CN110927515B - Power distribution network single-phase earth fault line selection method and system based on grounding transformer tap grounding - Google Patents
Power distribution network single-phase earth fault line selection method and system based on grounding transformer tap grounding Download PDFInfo
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Abstract
The invention discloses a method and a system for selecting a single-phase earth fault line of a power distribution network based on the tapping earthing of an earthing transformer, wherein firstly, earthing branches for uniformly adjusting the winding access amount are arranged at the tapping of a transformer winding, and when the single-phase earth fault occurs in the power distribution network, the switch of the earthing branch at the fault phase is closed; and secondly, adjusting a tapping point of a fault phase winding in the grounding transformer to two different access gears, simultaneously measuring zero sequence currents of all feeder lines of the system under different access gears, and calculating the variation of the zero sequence currents of all the feeder lines of the system before and after the change of the access gears, wherein the feeder line with the largest variation of the zero sequence currents is the fault feeder line, and completing fault line selection. The fault line selection can be completed only by adjusting the tap gear of the winding of the grounding transformer, the grounding transformer is already in the transformer substation, only corresponding taps and grounding branches need to be added, corresponding line selection equipment does not need to be added, the investment cost is greatly reduced, and the high-voltage grounding transformer has high economical efficiency.
Description
Technical Field
The invention belongs to the field of fault line selection of a power distribution network, and particularly relates to a single-phase ground fault line selection method and system of the power distribution network based on tapping and tapping grounding of a grounding transformer.
Background
The distribution network has a complex structure, more outgoing lines and is very easy to have single-phase earth faults. The distribution network in China widely uses a neutral point arc suppression coil grounding mode, but simultaneously reduces fault current, has unobvious fault characteristics and greatly reduces fault line selection accuracy. If the fault cannot be cleared in time, the earth fault is easily developed into an interphase fault, so that the power failure of a user is caused, and related electrical equipment is even damaged. Therefore, the necessary condition for ensuring timely fault clearing is to improve the accuracy of fault line selection.
The method for selecting the single-phase earth fault line of the power distribution network in the prior art mainly comprises the following two methods:
1. active line selection method
The active line selection method distinguishes the fault line by applying an external signal and generating additional fault characteristics, and in order to generate corresponding line selection characteristic quantity, the active line selection method usually requires matching with special primary equipment or relying on a special arc suppression coil device to complete the function of generating a line selection signal. The method has the advantages that the utilized characteristic quantity is single and definite, line selection can be carried out repeatedly during grounding, and the method has the defects that special primary equipment is highly depended on, the matching requirement of an arc elimination device and a line selection device is higher, so that the cost is increased and the economy is reduced, applied additional signals are small signals generally, and the applied additional signals are difficult to detect considering that the interference of the operating environment of a power distribution network is larger. The grounding transformer required by the invention is the existing transformer substation, only one branch is needed to be added to ground the tap, the cost is greatly reduced, the grounding transformer is simple and reliable, and the fault characteristic is more obvious and the detection is easy by actively regulating and controlling the power frequency voltage to judge the fault.
2. Passive line selection method
The passive line selection method can be divided into a steady-state line selection method and a transient-state line selection method. The steady-state line selection method is to select lines by utilizing steady-state signals which continuously exist in the grounding period, but the required active component or harmonic component is usually smaller in amplitude and much smaller in content than the steady-state zero-sequence power frequency current, so the steady-state line selection method is easily interfered by system noise, and accurate line selection may be difficult to perform in the fault transient period with higher system interference degree. The transient state line selection method utilizes transient state signals generated in the initial grounding stage to perform line selection, but the components have instability, uncertainty and instantaneity, and parameters such as frequency and amplitude have a large variation range under different system structures and fault conditions, so that difficulty in feature quantity extraction and protection fixed value setting is caused, and higher requirements are provided for device sampling frequency.
Based on the problems in the prior art, a more accurate method for selecting the single-phase earth fault of the power distribution network is urgently needed.
