CN110161361B - Power system grounding protection line selection method and line selection system - Google Patents

Power system grounding protection line selection method and line selection system Download PDF

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CN110161361B
CN110161361B CN201910527688.1A CN201910527688A CN110161361B CN 110161361 B CN110161361 B CN 110161361B CN 201910527688 A CN201910527688 A CN 201910527688A CN 110161361 B CN110161361 B CN 110161361B
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CN110161361A (en
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李晓明
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Li Xiaoming
Jining Power Supply Co
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/58—Testing of lines, cables or conductors

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Abstract

The utility model provides a power system ground protection route selection method and route selection system, obtain each power supply line and transformer neutral point earth connection's that is connected with the generating line zero mould current, remove power frequency current and all high frequency current more than the selected frequency with each zero mould current, obtain zero mould and remove power frequency and remove high frequency residual current, confirm that certain power supply line and other power supply lines or transformer neutral point earth connection's zero mould removes the circuit that the high frequency residual current opposite direction removes as the fault line, this disclosure can realize accurate interference signal that gets rid of, and the purpose of furthest remaining useful information. The sensitivity of grounding line selection is improved.

Description

Power system grounding protection line selection method and line selection system
Technical Field
The disclosure belongs to the field of relay protection of power systems, and particularly relates to a power system ground protection line selection method and a line selection system.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The small current grounding system comprises a neutral point ungrounded system and a neutral point arc suppression coil grounding system. The large-current grounding system comprises a neutral point direct grounding system and a neutral point grounding system through a small resistor. The sensitivity of the existing relay protection is unsatisfactory no matter a low-current grounding system generates high-resistance grounding or a high-current grounding system generates high-resistance grounding.
The existing low-current grounding line selection method is a transient state method, the existing transient state method only carries out fault line selection in the first half wave (10 milliseconds) after a fault occurs, the high-resistance grounding transient state quantity is small, and a fault line can not be selected correctly. If the first half wave can not select the fault line, the stable fifth harmonic wave is generally used for selecting the fault line, and when the energy of the fifth harmonic wave is insufficient, the line can not be correctly selected. The existing small-current grounding line selection method does not integrate positive energy of a plurality of criteria for line selection, and the line selection effect is poor.
The existing large-current grounding protection adopts zero-sequence current criterion. The zero sequence current of the line needs a zero sequence current transformer and a cable to be transmitted to the grounding protection device, the zero sequence current transformer and the cable can generate unbalanced current, and the unbalanced current and the zero sequence current are power frequency signals, so when the zero sequence current is utilized for fault line selection, the steady state unbalanced current can also influence the line selection result. When a high-resistance grounding fault occurs, the fault characteristic quantity is small, the interference of unbalanced current on a line selection result is large, and zero-sequence current grounding protection cannot act correctly. The prior art does not notice: under the condition that fault information is weak, the steady-state unbalanced current and the steady-state zero sequence current which are both power frequency are filtered, and the special waveforms of the residual transient fault quantity and the residual steady-state fault quantity are more convenient to judge the fault line.
Disclosure of Invention
The present disclosure provides a line selection method and a line selection system for ground protection of an electrical power system, which can effectively provide high-resistance ground fault protection operation sensitivity of electrical power systems with different ground types.
According to some embodiments, the following technical scheme is adopted in the disclosure:
a method for selecting lines of an electric power system for ground protection includes obtaining zero-mode currents of power supply lines connected with buses and a transformer neutral point grounding line, removing power frequency currents and all high-frequency currents above a selected frequency from the zero-mode currents to obtain zero-mode power frequency removed high-frequency residual currents, judging whether the directions of the two zero-mode power frequency removed high-frequency residual currents are opposite or not according to the integral of the energy of the difference/sum of the two zero-mode power frequency removed high-frequency residual currents in a time period, and determining a line of the power supply line and other power supply lines or the transformer neutral point grounding line with the zero-mode power frequency removed high-frequency residual currents in the opposite directions as a fault line.
In one or more other embodiments, when the power system is a low-current grounding system, the zero-mode power-frequency-removed high-frequency residual current i of each power supply line connected with the bus is obtained0,i,αIntegral W of the energy ofiIntegral W for each lineiSorting from big to small, selecting M lines sorted in front, if W existsi,M﹥Iset1If there is some power supply line zero-mode power frequency removing high-frequency residual current i0,i,α,1Satisfy the requirement of
Figure GDA0003182278670000021
And is
Figure GDA0003182278670000022
Wherein: m2, …, M, k1＝1～2，k2If the power supply line is 0-1, the power supply line is a fault line; if there is some power supply line, the zero-mode power frequency and high-frequency residual current i are removed0,i,α,1Satisfy the requirement of
Figure GDA0003182278670000031
And satisfy
Figure GDA0003182278670000032
Then it is a bus fault, where: m2, …, M, k1＝1～2，k2＝0～1， Wi,1To integrate the maximum value, Wi,MIs the minimum value of the integrals in M power supply lines, M is more than or equal to 3 and less than or equal to 5, Iset1Is the 1 st setting value.
