CN111880110A - Single-phase earth fault disappearance judgment method and system for neutral point non-effective earthing system - Google Patents
Single-phase earth fault disappearance judgment method and system for neutral point non-effective earthing system Download PDFInfo
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- CN111880110A CN111880110A CN201910301143.9A CN201910301143A CN111880110A CN 111880110 A CN111880110 A CN 111880110A CN 201910301143 A CN201910301143 A CN 201910301143A CN 111880110 A CN111880110 A CN 111880110A
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Abstract
The invention discloses a method and a system for judging disappearance of single-phase earth faults of a neutral point non-effective earthing system.A three-phase switch is arranged at a bus of a transformer substation, and the maximum capacitance current of a power supply system when single-phase earthing occurs is calculated according to the earth distribution capacitance values of all lines of a power distribution network; when a single-phase earth fault occurs, judging the phase of the fault according to the change condition of the voltage of the bus of the transformer substation, and controlling the corresponding earthing switch at the bus of the fault phase to be closed; after a certain short time delay and the resistance value of the adjustable resistor are adjusted, the current value of the adjustable resistor branch circuit after the resistance value is adjusted is obtained, and whether the actual fault of the circuit disappears or not is preliminarily judged; if the actual fault of the line is preliminarily judged to disappear, the current values of the adjustable resistance branches under a plurality of different resistance values are continuously obtained after a certain long time delay is carried out again and the resistance values of the adjustable resistance are adjusted from small to large, and whether the actual fault of the line disappears is judged again.
Description
Technical Field
The disclosure relates to the field of fault judgment, in particular to a method and a system for judging single-phase earth fault disappearance of a neutral point non-effective earth system based on an adjustable resistor.
Background
A distribution network with 35kV and below voltage class in China usually adopts an operation mode of non-effective grounding of a neutral point, and has the advantages that line voltage is still symmetrical when a single-phase grounding fault occurs, the normal work of a load cannot be influenced, and the operation system with the fault does not exceed 2 hours, so that the power distribution network has an important effect of improving the power supply reliability of the distribution network. However, this operation mode also causes certain problems, for example, the system neutral point voltage and the non-fault phase voltage are increased, which may cause damage to the system insulation, and may cause a multipoint ground fault or an inter-phase short circuit fault. The fault point may have an arc with continuous discharge, which brings great risk to various devices and personnel near the fault point. In addition, a single-phase ground fault is generally accompanied by a large transition resistance, the fault point to ground voltage may still maintain a high level, a large step voltage may be generated around the fault point, and once a human or an animal approaches the fault point, a personal injury accident may be generated due to the large step voltage. Data show that in recent years, the number of people who are injured and killed by electric shock due to single-phase earth fault of a power distribution network in China exceeds 8000, great threat is brought to life and property safety of people, and the number of the injured and killed people caused by the same accident in the United states is less than 400 every year, so that the time for fault operation of the power distribution network belt is required to be shortened, or the voltage of a fault point is reduced as far as possible during the fault operation of the power distribution network belt, and the personal injury and death accident caused by large step voltage is avoided.
In order to realize the purpose, the fault line can be quickly judged and cut off after the single-phase earth fault occurs, so that electric shock accidents can be avoided to the maximum extent. However, on one hand, the accuracy of the current single-phase earth fault line selection needs to be improved, and on the other hand, some users lack a standby power supply, so the scheme of quickly cutting off the fault line brings power failure of different time to the users, and is not beneficial to improving the power supply reliability.
In recent years, the following processing methods are adopted in some substations: an artificial grounding point is arranged in the transformer substation and is connected with a bus through a switch, and the switch keeps disconnected when the system normally operates. When a single-phase earth fault occurs in the system, the phase of the fault is judged according to the change rule of three-phase voltage, and then a control switch acts to connect a fault phase bus in the transformer substation with an artificial earth point, so that a reliable earth point is formed in the transformer substation. Because the fault point in the station is positioned near the bus and the grounding resistance is not large, the fault phase voltage can be controlled to be very low, so that the voltage at the actual fault point on the line can be ensured to be very low, the step voltage hazard is greatly reduced, and the method plays an important role in ensuring that a human body is not injured by the step voltage.
