A transformer turns ratio test is considered a low voltage test used to determine the ratio of a high voltage winding. The turns ratio test is performed on every tap of a winding with either a single-phase or three-phase model. During testing, the test sets are used to apply voltage to the H marked leads and measure the X marked lead. Ratio is then measured by dividing the induced voltage reading by the applied voltage reading.
**CAUTION** DO NOT ATTEMPT TO PERFORM THIS TEST IF YOU ARE NOT A CERTIFIED TECHNICIAN IN THE FIELD. TO FIND A CERTIFIED CALIBRATION LAB, CLICK HERE.
Disconnect and isolate the transformer from any incoming and outgoing cables. Be sure to apply working ground to the incoming and outside cables prior to disconnecting from the transformer. Notably, disconnected cables should have a significant amount of clearance from the switch gear terminals.
Connect the test set to the H designated lead – ensure that the connector is marked with H. Also, be sure to check that the connector’s index notch lines up precisely.
Same as step two but with the X designated lead. Ensure that the connector is marked with X and check the connector’s index notch is lined up properly.
When using a three-phase model, connect H1, H2 and H3 designated test leads to the corresponding terminal. Connect to the H0 test lead if present.
Same step as four but with the X designated test leads. Connect X1, X2 and X3 to the corresponding terminals.
After everything is connected, perform turns ratio measurements for every tap. It’s important to ensure that all measured ratios are with the calculated ratios.
Although this step-by-step guide is beneficial for understanding how a turns ratio test is performed, it is in your best interest to seek a professional to perform these tests on a transformer. Correct voltages are crucial for safe handling of any equipment dealing with electricity. By choosing a professional to complete this test procedure, safety can be guaranteed.
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