The said scheme removes the industrial frequency current from the zero-mode current and all the high-frequency current above the selected frequency SF, and uses the residual zero-mode removed industrial frequency current as the criterion for earthing and line selection. Therefore, the interference signals are accurately removed, the useful signals are reserved to the maximum extent, the main interference in the zero-mode current is eliminated, the useful fault signal characteristics of the zero-mode current are highlighted, and the purpose that the fault line can be judged by weak fault signals is achieved;
meanwhile, the amplitude characteristic and the direction change characteristic of the zero-mode interference electricity are comprehensively utilized, the amplitude characteristic and the direction change characteristic are fused in a criterion formula, and the sensitivity and the reliability of the line selection criterion are improved.
As a further limitation, the time period is selected in a manner that the time period is within a period of time after the protection device is started and before the time of the whole group of the devices is reset;
or a first half-wave time period;
or only transient current time periods;
or only steady state current periods;
or comprises a transient current time period and a steady state current time period;
or a combination of multiple spaced time periods.
In one or more other embodiments, when the power system is a high-current grounding system, the neutral point zero-mode de-power-frequency de-high-frequency residual current i is calculated0,R,αIs integrated over the time period
Figure GDA0003182278670000033
Calculating; calculating zero-mode power frequency and high-frequency residual current i of the circuit0,i,αIntegral of the energy of (2) over a time period
Figure GDA0003182278670000041
If W is presenti﹥Iset4And | WR-Wi|﹤Iset5And is and
Figure GDA0003182278670000042
the high resistance ground protection is active, otherwise, it is inactive, where k3＝0～0.5，Iset4、Iset5、Iset6All are setting values.
As a further limitation, before the high-resistance grounding protection is judged, whether the neutral zero-sequence current is greater than a first set value or/and whether the effective value of the sudden change of the neutral zero-sequence current is greater than a second set value is judged, if so, whether the high-resistance grounding protection acts is continuously judged, and otherwise, the high-resistance grounding protection does not act all the time.
In one or more other embodiments, when the power system is an extra-high voltage line, the neutral point zero-mode de-power frequency de-high frequency residual current i is calculated0,R,αIs integrated over the time period
Figure GDA0003182278670000043
Calculating; calculating zero-mode power frequency and high-frequency residual current i of the circuit0,i,αIntegral of the energy of (2) over a time period
Figure GDA0003182278670000044
If W isi﹥Iset4And is and
Figure GDA0003182278670000045
the high resistance ground protection is activated, otherwise, it is not activated, k3＝0～0.5，Iset4、Iset5、Iset6All are setting values.
A small current grounding line selection system obtains zero-mode current of each line current transformer, current of a neutral point grounding loop and zero sequence voltage of a bus voltage transformer by using a grounding line selection device, and the grounding line selection device adopts the method to perform protection action.
A zero-mode current of each line and a zero-mode current of a neutral point grounding loop are obtained by a zero-sequence current protection device, and the zero-sequence current protection device adopts the method to perform protection action.
A zero-mode current of each line and a zero-mode current of a neutral point grounding loop are obtained by utilizing a zero-sequence current protection device, and the zero-sequence current protection device adopts the method to perform protection action.
The grounding line selection system can be in a centralized grounding protection system structure or a distributed grounding protection system structure.
Compared with the prior art, the beneficial effect of this disclosure is:
(1) the method removes the power frequency current in the zero-mode current and removes all high-frequency currents above the selected frequency SF, so that the aims of accurately removing interference signals and reserving useful information to the maximum extent can be fulfilled.
(2) The zero-mode power-frequency-removing high-frequency residual current waveform constructed from the zero-mode current is more distinctive, and the fault line is analyzed by utilizing the similarity in the same direction or the similarity in the opposite direction of a group of distinctive current waveforms, so that the judgment result is more reliable, and the sensitivity is very high.
(3) The method adopts the characteristic of integral of the energy of the sum (difference) of all the zero-pair mode power frequency removing high-frequency residual currents in the time period to judge the fault line. The positive energy accumulated in the correct characteristic time section of each pair of zero-mode power-frequency-removing high-frequency residual current is far greater than the negative energy accumulated in the incorrect characteristic time section, so that the negative energy is not enough to influence the judgment result, and the energy integration can be carried out on the combination of the pair of zero-mode power-frequency-removing high-frequency residual currents in a longer time section. The extension of the integration time period can increase the resolution of the criterion and improve the reliability and the sensitivity of the grounding protection.
(4) The method aims at the line selection method of low-current grounding, and judges a fault line by applying the characteristic of integral of sum (difference) energy of all pairs of zero-mode power frequency-removing high-frequency residual currents in a time period. The integration period may be long, short, may be preceded, followed, or include only the transient current period, or include only the steady-state current period, or include both the transient current period and the steady-state current period, or a combination of several spaced periods. Can be flexibly applied according to specific system conditions to realize the best effect.
