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Type and use of high voltage test transformer

time:2021/1/13   source:华天电力  reading:581 time

High-voltage test transformer refers to a type of transformer that generates high voltage for high-voltage test. High-voltage test transformer has the characteristics of high voltage, small capacity, short continuous working time, thick insulation and usually one end of the high-voltage winding is grounded.

The high-voltage test transformer is referred to as the test transformer for short. The test transformer is generally a step-up transformer. This test transformer uses the power frequency high voltage induced by its secondary side to conduct insulation performance tests on various electrical products and insulating materials. The test transformer is An indispensable electrical equipment for withstand voltage test in the repair of motors, transformers and electrical products. The test transformer is mainly used for power frequency withstand voltage test of electrical products, partial discharge measurement, thermal stability test of insulating medium, etc. Medium and high-frequency electrical equipment can also use special frequency test transformers for withstand voltage test and measurement of related electrical parameters.

Hipot Test Set.png

The primary and secondary windings of the test transformer have a large voltage ratio. The primary voltage is 0.4kV, 3kV, 6kV, and 10kV. The secondary voltage can be made 100~2000kV or higher, and the capacity can be 3~9000kVA. Equipment field test generally uses light test transformers, 50kV step-up test transformers for withstand voltage test of 6kV, 10kV transformers and other power equipment, and withstand voltage test for high voltage and ultra-high voltage transformers of 35kV and above. Ultra-high voltage test transformers that are more than 5 times the primary rated voltage of the equipment under test, such as step-up test transformers of 500kV, 700kV, 800kV and a certain capacity.

1) High voltage: The primary voltage of the test transformer is 220V or 380V, but the secondary voltage of a single test transformer is often thousands to tens of thousands of volts, and the test transformer with a secondary voltage exceeding 750kV usually adopts multiple cascade types. structure.

2) Small current: The rated current of the test transformer is actually the capacitive current of the tested product, so it is generally less than 1A, but it is used for the test transformers of cables and large-scale motor tests, external insulation pollution tests, line corona tests, etc. The secondary current can reach several amperes.

3) Short working time: Due to the short withstand voltage time of the tested product, the test transformer is generally 0.5h or 1h short-time working system except for external insulation pollution test, line corona test, and cable test.

4) The test transformer is generally a single-phase, indoor device (also made into an outdoor device): all are oil-immersed self-cooling structure, the winding insulation layer is thick, and the high-voltage winding is usually grounded at one end.

5) The insulation level of the first and the end of the secondary winding of the test transformer is different: the first end is high potential, and the end is directly grounded or grounded through an ammeter.

6) High design and manufacturing process requirements: Due to the high working voltage, the insulation structure has a decisive influence on the overall size of the test transformer. The body generally requires vacuum drying, and vacuum oil injection is required for more than 100kV.

1) From the structure point of view, there are iron shell type and insulating shell type test transformers.

2) From the power frequency, there are several frequency level test transformers of power frequency, double frequency, intermediate frequency and high frequency.

3) According to the voltage level, it can be divided into low voltage, high voltage and ultra high voltage test transformers.

4) According to the form of use, it can be divided into light mobile type and fixed type, and there are single use and two or more cascade use test transformers.

The test transformer is generally a single-phase, indoor device, all of which is oil-immersed and self-cooled. Because of its high working voltage, its winding insulation layer is thick, and one end of the high-voltage winding is grounded.

The specific structure of the test transformer generally has three types: single bushing type, double bushing type and insulating barrel type.

① Output voltage waveform. The output voltage waveform of the test transformer should be as close as possible to the sine wave. In order to reduce the distortion of the voltage waveform caused by the harmonic component of the no-load current through the impedance of the voltage regulator and the transformer, the magnetic flux density should be Choose the straight line section of the iron core magnetization curve, and at the same time choose a voltage regulating device with small waveform distortion, and add a filter device if necessary.

②Impedance voltage. The secondary current of the test transformer is generally capacitive current. When the secondary current flows through the impedance of the voltage regulator and the test transformer, it will cause the output voltage to exceed the value determined by the voltage ratio, so the impedance of the test transformer The voltage should not be too high, otherwise it may affect the accuracy of the test results and reduce the short-circuit capacity of the test equipment. However, if the impedance voltage is too small, the short-circuit current may increase when the test product breaks down or flashovers. The impedance voltage of the transformer is generally 4.5~10%, and when multiple cascades are formed, it can reach 30~40%.

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