HZYA-3Z supports two testing methods: with winding testing and without winding (directly on the tap changer terminal) testing. Both methods can measure transition waveforms and various parameters, but the applicable scenarios and precautions are different.

Test with winding: closer to actual working conditions

When testing with windings, the test wire is connected to the high-voltage side bushing terminal of the transformer, and the current flows through the winding to the on load tap changer and then back to the instrument. Due to the fact that the winding itself is an inductive load, there is real winding inductance involved in the test circuit, and the action waveform is closer to the actual operating conditions of the on load tap changer.

Wiring requirements: Short circuit the non test end (usually the medium voltage side and low voltage side) to ground to prevent induced voltage from affecting the measurement. The yellow, green, red, and black test pliers are sequentially clamped onto the A, B, and C phases and neutral point N of the regulating side (high voltage side) bushing, corresponding to the A, B, C, and N terminals of the instrument.

The winding test reflects the operating characteristics of the on load tap changer under real inductive loads, and is the standard testing method for acceptance after major repairs.

Test without winding: faster and more direct

When testing without winding, connect the test wire directly to the X1/Y1/Z1 terminals of the voltage regulating switch, short-circuit the corresponding X2/Y2/Z2 with a short wire, and connect the black test clamp to the neutral point. Removing the influence of winding inductance, the test circuit impedance is smaller, charging is faster, and the test preparation time is shortened.

Suitable scenario: After the on load tap changer is lifted out of the transformer, it is tested separately; Or in situations where it is necessary to quickly troubleshoot the switch itself and eliminate the influence of windings.

The key differences between the two methods

The instruction manual clearly states an important data point: the action time of testing with winding is about 3-7ms longer than testing without winding. This difference is caused by the inductance of the winding, not instrument error or switch abnormality. When comparing data from two different testing methods, this difference needs to be considered.

When comparing historical data, it is necessary to ensure that the two testing methods are consistent (with or without windings), otherwise the time difference cannot be correctly determined whether it belongs to a switch state change.

Setting of trigger resistor

Regardless of the testing method, the triggering resistance parameter needs to be pre-set. It is recommended to set the trigger resistance to half of the predicted transition resistance value, which can make waveform capture more accurate and data more reliable. When unfamiliar with the tested switch model, first check the manufacturer's information to obtain the reference value of the transition resistance, and then calculate the set value of the trigger resistance.