(5) The method aims at low-current grounding line selection, and integrates the amplitude characteristic and the directional characteristic of each pair of zero-mode power-frequency high-frequency residual current and supports the amplitude characteristic and the directional characteristic of each pair of zero-mode power-frequency high-frequency residual current, so that the difference between fault characteristics and non-fault characteristics is more obvious, and the grounding line selection sensitivity is improved.
(6) The method aims at a large-current grounding system, the action quantity of the grounding protection starting condition is taken from neutral point grounding zero sequence current, the neutral point grounding zero sequence current is slightly influenced by unbalanced zero sequence current, the setting value of the starting condition is low, and the high sensitivity is realized.
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The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.
Fig. 1 is a schematic diagram of a centralized ground protection system;
fig. 2 shows a schematic diagram of a distributed earth protection system;
the specific implementation mode is as follows:
the present disclosure is further described with reference to the following drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The first embodiment is as follows:
in a typical embodiment, as shown in fig. 1, a low current grounding selection system with a neutral point grounded through an arc suppression coil, a power supply E feeds a transformer T, the transformer T feeds a bus M, and the neutral point of the transformer T is grounded through an arc suppression coil L. Suppose that N power supply lines are connected to bus M, and N is 6. The six lines are L1, L2, L3, L4, L5, L6, respectively. Zero sequence voltage of bus voltage transformer TV
Figure GDA0003182278670000071
Inputting a low-current grounding line selection device GZXX; zero mode current i of current transformers TA1, TA2, TA3, TA4, TA5 and TA6 of 6 power supply lines0,i(i ═ 1, 2, 3, 4, 5, 6) are respectively inputted with small current grounding line selection device GZXX and zero mode current i0,iIs in accordance with the convention that the busbars point towards the lines. Zero-mode current i output by current transformer TA0 of neutral point arc suppression coil grounding loop0,LThe reference direction of zero-mode current is consistent with the conventional mode, and the neutral point points to the ground. i.e. i0,iAnd i0,LThe representation is an instantaneous value of the value,
Figure GDA0003182278670000072
and
Figure GDA0003182278670000073
the expression is phasor. As is well known, the power frequency component of the zero-mode current is the zero-sequence current.
If the zero sequence voltage of the bus of the low-current grounding system is greater than the setting value, the power system is indicated to have a grounding fault, and the low-current grounding line selection device starts a line selection process. The line selection strategy and criterion for low-current grounding line selection are specifically as follows:
criterion of low-current grounding line selection: (1) removing zero-mode current i of each line0,iRemoving all high-frequency current above the selected frequency SF to obtain zero-mode power-frequency-removed high-frequency residual current i of each line0,i,α(ii) a (2) Calculating zero-mode power frequency and high-frequency removing residual current i of each line0,i,αIntegral W of the energy of (1) over the time periods t1 and t2iIs available
Figure GDA0003182278670000074
Calculating; (3) w for each lineiSorting from big to small; w of each line marked with sequencing resultiBy Wi,mRepresents; for example: if W of line 33Maximum, denoted as W3,1. W of the 4 th line4Minimum, denoted as W4,N. Zero-modulus power-frequency-removing high-frequency residual current i of each line marked with sequencing result0,i,αBy i0,i,α,mRepresents; if there is Wi,M﹥Iset1，Iset1Is the 1 st setting value; carrying out the subsequent steps; otherwise, turning to the step 6; wherein: m is more than or equal to 3 and less than or equal to 5; (4) if it is not
Figure GDA0003182278670000081
Figure GDA0003182278670000082
And is
Figure GDA0003182278670000083
Wherein: m2, …, M, k1＝1～2，k20-1; if the ith line is a fault line, ending the process; otherwise, carrying out the subsequent steps; (5) if it is not
Figure GDA0003182278670000084
Figure GDA0003182278670000085
And is
Figure GDA0003182278670000086
Wherein: m2, …, M, k1＝1～2，k20-1; if the bus is in fault, the bus is turned to be finished; otherwise, carrying out the subsequent steps; (6) if the fault line cannot be determined and the bus fault cannot be determined, carrying out problem processing on fault data; (7) and (6) ending.
Wherein: t is not less than 01，t1﹤t2﹤tset1；tset1The time from the start of the low-current grounding line selection device to the reset of the whole group is obtained.
Of course, in various embodiments, there are many ways to remove the power frequency and high frequency current with zero mode current, such as:
the method for removing power frequency current by using zero-mode current comprises the following steps: (1) and after the A/D sampling of the zero-mode current, obtaining the zero-mode power frequency-removed residual current through a digital power frequency wave trap. (2) Taking a steady-state current of a power frequency cycle after the transient current of the zero-mode current disappears as a sample, and carrying out power frequency Fourier transformation, wherein the expansion of the power frequency current information obtained by the transformation in the whole time period of the grounding protection is the power frequency current. The zero-mode current is zero-mode de-power-frequency residual current by subtracting the expanded power-frequency current in the whole time period of the grounding protection. (3) Taking a steady-state current of a power frequency cycle after the transient current of the zero-mode current disappears as a sample, wherein the expansion of the sample in the whole working time period of the grounding protection is the power frequency current. The zero-mode current is zero-mode power frequency residual current obtained by subtracting the expanded power frequency current in the whole working time period of the grounding protection. The side effect is that even order higher harmonic component in the zero mode current is removed, and odd order higher harmonic component in the zero mode current is amplified. But does not adversely affect the line selection decision. (4) Other methods.