Disclosure of Invention
The invention provides a method and a system for selecting a single-phase earth fault line of a power distribution network based on grounding of a tapping tap of a grounding transformer, aiming at actively regulating and controlling the grounding gear of the tapping tap of the grounding transformer and adopting the zero sequence current variation of a line to select the line, wherein the zero sequence current continuously exists during the period of the earth fault, the characteristics are obvious, the noise interference is not easy to occur, and the defects in the prior art are avoided.
A distribution network single-phase earth fault route selection method based on grounding of tapping points of an earthing transformer comprises the steps that firstly, earthing branches for uniformly adjusting winding access amount are arranged at tapping points of a winding of the transformer, and when a single-phase earth fault occurs in a distribution network, switches of the earthing branches at fault phases are closed; and secondly, adjusting a tapping point of a fault phase winding in the grounding transformer to two different access gears, simultaneously measuring zero sequence currents of all feeder lines of the system under different access gears, and calculating the variation of the zero sequence currents of all the feeder lines of the system before and after the change of the access gears, wherein the feeder line with the largest variation of the zero sequence currents is the fault feeder line, and completing fault line selection.
The switch of the grounding branch at the faulted phase is closed so that the grounding transformer winding tap of the faulted phase is grounded.
Furthermore, a transformer winding tap connected with the grounding branch for uniformly adjusting the winding access amount is provided with n access gears, and the value of n is an integer greater than or equal to 2.
Further, the fault phase is identified by:
if the neutral point voltage exceeds a first rated phase voltage threshold value, or the neutral point voltage variation exceeds a second rated phase voltage threshold value, judging that the ground fault occurs; the phase with the lowest voltage is determined as the fault phase.
Further, the fault phase is identified by:
firstly, by continuously measuring neutral point voltage and neutral point voltage variation of the grounding transformer, if the neutral point voltage exceeds a first rated phase voltage threshold value or the neutral point voltage variation exceeds a second rated phase voltage threshold value, a grounding fault possibly exists, a grounding branch which is arranged at a tap of a transformer winding and uniformly adjusts winding access amount is closed, namely a switch of the grounding branch of the three-phase winding is sequentially closed A, B, C, otherwise, the current grounding fault does not exist;
secondly, the A, B, C three-phase winding is sequentially and gradually increased to an access gear of a tapping tap of the winding of the grounding transformer, zero sequence current of a three-phase line of the system is measured, if the zero sequence current is linearly increased along with the increase of the access gear, no fault occurs, and if the zero sequence current of the line is nonlinearly changed when a certain phase tap is adjusted, the phase is judged to have a fault.
Further, the zero-sequence current linearly increases or decreases with the change of the access gear, which means that when the correlation coefficient r between the size of the access gear of the tapping tap of the winding of the grounding transformer and the size of the zero-sequence current is greater than or equal to 0.98, the zero-sequence current linearly increases with the increase of the access gear, and the zero-sequence current linearly decreases with the decrease of the access gear.
Further, a correlation coefficient r between the gear size and the zero sequence current size is obtained by calculating according to the following formula:
in the formula: i is the size of the access gear at which the tapping of the grounding transformer winding is positioned, I0iThe zero sequence current of the line at the ith gear is large, and n represents the total gear of the grounding transformer winding.
A distribution network single-phase earth fault line selection system based on grounding transformer tapping grounding comprises:
the power distribution network fault phase monitoring unit is used for monitoring whether the power distribution network has single-phase earth fault;
the transformer winding is connected to a gear adjusting unit, and according to the monitoring result of the power distribution network fault phase monitoring unit, if a single-phase ground fault of the power distribution network occurs, a fault phase winding tapping in the grounding transformer is adjusted to be connected to two different access gears;
the zero-sequence current measuring unit is used for measuring the magnitude and the variable quantity of the zero-sequence current;
the zero-sequence current change calculation unit is used for calculating the variable quantity of the zero-sequence current of each feeder line along with the change of the access gear according to the adjustment operation of the transformer winding access gear adjustment unit;
and the fault feeder line identification unit is used for obtaining a fault feeder line identification result according to the judgment result of the zero sequence current variation judgment unit: and the feeder line with the largest zero sequence current variation is the fault feeder line.
