Secondary injection proves that an installed protection relay measures correctly, applies the approved settings and operates the intended trip and alarm logic. A useful FAT test follows the signal from the test set through the relay and into the panel outputs—not merely the relay’s display.

Learning objectives

Define an auditable secondary-injection plan; test pickup, timing, logic and outputs; and preserve evidence that can be compared with the approved settings file.

Core engineering principles

Test against an approved baseline

Freeze the relay model, firmware, settings revision, CT/VT ratios and logic equations before testing. Record any temporary test-mode changes and restore them at completion.

Separate element accuracy from scheme logic

First verify measurement and protection-element performance. Then prove logic gates, blocking, latching, LEDs, contacts and communications using a controlled cause-and-effect sequence.

Measure both threshold and time

For time-dependent functions, test at several multiples of pickup and compare measured operating time with the selected characteristic and tolerance.

Engineering application method

  1. Step 1: Review the approved protection settings, drawings, trip matrix and relay test plan.
  2. Step 2: Isolate trip outputs as authorized and connect the calibrated secondary-injection set.
  3. Step 3: Verify phase sequence, channel mapping, metering accuracy and binary inputs.
  4. Step 4: Test pickup, dropout and operating time for each required protection element.
  5. Step 5: Prove output contacts, LEDs, event records, disturbance records and remote indications.
  6. Step 6: Restore normal links and test modes, then archive the report and native test file.

Practical example

For a phase overcurrent element, inject a value below pickup, raise current until operation, then test timing at selected current multiples. Confirm the expected relay contact and panel trip path without unintentionally energizing the breaker coil.

Common mistakes

  • Testing an obsolete settings revision.
  • Checking pickup but not operating time or logic.
  • Leaving relay test mode, blocked outputs or temporary settings active.
  • Recording only pass/fail without injected and measured values.

Design and review checklist

  • Approved settings and firmware identified.
  • Calibrated test equipment listed.
  • Element, logic and output results recorded.
  • Temporary changes reversed and independently checked.
  • Native relay event and test files archived.

Standards basis and official sources

Engineering note: Verify the contracted standard edition, amendments, manufacturer evidence and project-specific studies before applying these principles to a supplied assembly.

Similar Posts