The method for removing the high-frequency current by the zero-mode current comprises the following steps: (1) the zero-mode current is passed through an analog low-pass filter (e.g., a capacitor) before a/D sampling. (2) The zero mode current is passed through a digital low pass filter after a/D sampling. (3) Other methods.
The operating characteristics of the low current ground selection criterion are analyzed below.
Before or after the ground fault of the power system occurs, unbalanced zero sequence current exists in each line of the power system. Experience has shown that: the unbalanced zero sequence current is basically power frequency current. When the low-current grounding line selection is in a high-resistance grounding fault, the main reason that the line selection cannot be correctly performed is that a fault signal is very weak, and the amplitude of unbalanced current is close to the size of the fault signal. The power frequency current in the zero-mode current is removed, all high-frequency currents above the selected frequency SF are removed, and the remaining zero-mode power frequency removed high-frequency residual current is used as a grounding line selection criterion. Therefore, the interference signals are accurately removed, the useful signals are reserved to the maximum extent, the main interference in the zero-mode current is eliminated, the useful fault signal characteristics of the zero-mode current are highlighted, and the purpose that the fault line can be judged by weak fault signals is achieved.
When a ground fault suddenly occurs, the transient current amplitude of the zero-mode current of each line is several times or more than ten times larger than the power frequency zero-sequence current amplitude of the line; the transient current amplitude of the fault line zero-mode current is the largest. In half-wave time, the transient current of the zero-mode current of the non-fault line changes in the same direction, and the transient current of the zero-mode current of the fault line changes in the opposite direction.
A large amount of fault recording data show that: when a line has a ground fault, particularly a high-resistance ground, the arc resistance of a grounding point is mostly changed, and the arc ground generates a large amount of high-frequency attenuation current, and the arc ground may be interrupted. If the grounding is stable, the zero-mode power frequency removing high-frequency residual current also has fifth harmonic and other higher harmonics.
Thus, the power trainWhen the system has a ground fault, a non-fault line has zero-mode power frequency-removing high-frequency residual current flowing into the ground. Zero-mode power frequency-removing high-frequency residual current i for non-fault line flowing into earth0,i,αAll flow into the fault line from the earth point, the zero-mode power-frequency high-frequency residual current of the fault line flows into the earth, the sum of the zero-mode power-frequency high-frequency residual current of the non-fault line flows into the earth, and the zero-mode power-frequency high-frequency residual current of the upper arc elimination coil is added. Calculating zero-mode power frequency and high-frequency removing residual current i of each line0,i,αIntegral of the energy of (1) over the time periods t1 and t2
Figure GDA0003182278670000101
Comparing W of each lineiIf grounding occurs on the line, theoretically WiThe line on which the maximum value is located is the faulty line. Actual error, W for each lineiSorting from big to small; selecting a larger M lines to perform a subsequent line selection step; the probability of a faulty line among M lines is high. WiThe zero-mode power frequency and high-frequency residual current of a circuit with a small value is easily interfered, the current waveform and the waveform direction thereof are influenced, and the W is converted into the zero-mode power frequency and high-frequency residual currentiThe lines with smaller values are first excluded to avoid interfering with the judgment result. The reliability of grounding line selection can be improved.
If three lines with larger transient current amplitude are selected to compare the transient current directions, one line is a fault line opposite to the transient current directions of the other two lines. If the transient current of one non-fault line is disturbed, the direction of the transient current is changed, and the other non-fault line is selected as the fault line. In order to prevent the phenomenon, four lines (or five lines) with larger transient current amplitude are selected to compare the transient current directions, so that the wrong line selection can be prevented. Therefore, in the embodiment, M lines with larger energy of zero-mode power frequency and high-frequency residual current are selected, M is more than or equal to 3 and less than or equal to 5, and the step of comparing and selecting the directions of the zero-mode power frequency and high-frequency residual current is performed.
Computing
Figure GDA0003182278670000102
Is to push i0,i,α,mIs amplified to i0,i,α,1The same level degree. If i0,i,α,1Removing power frequency and high frequency residual current from zero module of fault line
Figure GDA0003182278670000103
Waveform of (a) and-i0,i,α,1Are identical, then have
Figure GDA0003182278670000111
And
Figure GDA0003182278670000112
this is an ideal situation. In practice, the amount of the liquid to be used,
Figure GDA0003182278670000113
and-i0,i,α,1The waveforms of (a) are very similar, so that k is taken1＝1～2，k2The number of the grooves is 0-1, which can meet the practical situation.
Similarly, if it is a bus fault, if
Figure GDA0003182278670000114
Waveform of (a) and (i)0,i,α,1Are identical, then have
Figure GDA0003182278670000115
And
Figure GDA0003182278670000116
this is an ideal situation. In practice, the amount of the liquid to be used,
Figure GDA0003182278670000117
and i0,i,α,1The waveforms of (a) are very similar, so that k is taken1＝1～2，k2The number of the grooves is 0-1, which can meet the practical situation.
