3KVA/100KV AC/DC High Voltage Test Transformer
Darui Electric recommends for you
Working Principle:
The light high-voltage test transformer is a single-phase transformer with connection group label I.I. It uses a two-frequency 220V (above 10KVA, 380V) power supply connected to the series operation box (console). Through the auto-transformer (for above 50KVA, external) inside the operation box, the voltage is adjusted to 0-200V (or 0-400V).
The voltage is output 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 test transformer.
In the power frequency withstand voltage test, the current limiting resistor R1 should be selected based on the rated capacity of the test transformer. If the rated output current on the high-voltage side is 100-300MA, it can be 0.5-1Ω/V (test voltage); if the rated output current on the high-voltage side is above 1A, it can be 1Ω/V (test voltage). Commonly, water resistance is used as the current limiting resistor. The tube length can be considered as 150KV/m, and the tube and its thickness should have sufficient heat capacity (method for preparing water resistance solution: add an appropriate amount of copper sulfate to distilled water to prepare various resistance values).
Sphere gap and protective resistor: When the voltage exceeds the set value of the sphere gap (generally 110%-120% of the test voltage), the sphere gap discharges, protecting the test object. The protective resistor for the sphere gap 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, on which there is inevitably a voltage drop or capacitive rise, causing the voltage on the test object to be lower or higher than the voltage reflected on the low-voltage side voltmeter. 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 must have a voltage drop. To accurately measure the voltage applied to the test object, an RCF resistive-capacitive voltage divider is often connected on the high-voltage side to measure the voltage.
Precautions for power frequency withstand voltage test operation
(1) Test personnel should divide the work and clarify the methods among themselves. There should be a dedicated person to monitor the safety of the site and observe the state of the test object.
(2) The test object should be cleaned and absolutely dry to avoid damage to the test object and errors in the test.
(3) For large-scale tests, a no-load test should generally be conducted first. That is, without connecting the test object, raise the voltage to the test voltage, calibrate various meters, and adjust the gap.
(4) The voltage increase speed should not be too fast, and sudden pressurization must be prevented. For example, sudden closing when the voltage regulator is not at zero position, and sudden cutting off of the power supply should also be avoided. Generally, the switch should be turned off when the voltage regulator is reduced to zero.
(5) When the voltage rises to the test voltage, start timing. After 1 minute, quickly reduce to below 1/3 of the test voltage before cutting off the power.
(6) During the voltage increase or withstand voltage test, if the following abnormal conditions are found, immediately reduce the voltage, cut off the power, stop the test, and find out the cause: ① The voltmeter pointer swings greatly; ② Insulation is found burnt or smoking; ③ Abnormal sounds inside the test object.
(7) Before and after the withstand voltage test, measure the insulation resistance and check the insulation condition.
Operation and precautions for leakage test
(1) Before the test, check whether the test object is de-energized, grounded and discharged, and whether all external connections are clean. Strictly prevent the test voltage from being applied to working parts of the human body.
(2) After connecting the test device wiring, recheck that it is correct before applying voltage. Special attention should be paid to checking the safety distance between high-voltage equipment and leads, and the ground and operators, and whether the shell of the test object is reliably grounded. The test should be carried out according to the contents specified in the safety regulations.
(3) For large-capacitance equipment, the voltage should be increased slowly to prevent the charging current of the test object from burning out the microammeter. If necessary, pressurize in stages and read the stable readings of the microammeter at each voltage level.
(4) During the test, closely monitor the test object, test device, and microammeter. Once abnormal phenomena such as breakdown or flashing occur, immediately reduce the voltage, cut off the power, find out the cause, and record in detail.
(5) After the test, reduce the voltage, cut off the power, and fully discharge the test object and the test device itself.
Precautions
1. Connect the working circuit according to the test you are conducting. The shell of the test transformer and the shell of the operating system must be reliably grounded. The x terminal (high-voltage tail) of the high-voltage winding of the test transformer and the F terminal of the measuring winding must be reliably grounded.
2. When doing cascade tests, the X terminal of the low-voltage winding, the F terminal of the measuring 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 current stage test transformer. The shells of the second and third stage test transformers must be grounded through insulating supports.
3. Before connecting the power supply, the voltage regulator of the operating system must be adjusted to zero before connecting the power, closing the switch, and starting to increase the voltage.