The inventor finds that the scheme of arranging the artificial ground fault point in the transformer substation and forcibly reducing the fault phase voltage does not affect the normal power supply of the system, and can reduce the electric shock risk to a great extent, but because the artificial ground fault point exists, a bypass can be formed on the actual fault point of the line, so that when the actual fault point disappears, an operator cannot timely and reliably judge whether the actual fault point disappears from the transformer substation, and cannot determine when to disconnect the switch of the artificial ground fault point, so that the power grid enters a normal operation state as soon as possible.
The method generally adopted at present is a heuristic method, namely, after a certain time delay occurs, a switch of an earth point in a station is disconnected, whether the three-phase voltage of a bus is recovered to be normal or not is observed, and if the three-phase voltage is recovered to be normal, the actual fault point on a line disappears, and a power grid can enter a normal operation state; if the three-phase voltage cannot be recovered to be normal, the actual fault point on the line still exists, and at the moment, the on-station internal grounding switch is closed again until a maintainer finds and eliminates the fault. The inventor finds that the manual probing method has great contingency and randomness in the research and development process, and multiple switching operations also have certain safety risks for operating personnel and related equipment.
Disclosure of Invention
In order to overcome the defects of the manual heuristic method, on the premise of considering safety and reliability, the disclosure provides a method and a system for judging whether the single-phase ground fault of the neutral point non-effective grounding system disappears based on the adjustable resistor.
The technical scheme of the system for judging the disappearance of the single-phase earth fault of the neutral point non-effective grounding system in the first aspect of the disclosure is as follows:
a single-phase earth fault disappearance judgment system of a neutral point non-effective grounding system comprises a three-phase switch, an adjustable resistor, a current transformer and a control system, wherein the three-phase switch, the adjustable resistor, the current transformer and the control system are installed at a bus of a transformer substation;
one end of the three-phase switch is connected with a three-phase bus of the transformer substation, the other end of the three-phase switch is grounded through an adjustable resistor, the current transformer is arranged on the adjustable resistor branch, and the current transformer is used for collecting the current value of the adjustable resistor branch and transmitting the current value to the control system;
the control system comprises a maximum capacitance current calculation module, a fault phase judgment module and a fault point disappearance judgment module; wherein:
the maximum capacitance current calculation module is used for calculating the maximum capacitance current of the power supply system when single-phase grounding occurs according to the ground distribution capacitance values of all lines of the power distribution network;
the fault phase judging module is used for judging the fault phase according to the change condition of the three-phase voltage of the bus of the transformer substation when a single-phase earth fault occurs, and controlling the corresponding earth switch at the fault phase bus to be closed;
the fault point disappearance judgment module is used for obtaining the current value of the adjustable resistance branch after the resistance value is adjusted after certain time delay and after the resistance value of the adjustable resistance branch is adjusted, and preliminarily judging whether the actual fault of the line disappears; and if the actual fault of the line disappears in the initial judgment, continuously acquiring the current values of the adjustable resistance branches under a plurality of different resistance values after the resistance value is adjusted in a certain time delay mode again, and judging whether the actual fault of the line disappears again.
The technical scheme of the method for judging the disappearance of the single-phase earth fault of the neutral point non-effective earthing system in the second aspect of the disclosure is as follows:
a single-phase earth fault disappearance judgment method of a neutral point non-effective earthing system is realized based on the single-phase earth fault disappearance judgment system of the neutral point non-effective earthing system, and comprises the following steps:
calculating the maximum capacitance current of the power supply system when single-phase grounding occurs according to the ground distribution capacitance values of all lines of the power distribution network;
when a single-phase earth fault occurs, judging the phase of the fault according to the change condition of the voltage of the bus of the transformer substation, and controlling the corresponding earthing switch at the bus of the fault phase to be closed;
after the resistance value of the adjustable resistor is adjusted in a certain time delay manner, the current value of the adjustable resistor branch circuit after the resistance value is adjusted is obtained, and whether the actual fault of the circuit disappears or not is preliminarily judged;
if the actual fault of the line is preliminarily judged to disappear, the resistance values of the adjustable resistors are adjusted in sequence from small to large after a certain time delay, the current values of the adjustable resistor branches under a plurality of different resistance values are continuously obtained, and whether the actual fault of the line disappears is judged again.