If the calculation formula of the embodiment takes t1＝0，t210 ms, namely, only the transient current characteristic of the first half wave is utilized; this is equal to the transient current characteristic of the first half wave utilized by the current widely used transient method grounding line selectionSo that the effect is achieved. However, the present embodiment is innovative in the method for distinguishing the transient current characteristics of the first half wave. The transient method line selection respectively utilizes the amplitude characteristic and the direction change characteristic of the transient current, but the amplitude characteristic and the direction change characteristic are not integrated into a formula for utilization. The amplitude characteristic and the direction change characteristic are integrated into a formula for utilization, and the two characteristics are fused and mutually supported in the formula. Therefore, the sensitivity and reliability of the small-current grounding line selection criterion of the embodiment are better than those of the line selection by the transient method.
If t of the calculation formula of the present embodiment1And t2The transient process is excluded from the time period, and only the time period of the steady state process is taken, namely, the steady state current characteristic in the zero-mode current is utilized; the amplitude of each harmonic in the zero-mode current of the fault line is respectively greater than that of each harmonic in other lines, and the phase of each harmonic in the zero-mode current of the fault line is 180 degrees different from that of each harmonic in other lines. In the conventional zero-mode steady-state current grounding line selection, the waveform of a fifth harmonic with relatively large harmonic component is used for phase comparison, and other harmonics are all taken as interference and eliminated. The phase comparison of the harmonic waves is converted into energy comparison, so that the phase comparison of all the harmonic waves can be integrated into one energy comparison formula, the phases of a plurality of harmonic waves are compared by one formula at the same time, all the harmonic waves become useful signals, all the harmonic waves support each other, and the reliability and the sensitivity of grounding line selection are improved.
If t of the calculation formula of the present embodiment1And t2The time period is only the last section of the transient current, and the low-current ground line selection result of the embodiment may be wrong. The time of the end section of the transient current is longer than that of the initial section of the transient current, but the transient process is exponentially decayed, the energy of the initial section of the transient current is far larger than that of the end section, and the judgment result cannot be changed by the error of the end section.
And (3) comparing the initial direction and amplitude of the transient waveform of the zero-mode current of each line only in the first half-wave time of the fault by the transient method grounding line selection. After the first half-wave time, the criterion is invalid. Effective time period of criterionIs very short. T of the present embodiment1And t2A relatively long section may be taken. The criterion algorithm of the embodiment can comprise a fault characteristic section conforming to the transient method grounding line selection, and can also comprise a fault characteristic section not conforming to the transient method grounding line selection. The fault signature section that does not meet the transient method ground route selection can be used in the algorithm of the present embodiment because: each disturbance of the line to ground begins with a large current rise (or fall) waveform, and then the fault signature is exponentially decaying. The sections that provide the correct information are all in the front part (i.e. the first half wave) of the fault waveform, and the energy of the fault waveform in this part is much larger than that in the incorrect section (the last section of the transient current). The fault signature energy of the correct segment is sufficient to bury the fault signature energy of the incorrect segment. The transient method grounding line selection only utilizes the waveform characteristic of the transient current and does not utilize the energy characteristic, so that the line selection can be applied only in the first half wave and cannot be applied after the first half wave. The present embodiment converts the waveform characteristics of the transient current into energy characteristics, and the fault characteristic waveform energy of an incorrect section cannot play a main role. Thus, the grounding line selection can be carried out in a larger time period by using an integration method of the energy function in the time domain. The method is convenient to calculate, and the reliability and the sensitivity of grounding line selection are improved.
The low-current grounding line selection method of the embodiment applies the characteristic of integral of the energy of the sum (difference) of two zero modes, power frequency and high-frequency residual current, in a time period to judge a fault line. The time period can be long or short, can be adjusted before or after the operation according to the operation experience, and different time periods are adopted according to the actual field situation. The transient current time period may be included only, the steady-state current time period may be included only, the transient current time period and the steady-state current time period may be included, or a combination of several interval time periods may be included. Flexible application and optimal effect.
Because the arc suppression coil is an inductance device, the high-frequency component of the zero-mode current flowing through the arc suppression coil is very small, and the high-frequency component is an attenuated direct-current component except the power-frequency current. The operation experience shows that: the attenuated dc component is also small. Zero-mode power frequency removing device of arc suppression coilHigh-frequency residual current only flows into one line of the fault line, i.e. only i0,i,α,1The zero mode of the arc suppression coil is used for removing power frequency and high frequency residual current. It can be seen that the faulty line judgment inequality
Figure GDA0003182278670000131
And is
Figure GDA0003182278670000132
The influence of zero-mode power frequency removal and high-frequency residual current removal of the arc suppression coil can be eliminated, and no error result is generated on small-current grounding line selection. The small current grounding line selection criterion can be used for a system with a neutral point not grounded and can also be used for a system with a neutral point grounded through an arc suppression coil.
