Secondary Injection Testing

Accurate Verification of Protection Relay Performance

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Secondary injection tests are performed by injecting currents into relay terminals to ensure that relays operate correctly and according to their settings. These tests are typically carried out in substations on panels provided for this purpose.

The testing process involves injecting currents of various magnitudes, from minimum operation levels up to 6 or 10 times the current setting, while measuring the relay’s operating time. Both overcurrent and earth fault schemes are tested on protection relays. Certain relays have additional settings that must be considered, such as instantaneous overcurrent, earth fault, or sensitive earth fault settings.

If a protection relay is off-characteristic during secondary injection testing, it may affect coordination with other schemes in the network, potentially causing unnecessary nuisance tripping of the supply. Performing these tests provides a reasonable verification of the correct operation of the protection scheme.

AMP is capable of performing secondary injection testing on nearly all protection relays according to the OEM’s specifications. We have 3-phase and single-phase injection test sets, as well as dedicated instruments for secondary injection on LV switchgear protection.

Typically, secondary injection testing is combined with servicing and testing of MV switchgear and the Battery Tripping Unit (BTU). This approach requires only a single outage, minimising downtime and ensuring efficient operations.