Power transformer high voltage test method

1, power transformer high voltage test method

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Power transformer high-voltage test method:

(1) according to the power transformer wiring schematic diagram for the connection of the lead, and to ensure that the transformer and the control box grounding safety, reliability;

(2) before the power transformer high-voltage test, carefully check whether the parts of the wiring contact is good, and check whether the regulator in the control box is adjusted to “zero”.

(3) in the power transformer connected to the power supply, the green indicator light, you can press the start button; red indicator light, waiting for the voltage;

(4) test personnel clockwise, rotate the handle of the regulator in the control box at a constant speed, slowly boosting, and closely observe the changes in the indication of the meter and the operation of the test specimen;

(5) power transformer high-voltage test is completed, quickly adjust the voltage to zero, and press the stop button and cut off the power supply, unlock the test leads connected.

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2, power transformer high voltage test content

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In order to ensure the accuracy and authenticity of the results of the power transformer high-voltage test, must be in strict accordance with the relevant provisions, reasonable selection of the test content. Power transformer high-voltage test content mainly includes: insulation resistance measurement, leakage current measurement, dielectric loss factor test, AC withstand voltage test, etc., the following specific introduction.

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2.1 insulation resistance measurement

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In the high-voltage test of power transformer, insulation resistance measurement is the most convenient and simple preventive test. In the insulation resistance measurement of the transformer, the insulation of the overall degree of moisture, overheating aging degree, filth, etc. can be reflected with the size of the insulation resistance. To a high voltage side voltage 110 kV, capacity 31 500 kVA transformer insulation resistance measurement, for example, the absorption ratio of insulation and temperature change has a close relationship, when the temperature reaches 35 ℃ or more, the absorption ratio of dry insulation reaches the limit and then began to decline, while the absorption ratio of damp insulation will occur irregular changes. Therefore, in the insulation resistance measurement of the transformer, the temperature of the test room must be reasonably controlled to ensure the authenticity of the measured insulation absorption ratio.

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2.2 Measurement of leakage current

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In the power transformer leakage current measurement, mainly using digital leakage current tester for measurement, its rated working voltage is generally below 2.5kV, significantly lower than the rated working voltage of the transformer. If the use of DC megohmmeter can not meet the test for the voltage requirements, you can take the DC high voltage test method to ensure the accuracy of the transformer leakage current measurement results. In the case of high voltage, if the transformer leakage current is significantly higher than the current in the case of low voltage, it indicates that the transformer's high-voltage insulation resistance is less than the low-voltage insulation resistance, that is, there are quality defects in the transformer itself, the anti-leakage function can not meet the use of requirements.

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2.3 partial discharge test

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Power transformer partial discharge test is a common “non-destructive” test items, test methods are: (1) frequency withstand voltage as a pre-excitation voltage, down to the partial discharge test voltage, duration of 10 ~ 15 min, measure the partial discharge; (2) to simulate the operation of overvoltage as a pre-excitation voltage, down to the partial discharge test voltage, duration of 10 ~ 15 min, measure the amount of partial discharge; (2) to simulate the operation of the overvoltage as a pre-excitation voltage, down to the partial discharge test voltage, duration of 10 ~ 15 min, measure the amount of partial discharge. to the partial discharge test voltage for 1～1.2 h, and measure the partial discharge quantity.

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The second test method can measure the transformer in the long-term working voltage, whether the partial discharge phenomenon, in order to ensure the safe operation of power transformers in the application. In addition, in the partial discharge test of power transformer, insulation structure design, insulation medium to withstand the field strength, charged and grounded electrode surface field, insulation parts processing and technology processing and so on to make the partial discharge is less than the specified value to consider, rather than to the main, longitudinal insulation whether the discharge as the main basis.

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In the partial discharge test of power transformer, the frequency withstand voltage as the pre-excitation voltage, the duration of the test voltage is about 15 min, appropriately extend the voltage duration of the partial discharge test, the insulation performance test has a certain role, if the transformer's insulation performance is not ideal, may cause different degrees of destructive damage. To simulate the operation of the overvoltage as a pre-excitation voltage, partial discharge test voltage duration standard requirements for 1h, the transformer can withstand how long the pre-excitation voltage and the insulation structure of the volt-second characteristic has a close connection.

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In the partial discharge test of power transformer, the amount of partial discharge is usually related to the field strength of the charged and grounded electrode surface, while there is no correlation with the frequency of the power supply, so the noise of the test site should be controlled as much as possible, and the amount of partial discharge of the power supply should also be isolated.

