Common technical issues during transformer tester testing

In fact, the accuracy of transformer testers is not an important indicator of the instrument. In the transformer calibration regulations, it is required that the testing error caused by the entire circuit should not exceed 20% of the level of the tested transformer, and the presented data must be true. The common technical issues during the testing process are as follows:

1. Frequency selection filter performance

Transformer calibration is the measurement of fundamental waves. Due to the large distortion and modulation caused by high-frequency interference in the standard secondary current and the secondary and tertiary error current waveforms of the tested transformer, the tester must have good frequency selection. The factors that cause distortion, such as filtering performance, separating fundamental waves, and conducting measurements, are very complex. In low precision (less than 0.5) transformer tests without saturated iron core compensation, the distortion is generally around 10%, and the impact is not significant.

The national standard requires that the harmonic attenuation of the testing instrument should be more than 32dB, which is sufficient to meet the requirements for use. But when testing high-precision transformers or transformers with saturated iron cores, this indicator is relatively low. The domestic validation of this project has not been measured, and generally manufacturers do not provide indicators. When purchasing a new instrument, users should compare it with the old instrument to determine if it is trustworthy.

2. Introduce load and match with standard transformer

The additional load brought by the tester to the tested transformer and the load brought by the tester to the standard transformer are strictly specified in the regulations. Domestic metrological verification does not detect these indicators, and most manufacturers do not provide indicators, but they are one of the main reasons for the different test data of different units.

3. Line load

When doing the load, a resistance of 0.06 ohms is reserved for the connecting wires (some may have 0.05 ohms), so the sum of the resistances of wires A, B, and C is required to be tested at 0.06 ohms. When verifying current transformers under small fixed loads (10VA), the wire resistance has a significant impact on the data.

4. Ground wire

Due to being a power frequency measurement, the spatial electromagnetic field and floating ground potential have a significant impact on the measurement. In testing, the ground wire plays an important role. The ground wire must be properly grounded according to regulations, which is particularly important for tests above 0.05 or high voltage. It is recommended to choose a complete set of equipment manufacturer with years of industry foundation when purchasing instruments, rather than a single piece manufacturer. There is a fundamental difference in the theory and experience of transformer testing between the two. The correct choice can ensure that the various indicators of the instrument meet the requirements of regulations.

Weshine Electric Manufacturing Co., Ltd.