4. From zero, evenly rotate the voltage regulator handwheel to increase the voltage. The voltage increase methods include: fast voltage increase method, i.e., 20S step-by-step voltage increase method; slow voltage increase method, i.e., 60S step-by-step voltage increase method; and extremely slow voltage increase method for selection. The voltage starts from zero and rises to 75% of the required rated test voltage according to a certain voltage increase method and speed, then rises to the required rated test voltage at a rate of 2% of the rated test voltage per second, while closely paying attention to the indications of the measuring instruments and the condition of the test object. If abnormal indications of the measuring instruments or the condition of the test object are found during the voltage increase or test process, immediately reduce the voltage, cut off the power, and find out the situation.
5. After the test, uniformly return the voltage regulator to zero within a few seconds, then cut off the power.
6. This product must not be used beyond the rated parameters. Except for necessary tests, full voltage energization or de-energization is absolutely not allowed.
7. When using this product for high-voltage tests, in addition to being familiar with this manual, you must strictly implement relevant national standards and operating procedures. You can refer to GB311-83 "Insulation Coordination of High Voltage Transmission and Transformation Equipment, High Voltage Test Techniques"; "Preventive Test Regulations for Electrical Equipment", etc.
Supporting Products
1. Operating system:
XZC series operation box: Capacity: 1KVA-5KVA, Input voltage: 0.22KV
KZT series operation console: Capacity: 10K/A-300KVA, Input voltage: 0.22KV, 0.38KV
2. Protective digital microammeter SWB-Ⅱ
3. Resistive-capacitive AC/DC voltage divider FYQ-50, 100, 150, 220KV
4. High-voltage DC discharge rod FZ-70, 140, 210KV
5. High-voltage silicon stack: 2DL-150, 300, 450KV
6. Insulating support 50, 100, 200, 300KV
7. High-voltage filter capacitor 0.01UF, 40-100KV
8. Voltage equalizing ball
9. Protective sphere gap: Q-50, 100, 150, 200, 250, 500
10. Standard oil test cup 400ml
11. Dielectric oil cup
12. Folding trolley 150, 300 type
13. Water resistor
14. High-voltage electroscope 10KV, 35KV
15. High-voltage phase detector 10KV, 35KV/110KV, 220KV
16. Various multimeters, megohmmeters, and test leads
7. Capacity selection of test transformer:
The formula for determining the standard test transformer capacity Pn: Pn=KVn2ωct×10-9.
Where: Pn—nominal test transformer capacity (KVA)
Vn—effective value of the rated output high voltage of the test transformer (KV)
K—safety factor. K≥1, when the nominal voltage Vn≥1MV, K=2, when the nominal voltage is lower, the K value can be taken higher,
ct—capacitance of the test object (PF)
ω—angular frequency, 2лf. F - frequency of the test power supply.
The capacitance ct of the test equipment can be measured by an AC bridge. Ct varies greatly and can be determined by the type of equipment.
Typical data are as follows:
Simple rod or suspension insulators tens of microfarads
Simple graded bushings 100-1000PF
Voltage transformers 200-500PF
Voltage transformers <1000KVA -1000PF
>1000KVA 1000-10000PF
High-voltage power cables and oil-impregnated paper insulation 250-300PF/m
Gas insulation -60PF/m
Enclosed substations, SF6 gas insulation 100-10000PF
For different test voltages Vn, select different (appropriate) safety factors K. The following lists the K values selected for different Vn for reference.
Vn=50-100KV K=4
Vn=150-300KV K=3
Vn>300KV K=2
Main Technical Parameter Table of Test Transformer
(1) Light AC/DC test transformer (see Table 1)
(2) Light AC/DC test transformer (see Table 2)
Table 1, Light AC/DC test transformer
|
Model
|
Capacity
|
High Voltage (KV)
|
High Voltage Current (mA)
|
Low Voltage Input
|
Ratio
|
Temperature Rise ℃
|
|
(KVA)
|
AC
|
DC
|
AC
|
DC
|
Voltage (V)
|
Current (A)
|
High/Instrument
|
30 minutes
|
|
1.5/50
|
1.5
|
50
|
70
|
30
|
15
|
200
|
7.5
|
500
|
10
|
|
3/50
|
3
|
50
|
70
|
60
|
15
|
200
|
15
|
500
|
10
|
|
5/50
|
5
|
50
|
70
|
100
|
15
|
200
|
25
|
500
|
10
|
|
10/50
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
| | 