If the low-current grounding line selection criterion cannot determine the fault line and cannot determine that the fault line is a bus fault, the fault data is in question. The low-current grounding line selection device can display fault data problem information and is processed by an operator on duty. The technology disclosed by the Chinese patent 201811004696.X can also be adopted to repair the fault data with problems and then reselect the fault line. The technique disclosed in chinese patent 20161094094.1 can also be used to select three lines most likely to be faulty lines, and display them in sequence for the reference of the operator on duty. The technology disclosed in chinese patent 201710796987.6 can also be used to select the most likely fault line to be tripped directly, and then the backup protection selects the real fault line to be tripped.
The grounding line selection method of the low-current grounding system provided by the embodiment can be completely realized. Has wide application prospect.
Example two:
an exemplary embodiment is a power distribution network as shown in fig. 2. And a power supply E supplies power to a transformer T, the transformer T supplies power to a bus M, and a neutral point of the transformer T is grounded through a resistor R. Suppose that N power supply lines are connected to bus M, and N is 6. The six lines are L1, L2, L3, L4, L5, L6, respectively. Each line is provided with a set of grounding protection devices, namely BH1, BH2, BH3, BH4, BH5 and BH 6. Of current transformers TA1, TA2, TA3, TA4, TA5 and TA6 of six power supply linesZero mode current i0,iThe zero-sequence current protection devices BH1, BH2, BH3, BH4, BH5 and BH6 are respectively input (I is 1, 2, 3, 4, 5 and 6). Zero-mode current i output by current transformer TA0 of neutral point resistance grounding loop0,RSequentially inputting zero sequence current protection devices BH1, BH2, BH3, BH4, BH5 and BH 6.
The grounding short circuit protection of the large-current grounding system (such as direct grounding of a neutral point and low-resistance grounding of the neutral point) of the power distribution network consists of the existing zero-sequence current protection and high-resistance grounding protection. The existing zero sequence current protection is public knowledge and is not redundant. When the power distribution network is in a ground short circuit, the existing zero sequence current protection firstly judges that the amplitude of the zero sequence current is larger than a setting value, the action is tripped, otherwise, the action is not carried out. The existing zero sequence current protection sensitivity is not enough, and when the action can not be judged, the action is judged by high-resistance grounding protection.
The high-resistance grounding protection method comprises the following steps: high resistance ground protection has an initiating element as I0,R﹥Iset2And (or) Δ I0,R﹥Iset3And starting the high-resistance grounding protection, otherwise, the high-resistance grounding protection does not work. Once the starting element acts, the high-resistance grounding protection is detected and judged until the working time setting value t of the high-resistance grounding protectionset2And when the current reaches the preset value, the high-resistance grounding protection is carried out on the whole group. Setting value 2set23 rd setting value Iset3And a2 nd time setting value tset2The fixed value is determined empirically. Wherein: delta I0,RThe effective value of the abrupt change of the power frequency phasor (zero sequence current) of the zero mode current of the neutral point grounding loop.
And entering a high-resistance grounding protection algorithm after the element is started to act. And (3) a high-resistance grounding protection algorithm: (1) removing the zero-mode current i of the line0,iRemoving all high-frequency current above the selected frequency SF to obtain zero-mode power-frequency-removed high-frequency residual current i of the circuit0,i,α(ii) a Removing neutral point zero mode current i0,RRemoving all high-frequency current above the selected frequency SF to obtain neutral point zero-mode power frequency removed high-frequency residual current i0,R,α(ii) a (2) Calculating zero-mode power frequency and high-frequency removing residual current i of neutral point0,R,αAt energy of t3And t4Integral of time period WRIs available
Figure GDA0003182278670000151
Calculating; calculating zero-mode power frequency and high-frequency residual current i of the circuit0,i,αAt energy of t3And t4Integral of time period WiIs available
Figure GDA0003182278670000152
Calculating; (3) if W isi﹥Iset4And | WR-Wi|﹤Iset5And is and
Figure GDA0003182278670000153
the high-resistance grounding protection acts; otherwise, not acting; (4) and (6) ending.
Wherein: setting value 4set45 th setting value Iset56 th setting value Iset6The size is determined empirically. K3＝0～0.5，0≤t3，(t3+20mS)≤t4﹤tset2。
The operating characteristics of the high resistance ground protection are analyzed below.
For a large-current grounding system, when a grounding short circuit occurs, the zero-sequence voltage of the system is very small, the capacitive zero-sequence current of a non-fault line is very small, and the capacitive zero-sequence current can be ignored.
Whether the power system has unbalanced zero sequence current before or after the ground fault occurs, experience shows that: the unbalanced zero sequence current is basically power frequency current. Experience has shown that: when the power system normally operates, the neutral point grounding current is nearly equal to zero, and the neutral point grounding unbalanced zero sequence current is very small. The power system is grounded in a high-resistance mode, and very small zero-sequence current necessarily flows through a neutral point of the power system. Starting element setting value Iset2And Iset3The setting is very small, and the starting element has very high sensitivity. The circuit is grounded in a high-resistance mode, and the starting element can be started sensitively.
