Product Details

20KVA/100KV AC/DC Test Transformer

The test transformer coil adopts a concentric cylindrical multi-layer tower structure. The primary low-voltage winding is wound on the iron core, and the secondary high-voltage winding is wound outside the low-voltage winding. This coaxial arrangement reduces the coupling loss between windings. The high-voltage silicon stack is encapsulated in the bushing with special technology, and the product shell is made into an octagonal structure that fits well with the core, making the overall appearance beautiful and elegant.

20KVA/100KV AC/DC Test Transformer

2. Product Structure

   The iron core is a single-frame type. The coil adopts a concentric cylindrical multi-layer tower structure. The primary low-voltage winding is wound on the iron core, and the secondary high-voltage winding is wound outside the low-voltage winding. This coaxial arrangement reduces the coupling loss between windings. The high-voltage silicon stack is encapsulated in the bushing with special technology, and the product shell is made into an octagonal structure that fits well with the core, making the overall appearance beautiful and elegant. Its internal and external structure is shown in Figure 1.

Product model meaning:

Y  D  Q   C（  ）—□ / □

                         Figure 1: Structural schematic diagram
  1- Voltage equalizing ball; 2- Silicon stack short-circuit rod; 3- High-voltage bushing; 4- Oil valve; 5- Shell; 6, 7- Adjusting voltage input a, x terminals; 8, 9- Instrument measurement E, F terminals; 10- High-voltage tail X terminal; 11- Transformer shell grounding terminal; 12- High-voltage output A terminal; 13- High-voltage rectifier silicon stack; 14- Internal voltage equalizing ring; 15- Transformer iron core; 16- Primary low-voltage winding; 17- Measuring instrument winding; 18- Secondary high-voltage winding; 19- Transformer oil.

3. Working Principle

    It is a single-phase transformer with connection group label II. The working process of a single transformer: use AC 220V (above 10KVA is 380V) voltage to connect to the power control box (console), adjust the voltage from 0 to 200V (above 10KVA is 0~400V) to the primary winding of the test transformer through the built-in auto-transformer (above 50KVA the voltage regulator is external) in the power control box (console). According to the principle of electromagnetic induction, the required high voltage for testing can be obtained on the high-voltage winding of the transformer. Its working principle diagram is shown in Figure 2.

  1. Working principle schematic diagram

                           Figure 2 : Working principle schematic diagram
In the test transformer: a, x are low-voltage input terminals; A, X are high-voltage output terminals; E, F are instrument measurement terminals.
 2. The working principle of a single AC/DC dual-purpose transformer is shown in Figure 3. 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 using three transformers in series to obtain higher voltage is shown in Figure 4. Series transformers have great advantages because the entire test device is composed of multiple single series-excited 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 has low investment and is economical. As shown in Figure 3: In the series use of three series-excited test transformers, the output voltage of each single transformer B1, B2, B3 is U. The first and second 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 test transformer B2, and the excitation winding A2, C2 of the second-stage test transformer B2 supplies power to the primary winding of 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.

                 Figure 3: Schematic diagram of the series excitation working principle of three high-voltage test transformers
B1, B2, B3- Series-excited high-voltage transformers; 1U, 2U, 3U- Voltage to ground at each stage;
PV- High-voltage indicator meter (KV); ZJ1, ZJ2- Insulating supports.

LYYD-20KVA/100KV AC/DC Test Transformer

4. Usage Methods and Precautions    

 1. The wiring method for power frequency withstand voltage test 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. In order 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.

                      Figure 4: Schematic diagram of wiring principle for power frequency withstand voltage test
R1, R2- Current limiting resistors; Qx- Discharge ball gap; Zx- Test object;
FRC- Resistive-capacitive voltage divider; V- Voltage divider high-voltage meter. 
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 (console) must be reliably grounded.
When using three test transformers in series 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 body of the second and third-stage test transformers must be placed on insulating supports. Except for the first stage, the main body 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 (console) 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 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, and closely observe the indication of the measuring instrument 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, 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 cord, and the test is completed.

Precautions during power frequency withstand voltage test operation

1. Test personnel should divide responsibilities, set the safe distance at the test site, carefully check the grounding of the test object and 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 absolutely dry to avoid damage to the test object and errors in test values.
3. For tests on large equipment, generally the no-load test of the test transformer should be carried out first, i.e., boost to the test voltage without connecting the test object, in order 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 failure 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 process, if the following abnormal conditions are found: 1. The voltage and current meter pointers 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 should be cut off, the test should be stopped, and the cause should be 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. The wiring method for DC withstand voltage and leakage test 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 principle 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, and 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. In order 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. 

                      Figure 5: Schematic diagram of wiring principle for DC leakage test
R- Current limiting resistor; C- High-voltage filter capacitor; Zx- Test object; G- Silicon stack short-circuit rod;
FRC- Resistive-capacitive voltage divider; V- Voltage divider high-voltage meter; uA- Microammeter; D- High-voltage rectifier silicon stack.
According to Figure 5, combined with Figure 3, connect the working circuit for the DC leakage 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 (console) must be reliably grounded.

                           Wiring schematic diagram

                                Wiring schematic diagram
 Before connecting the power supply, the voltage regulator of the power control box (console) 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 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 the rated test voltage you need or the reference voltage under the rated DC current at the selected boosting speed. During the test, close attention should be paid to the indications of the DC high-voltage meter, leakage current meter, and the condition of the test object. After the test is completed, the high voltage should be quickly and uniformly reduced to zero, press the stop button, the high-voltage and low-voltage outputs stop, then cut off the power supply. At this time, a DC high-voltage discharge rod should be used to fully discharge the test object and the test device itself.

Precautions

(1) Test personnel should divide responsibilities, set the safe distance at the test site, carefully check the grounding of the test object and test transformer, and have a dedicated person to monitor safety and observe the condition of the test object.
(2) Before testing the test object, all external connections should be removed, and it should be fully discharged. The main parts should be cleaned and kept absolutely dry to avoid damage to the test object and errors in test values.
(3) For large-capacity test objects (capacitors, ultra-long cables, etc.), the voltage should be increased slowly during the test to prevent the charging current of the test object from being too large and burning out the microammeter. If necessary, the voltage should be increased in stages and the stable readings of the microammeter at each voltage level should be recorded separately.
(4) During the test, the test object, microammeter, and test device should be closely monitored. Once flashing, breakdown, or other phenomena occur, the voltage should be immediately reduced, the power should be cut off, and the cause should be investigated.

5. Optional Supporting Products

The following products are for selection only, and need to be priced separately when purchasing.
1. KZX series power control box  Capacity: 1KVA-5KVA, Input voltage: 220V
2. KZT series power control console  Capacity: 10KVA~300KVA, Input voltage: 220V or 380V
3. Digital microammeter: SWB-II
4. High-voltage filter capacitor: 0.01MF, 40 ~ 100KV
5. High-voltage DC discharge rod: FBR— 70, 140, 210KV
6. Discharge ball gap: Q—50, 100, 150, 200, 250, 500
7. Standard test oil cup: 400ml
8. Folding handcart: 150, 300 type
9. Insulating support: 50, 100, 200, 300, 400KV
10. Resistive-capacitive voltage divider: FRC—50, 100, 150, 200KV
11. High-voltage silicon stack: 2DL—150, 300, 450KV
12. Water resistor: 50, 100