CN109038491B - Large power transformer magnetizing inrush current suppression method - Google Patents

Large power transformer magnetizing inrush current suppression method Download PDF

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CN109038491B
CN109038491B CN201810742543.9A CN201810742543A CN109038491B CN 109038491 B CN109038491 B CN 109038491B CN 201810742543 A CN201810742543 A CN 201810742543A CN 109038491 B CN109038491 B CN 109038491B
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transformer
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residual magnetic
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曹斌
原帅
张叔禹
刘永江
张伟
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Inner Mongolia Electric Power Research Institute of Inner Mongolia Power Group Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/04—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/04—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for transformers
    • H02H7/045—Differential protection of transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Protection Of Transformers (AREA)

Abstract

The invention discloses a large power transformer magnetizing inrush current suppression method, which comprises the following steps of 1: respectively collecting voltage signals at two sides of a circuit breaker at the high-voltage side of a main transformer, wherein the data close to the power grid side is U1a、U1b、U1cData near the main transformer side is U2a、U2b、U2c(ii) a Step 2: calculating the opening time of a breaker at the high-voltage side of the transformer; and step 3: according to the opening time and the U of the circuit breaker1a、U1b、U1cRespectively calculating A, B, C three-phase flux average values; and 4, step 4: by means of U2a、U2b、U2cRespectively calculating three-phase residual magnetic fluxes of the transformer and comparing and calculating a maximum residual magnetic phase and a maximum residual magnetic flux thereof; and 5: and 4, calculating a closing phase angle of the breaker by considering the delay of the breaker according to the maximum residual magnetic phase and the residual magnetic flux thereof obtained in the step 4. The problems that differential protection misoperation can be generated by excitation inrush current, the electric energy quality is deteriorated, and the damage to equipment caused by operation overvoltage is avoided.