Through above-mentioned technical scheme, this disclosed beneficial effect is:
(1) the method has the advantages that the resistance value of the grounded adjustable resistor at the bus in the transformer substation is adjusted, the current amplitude of the branch of the adjustable resistor is analyzed and compared, whether the actual fault point disappears or not can be judged quickly and reliably, the long-time operation of the system with faults is avoided, and the impact on the operation of power supply equipment and a power grid caused by blind probing through the operation of the grounding switch in the substation can also be avoided; when a fault handling mode of arranging an artificial grounding point in the transformer substation is adopted, whether an actual fault point disappears or not can be judged timely and reliably;
(2) according to the method, after the fault occurs, whether the fault disappears is judged by adjusting the resistance value with short time delay, and the objective fact that the transient fault in the current power grid is more is mainly considered, so that the system can be rapidly recovered to a normal operation state after the transient fault disappears;
(3) according to the method, for some faults with longer discharge time and longer required time for system insulation recovery, by setting a plurality of longer delays, the ground switch in the station can be tripped as soon as possible after the faults disappear, so that the system can recover the normal operation state;
(4) the adjustment operation of the grounding resistor is carried out in the transformer substation, and compared with the line capacitive reactance, the grounding resistor is small in resistance value, small in current value flowing through the grounding resistor, low in voltage at two ends of the resistor and small in operation risk.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this disclosure, are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the disclosure and together with the description serve to explain the application and not to limit the disclosure.
Fig. 1 is a structural diagram of a single-phase earth fault disappearance determination system of a neutral point non-effective earth system according to an embodiment;
FIG. 2 is a flowchart of a single-phase earth fault disappearance determination method for a system with a non-effectively grounded neutral point according to the second embodiment;
FIG. 3 is a current variation curve of the adjustable resistance branch circuit under the three permanent faults of the embodiment;
fig. 4 is a current variation curve of the adjustable resistance branch circuit under the three transient faults of the embodiment.
Detailed Description
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 application. 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.
Example one
The embodiment provides a single-phase earth fault disappearance judgment system of a neutral point non-effective grounding system, which is characterized in that a three-phase switch is arranged on a substation bus, one end of the three-phase switch is grounded through an adjustable resistor, the resistance value of a grounding resistor is adjusted in a substation to judge whether a fault disappears, and whether the actual fault of a line disappears can be judged quickly, timely and reliably.
Referring to fig. 1, the system for judging the disappearance of the single-phase ground fault of the neutral point non-effective grounding system comprises a three-phase switch, an adjustable resistor, a current transformer and a control system, wherein the three-phase switch is installed at a bus of a transformer substation, one end of the three-phase switch is connected with the three-phase bus of the transformer substation, the other end of the three-phase switch is grounded through the adjustable resistor, and a high-precision current transformer is installed on a branch of the adjustable; and the current transformer is used for collecting the current value of the adjustable resistance branch and transmitting the current value to the control system.
The control system is used for receiving three-phase voltage of a transformer substation, analyzing the change rule of the three-phase voltage when a single-phase earth fault occurs, judging the fault phase, and if one phase voltage is reduced and the other two phase voltages are increased and zero-sequence voltage occurs, reducing the voltage to be the fault phase; then controlling the grounding switch of the fault phase in the transformer substation to be closed to form an artificial grounding branch with fixed reliability in the transformer substation; in order to judge whether the actual fault point on the fault line disappears, the resistance value of an adjustable resistor at the internal connection point of the transformer substation is adjusted after a certain time delay, the change condition of the branch current of the adjustable resistor in the transformer substation is analyzed, and whether the actual fault point on the line disappears is judged; if the actual fault disappears, disconnecting the grounding switch in the transformer substation, and recovering the normal operation of the system; if the fault still exists, the grounding switch in the transformer substation is kept closed, and then the resistance value of the adjustable resistor is continuously adjusted after a certain time delay to judge whether the fault disappears or not until the actual fault point disappears.
