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site last edited:

11/7/06

Primary Injection

The term “Primary Injection” suggests that (relatively) high current is applied to the primary conductors. This is done to prove the CTs (current transformers), current-circuits, and protective devices are all properly connected.

Depending on the equipment, “Primary Injection” has different implications and can have vastly different setup requirements and measurement expectations. Three common tests are described below:

 

Power Transformers - (Sometimes called a “Through-Fault” or “Thru-Fault” test.) Essentially, a three-phase source (of sufficient Voltage. Current, and VA rating) is connected to a short-circuited transformer, to supply current through the windings. The CT circuits are then checked (for magnitude and angle) to verify that all test-switches and protective relays receive the proper current at the proper angle, as expected. Usually, the test is set up to include the high-side and low-side breakers. Often, the test is expanded to simultaneously test the CT circuits from other breakers connected to the same, or adjacent, bus.

 

Bus-work, Switchgear, and HV Breakers - Sufficiently high current is applied to the primary conductors. The CT circuits are then checked (for magnitude and angle) to verify that all test-switches and protective relays receive the proper current at the proper angle, as expected.

 

Low Voltage Breakers - Very high (fault level) current is applied to the breaker for short duration, to measure how the Trip-Unit reacts. The trip-unit’s time delay is measured at various current magnitudes to verify compliance with manufacturer’s published time-current curves.

 

In all cases, PTS determines expected values PRIOR to testing. Measured values are documented alongside predicted values, so any anomalies are easily identified.

(Click on the button below to view PTS’ documentation from a past project.)

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