Communication withstand voltage test? Wuhan UHV specializes in producing series resonant devices with a wide range of product options. When looking for a series resonant device, choose Wuhan UHV.         

The AC withstand voltage test is the most direct method for evaluating the insulation strength of electrical equipment. It has a decisive significance in determining whether the electrical equipment can be put into operation and is also an important means to ensure the insulation level of the equipment and avoid insulation accidents. Because the AC withstand voltage test can fully reflect the actual situation of electrical equipment operating under AC voltage, and can truly and effectively detect insulation defects.         

The AC withstand voltage test is a destructive test. Before the test, the insulation resistance, absorption ratio, leakage current, dielectric loss angle and other items of the tested object must be tested first, and the AC withstand voltage test can be carried out only after the test results are normal. If the equipment insulation is found to be in poor condition, the withstand voltage test should be carried out after progressiveness treatment to avoid unnecessary insulation breakdown.

1. Generation of AC test voltage

High frequency high voltage is usually generated using high-voltage test transformers. For test samples with large capacitance, a series resonant circuit can be used to generate high voltage;          

For test samples with windings such as power transformers and voltage transformers, a 100-300Hz intermediate frequency power supply can be used to excite the low-voltage winding and induce high voltage in the high-voltage winding.

1.1 High Voltage Test Transformer Circuit

The wiring for the AC withstand voltage test should be determined based on the voltage, capacity, and actual test equipment conditions of the tested object on site. Usually, the test transformer is a complete set of equipment. Figure 1 shows a typical experimental wiring.

Figure 1 Power frequency withstand voltage principle test diagram

Ty - regulator; T-test transformer; R - current limiting resistor; R-ball gap protection resistor;

G - Ball gap; Cx - test substance; C1, C2- high and low voltage arms of capacitive voltage dividers; V - voltmeter

When conducting AC withstand voltage tests on test objects with large capacitance such as transformers and capacitors, the capacity of the test transformer is often difficult to meet the test requirements, and reactors are often used in parallel for compensation on site. When the parameters are selected appropriately to make the capacitance and inductance of the two parallel branches equal, the circuit is in parallel resonance state, and the load of the test transformer is minimized at this time. Special attention should be paid to the use of parallel resonant circuits, and overcurrent protection devices should be installed on the test transformer, because when the tested object breaks down, resonance disappears and there is a risk of overcurrent in the test transformer.

1.2 Series resonant circuit

To conduct AC withstand voltage tests on SF6 composite electrical appliances (GIS), generators, transformers, and other test objects with large capacitance, large capacity testing equipment is required. A series resonance testing device can be used, which can test larger capacitance and higher test voltage test objects with a smaller power supply capacity. The circuit consists of the load capacitance of the test object, the reactor connected in series with it, and the power supply, as shown in Figure 2.

Figure 2 Schematic wiring diagram of series resonant circuit

1.3 Medium frequency power supply device

The induction withstand voltage test and partial discharge test of transformers require an intermediate frequency power supply. The main ways to obtain intermediate frequency power supply on site include: complete sets of intermediate frequency power supply units, triple frequency power supply units, intermediate frequency synchronous generator units, and electronic frequency converters. For large-scale transformer testing, the most commonly used equipment on site is the complete set of intermediate frequency power supply units.