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The purpose of the impact test before the power transformer series is put into operation

The purpose of the impact test before the power transformer series is put into operation

  • Categories:Industry News
  • Author:Li Xiulei
  • Origin:http://www.cl-dq.com/
  • Time of issue:2020-01-06
  • Views:0

(Summary description)

  In addition to some necessary tests, protection and secondary tests in accordance with the handover test standards for the newly put into operation of the power transformer series, the no-load full-voltage closing impulse test is usually done before it is officially put into operation.

  Why do impact tests?

  1. Check whether there are weaknesses or defects in the insulation of the power transformer series and its circuits

  When the no-load transformer is opened, operating overvoltage may occur. When the neutral point of the power system is not grounded or the arc suppression coil is grounded, the overvoltage amplitude can reach 4 to 4.5 times the phase voltage; when the neutral point is directly grounded, the overvoltage amplitude can reach 3 times the phase voltage. In order to check whether the insulation strength of the transformer can withstand the effects of full voltage or operating overvoltage, it is necessary to do a no-load full voltage impulse test before the transformer is put into operation. If the transformer and its circuit have insulation weaknesses, they will be exposed by operating overvoltage breakdown.

  2. Check whether the transformer differential protection is malfunctioning

  When the no-load transformer is powered on, an excitation inrush current will be generated, which can reach 6 to 8 times the rated current. The magnetizing inrush current begins to decay relatively quickly, generally it can be reduced to 0.25-0.5 times the rated current after 0.5 to 1s, but it takes a long time to complete the attenuation, which is about a few seconds for small and medium transformers, and 10 to 20 seconds for large transformers, so the magnetizing inrush current decays In the initial stage, the differential protection is often malfunctioning, causing the transformer to fail to be put into operation. Therefore, during the no-load impact closing, under the action of the magnetizing inrush current, the wiring, characteristics and fixed value of the differential protection can be actually checked, and the evaluation and conclusion of whether the protection can be put into use can be made.

  3. Assess the mechanical strength of the power transformer series

  Since the magnetizing inrush current produces a large amount of electromotive force, in order to assess the mechanical strength of the transformer, a no-load impact test is required.

  Generally five times?

  The number of full-voltage no-load impulse tests. Generally, five consecutive no-load impulses should be carried out before the new product is put into operation. Because the closing angle is different at each closing time, the corresponding excitation inrush current is also different, sometimes large and sometimes small. Generally, five times of no-load closing are required to comprehensively detect the transformer's insulation, mechanical strength and the action of the differential protection.

  What is the magnetizing inrush current?

  Characteristics of magnetizing inrush current:

  1. Contains aperiodic components with a large component, which tends to make the inrush flow to one side of the time axis. Generally, one phase is opposite to the other two phases.

  2. Contains a large number of high-order harmonics, and the second harmonic component is the largest

  3. There is a discontinuous angle between the inrush current waveforms

  4. In the initial stage, the inrush current has a large value, which can reach 6-8 times the rated current, and then gradually decays.


The purpose of the impact test before the power transformer series is put into operation

(Summary description)

  In addition to some necessary tests, protection and secondary tests in accordance with the handover test standards for the newly put into operation of the power transformer series, the no-load full-voltage closing impulse test is usually done before it is officially put into operation.

  Why do impact tests?

  1. Check whether there are weaknesses or defects in the insulation of the power transformer series and its circuits

  When the no-load transformer is opened, operating overvoltage may occur. When the neutral point of the power system is not grounded or the arc suppression coil is grounded, the overvoltage amplitude can reach 4 to 4.5 times the phase voltage; when the neutral point is directly grounded, the overvoltage amplitude can reach 3 times the phase voltage. In order to check whether the insulation strength of the transformer can withstand the effects of full voltage or operating overvoltage, it is necessary to do a no-load full voltage impulse test before the transformer is put into operation. If the transformer and its circuit have insulation weaknesses, they will be exposed by operating overvoltage breakdown.

