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LYYD-5KVA/100KVAC/DC Test Transformer
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I. Product Overview
The test transformer is a new type of product improved from the same type YDJ (G) series high-voltage test transformer, in accordance with the national standard ZBK41006—89 for test transformers. This series has the characteristics of small size, light weight, compact structure, complete functions, and convenient use. It is suitable for power, industrial, mining, scientific research and other departments, for power frequency withstand voltage test and DC leakage test on various high-voltage electrical equipment, electrical components, and insulating materials. It is an indispensable instrument in high-voltage testing.
II. Product Structure
Test transformer iron core is single-frame type. The coil adopts 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 process. The outer shell of the product is made into an octagonal structure that matches the core well, and the overall appearance is beautiful and generous. Its internal and external structure is shown in Figure 1.
Product model meaning
Figure 1: YDQC AC Withstand Voltage Test Transformer Structure Diagram
1-Voltage equalizing ball; 2-Silicon stack short-circuit rod; 3-High-voltage bushing; 4-Oil valve; 5-Housing; 6,7-Adjusting voltage input terminals a, x; 8,9-Instrument measurement terminals E, F; 10-High-voltage tail terminal X; 11-Transformer shell grounding terminal; 12-High-voltage output terminal A; 13-High-voltage rectifier silicon stack; 14-Internal voltage equalizing ring; 15-Transformer iron core; 16-Primary low-voltage winding; 17-Measurement instrument winding; 18-Secondary high-voltage winding; 19-Transformer oil.
III. Working Principle
Test transformer is a single-phase transformer with connection group label II. The working process of a single high-voltage test transformer: AC 220V (above 10KVA is 380V) voltage is connected to the power control box (console), and the voltage is adjusted to 0~200V (above 10KVA 0~400V) by the auto-transformer (above 50KVA external) inside the power control box (console) to the primary winding of the test transformer. According to the principle of electromagnetic induction, the high voltage required for the test can be obtained in the high-voltage winding of the test transformer. Its working principle diagram is shown in Figure 2.
1. Schematic diagram of the working principle of a single YDQC high-voltage test transformer
Figure 2: Schematic diagram of the working principle of a single YDQC AC Withstand Voltage Test Transformer
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 high-voltage test transformer is shown in Figure 3. In the figure: the high-voltage bushing contains a high-voltage silicon stack, 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 high-voltage test transformers is shown in Figure 4. The cascaded high-voltage test 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 has low investment and is economical. As shown in Figure 3: In the cascaded use of three cascaded test transformers, the output voltage of each single test transformer B1, B2, B3 is U. The first and second stage test transformers have an excitation winding inside, respectively A1, C1 and A2, C2. When the control voltage is applied to the primary winding a1, x1 of the first stage test 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 test transformer B1 are grounded, the second and third stage test transformers B2 and B3 are isolated from the ground by insulating supports, so the output voltages of test transformers B1, B2, B3 to ground are 1U, 2U, 3U respectively.
Figure 3: Schematic diagram of the cascaded working principle of three high-voltage test transformers
B1, B2, B3- Cascaded high-voltage transformers; 1U, 2U, 3U- Voltage to ground at each stage;
PV- High-voltage indicator meter (KV); ZJ1, ZJ2- Insulating supports.
IV. Usage Methods and Precautions
1. YDQC AC Withstand Voltage Test Transformer 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 distance 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- 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 (console) 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 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 the voltage. (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. When the high voltage drops 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 safety distance of 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 state 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 a no-load boost test of the test transformer should be carried out first, that is, 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 distance 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, and sudden power failure should also be prevented. Generally, the switch should be opened after the voltage regulator is reduced to zero.
5. During the boosting or withstand voltage test, 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 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, national standards and operating procedures must be strictly implemented.
2. YDQC AC Withstand Voltage Test Transformer wiring method for DC withstand voltage and leakage test is shown in Figure 5. Since it is an AC/DC dual-purpose high-voltage test transformer, the high-voltage silicon stack short-circuit rod should be pulled out from the bushing to make the test 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, 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- High-voltage meter of the divider; 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.
YDQC Test Transformer Wiring Principle Diagram for AC Test
YDQC Test Transformer Wiring Principle Diagram for AC Leakage Test
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 the voltage. (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 required rated test voltage or the reference voltage under the rated DC current at the selected boosting speed. During the test, closely observe the indication of the DC high-voltage meter, leakage current meter, and the condition of the test object. After the test is completed, quickly and uniformly reduce the high voltage to zero, press the stop button, the high-voltage and low-voltage outputs stop, and then cut off the power supply. At this time, use a DC high-voltage discharge rod to fully discharge the test object and the test device itself.
Precautions during DC leakage test operation
(1) Test personnel should divide responsibilities, set the safety distance of 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 state of the test object.
(2) Before testing the test object, all external connections should be removed, and 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, apply voltage in stages and read the stable readings of the microammeter at each voltage level.
(4) During the test, closely monitor the test object, microammeter, and test device. Once flashing, breakdown, or other phenomena occur, immediately reduce the voltage, cut off the power, and investigate the cause.
V. Optional Products
The following products are for selection only and are priced separately when purchased.
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 oil test 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&mda
Yangzhou Darui Electric Co., Ltd.
主营产品：Dielectric Loss Tester、Transformer Ratio测试仪、Loop Resistance Tester、高压None线核相仪、Insulation Resistance Tester、Partial Discharge Tester、Cable Fault Tester、DC Resistance Tester等。
☎ Phone: 18952707000（关经理）📞 Landline: 0514-88770377✉ Email: 195214804@qq.com
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