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?2.4 Measurement of transformer turn ratio

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Power transformer transformer ratio measurement methods are: double voltmeter method, transformer ratio bridge method, etc., of which the transformer ratio bridge method is commonly used in the field test method, which mainly has the following advantages: not subject to the limitations of the degree of stability of the power supply; accuracy and sensitivity is high; error can be read directly: test voltage can be adjusted, more secure. In the power transformer transformer ratio test, can also be synchronized to complete the continuous group test, and the junction group is the same transformer parallel operation of one of the basic conditions, so . Judgement of power transformer junction group is also an indispensable item in the high voltage test. Commonly used test methods are: ac voltmeter method, phase table method, variable ratio bridge method, dc induction method, grouping table method. Group table is a common test power transformer group, phase sequence, polarity of the special instrument, the table has the advantages of easy to use, reflecting intuitive, correct instructions.

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2.5 Dielectric loss factor test

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In the high-voltage test of power transformer, dielectric loss factor test is one of the basic insulation preventive test program, its main test purpose is based on the size of the dielectric loss factor, determine the insulation performance of the transformer. In the normal operation of the transformer, the change of the dielectric loss factor and the size of the insulation loss has a close relationship. In the test process, the test personnel can through the relevant results, grasp the transformer insulation of the overall degree of moisture and deterioration of deterioration, so as to derive accurate test results.

In the power transformer dielectric loss factor test, the results are significantly better than the insulation resistance measurement and leakage current test, mainly because the test process, and the test voltage and equipment size and other factors less correlation, the test personnel can accurately determine the transformer insulation changes.

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2.6 AC withstand voltage test

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AC withstand voltage test of power transformer is mainly applied to identify the size of its insulation strength, using this test method can directly reflect the concentrated performance defects of the transformer, so as to ensure that the insulation performance of the transformer can be improved, and to avoid serious safety accidents due to insulation aging. Before carrying out AC withstand voltage test of power transformer, the insulation resistance, leakage current, dielectric loss factor of voltage apparatus must be measured carefully, and the AC withstand voltage test can only be organized after obtaining the relevant test results. If the statistics and calculation of the relevant test results are unreasonable, it will directly affect the accuracy of the AC withstand voltage test results.

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3, Power transformer high-voltage test safety design methods

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In the power transformer high-voltage test, due to the required test voltage is large, if you can not take effective safety design methods, will be directly related to the accuracy of the test results, as well as the safety of the test personnel. Therefore, in the process of power transformer high-voltage test, must pay attention to the research and application of safety design methods, and then guarantee the smooth development and conduct of the test work.

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3.1 Prevent induced voltage and discharge backlash

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In the power transformer high-voltage test, between the test equipment and other equipment must take effective measures to prevent induced voltage, usually the test equipment and other instruments and equipment for short connection, and reliable grounding. In the high-voltage test room, according to the test requirements to set up a special short-circuit grounding well, grounding system, for the test room in the idle capacitive equipment should also be in accordance with the requirements of short-circuit grounding.

As the power transformer high-voltage test is carried out in a closed six-sided shielded environment, in the test process there may be instantaneous discharge phenomenon, so, for the test room in the high-voltage cable must be added to the metal tube protection, and buried laying. In general, the length of the metal protection pipe should be > 15 m, and every 5 m and grounding pole to connect, so as to strictly control the chances of discharge backlash phenomenon.

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3.2 Reliable grounding

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In the high-voltage test of power transformers, must ensure that the grounding system of the test room is good, the grounding resistance generally needs to be below 0.5 Ω, so as to protect the test equipment and the safety of test personnel. In the case of good grounding conditions, the test room should also be regarded as a special equipotential body, the test room of all metal instruments, equipment shells should be kept well grounded, especially in the electrical transformer and test equipment must have a reliable, safe, stable metal connection. In the high-voltage test room, the location of the grounding point should be clearly labeled to prevent personnel electrocution in the test.

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3.3 Fire prevention, explosion-proof

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In the high-voltage test of power transformer, must strictly prevent the transformer in operation in the occurrence of overload or short-circuit phenomenon, pay special attention to the insulating materials, insulating oil due to high temperature, sparks and other factors, and produce decomposition, expansion, resulting in gasification, resulting in a sharp increase in pressure inside the transformer, may cause the transformer shell explosion so that a large number of insulating oil spray burning, oil flow will further expand the fire hazard. Therefore, in the high-voltage test process of power transformers, must pay attention to the prevention of safety issues to ensure the safety of the test.

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4, Conclusion

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High-voltage test of power equipment is a highly technical and complex project, in the high-voltage test of power transformers, we must select reasonable test conditions, methods and content, and pay attention to the safety design of the test process to ensure that the test operation is carried out smoothly, to obtain the corresponding test data, and then scientifically determine the comprehensive performance of the transformer.

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