Advantageous effects
The invention provides a method and a system for selecting a single-phase earth fault line of a power distribution network based on grounding of a tapping point of a grounding transformer.
According to the single-phase earth fault line selection method for the power distribution network, the difference of zero sequence current change quantities of a fault feeder line and a non-fault feeder line is large, the fault feeder line can be obviously judged, and the line selection accuracy rate is high; the fault line selection can be completed only by adjusting the tap gear of the winding of the grounding transformer, the grounding transformer is already in the transformer substation, only corresponding taps and grounding branches need to be added, corresponding line selection equipment does not need to be added, the investment cost is greatly reduced, and the high-voltage grounding transformer has high economical efficiency. The following differences with respect to the conventional transformer arrangement method are present:
(1) different gear setting modes
The invention uniformly arranges taps on the transformer winding, and if the number of turns of the winding is 600 turns, if 6 taps are arranged, as shown in figure 1, n is 6, the number of turns from 1 to 6 to the neutral point is 100, 200, 300, 400, 500 and 600 in sequence, and only the single-phase grounding tap is adjusted during regulation, so that the voltage level of a certain phase voltage can be changed in a large range. The traditional transformer can only be adjusted near a rated voltage tap, the tap does not cover the whole winding, the adjustable range is limited, three-phase taps need to be adjusted simultaneously during adjustment and control, and the tap is not grounded, so that the system voltage is stabilized in the rated range by slightly adjusting the voltage when the system voltage deviates;
(2) different wiring modes of transformer
The traditional transformer only has two ends of a transformer winding connected into a system, and the total turns of the transformer winding are changed by adjusting a tap at one end so as to adjust the voltage. The total number of turns of the winding is not changed, a branch circuit is added at a winding tap and grounded, and the phase voltage is adjusted by adjusting the access gear of the branch circuit tap.
(3) Different gear shifting methods
In the traditional method, three-phase taps are adjusted simultaneously, so that three-phase voltages are always symmetrical, zero-sequence voltage cannot be generated, zero-sequence current cannot be generated on a circuit, and faults cannot be identified through the change condition of the zero-sequence current; the invention only adjusts the grounding branch tap of the single phase, and the other two phases do not change, thereby being capable of adjusting the zero sequence voltage and the zero sequence current. In addition, the invention carries out fault line selection by adjusting tap positions, and is different from the traditional method that a tap is usually fixed and only stays at a certain position, and the invention needs to adjust the tap position of a fault phase winding in the grounding transformer to two different access positions.
In summary, the method for selecting the single-phase earth fault of the power distribution network provided by the invention can judge whether the line has the earth fault through the linear variable quantity of the zero sequence current, and the identification accuracy is high.
Drawings
FIG. 1 is a wiring diagram of a grounding transformer;
fig. 2 is a flowchart of a power distribution network single-phase earth fault line selection method based on grounding transformer tap grounding according to the embodiment of the invention.
Detailed Description
The invention will be further described with reference to the following figures and examples.
As shown in fig. 2, in order to implement the method for selecting a single-phase ground fault of a power distribution network based on grounding of tapping points of a grounding transformer according to the embodiment of the present invention, first, grounding branches for uniformly adjusting winding access amount are arranged at tapping points of windings of a transformer, and when a single-phase ground fault occurs in the power distribution network, switches of the grounding branches at a fault phase are closed; and secondly, adjusting a tapping point of a fault phase winding in the grounding transformer to two different access gears, simultaneously measuring zero sequence currents of all feeder lines of the system under different access gears, and calculating the variation of the zero sequence currents of all the feeder lines of the system before and after the change of the access gears, wherein the feeder line with the largest variation of the zero sequence currents is the fault feeder line, and completing fault line selection.