If the line L1 is short-circuited to ground, it flows to earth via the neutral point in the case of a distribution networkThe zero mode current of (a) is not stored in the ground but flows only from the ground point, the fault line L1 to the bus. The power distribution network has WR＝Wi。
The zero-mode current i of the circuit is removed in the first step of the high-resistance grounding protection algorithm0,iAfter the power frequency current in the circuit is obtained, the zero-mode power frequency-removing high-frequency residual current i of the circuit is obtained0,i,α(ii) a Removing neutral point zero mode current i0,RNeutral point zero-mode power frequency-removed high-frequency residual current i is obtained after medium power frequency current0,R,α。
Experience has shown that: the arc resistance of the grounding point is mostly changed, and the grounding arc can generate a large amount of high-frequency attenuation current, and the grounding arc can also exist intermittently. Therefore, no matter what the state of the grounding point electric arc is, the zero-mode power-frequency-removing high-frequency residual current of the non-fault line is almost equal to zero, the zero-mode power-frequency-removing high-frequency residual current of the fault line has a larger value, and the zero-mode power-frequency-removing high-frequency residual current of the neutral point is equal to the zero-mode power-frequency-removing high-frequency residual current of the fault line in magnitude and opposite in direction. Theoretically neutral point zero-mode power frequency-removing high-frequency residual current i0,R,αThe waveform and the fault line zero-mode power frequency-removing high-frequency residual current reverse direction-i0,i,αThe difference between the waveforms of (a) is equal to zero.
It can be seen that if a line has Wi﹥Iset4And | WR-Wi|﹤Iset5And is and
Figure GDA0003182278670000161
Figure GDA0003182278670000162
the line must be a faulty line.
Non-fault line W of power distribution networki﹥Iset4Cannot be established and the protection will not operate. Also, non-faulty lines of the distribution network
Figure GDA0003182278670000163
If not, the protection will not be operated.
The high-resistance grounding protection method for the large-current grounding system can be completely realized. Has wide application prospect.
Example three:
for the ultrahigh voltage line high-resistance grounding protection algorithm: (1) removing the zero-mode current i of the line0,iRemoving all high-frequency current above the selected frequency SF to obtain zero-mode power-frequency-removed high-frequency residual current i of the circuit0,i,α(ii) a Removing neutral point zero mode current i0,RRemoving all high-frequency current above the selected frequency SF to obtain neutral point zero-mode power frequency removed high-frequency residual current i0,R,α(ii) a (2) Calculating zero-mode power frequency and high-frequency removing residual current i of neutral point0,R,αAt energy of t3And t4Integral of time period WRIs available
Figure GDA0003182278670000171
Calculating; calculating zero-mode power frequency and high-frequency residual current i of the circuit0,i,αIntegral W of the energy of (1) over the time periods t3 and t4iIs available
Figure GDA0003182278670000172
Calculating; (3) if W isi﹥Iset4And is and
Figure GDA0003182278670000173
the high-resistance grounding protection acts; otherwise, not acting; (4) and (6) ending.
Wherein: setting value 4set46 th setting value Iset6The size is determined empirically. K3＝0～0.5，0≤t3， (t3+20mS)≤t4﹤tset2。
The extra-high voltage line has parallel double circuit lines, and the neutral points of two transformers are possible to be grounded, in this case, WRW with faulty lineiNot equal. Theoretically neutral point zero-mode power frequency-removing high-frequency residual current
Figure GDA0003182278670000174
The waveform and the fault line zero-mode power frequency-removing high-frequency residual current reverse direction-i0,i,αThe difference between the waveforms of (a) is equal to zero.
The rest of the analysis method is the same as the second embodiment and is not redundant.
As will be appreciated by one skilled in the art, embodiments of the present disclosure may be provided as a method, system, or computer program product. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present disclosure may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and so forth) having computer-usable program code embodied therein.
The present disclosure is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the disclosure. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
Although the present disclosure has been described with reference to specific embodiments, it should be understood that the scope of the present disclosure is not limited thereto, and those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.

Claims (9)

1. A power system grounding protection line selection method is characterized in that: obtaining zero-mode current of each power supply line connected with a bus and a neutral point grounding wire of a transformer, removing power frequency current and all high-frequency current above a selected frequency from each zero-mode current to obtain zero-mode power frequency removed high-frequency residual current, judging whether the directions of the two zero-mode power frequency removed high-frequency residual currents are opposite according to the integral of the energy of the difference and/or sum of the two zero-mode power frequency removed high-frequency residual currents in a time period, and determining a line of a certain power supply line and other power supply lines or the neutral point grounding wire of the transformer, wherein the direction of the zero-mode power frequency removed high-frequency residual currents is opposite to the direction of the zero-mode power frequency removed high-frequency residual currents.