Description

Large power transformer magnetizing inrush current suppression method
Technical Field
The invention relates to the technical field of high voltage and insulation, in particular to the field of transformers, and particularly relates to a large power transformer magnetizing inrush current suppression method.
Background
The power transformer plays a role in connecting power grids with different voltage levels in a power system, is one of the most important electrical equipment in the system, and whether the transformer works normally is directly related to the reliability of the power system. The transformer may be accompanied by a large current, i.e., a magnetizing inrush current, during switching. The magnetizing inrush current may be several times as large as the rated current and contain a large amount of non-periodic components and higher harmonics. The suppression of transformer magnetizing inrush current is one of the most important concerns in various power industries because a large magnetizing inrush current may cause damage such as differential protection malfunction, deterioration of power quality, and damage to equipment due to an overvoltage operation.
Colleges and universities and research institutes at home and abroadMany studies have been made in the field of magnetizing inrush current. John h. brunke, Klaus J.
Figure BSA0000166731850000011
The method is characterized in that the residual magnetism and the closing phase angle of the transformer are considered to be main factors for generating the magnetizing inrush current, if the closing phase angle is reasonably controlled to enable the magnetic flux generated at the closing moment to be the same as the residual magnetism magnetic flux of the transformer, the magnetizing inrush current basically cannot be generated, and the method for calculating the residual magnetism of the transformer is provided based on a hysteresis loop. Then, many scholars have conducted a great deal of research work on the suppression of the magnetizing inrush current based on this theory. On the other hand, from the characteristics of the magnetizing inrush current, the discrimination characteristics are studied, for example, the basis for discriminating the magnetizing inrush current is provided based on the characteristics that the magnetizing inrush current has large even harmonics, contains a large amount of higher harmonics, and has a discontinuous angle in waveform, and the control protection strategy of the transformer is further studied.
Most of the research works belong to theoretical research, and the algorithm is complex, especially the residual magnetism calculation algorithm needs to consume a lot of calculation resources. Therefore, the application difficulty in the actual power grid engineering is very high, and the conventional processing method is to quit the charging protection in the transformer switching process to avoid the protection misoperation when the transformer is newly put into the transformer substation. Therefore, the research and development of the excitation inrush current suppression device with a simple method, practicality and effectiveness has important significance on the operation of the power grid. The transformer excitation inrush current suppression device is simple to operate, effective, practical and convenient to maintain by combining abundant transformer substation main transformer starting and debugging engineering experience through years of industrial experience and production accumulation.
Disclosure of Invention
The invention discloses a method for inhibiting excitation surge current of a large power transformer, and aims to provide a practical, effective and convenient method for inhibiting excitation surge current of a large power transformer in practical engineering application, so that excitation surge current in the processes of closing null-change testing and switching of a main transformer is avoided or reduced, impact on a transformer winding is effectively prevented, and the safety of a power system is ensured.
In order to achieve the above object, the present inventionThe method for suppressing the magnetizing inrush current of the large power transformer comprises the following steps: step 1: respectively collecting voltage signals at two sides of a circuit breaker at the high-voltage side of a main transformer, wherein data close to the power grid side is channel 1 data U1a、U1b、U1cThe data close to the main transformer side is channel 2 data U2a、U2b、U2c(ii) a Step 2: according to U in step 11a、U1b、U1cAnd U2a、U2b、U2cCalculating the opening time of the breaker at the high-voltage side of the transformer; and step 3: according to the opening time and the U of the circuit breaker1a、U1b、U1cRespectively calculating A, B, C three-phase flux average values; and 4, step 4: based on the opening time of the circuit breaker in the step 2 and the three-phase average residual flux in the step 3, U is utilized2a、U2b、U2cRespectively calculating three-phase residual magnetic fluxes of the transformer and comparing and calculating a maximum residual magnetic phase and a maximum residual magnetic flux thereof; step 5; calculating a closing phase angle of the breaker by considering the delay of the breaker according to the maximum residual magnetic phase and the residual magnetic flux thereof obtained in the step 4;
a, B, C three-phase voltage derivative dU in channel 22a/dt、dU2b/dt、dU2cThe/dt and the channel 1 correspond to the three-phase voltage derivative dU1a/dt、dU1b/dt、dU1cThe difference of/dt exceeds 1 percent and the three-phase voltage U in the channel 2 is monitored in one period2a、U2b、U2cWhen the voltage difference of the three-phase voltage is less than 2%, determining the opening time T of the circuit breaker according to the time when the derivative difference of the three-phase voltage is more than 1%1Then reading T1-0.2s to T1Three-phase voltage data over a time period;
step 3, voltage data U in channel 1 is utilized1a、U1b、U1cCalculating the average value of each phase of remanence;
step 4, voltage data U in channel 2 is utilized2a、U2b、U2cAnd calculating three-phase residual magnetic flux after the breaker is disconnected according to the average residual magnetic data in the step 3;
and 4, calculating the optimal closing phase angle of the next circuit breaker according to the principle that the residual magnetic flux of the maximum residual magnetism phase is the same as the magnetic flux generated in the phase at the closing time of the next circuit breaker according to the maximum residual magnetism phase and the residual magnetic flux thereof in the step 4.
By adopting the technical means, the invention respectively collects the voltage signals at two sides of the main transformer high-voltage side circuit breaker, calculates the switching-off time of the transformer high-voltage side circuit breaker and respectively calculates A, B, C three-phase magnetic flux average values, and utilizes U2a、U2b、U2cRespectively calculating three-phase residual magnetic fluxes of the transformer and comparing and calculating a maximum residual magnetic phase and a maximum residual magnetic flux thereof; and calculating the optimal closing phase angle of the breaker by considering the delay of the breaker according to the obtained maximum residual magnetic phase and residual magnetic flux thereof, thereby realizing the function of inhibiting the magnetizing inrush current of the transformer and solving the problems that the magnetizing inrush current can generate differential protection maloperation, deteriorate the electric energy quality and cause operation overvoltage so as to damage equipment and the like.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic diagram of the working principle of the magnetizing inrush current suppression method for a large power transformer according to the present invention;
FIG. 2 is a schematic diagram of a data reading strategy of a large power transformer magnetizing inrush current suppression method according to the present invention;
fig. 3 is a flow chart of a calculation of a closing phase angle of a large power transformer magnetizing inrush current suppression method according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example one
Fig. 1 is a general working flow chart of a large power transformer magnetizing inrush current suppression method according to the present invention. Mainly comprises the following steps of 1: respectively reading voltage signals at two sides of a main transformer high-voltage side circuit breaker; step 2: calculating the opening time of the breaker at the high-voltage side of the transformer according to the three-phase voltage waveform data in the step 1; and step 3: respectively calculating the three-phase magnetic flux average value according to the breaker opening time and voltage waveform data calculated in the step 2; and 4, step 4: respectively calculating the three-phase residual magnetic flux of the transformer according to the opening time of the circuit breaker in the step 2 and the voltage waveform data of the channel 2 in the step 3, and comparing to obtain the maximum residual magnetic phase; and 5: and 4, calculating the optimal closing phase angle of the next circuit breaker according to the maximum remanence phase and the remanence flux thereof obtained in the step 4 and the principle that the remanence flux of the maximum remanence phase is the same as the flux generated in the phase at the closing time of the next circuit breaker.
Fig. 2 is a voltage data reading flow chart of a large power transformer magnetizing inrush current suppression instrument. A, B, C three-phase voltage derivative dU in channel 22a/dt、dU2b/dt、dU2cThe/dt and the channel 1 correspond to the three-phase voltage derivative dU1a/dt、dU1b/dt、dU1cThe difference of/dt exceeds 1 percent and the three-phase voltage U in the channel 2 is monitored in one period2a、U2b、U2cWhen the voltage difference of the three-phase voltage is less than 2%, determining the opening time T of the circuit breaker according to the time when the derivative difference of the three-phase voltage is more than 1%1Then reading T1-0.2s to T1Three-phase voltage data over a time period.
Fig. 3 is a flow chart of calculating a closing phase angle of a magnetizing inrush current suppression instrument of a large power transformer. As shown in fig. 3, there are mainly the following steps: the three-phase flux average is first calculated. Respectively integrating a positive half wave of the three-phase voltage waveform data of the channel 1, and calculating the average magnetic flux of each phase of the transformer:
Figure BSA0000166731850000041
Figure BSA0000166731850000049
Figure BSA00001667318500000410
wherein t is1Calculating the starting moment for integration, namely the moment when the voltage waveform crosses zero and the derivative is greater than zero;
t is the waveform period, here 0.02s
Δ t is the three-phase time difference, here taken to be 6.67ms
From the channel 2 three-phase voltage waveforms, a per-phase flux accumulation function is calculated:
Figure BSA0000166731850000042
Figure BSA00001667318500000411
Figure BSA00001667318500000412
the magnetic flux accumulation function of each phase is a variable upper limit integral function, where T1For the on-off time of the circuit breaker, the initial point of each magnetic flux function calculation is the first 10 cycles of the circuit breaker on-off time, and the integral variable satisfies T ≤ T1。
And calculating a magnetic flux function of each phase according to the calculation results of the magnetic flux functions of the channel 1 and the channel 2:
φA＝φAI-ΦAave
φB＝φBI-ΦBave
φC＝φCI-ΦCave
and calculating the residual magnetism of each phase after the circuit breaker is disconnected according to the magnetic flux function of each phase:
φAT＝φA|t＝T1
φBT＝φB|t＝T1
φCT＝φC|t＝T1
comparing the three-phase residual magnetism calculation results, selecting the maximum phase of the residual magnetism, and calculating an ideal closing phase angle:
Figure BSA0000166731850000045
wherein
Figure BSA0000166731850000048
Is the phase angle at which the maximum phase of remanence is open,
Figure BSA0000166731850000047
is an ideal closing phase angle.
Calculating a closing phase angle of the circuit breaker:
Figure BSA0000166731850000046
wherein
Figure BSA0000166731850000051
The angle corresponding to the closing delay time of the circuit breaker,
Figure BSA0000166731850000052
and a closing phase angle of the circuit breaker. And calculating and outputting a closing signal according to the closing phase angle of the circuit breaker.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (2)

