15KVA/50KV AC/DC Withstand Voltage Test Device
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Overview:
The high-voltage test transformer is designed and produced based on the "Test Transformer" standard, on the basis of oil-immersed test transformers. SF6 gas has good electrical insulation properties and excellent arc extinguishing performance. Its withstand voltage strength is 2.5 times that of nitrogen at the same pressure, and its breakdown voltage is 2.5 times that of air. At 0.25MPa, it is equal to the breakdown voltage of oil, and at 0.45MPa, it is twice the breakdown voltage of oil. It is a new generation of ultra-high voltage insulation dielectric material replacing oil. The technical requirements of this product fully comply with the "ZBK-41006-89" standard. It is a replacement product for oil-immersed light test transformers. This product has the characteristics of small size, light weight, not affected by climate change, small corona, no need to stand still after on-site handling, long service life, and maintenance-free. It is suitable for power systems, industrial and mining enterprises, scientific research departments, etc. to conduct power frequency or DC high-voltage insulation strength tests on various high-voltage electrical equipment, electrical components, and insulating materials.
Product Structure:
The high-voltage test transformer adopts a single-frame core-type iron core structure. The primary winding is wound on the iron core, and the high-voltage winding is on the outside. This coaxial arrangement reduces leakage flux, thereby increasing the coupling between windings. The shell of the product is a cylindrical pot-type container structure, which can withstand pressures above 0.8MPa.
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Working Principle:
The YDQ series high-voltage test transformer is a single-phase transformer with connection group label Ⅰ.Ⅰ. Use power frequency 220V (above 10kVA is 380V) power supply to connect to (special equipment matching the test transformer produced by our company, please refer to its specific instruction manual for details) series operation box (table), adjust through the auto-transformer inside the operation box (above 50kVA the voltage regulator is external) to output 0～200V (or 0～400V) voltage to the primary winding of the YDQ test transformer. According to the principle of electromagnetic induction, the required high voltage for testing can be obtained on the high-voltage winding of the test transformer. The working principle diagram of a single YDQ series AC/DC high-voltage test transformer is shown in Figure 3. In the figure, a high-voltage silicon stack is installed in the high-voltage bushing, connected in series in the high-voltage circuit for half-wave rectification to obtain DC high voltage. When a short-circuit rod is used to short-circuit the high-voltage silicon stack, power frequency high voltage can be obtained as the AC output state; when the short-circuit rod is removed, it is the DC output state. The cascade high-voltage test transformer has great advantages because the entire test device is composed of several single test transformers. The single test transformer has small capacity, low voltage, light weight, and is easy to transport and install. It can be connected in series to combine outputs several times higher than a single test transformer, or it can be separated into several sets of single test transformers for independent use. The entire device has low investment and is economical. In the first and second stages, each unit test transformer has an excitation winding A1, C1 and A2, C2. In the basic principle of three cascade test transformers, the low-voltage power supply is applied to the primary winding a1x1 of test transformer I, and the output voltages of single test transformers I, II, and III are all V. The excitation winding A1, C1 supplies power to the primary winding of the second-stage test transformer II; the excitation winding A2, C2 of the second-stage test transformer II supplies power to the primary winding of the third-stage test transformer III. The boxes of the second-stage test transformer II and the third-stage test transformer III are respectively at high potentials of 1V and 2V to ground, so the boxes are insulated from ground, and the box of test transformer I is grounded. In this way, the rated output voltages to ground of the first, second, and third-stage test transformers are 1V, 2V, and 3V respectively; their rated capacities are 3P, 2P, and 1P respectively. In the power frequency withstand voltage test, the current-limiting resistor R1 should be selected according to the rated capacity of the test transformer. If the rated output current on the high-voltage side is 100～300mA, 0.5～1Ω/V (test voltage) can be taken; if the rated output current on the high-voltage side is above 1A, 1Ω/V (test voltage) can be taken. Commonly use water resistance as the current-limiting resistor. The tube length can be considered as 150kV/m, and the tube thickness should have sufficient heat capacity (water resistance liquid preparation method: use distilled water with an appropriate amount of copper sulfate to prepare various resistance values).
Ball gap and protective resistor: When the voltage exceeds the set value of the ball gap (generally 110%~120% of the test voltage), the ball gap discharges, protecting the test object. The ball gap protective resistor can be selected as 1Ω/V (test voltage).
In the power frequency withstand voltage test, the voltage measured on the low-voltage side (instrument voltage) is not very accurate because the test transformer has leakage reactance, and there must be a voltage drop or capacitive rise on this leakage reactance, making the voltage on the test object lower or higher than the voltage reflected by the voltmeter on the low-voltage side. During the power frequency withstand voltage test, the voltage on the test object is higher than the output voltage of the test transformer, which is the so-called capacitive rise phenomenon. During the induced withstand voltage test, the leakage reactance of the test transformer inevitably has a voltage drop. In order to accurately measure the voltage applied to the test object, an FRC resistive-capacitive voltage divider is often connected to the high-voltage side to measure the voltage.
Note: The above information and technical parameters are compiled and released by Yangzhou Darui Electric Co., Ltd.