In this embodiment, the control system includes a maximum capacitance current calculation module, a fault phase determination module, a preliminary fault point disappearance determination module, and a long-term fault point disappearance determination module, where:
the maximum capacitance current calculation module is used for calculating the maximum capacitance current I of the power supply system when single-phase grounding occurs according to the ground distribution capacitance values of all lines of the power distribution network0And the threshold value is used as the threshold value of subsequent judgment.
The fault phase judgment module is used for acquiring three-phase voltage of a bus of the transformer; if one phase voltage is reduced and the other two phase voltages are increased to generate zero sequence voltage, the voltage reduction phase is a fault phase, and the grounding switches of the corresponding fault phase at the bus of the transformer substation are controlled to be closed.
The primary fault point disappearance judgment module is used for acquiring the current value I of the adjustable resistance branch after the resistance value of the adjustable resistance is adjusted through certain time delaymComparing the current value I of the adjustable resistance branchmAnd the calculated system maximum capacitance current threshold value I0Size, if I0-Im|≥10％|I0If yes, preliminarily judging that the actual fault of the line does not disappear, keeping a grounding switch connected with the fault of the bus in the transformer substation closed, waiting for a long time delay (10 minutes in the embodiment), and judging again until the fault disappears; if after the first delay I0-Im|<10％|I0And I, preliminarily judging that the actual fault of the line disappears.
The long-time fault point disappearance judgment module is used for preliminarily judging the disappearance of the actual fault of the line, continuously adjusting the resistance value of the adjustable resistor from small to large with small delay (set to 1 minute in the embodiment), and then continuously collecting the fault pointsCurrent value I of adjustable resistance branch circuit integrating three resistance valuesmIf the current value of the adjustable resistance branch circuit under three continuous resistance values is ImAll satisfy | I0-Im|<10％|I0If yes, the actual fault of the line disappears, at the moment, a bus grounding switch in the transformer substation is disconnected, and the system recovers to a normal operation state.
According to the single-phase ground fault disappearance judgment system of the neutral point non-effective grounding system provided by the embodiment, the three-phase switch, the adjustable resistor and the current transformer are arranged at the bus of the transformer substation, after the resistance value of the adjustable resistor is adjusted, the current amplitude value of the branch of the adjustable resistor is obtained through the control system, and the current amplitude value of the branch of the adjustable resistor is analyzed and compared with the maximum capacitance current of the system, so that whether the fault disappears or not can be judged by analyzing and comparing the current value of the branch of the adjustable resistor and the maximum capacitance current after the resistance value is adjusted with a short delay after the fault occurs, and the system can be helped to quickly recover to a normal operation state after the; and the current value of the adjustable resistance branch circuit under different resistance values after the resistance value is adjusted is continuously obtained to analyze and compare with the maximum capacitance current to judge whether the fault disappears or not with longer time delay after the fault occurs, so that the ground switch in the station can be tripped as soon as possible after the fault which has longer discharge time and longer time required for system insulation recovery disappears, and the system can be recovered to a normal operation state.
Example two
The embodiment provides a method for judging disappearance of single-phase earth faults of a neutral point non-effective earthing system based on an adjustable resistor.
Referring to fig. 2, the method for determining disappearance of single-phase ground fault of the neutral point non-effective grounding system includes the following steps:
s101, installing a three-phase switch capable of performing split-phase operation at a three-phase bus in a 10kV (or 35kV) transformer substation, wherein one end of the three-phase switch is connected with the three-phase bus of the transformer substation, and the other end of the three-phase switch is connected with the ground through a group of adjustable resistors; and a high-precision current transformer CT is arranged on the adjustable resistance branch.
Fig. 1 shows a 10kV power supply system, a three-phase switch is connected at a bus of a transformer substation, the three-phase switch is grounded through a group of adjustable resistors, and a high-precision current transformer is installed on a branch of the adjustable resistors. Normally the three-phase switch is in an off state. The bus is connected with 12 outgoing lines with different lengths, and the outgoing line comprises 5 overhead lines of 7km, 3 overhead lines of 5km and 4 overhead lines of 8km in the embodiment.