  2. Check whether the transformer differential protection is malfunctioning

  When the no-load transformer is powered on, an excitation inrush current will be generated, which can reach 6 to 8 times the rated current. The magnetizing inrush current begins to decay relatively quickly, generally it can be reduced to 0.25-0.5 times the rated current after 0.5 to 1s, but it takes a long time to complete the attenuation, which is about a few seconds for small and medium transformers, and 10 to 20 seconds for large transformers, so the magnetizing inrush current decays In the initial stage, the differential protection is often malfunctioning, causing the transformer to fail to be put into operation. Therefore, during the no-load impact closing, under the action of the magnetizing inrush current, the wiring, characteristics and fixed value of the differential protection can be actually checked, and the evaluation and conclusion of whether the protection can be put into use can be made.

  3. Assess the mechanical strength of the power transformer series

  Since the magnetizing inrush current produces a large amount of electromotive force, in order to assess the mechanical strength of the transformer, a no-load impact test is required.

  Generally five times?

  The number of full-voltage no-load impulse tests. Generally, five consecutive no-load impulses should be carried out before the new product is put into operation. Because the closing angle is different at each closing time, the corresponding excitation inrush current is also different, sometimes large and sometimes small. Generally, five times of no-load closing are required to comprehensively detect the transformer's insulation, mechanical strength and the action of the differential protection.

  What is the magnetizing inrush current?

  Characteristics of magnetizing inrush current:

  1. Contains aperiodic components with a large component, which tends to make the inrush flow to one side of the time axis. Generally, one phase is opposite to the other two phases.

  2. Contains a large number of high-order harmonics, and the second harmonic component is the largest

  3. There is a discontinuous angle between the inrush current waveforms

  4. In the initial stage, the inrush current has a large value, which can reach 6-8 times the rated current, and then gradually decays.


  • Categories:Industry News
  • Author:Li Xiulei
  • Origin:http://www.cl-dq.com/
  • Time of issue:2020-01-06
  • Views:0
Information

  In addition to some necessary tests, protection and secondary tests in accordance with the handover test standards for the newly put into operation of the power transformer series, the no-load full-voltage closing impulse test is usually done before it is officially put into operation.

  Why do impact tests?

  1. Check whether there are weaknesses or defects in the insulation of the power transformer series and its circuits

  When the no-load transformer is opened, operating overvoltage may occur. When the neutral point of the power system is not grounded or the arc suppression coil is grounded, the overvoltage amplitude can reach 4 to 4.5 times the phase voltage; when the neutral point is directly grounded, the overvoltage amplitude can reach 3 times the phase voltage. In order to check whether the insulation strength of the transformer can withstand the effects of full voltage or operating overvoltage, it is necessary to do a no-load full voltage impulse test before the transformer is put into operation. If the transformer and its circuit have insulation weaknesses, they will be exposed by operating overvoltage breakdown.

  2. Check whether the transformer differential protection is malfunctioning

  When the no-load transformer is powered on, an excitation inrush current will be generated, which can reach 6 to 8 times the rated current. The magnetizing inrush current begins to decay relatively quickly, generally it can be reduced to 0.25-0.5 times the rated current after 0.5 to 1s, but it takes a long time to complete the attenuation, which is about a few seconds for small and medium transformers, and 10 to 20 seconds for large transformers, so the magnetizing inrush current decays In the initial stage, the differential protection is often malfunctioning, causing the transformer to fail to be put into operation. Therefore, during the no-load impact closing, under the action of the magnetizing inrush current, the wiring, characteristics and fixed value of the differential protection can be actually checked, and the evaluation and conclusion of whether the protection can be put into use can be made.

  3. Assess the mechanical strength of the power transformer series

  Since the magnetizing inrush current produces a large amount of electromotive force, in order to assess the mechanical strength of the transformer, a no-load impact test is required.

  Generally five times?

  The number of full-voltage no-load impulse tests. Generally, five consecutive no-load impulses should be carried out before the new product is put into operation. Because the closing angle is different at each closing time, the corresponding excitation inrush current is also different, sometimes large and sometimes small. Generally, five times of no-load closing are required to comprehensively detect the transformer's insulation, mechanical strength and the action of the differential protection.

  What is the magnetizing inrush current?

  Characteristics of magnetizing inrush current:

  1. Contains aperiodic components with a large component, which tends to make the inrush flow to one side of the time axis. Generally, one phase is opposite to the other two phases.

  2. Contains a large number of high-order harmonics, and the second harmonic component is the largest

  3. There is a discontinuous angle between the inrush current waveforms

  4. In the initial stage, the inrush current has a large value, which can reach 6-8 times the rated current, and then gradually decays.

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