How to do CT primary injection test?

The Primary Current Injection Test Kit under HV Hipot Electric Co., Ltd. can help many power workers conduct various power tests more conveniently.

I. Safety Preparation

De-energize: Disconnect system power. Implement LOTO (Lockout-Tagout).

Ground: Short-circuit and earth all primary conductors.

Prevent Open-Circuit: Short-circuit and earth all CT secondary windings (only disconnect the winding under test temporarily).

PPE: Wear arc-flash suit and insulated gloves.

II. Test Steps

1. Connections

Primary Side: Connect high-current injector to CT primary conductor (e.g., clamp onto busbar).

Secondary Side: Connect test winding terminals to CT analyzer. Keep other secondaries shorted/earthed.

2. Ratio & Polarity Test

Ramp Current: Inject current from low → high (e.g., 10% → 100% rated current).

Record:

Primary current  I p  (from injector)

Secondary current  I s  (from analyzer)

Calculate Ratio Error:

Error = ( I p / I s ) − Rated Ratio Rated Ratio × 100 % Error=Rated Ratio(Ip/Is)−Rated Ratio×100%

Pass Criteria: Error ≤ ±3% (protection CTs) or ≤ ±1% (metering CTs).

3. Excitation (Saturation) Test

Reconfigure: Leave primary side open. Connect CT analyzer directly to secondary winding.

Ramp Voltage: Increase secondary voltage from 0V, recording voltage  V e x c  and excitation current  I e x c .

Identify Knee Point:

Locate voltage where  I e x c Iexc surges → Knee-point voltage  V k .

Pass Criteria:  V k  ≥ system fault-induced secondary voltage (per design specs).