Choosing a transformer turns ratio tester involves more than comparing maximum test voltage and measurement accuracy. The transformer type, required test method, expected ratio range, workflow automation, and data management requirements should all influence the decision.

The DV Power TRT Standard Series includes the TRT03, TRT33, and TRT63 model families. These instruments are designed for testing power, distribution, instrument, and autotransformers. Depending on the model, the series offers single-phase and true three-phase test voltages, a ratio range from 0.8 to 50,000, and typical accuracy as high as ±0.03%. The instruments can also measure excitation current and phase angle.

1. Determine Whether True Three-Phase Testing Is Required

This is the most important decision when selecting a TRT Standard model.

• TRT03: Provides single-phase test voltage and can test three-phase transformers sequentially, one phase at a time.
• TRT33: Provides both single-phase and true three-phase test voltages up to 100 V AC.
• TRT63: Provides both single-phase and true three-phase test voltages up to 250 V AC.

The TRT03 may be sufficient for routine single-phase testing or sequential testing of conventional three-phase transformers.

Choose the TRT33 or TRT63 when you need to measure a three-phase transformer’s nameplate voltage ratio directly or test special transformers, including phase-shifting, rectifier, arc-furnace, and traction transformers. A true three-phase source energizes all three phases simultaneously and allows the instrument to determine actual phase relationships between the high- and low-voltage sides.

2. Select the Appropriate Maximum Test Voltage

A higher test voltage can move the transformer core closer to the linear region of its magnetization curve, reducing errors associated with very low excitation voltage. This can be particularly important when a measured ratio deviation is close to the acceptance limit.

For large power transformers, commissioning work, critical assets, or higher-ratio applications, the TRT63 generally provides the widest testing capability.

3. Choose Between the A, B, and C Variants

The A, B, and C variants primarily differ in their available test-voltage steps:

• A variants: Include an 8 V test setting and a maximum of 100 V or 250 V.
• B variants: Include a 10 V setting instead of 8 V and a maximum of 100 V or 250 V.
• C variants: Include 8 V and 80 V settings. The TRT03C and TRT33C have a maximum of 80 V, while the TRT63C still reaches 250 V.

For example, the TRT63A offers 1, 8, 40, 100, and 250 V AC. The TRT63B offers 1, 10, 40, 100, and 250 V AC, while the TRT63C offers 1, 8, 40, 80, and 250 V AC.

Review your company’s test procedures and historical records before choosing a variant. Using the same test-voltage level as previous measurements makes trend comparison more consistent.

4. Consider Current Transformer Testing

TRT33 and TRT63 models can generate test voltage as low as 1 V AC, enabling turns-ratio verification on many current transformers.

The TRT03 models start at 8 V or 10 V and do not include a 1 V setting. If the testing program includes both power transformers and CTs, the TRT33 or TRT63 will normally be the more suitable choice. The exact CT construction and required test method should still be verified before purchase.

5. Look Beyond the Ratio Reading

A suitable transformer ratio tester should provide diagnostic information in addition to the ratio result. The TRT Standard Series supports:

• Turns-ratio and ratio-deviation measurement
• Excitation-current measurement
• Phase-angle measurement
• Automatic vector-group detection
• Magnetic-balance testing
• Demagnetization-process verification

Excitation-current trends can reveal possible core or winding abnormalities. Phase-angle measurement helps verify winding connections and instrument-transformer polarity, while automatic vector-group detection reduces manual setup and interpretation errors.

6. Evaluate Tap-Changer Automation

When testing transformers equipped with an on-load tap changer, consider how many tap positions must be tested and recorded.

TRT Standard instruments have an integrated tap-changer control unit. With DV-TR software, the testing process can be programmed to run ratio measurements, change OLTC positions, and save the results automatically. This is especially valuable for transformers with many tap positions and for repetitive maintenance programs.

DV-TR software also supports test-plan creation, graphical analysis, Excel export, and customizable test reports.

7. Confirm the Field Configuration and Accessories

Before requesting a quotation, confirm:

• Required H- and X-side test-lead lengths
• Whether 5, 10, 15, or 20 m cables are needed
• Whether an integrated thermal printer is required
• Whether an optional RS232 interface is needed
• Whether the cables must be shared with a DV Power TWA winding-resistance instrument
• Whether a portable enclosure or 19-inch rack version is more suitable

Compatible TRT and TWA test leads can help reduce reconnection work when performing turns ratio, excitation current, phase angle, winding resistance, OLTC, and demagnetization tests on the same transformer.