers, valuable information can be extracted. From a technical maintenance perspective, these diagnostic tests provide critical information about the condition of the HV Circuit Breakers.

Standard field tests widely applied today in HV Circuit Breaker diagnostics include:

1. Timing and Travel
2. Power Factor
3. Contact Resistance (Static and Dynamic)
4. Minimum Pick-Up

These specific diagnostic tests have been selected as the primary focus for this paper and discussion.

The audience will be provided with an understanding, application, and analysis of these tests, supported by case studies validating the value that these diagnostic tests bring to HV circuit breaker testing.

Introduction

Circuit breaker technology varies depending on the application. Also, the preferred technology is dependent on the geographical region in which it is applied. Case in point, Dead Tank SF6 Filled Circuit Breakers and Bulk Oil Circuit Breakers are primarily used in North America in HV applications, while the rest of the world prefers Live Tank Circuit Breaker technology.

Overall, circuit breakers, regardless of type and technology, are designed with the following three functions in mind:

1. Direct current flow between desired sections of an electric power system
2. Interrupt current flow under abnormal power system events and conditions (faults)
3. Carry load current under normal power system conditions with minimal losses

Circuit breakers vary by subsystems:

1. Insulation System
2. Arc Quenching Method
3. Mechanism
4. Contact Technology
5. Control Circuit Schemes
6. CT’s

These subsystems above need to be analyzed both separately and as a complete electro-mechanical system.

Diagnostic testing can be performed in either an on-line/in-service state or an off-line/de-energized state. The manufacturer’s recommendations, duty, number of operations, and past experience should be considered when justifying the test and maintenance requirements.