Wherein the wiring of the grounding transformer is shown in fig. 1,
a, B, C three-phase power supply electromotive force, N is neutral point, As、Bs、CsFor the high-voltage side winding of the grounding transformer, the number of turns of each phase winding is N1N ground tapping taps are uniformly arranged on each phase of the side winding, the tap positions of the winding from a neutral point to a system side are 1,2, … and N in sequence, and the number of turns to the neutral point is N in sequence1/n、2N1/n、…、N1. Assuming that the number of winding turns is 600 turns, if 6 taps are provided, n is 6, and the number of turns from gear positions 1 to 6 to the neutral point is 100, 200, 300, 400, 500, and 600 in this order. One end of the high-voltage side winding is connected with the system, the other end of the high-voltage side winding is connected with the neutral point, a grounding branch is additionally arranged at a tap of the high-voltage side winding, and S is a grounding branch switch. Z is neutral point ground impedance, as、bs、csIs a low voltage side winding.The fault line is set as a feeder j, and the earth leakage resistance and the earth capacitance are respectively rj、Cj，RfA fault transition resistance; the total m non-fault lines are respectively feeder lines 1,2, … and m, and the earth leakage resistance is r in sequence1、r2、…、rmThe capacitance to ground is C in sequence1、C2、…、Cm. And the following relationships exist:whereinFor faulted phase voltages, NXThe number of winding turns between the ground tap and the neutral point,
is the power supply electromotive force of the failed phase,
is neutral zero sequence voltage. With increasing gear NXIncreasing, failing phase voltage
Decrease is thenWill be increased; similarly, as the gear is reduced, NXReducing, faulted phase voltages
The number of the grooves is increased, and the,
will be reduced.
The earth parameter zero sequence impedance of the fault feeder j is Z0j(Z0j＝rj/3+1/(jωCj) ); the zero-sequence impedance of the earth parameters of the non-fault feeder lines 1,2, … and m is Z in sequence01、Z02、…、Z0mFor one of them being non-faultyA barrier feed line k (k ∈ {1, 2.., m }), with a leakage resistance to ground rkCapacitance to ground CkZero-sequence impedance of the earth reference is Z0kThen Z is0k＝rk/3+1/(jωCk). Neutral point voltage of grounding transformer isIf the C phase has a ground fault, then
For a faulty feeder j, zero sequence currentComprises the following steps:
will be provided with
Substitution can be simplified to
For non-faulted feeder k, zero sequence currentComprises the following steps:
will be provided withSubstitution can be simplified to
Regulating the tap position of the grounding transformer, and changing the fault phase voltage into variable quantity
The variation of the zero sequence current of the fault feeder line j before and after gear shiftingComprises the following steps:k zero sequence current of non-fault feeder line
Comprises the following steps:
as the fault transition resistance is far smaller than the zero sequence earth impedance of the line, the fault transition resistance is smaller than the zero sequence earth impedance of the line
Can obtain the productNamely, the zero sequence current variation of the fault feeder before and after the gear shifting of the grounding transformer is larger than that of the non-fault feeder, and the feeder with the largest zero sequence current variation is the fault feeder.
Assuming that the phase C has a ground fault, the fault line selection steps are as follows: if the system has ground fault, the grounding phase-to-fault grounding branch switch S is closed, namely CsThe tap is grounded, the tap is adjusted to any two gears, the zero sequence current of each feeder line under each gear is measured, the variable quantity of the zero sequence current of each feeder line is calculated, and the feeder line with the maximum variable quantity is the fault feeder line.
The identification method of the fault phase can adopt the following two methods:
1. if the neutral point voltage exceeds a first rated phase voltage, namely 15% rated phase voltage, or the neutral point voltage variation exceeds a second rated phase voltage, namely 3% rated phase voltage, the ground fault is judged to occur; the phase with the lowest voltage is determined as the fault phase.
2. In order to identify a fault phase more accurately, firstly, by continuously measuring neutral point voltage and neutral point voltage variation of a grounding transformer, if the neutral point voltage exceeds 15% of rated phase voltage, or the neutral point voltage variation exceeds 3% of rated phase voltage, a grounding fault possibly exists, a grounding branch which is arranged at a tap of a transformer winding and uniformly adjusts winding access amount is closed, namely a switch of the grounding branch of a three-phase winding is sequentially closed A, B, C, otherwise, the current grounding fault does not exist;
secondly, the A, B, C three-phase winding is sequentially and gradually increased to an access gear of a tapping tap of the winding of the grounding transformer, zero sequence current of a three-phase line of the system is measured, if the zero sequence current is linearly increased along with the increase of the access gear, no fault occurs, and if the zero sequence current of the line is nonlinearly changed when a certain phase tap is adjusted, the phase is judged to have a fault.
