Impulse voltage tests on transformers before they are officially put into operation using an impulse
Mar. 22, 2024
Impulse voltage tests on transformers before they are officially put into operation using an impulse voltage generator：
1.When the no-load transformer is opened,there is a possibility of operating overvoltage,and the overvoltage amplitude can reach 4-4.5 times the phase voltage when the neutral point of the power system is not grounded or when it is grounded through the arc suppression coil;When the neutral point is directly grounded,it can reach three times the phase voltage.In order to check whether the insulation strength of the transformer can withstand the impact of full voltage or operating overvoltage,an impulse test is required.
2.When a live load transformer is put into operation,it will generate excitation inrush current,which can exceed the rated current and have a long decay time,even reaching several tens of seconds.Due to the significant electrical force generated by excitation inrush current,in order to assess the mechanical strength of each part of the transformer,it is necessary to conduct an impulse closing test,which means closing several times at the rated voltage.
3.There is a possibility of operating overvoltage when switching off the no-load transformer.For ungrounded windings,this voltage can reach 4 times the phase voltage;For windings directly grounded to the neutral point,this voltage can still reach 2 times the phase voltage.In order to assess whether the insulation strength of the transformer can withstand it,a breaking test must be conducted.If there is a cut,it must be closed,that is,multiple cuts are required.Due to the possibility of significant excitation inrush current during closing,in order to verify whether excitation inrush current will cause relay protection misoperation,it is necessary to conduct several impulse closing tests.
4.This is to replace the lightning impulse test with an overvoltage test.There is a lightning impulse generator in the transformer manufacturing factory,but it is impossible to have it on the installation site.But transformers do indeed experience lightning strikes and overvoltage surges during operation.This is the insulation performance index that transformers must be able to meet.
5.There are strict indicators for conducting lightning strikes in transformer manufacturing plants,such as full wave,cutoff,and duration.But there cannot be such strict and precise control on site.And in many cases,the multiple of operating overvoltage often cannot reach the multiple of lightning impulse.Therefore,we will compensate by increasing the number of closing times.The instantaneous operation overvoltage multiple is highest when the closing occurs at zero voltage crossing.
6.After each impact closing test,check the transformer for any abnormal sounds or shapes.Before the new transformer is put into operation,it undergoes 5 no-load closing cycles with an interval of no less than 5 minutes each time,in order to restore the insulation of the transformer.The number of times a transformer can be overhauled can be 3.
2.When a live load transformer is put into operation,it will generate excitation inrush current,which can exceed the rated current and have a long decay time,even reaching several tens of seconds.Due to the significant electrical force generated by excitation inrush current,in order to assess the mechanical strength of each part of the transformer,it is necessary to conduct an impulse closing test,which means closing several times at the rated voltage.
3.There is a possibility of operating overvoltage when switching off the no-load transformer.For ungrounded windings,this voltage can reach 4 times the phase voltage;For windings directly grounded to the neutral point,this voltage can still reach 2 times the phase voltage.In order to assess whether the insulation strength of the transformer can withstand it,a breaking test must be conducted.If there is a cut,it must be closed,that is,multiple cuts are required.Due to the possibility of significant excitation inrush current during closing,in order to verify whether excitation inrush current will cause relay protection misoperation,it is necessary to conduct several impulse closing tests.
4.This is to replace the lightning impulse test with an overvoltage test.There is a lightning impulse generator in the transformer manufacturing factory,but it is impossible to have it on the installation site.But transformers do indeed experience lightning strikes and overvoltage surges during operation.This is the insulation performance index that transformers must be able to meet.
5.There are strict indicators for conducting lightning strikes in transformer manufacturing plants,such as full wave,cutoff,and duration.But there cannot be such strict and precise control on site.And in many cases,the multiple of operating overvoltage often cannot reach the multiple of lightning impulse.Therefore,we will compensate by increasing the number of closing times.The instantaneous operation overvoltage multiple is highest when the closing occurs at zero voltage crossing.
6.After each impact closing test,check the transformer for any abnormal sounds or shapes.Before the new transformer is put into operation,it undergoes 5 no-load closing cycles with an interval of no less than 5 minutes each time,in order to restore the insulation of the transformer.The number of times a transformer can be overhauled can be 3.
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