The Primary Current Injection Test Kit under Wuhan UHV 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:

$$\text{Error}=\frac{(I_p\mathrm{/}{I}_s)-\text{Rated Ratio}}{\text{Rated Ratio}}\times 100\mathrm{\%}$$

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 $V_{exc}$ and excitation current $I_{exc}$.

Identify Knee Point:

Locate voltage where $I_{exc}$Iexc surges → Knee-point voltage $V_k$.

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