The zero-sequence current is linearly increased or decreased along with the change of the access gear, namely when the correlation coefficient r between the size of the access gear of the tapping of the grounding transformer winding and the size of the zero-sequence current is greater than or equal to 0.98, the zero-sequence current is linearly increased along with the increase of the access gear, and the zero-sequence current is linearly decreased along with the decrease of the access gear.
The correlation coefficient r of the gear size and the zero sequence current size is obtained by adopting the following formula:
in the formula: i is the size of the access gear at which the tapping of the grounding transformer winding is positioned, I0iThe zero sequence current of the line at the ith gear is large, and n represents the total gear of the grounding transformer winding.
The utility model provides a distribution network single-phase earth fault route selection system based on earthing transformer tapping ground connection which characterized in that includes:
the power distribution network fault phase monitoring unit is used for monitoring whether the power distribution network has single-phase earth fault;
the transformer winding is connected to a gear adjusting unit, and according to the monitoring result of the power distribution network fault phase monitoring unit, if a single-phase ground fault of the power distribution network occurs, a fault phase winding tapping in the grounding transformer is adjusted to be connected to two different access gears;
the zero-sequence current measuring unit is used for measuring the magnitude and the variable quantity of the zero-sequence current;
the zero-sequence current change calculation unit is used for calculating the variable quantity of the zero-sequence current of each feeder line along with the change of the access gear according to the adjustment operation of the transformer winding access gear adjustment unit;
and the fault feeder line identification unit is used for obtaining a fault feeder line identification result according to the judgment result of the zero sequence current variation judgment unit: and the feeder line with the largest zero sequence current variation is the fault feeder line.
It should be understood that the functional unit modules in the embodiments of the present invention may be integrated into one processing unit, or each unit module may exist alone physically, or two or more unit modules are integrated into one unit module, and may be implemented in the form of hardware or software.
To verify the feasibility of the method of the invention, the following analysis was performed in conjunction with the specific examples.
A model shown in figure 1 is built in PSCAD simulation software, 4 feeders are arranged in total, the feeders 1,2 and 3 are normal feeders, and the feeder 4 is a fault feeder. Each phase of the high-voltage side winding is provided with 5 gears, the tap gear of the grounding transformer winding is adjusted to the gear 1 and the gear 5, the zero sequence current of each feeder line is measured respectively, the zero sequence current variable quantity is calculated, and the result is shown in table 1.
TABLE 1
As can be seen from the table, the zero sequence current variation of the feeder line 4 is the largest, the line is easy to judge to be a fault feeder line, the simulation hypothesis is verified, and the feasibility of the method provided by the invention is proved.
The grounding described above becomes a Y/Δ junction transformer. The Z-type grounding transformer and the Y/Y/delta wiring transformer are also applicable, and the tap arrangement mode, the judgment method and the like are also completely the same.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (6)
1. A distribution network single-phase earth fault line selection method based on grounding of a tapping point of an earthing transformer is characterized in that firstly, an earthing branch for uniformly adjusting winding access amount is arranged at a tapping point of a winding of the transformer, and when a single-phase earth fault occurs in the distribution network, a switch of the earthing branch at a fault phase is closed; secondly, adjusting a tapping point of a fault phase winding in the grounding transformer to two different access gears, simultaneously measuring zero sequence currents of all feeder lines of the system under different access gears, and calculating the variation of the zero sequence currents of all the feeder lines of the system before and after the change of the access gears, wherein the feeder line with the largest variation of the zero sequence currents is the fault feeder line, and completing fault line selection;
the fault phase is identified by:
firstly, continuously measuring neutral point voltage and neutral point voltage variation of a grounding transformer, if the neutral point voltage exceeds a first rated phase voltage threshold value or the neutral point voltage variation exceeds a second rated phase voltage threshold value, a grounding fault possibly exists, closing grounding branches which are arranged at taps of windings of the transformer and uniformly adjust winding access, namely closing switches of the grounding branches of the three-phase windings in sequence A, B, C, and otherwise, if the neutral point voltage does not exceed the first rated phase voltage threshold value and the neutral point voltage variation does not exceed the second rated phase voltage threshold value, judging that the current grounding fault does not exist;
secondly, the A, B, C three-phase winding is sequentially and gradually increased to an access gear of a tapping tap of the winding of the grounding transformer, zero sequence current of a three-phase line of the system is measured, if the zero sequence current is linearly increased along with the increase of the access gear, no fault occurs, and if the zero sequence current of the line is nonlinearly changed when a certain phase tap is adjusted, the phase is judged to have a fault.