1. A method for suppressing the magnetizing inrush current of large-scale power transformer,
step 1: respectively collect mainChanging voltage signals at two sides of a high-voltage side breaker, wherein data close to the power grid side is channel 1 data U1a、U1b、U1cThe data close to the main transformer side is channel 2 data U2a、U2b、U2c；
Step 2: according to U in step 11a、U1b、U1cAnd U2a、U2b、U2cCalculating the opening time of the breaker at the high-voltage side of the transformer;
and step 3: according to the opening time and the U of the circuit breaker1a、U1b、U1cRespectively calculating A, B, C three-phase flux average values;
and 4, step 4: based on the switching-off time of the circuit breaker in the step 2 and the three-phase magnetic flux average value in the step 3, U is utilized2a、U2b、U2cRespectively calculating three-phase residual magnetic fluxes of the transformer and comparing and calculating a maximum residual magnetic phase and the residual magnetic flux thereof;
and 5: calculating a closing phase angle of the breaker by considering the delay of the breaker according to the maximum residual magnetic phase and the residual magnetic flux thereof obtained in the step 4;
a, B, C three-phase voltage derivative dU in channel 22a/dt、dU2b/dt、dU2cThe/dt and the channel 1 correspond to the three-phase voltage derivative dU1a/dt、dU1b/dt、dU1cThe difference of/dt exceeds 1 percent and the three-phase voltage U in the channel 2 is monitored in one period2a、U2b、U2cWhen the voltage difference of the three-phase voltage is less than 2%, determining the opening time T of the circuit breaker according to the time when the derivative difference of the three-phase voltage is more than 1%1Then reading T1-0.2s to T1Three-phase voltage data over a time period.
2. The method for suppressing the magnetizing inrush current of a large power transformer as recited in claim 1, wherein the optimal closing phase angle of the next circuit breaker is calculated according to the maximum remanence phase and the remanence flux thereof in step 4 and the principle that the remanence flux of the maximum remanence phase is the same as the flux generated in the phase at the closing time of the next circuit breaker.
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