2. The method for selecting the grounding protection line of the electric power system as claimed in claim 1, wherein: when the power system is a low-current grounding system, the zero-mode power frequency-removed high-frequency residual current i of each power supply line connected with the bus is obtained0,i,αIntegral W of the energy ofiIntegral W for each lineiIs carried out from large to largeSmall sequence, selecting M lines in the front sequence, when W existsi,M﹥Iset1If there is a power supply line, the zero-mode power frequency and high-frequency residual current i are removed0,i,α,1Satisfy the requirement of
Figure FDA0003167150340000011
And is
Figure FDA0003167150340000012
Wherein: m2, …, M, k1＝1～2，k2If the power supply line is 0-1, the power supply line is a fault line; otherwise, a certain power supply line zero-mode power frequency and high-frequency residual current i is removed0,i,α,1Satisfy the requirement of
Figure FDA0003167150340000013
And satisfy
Figure FDA0003167150340000014
Then it is a bus fault, where: m2, …, M, k1＝1～2，k2＝0～1，Wi,1To integrate the maximum value, Wi,MIs the minimum value of the integrals in M power supply lines, M is more than or equal to 3 and less than or equal to 5, Iset1Is the 1 st setting value;
wherein: 1, 2, 3, …, N; n is the total number of power supply lines connected with the bus; subscript 0 refers to zero sequence; subscript alpha refers to power frequency and high frequency residual current removal;
i0,i,αrepresenting zero-mode power frequency and high-frequency residual current removal of the ith line; wiZero-mode power frequency and high-frequency removing residual current i of each line0,i,αAt energy of t1And t2Integration of the time period.
3. The method for selecting the grounding protection line of the electric power system as claimed in claim 1, wherein: the time period is selected in a mode of being within a period of time after the protection device is started and before the time of resetting the whole group;
or a first half-wave time period;
or only transient current time periods;
or only steady state current periods;
or comprises a transient current time period and a steady state current time period;
or a combination of multiple spaced time periods.
4. The method for selecting the grounding protection line of the electric power system as claimed in claim 1, wherein: when the power system is a large-current grounding system, calculating zero-mode power-frequency-removing high-frequency residual current i of a neutral point grounding wire0,R,αIs integrated over the time period
Figure FDA0003167150340000021
Calculating zero-mode power frequency and high-frequency residual current i of each power supply line0,i,αIs integrated over the time period
Figure FDA0003167150340000022
If W is presenti﹥Iset4And | WR-Wi|﹤Iset5And is and
Figure FDA0003167150340000023
the high resistance ground protection is active, otherwise, it is inactive, where k3＝0～0.5，Iset4、Iset5、Iset6Are all setting values;
wherein: 1, 2, 3, …, N; n is the total number of power supply lines connected with the bus; subscript 0 refers to zero sequence; subscript alpha refers to power frequency and high frequency residual current removal;
i0,i,αrepresenting zero-mode power frequency and high-frequency residual current removal of the ith line; wiZero-mode power frequency and high-frequency removing residual current i of each line0,i,αAt energy of t3And t4Integration of the time period.
5. The method of claim 4, wherein the method comprises the following steps: before the high-resistance grounding protection is judged, whether the neutral zero-sequence current is larger than a first set value or/and whether the effective value of the sudden change of the neutral zero-sequence current is larger than a second set value is judged, if yes, whether the high-resistance grounding protection acts is continuously judged, and otherwise, the high-resistance grounding protection does not act all the time.
6. The method for selecting the grounding protection line of the electric power system as claimed in claim 1, wherein: when the power system is an ultrahigh voltage line, calculating zero-mode power frequency-removing high-frequency residual current i of a neutral point grounding wire0,R,αIs integrated over the time period
Figure FDA0003167150340000031
Calculating zero-mode power frequency and high-frequency residual current i of each power supply line0,i,αIs integrated over the time period
Figure FDA0003167150340000032
If W isi﹥Iset4And is and
Figure FDA0003167150340000033
Figure FDA0003167150340000034
the high resistance ground protection is activated, otherwise, it is not activated, k3＝0～0.5，Iset4、Iset6Are all setting values;
wherein: 1, 2, 3, …, N; n is the total number of power supply lines connected with the bus; subscript 0 refers to zero sequence; subscript alpha refers to power frequency and high frequency residual current removal;
i0,i,αrepresenting zero-mode power frequency and high-frequency residual current removal of the ith line; wiZero-mode power frequency and high-frequency removing residual current i of each line0,i,αAt energy of t3And t4Integration of the time period.
7. A low current grounding line selection system is characterized in that: acquiring zero-mode current of a current transformer of each power supply line and zero-mode current of a neutral point grounding line by using a grounding line selection device, wherein the grounding line selection device adopts the method as claimed in any one of claims 1 to 3 for grounding line selection.
8. A kind of heavy current earthing route selection system, its characteristic is: obtaining zero-mode current of each power supply line and zero-mode current of a neutral point grounding line by using a zero-sequence current protection device, wherein the zero-sequence current protection device adopts the method of claim 1, 4 or 5 to perform grounding line selection.
9. An ultra-high voltage line grounding line selection system is characterized in that: obtaining the zero-mode current of each power supply line and the zero-mode current of a neutral point grounding line by using a zero-sequence current protection device, wherein the zero-sequence current protection device adopts the method of claim 1 or 6 to perform grounding line selection.
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