The Transformer Turns Ratio tester under Wuhan UHV can help many power workers conduct various power tests more conveniently.

1. Safety Preparation

Isolate and De-energize: Disconnect all HV/LV power sources. Verify de-energization and apply safety grounds.

Discharge & Ground: Short-circuit and ground all windings for discharge.

PPE: Wear insulated gloves and safety glasses.

2. Instrument Connection

Use a dedicated TTR tester.

Connect HV leads (H1/H2/H3) to transformer HV terminals.

Connect LV leads (X1/X2/X3) to LV terminals.

Ground both tester and transformer tank reliably.

3. Parameter Setup

Enter rated HV/LV values (e.g., 11kV/400V).

Select winding configuration (e.g., Dyn11).

Set tap changer to rated position.

4. Execute Test

Start tester. Measure phase-by-phase (A-a, B-b, C-c).

Record measured ratio and % error.

Acceptance Criteria:

% error ≤ ±0.5% (GB/IEEE standards);

Phase deviation ≤ 0.2%.

5. Tap Changer Check

Cycle through all tap positions (e.g., +5%, 0, -5%).

Verify ratio matches step value at each tap (e.g., ±0.625%/step).

6.Result diagnosis

Excessive error: incorrect number of turns, poor tap contact.

The ratio of one stage is significantly lower: the high-voltage turn to turn short circuit in this stage.

No reading/infinite ratio: open circuit winding.

Abnormal tapping behavior: burnt or misaligned contacts.

7. Key Notes

Off-circuit tap changers: Must be switched manually after de-energization.

OLTC (On-Load Tap Changer): Use tester’s remote control. Strictly prohibit manual switching under voltage!

Re-ground windings after testing.