Series Resonant Transformer
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With the development of power electronics technology, it has become possible to conduct power frequency withstand voltage tests on large-capacity electrical equipment using high-voltage resonance technology. It has been widely used for AC tests on power equipment with large capacitance such as cables, capacitors, generators, etc.. The principle is to obtain a continuously variable inductance L by adjusting the air gap length of the iron core magnetic circuit, causing it to resonate with the ground capacitance C of the test object. This article uses a 150kVA test device as a model to explain the principle and calculation of relevant parameters of the high-voltage resonant transformer.
Advantages of Series Resonance
1. The required power supply capacity is greatly reduced. The series resonant power supply uses the resonance between the resonant reactor and the test object's capacitance to generate high voltage and large current. In the entire system, the power supply only needs to provide the active power consumption part of the system. Therefore, the power required for the test is only 1/Q of the test capacity.
2. The weight and volume of the equipment are greatly reduced. In the series resonant power supply, not only the bulky high-power voltage regulation device and ordinary high-power power frequency test transformer are omitted, but also the resonant excitation power supply only needs 1/Q of the test capacity, greatly reducing the system weight and volume, generally 1/3 to 1/5 of ordinary test devices.
3. Improve the waveform of the output voltage. The resonant power supply is a resonant filter circuit that can improve the waveform distortion of the output voltage, obtain a good sine waveform, and effectively prevent harmonic peaks from causing false breakdown of the test object.
4. Prevent large short-circuit currents from burning the fault point. In the series resonance state, when the insulation weakness of the test object is broken down, the circuit immediately detunes, and the loop current rapidly drops to 1/Q of the normal test current. In contrast, when using parallel resonance or test transformer method for withstand voltage tests, the breakdown current immediately rises dozens of times. Comparing the two, the short-circuit current and breakdown current differ by hundreds of times. Therefore, series resonance can effectively find insulation weaknesses without the concern of large short-circuit currents burning the fault point.
5. No recovery overvoltage will occur. When the test object breaks down, due to the loss of resonance conditions, the high voltage immediately disappears, the arc can be extinguished, and the recovery voltage establishment process is very long, making it easy to disconnect the power supply before reaching the flashover voltage again. This voltage recovery process is an intermittent oscillation process of energy accumulation, with a long duration, and no recovery overvoltage will occur.
Series Resonance Configuration Table
Model interpretation: 44/22, capacity 44KVA, voltage 22KV
I. Cable AC Withstand Voltage Test
Model |
Test Items Satisfied |
Equipment Reactor |
|
100/50 |
10kV (300mm) cable 1KM |
22kV Ⅹ 1 unit |
Portable |
160/40 |
1. 10kV (300mm) cable 3KM
2. 35kV (300mm) cable 1KM |
22kV Ⅹ 3 units |
Portable |
216/54 |
1. 10kV (300mm) cable 5KM
2. 35kV (300mm) cable 2KM
3. 35kV transformers, switches,
4. 10kV motors, transformers
5. Generators up to 600MW and below, etc. |
22kV Ⅹ 6 units |
Portable |
324/32 |
110kV (300mm) cable 3KM |
130kV Ⅹ 2 units |
Non-portable |
II. Generator Power Frequency Withstand Voltage Test
Model |
Test Items Satisfied |
Equipment Reactor Configuration |
Remarks |
100/50 |
1. Generators up to 100MW and below, phase capacitance 0.1-0.3uF
2. 10kV (300mm) cable 1KM |
22kV Ⅹ 1 unit |
Portable |
160/40 |
1. Generators up to 600MW and below, phase capacitance 0.1-0.25uF
2. 10kV (300mm) cable 1.5KM |
18kV Ⅹ 2 units |
Portable |
216/54 |
1. Generators up to 600MW and below, phase capacitance 0.1-0.3uF
2. 10kV (300mm) cable 3KM 3. Can also cover generator busbars, main transformers, etc. |
22kV Ⅹ 4 units |
Portable |
III. GIS and SF6 Switch AC Withstand Voltage Test
Model |
Test Items Satisfied |
Reactor Configuration |
Remarks |
216/54 |
1. AC withstand voltage test for 110kV GIS
2. 35kV (300mm) cable 1KM
3. 10kV (300mm) cable 3KM
4. Power frequency withstand voltage for transformers below 220kV 5. AC withstand voltage for 110kV instrument transformers |
40kV Ⅹ 5 units |
Portable |
100/50 |
1. AC withstand voltage test for 110kV GIS 2. AC withstand voltage for 110kV instrument transformers |
50kV Ⅹ 4 units |
Portable |
IV. Power Frequency AC Withstand Voltage Test for Transformers, Motors, and Other Equipment
Model |
Test Items Satisfied |
Reactor Configuration |
Remarks |
216/54 |
1. Power frequency withstand voltage test for 110kV transformers
4. 10kV (300mm) cable 1KM |
28kV Ⅹ 3 units |
Portable |
100/50 |
1. Power frequency withstand voltage test for 110kV transformers
2. Power frequency withstand voltage test for 10kV motors 3. AC withstand voltage test for 35kV switches
4. 10kV (300mm) cable 1KM |
40kV Ⅹ 2 units |
Portable |
Note: The above information and technical parameters are compiled and released by Yangzhou Darui Electric Co., Ltd.
