Injection Testing for Circuit Breakers

Circuit breakers can go long periods of time without activation. If they fail when activated, this can have catastrophic consequences for your staff and plant if an arc flash were to occur; and will certainly cause extensive damage to your electrical systems. Primary & Secondary injection testing should be included as part of your Preventative Maintenance plan to ensure the reliability and safety of your power circuit breakers.

Primary Injection Testing
Primary current injection is usually the preferred test method because it includes the current sensors, wiring and the current conduction path in the circuit breaker as part of the test. However, it will not always detect sensor wiring and polarity problems.

Primary injection tests work by injecting a calculated amount of low voltage (Typically 5 to 10 Volts) with high current through the breaker and measuring how long it takes for the breaker to trip. The calculated amount of current is different for each type of function you want to test. Based on the time-current curve for the breaker, each testing current value will have a required time response for determining acceptability.

Common primary injection tests include:

  • Power Transformers (Through Faults)
  • Relay Testing
  • Bus-work, Switchgear and HV Breakers
  • Low voltage breakers
  • Switchgear Testing
  • Heat runs
  • Stability tests
  • Loose Connections
  • Core Identification

Secondary Injection Testing:
Secondary Injection Tests are always completed before the Primary Injection Tests. It is done to minimize the risks during the initial testing to the Low Voltage side of equipment under test. This check verifies the correct operation of the protection controls that are downstream from the inputs to the protection relays.

Some trip units allow for just testing of the electronic trip functions of the breakers, this form of testing is much more readily accessible and easier to complete. Secondary trip testing differs from Primary in that the high currents are not applied through the line and load contacts of the breaker. This generally involves disconnecting the trip from its standard operating circuitry and connecting it to a specialist test that can inject, measure and record the actual operation characteristics of the breaker under test.

If you need help incorporating primary and secondary injection testing as part of your preventative maintenance programme get in touch with EAS, your specialist industrial electrical team today on 07 834 0505.


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