Primary Current Injection Testing is utilised in high current/high voltage scenarios found at large electrical installations such as substations. A large current (between 100A and 20,000A depending on system specifications and test requirements) is injected directly on the primary side of the electrical system such as a circuit breaker.

The objective of the test is to identify how the system operates under various levels of current load. Primary injection testing is suitable for testing over-current trip relays attached to a circuit breaker. By injecting the current into the system, we can measure if the breaker will trip or fail, and how long the current is live before the circuit is broken. 

Our electrical teams are able undertake primary and secondary current injection testing of most circuit breakers, this is done by removing and “bench” testing the circuit breaker using advanced equipment which can record, trip times, and compare to manufactures recommended guidelines, print out diagnostics and much more. This is the only way to measure the mechanical parts of the protection are in good working order to deal with a real fault.


Proper functioning of a circuit breaker is reliant on several individual components that need to be calibrated and tested at regular intervals. The trigger for maintenance intervals differs greatly between power utilities but the intervals are often based on time since last test, number of operations, or severity of fault current operations. Environmental considerations such as humidity and temperature, whether the breaker is in a desert or coastal region, also play into the maintenance scheme that should be adopted.

The following is a list of comprehensive circuit breaker tests recommended on the majority of circuit breaker types:

  • Timing and Travel
  • Motion, Coil current
  • Static (contact) resistance measurements (SRM)
  • Dynamic (contact) resistance measurements (DRM)
  • Vibration
  • Motor current
  • Minimum pick-up measurement
  • Minimum voltage
  • Station voltage
  • Air pressure test

As with any mechanical and electrical components or equipment, wear and lubrication often affects the performance of circuit breakers, so being able to trend mission critical parameters and compare these with factory thresholds helps to verify proper breaker function. Circuit breakers can go long periods of time without activation, and failure now of activation can cause catastrophic damage to the electrical system. Circuit breaker testing with primary current injection on a breaker that has not triggered in some time is the best way to recreate the real operating conditions of a current spike.

OES have a dedicated electrical teams which can complete these surveys and perform this testing. OES can offer this service on offshore and onshore drilling units. OES have an extensive track record over the course of three decades.