2. The method according to claim 1, wherein the transformer winding taps connected to the grounding branch for uniformly adjusting the winding access amount are provided with n access gears, and n is an integer greater than or equal to 2.
3. The method of claim 1, wherein the faulted phase is identified by:
if the neutral point voltage exceeds a first rated phase voltage threshold value, or the neutral point voltage variation exceeds a second rated phase voltage threshold value, judging that the ground fault occurs; the phase with the lowest voltage is determined as the fault phase.
4. The method according to claim 1, wherein the zero sequence current linearly increases or decreases with the change of the access gear position means that when the correlation coefficient r between the size of the access gear position of the tapping tap of the winding of the grounding transformer and the size of the zero sequence current is greater than or equal to 0.98, the zero sequence current linearly increases with the increase of the access gear position, and the zero sequence current linearly decreases with the decrease of the access gear position.
5. The method according to claim 4, wherein the correlation coefficient r of the gear step size and the zero sequence current size is calculated by using the following formula:
in the formula: i is the size of the access gear at which the tapping of the grounding transformer winding is positioned, I0iThe zero sequence current of the line at the ith gear is large, and n represents the total gear of the grounding transformer winding.
6. The utility model provides a distribution network single-phase earth fault route selection system based on earthing transformer tapping ground connection which characterized in that includes:
the power distribution network fault phase monitoring unit is used for monitoring whether the power distribution network has single-phase earth fault;
the transformer winding is connected to a gear adjusting unit, and according to the monitoring result of the power distribution network fault phase monitoring unit, if a single-phase ground fault of the power distribution network occurs, a fault phase winding tapping in the grounding transformer is adjusted to be connected to two different access gears;
the zero-sequence current measuring unit is used for measuring the magnitude and the variable quantity of the zero-sequence current;
the zero-sequence current change calculation unit is used for calculating the variable quantity of the zero-sequence current of each feeder line along with the change of the access gear according to the adjustment operation of the transformer winding access gear adjustment unit;
and the fault feeder line identification unit is used for obtaining a fault feeder line identification result according to the judgment result of the zero sequence current variation judgment unit: the feeder line with the largest zero sequence current variation is the fault feeder line;
the fault phase is identified by:
firstly, continuously measuring neutral point voltage and neutral point voltage variation of a grounding transformer, if the neutral point voltage exceeds a first rated phase voltage threshold value or the neutral point voltage variation exceeds a second rated phase voltage threshold value, a grounding fault possibly exists, closing grounding branches which are arranged at taps of windings of the transformer and uniformly adjust winding access, namely closing switches of the grounding branches of the three-phase windings in sequence A, B, C, and otherwise, if the neutral point voltage does not exceed the first rated phase voltage threshold value and the neutral point voltage variation does not exceed the second rated phase voltage threshold value, judging that the current grounding fault does not exist;
secondly, the A, B, C three-phase winding is sequentially and gradually increased to an access gear of a tapping tap of the winding of the grounding transformer, zero sequence current of a three-phase line of the system is measured, if the zero sequence current is linearly increased along with the increase of the access gear, no fault occurs, and if the zero sequence current of the line is nonlinearly changed when a certain phase tap is adjusted, the phase is judged to have a fault.
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