50KVA/150KV High Voltage Withstand Test Complete Set
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Working Principle
1. It is a single-phase transformer with connection group label II. The working process of a single transformer: AC 220V (380V for above 10KVA) is connected to the power control box (cabinet), and the voltage is adjusted to 0~200V (0~400V for above 10KVA) by the auto-transformer (external for above 50KVA) inside the power control box (cabinet), which is then applied to the primary winding of the 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 transformer.
2. The working principle of a single AC/DC dual-purpose transformer is shown in Figure 3. As shown in the figure: a high-voltage silicon stack is installed inside the high-voltage bushing, connected in series in the high-voltage circuit for high-voltage rectification to obtain DC high voltage. When a short-circuit rod is used to short-circuit the high-voltage silicon stack, AC high voltage can be obtained, and its state is AC output; conversely, when the short-circuit rod is pulled out, its state is DC output.
3. The principle of obtaining higher voltage by cascading three transformers: The cascaded transformer has great advantages because the entire test device is composed of multiple single cascaded test transformers. A single test transformer has the characteristics of small size, light weight, and easy transportation. It can be used in series to combine output voltages several times higher than a single test transformer, or it can be used separately. The entire test device is low-cost and economical. As shown in Figure 3: In the cascaded use of three cascaded test transformers, the output voltage of each single transformer B1, B2, B3 is U. The second and third stage test transformers each have an excitation winding, namely A1, C1 and A2, C2. When the control voltage is applied to the primary winding a1, x1 of the first stage transformer B1, the excitation winding A1, C1 supplies power to the primary winding of the second test transformer B2, and the excitation winding A2, C2 of the second stage test transformer B2 supplies power to the primary winding of the third test transformer B3. Since the high-voltage tail and shell of the first stage transformer B1 are grounded, the second and third stage transformers B2 and B3 are isolated from the ground by insulating supports, so the output voltages of transformers B1, B2, B3 to ground are 1U, 2U, 3U respectively.
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Usage Methods and Precautions
1. For power frequency withstand voltage test, the wiring method is shown in Figure 5. Before the power frequency withstand voltage test, first select the resistance value of the current limiting resistor (water resistor) according to the rated capacity of the test transformer, then adjust the ball gap spacing of the discharge ball gap according to the high voltage value to be applied to the test object. To improve the measurement accuracy of the voltage applied to the test object, an FRC resistive-capacitive voltage divider should be connected on the high-voltage side to measure the voltage.
R1, R2- Current limiting resistors; Qx- Discharge ball gap; Zx- Test object;
FRC- Resistive-capacitive voltage divider; V- High voltage meter of the divider.
According to Figure 4, combined with Figure 2, connect the working circuit for the power frequency withstand voltage test. The X terminal (high-voltage tail) of the high-voltage winding of the test transformer, the F terminal of the instrument measurement winding, the shell of the test transformer, and the shell of the power control box (cabinet) must be reliably grounded.
When using three test transformers in cascade for power frequency withstand voltage test, the X terminal of the primary winding, the F terminal of the instrument measurement winding, and the X terminal (high-voltage tail) of the high-voltage winding of the second and third stage test transformers are all connected to the shell of the respective stage test transformer. The main bodies of the second and third stage test transformers must be placed on insulating supports. Except for the first stage, the main bodies of the second and third stage test transformers should not be grounded. The wiring method is shown in Figure 3.
Before connecting the power supply, the voltage regulator of the power control box (cabinet) must be adjusted to zero. After connecting the power supply, the green indicator light is on. Press the start button, the red indicator light is on, indicating that the test transformer has been connected to the control power supply and starts to boost voltage.
From the zero position, rotate the voltage regulator handwheel clockwise at a uniform speed to boost the voltage. (The boosting methods include: fast boosting method, i.e., 20S step-by-step boosting method, slow boosting method, i.e., 60S step-by-step boosting method, and extremely slow boosting method for selection) The voltage starts from zero and rises to 75% of the rated test voltage you need at the selected boosting speed, then rises to the required test voltage at a speed of 2% of the rated test voltage per second, while closely observing the indication of the measuring instruments and the condition of the test object. After the time of applying voltage to the test object is reached, the voltage regulator should be returned uniformly within a few seconds, and the high voltage should be reduced to below 1/3 of the test voltage. Press the stop button, the high voltage and low voltage outputs stop, then cut off the power line, and the test is completed.
Precautions for Power Frequency Withstand Voltage Test Operation Process
1. Test personnel should divide responsibilities clearly, set the safety distance at the test site, carefully check the grounding of the test object and the test transformer, and have a dedicated person to monitor safety and observe the condition of the test object.
2. The main parts of the test object should be cleaned and kept dry to avoid damage to the test object and errors in test values.
3. For tests on large equipment, a no-load test of the test transformer should generally be conducted first, i.e., boosting to the test voltage without connecting the test object, to calibrate the indication accuracy of the instruments and adjust the ball gap spacing of the discharge ball gap.
4. During the withstand voltage test, the boosting speed should not be too fast, and sudden pressurization should be prevented, such as sudden closing when the voltage regulator is not at zero position, and sudden power off should also be prevented. Generally, the switch should be opened after the voltage regulator is reduced to zero position.
5. During the boosting or withstand voltage test, if the following abnormal conditions are found: 1. The pointers of the voltage and current meters swing greatly, 2. The test object makes abnormal sounds, 3. Insulation is found to be burnt or smoking, the voltage should be immediately reduced, the power cut off, the test stopped, and the cause investigated.
6. When using this product for high voltage tests, in addition to being familiar with this manual, the relevant national standards and operating procedures must be strictly implemented. 2. For DC withstand voltage and leakage tests, the wiring method is shown in Figure 5. Since it is an AC/DC dual-purpose transformer, the high-voltage silicon stack short-circuit rod should be pulled out from the bushing to make the transformer in DC output state. Before the DC leakage test, first select the resistance value of the current limiting resistor (water resistor) according to the requirement that the open-circuit current at the output end during the leakage test does not exceed the maximum rectification of the high-voltage silicon stack, then select the capacitance value of the high-voltage filter capacitor according to the requirements of the test object for the DC high voltage waveform. To improve the measurement accuracy of the voltage applied to the test object, an FRC resistive-capacitive voltage divider should be connected on 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.
