Automatic CT Turns Ratio Tester Transformer Voltage Ratio Meter TTR Tester
The Transformer Turns Ratio test, commonly referred to as the TTR test, is a critical evaluation that confirms the correct ratio of primary turns to secondary turns within a transformer. A correctly conducted TTR test can help diagnose various faults, such as shorted turns, open windings, incorrect winding connections, and tap changer performance issues. Our TTR testers are designed to be sturdy and durable, capable of withstanding harsh testing conditions. The range of TTR testers we offer includes various features that simplify and expedite the testing process, including 3-phase TTR testers and PT and CT TTR testers.
Transformer Ratio Test
The performance of a transformer relies heavily on the precision of its voltage ratio or specific turns, making the transformer ratio test an indispensable type of test. To ensure safety during this test, it is necessary to apply voltage solely to the high voltage winding while avoiding any exposure to unsafe voltage levels.
Turns Ratio Test Procedure
- Start by setting the tap changer of the transformer to the lowest position and keep the LV terminals open.
- Apply a 3-phase 415 V supply to the HV terminals. Simultaneously, measure the voltages applied to each phase (phase-phase) on the HV side and the induced voltages at the LV terminals.
- After measuring the voltages at HV and LV terminals, raise the tap changer of the transformer by one position and repeat the test.
- Repeat the same procedure for each tap position separately.
The above transformer ratio test can also be conducted using a portable Transformer Turns Ratio (TTR) meter. These meters have a built-in power supply, typically operating at very low voltages such as 8-10 V and 50 Hz. The HV and LV windings of one phase of the transformer are connected to the meter, and the internal bridge elements are adjusted to achieve a null indication on the detector.
Test Methods
The transformer ratio test involves applying a phase voltage to one of the windings using a bridge circuit, and then measuring the ratio of induced voltage at the bridge. The measuring instrument used for this test has high accuracy, with a precision level of less than 0.1%.
The adjustable transformer, as depicted in the diagram, is utilized to fine-tune the theoretical turn ratio during the TTR test. The goal is to adjust the transformer until a balance is achieved in the percentage error indicator.
The reading on this indicator indicates the percentage deviation between the measured turn ratio and the expected turn ratio.
An out-of-tolerance ratio test in a transformer can be caused by shorted turns or open turns in the windings. Shorted turns result in high excitation currents, while open turns in the HV winding lead to no excitation current and no induced voltage. Open turns in the LV winding cause normal excitation currents but very low and unstable output voltages. The ratio test can also detect high resistance connections or contact issues in the circuitry.
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