One end of the adjustable resistor is connected with a common point of the three-phase switch, the other end of the adjustable resistor is directly connected with the ground, the resistance value adjusting range of the adjustable resistor is between 0.5 omega and 20 omega, adjusting gears are set to be 0.5 omega, 5 omega, 10 omega, 15 omega and 20 omega, and an initial value is set to be 0.5 omega.
It should be noted that the selection of the upper limit of the resistance adjustment and the equivalent ground capacitive reactance X of the power distribution systemcIn connection with, to make Z0And XCCan be regarded as approximately equal in engineering, in principle should be
In this embodiment, the current transformer CT can accurately measure the current value I directly flowing to the ground through the adjustable resistorm。
S102, calculating the maximum capacitance current I of the power supply system when single-phase grounding occurs according to the ground distribution capacitance values of all lines of the power distribution network0And the threshold value is used as the threshold value of subsequent judgment.
In the embodiment, the maximum capacitance current I of the system when single-phase grounding occurs0The calculation expression of (a) is:
wherein, U0Is zero sequence voltage in case of fault, UNIn the normal operation state of the systemEffective value of phase voltage of, Z0Is the zero sequence loop equivalent impedance, XCIs the equivalent capacitive reactance to the ground of the system.
It should be noted that, for a system with a non-effective grounding neutral point, the zero-sequence loop equivalent impedance Z is due to the existence of the distributed capacitance to the ground0Usually much larger than the positive sequence loop equivalent impedance Z1Therefore, before and after the single-phase earth fault of the system, U should be applied0＝UN. In addition, in the zero sequence loop, capacitive reactance X is distributed to the groundCIs generally far larger than the values of other zero sequence parameters, and can be approximately considered as Z0＝XCTherefore, in the process of adjusting the adjustable resistance, the total zero sequence ground current I of the system0Remain substantially unchanged.
Effective value of normal operation phase voltage of 10kV distribution line
In this embodiment, the equivalent ground capacitive reactance of the whole distribution network is XC741.6 omega, the maximum capacitance current of the system can be calculated when single-phase grounding occurs
And S103, when the single-phase grounding fault occurs, judging the fault phase according to the change condition of the voltage of the substation bus, and controlling the grounding switch corresponding to the fault phase bus to be closed.
Specifically, in step 103, when a single-phase ground fault occurs, the specific implementation manner of determining the fault phase according to the change condition of the bus voltage of the substation is as follows:
acquiring three-phase voltage of a bus of the transformer; if one phase voltage is reduced and the other two phase voltages are increased, and zero sequence voltage appears, the voltage reduction phase is a fault phase.
And then, the grounding switches corresponding to the fault phases at the bus of the transformer substation are controlled to be closed, namely the fault phase bus is forcibly grounded through a small resistor, and the fault current mainly flows through a small resistor branch circuit instead of a fault point, so that the lower voltage of the fault phase can be ensured, and the possibility of electric shock injury of a human body is greatly reduced.
As shown in fig. 1, when the system operates normally, the three-phase voltages are basically symmetrical, and the three-phase switch keeps an off state. When a single-phase earth fault occurs to the line (phase A is grounded at F1), the phase A voltage at the bus can be obviously reduced, the phase B, C voltage can be increased, and zero sequence voltage is generated at the same time. At the moment, the control system can judge that the A-phase grounding fault occurs, then control the A-phase of the three-phase switch to be closed, and the A-phase bus is grounded through the switch and the adjustable resistor.
Because the initial value of the adjustable resistor is smaller than 0.5 omega, the voltage of the A-phase bus can be limited to a small value, so that the voltage at the fault point F1 is also low, and the risk of electric shock accidents at the F1 is greatly reduced.
And S104, judging whether the actual fault of the line disappears.
Specifically, in the step 104, it is determined whether the actual fault of the line disappears, and the specific implementation process is as follows:
and S1041, after a certain time delay, adjusting the resistance value of the adjustable resistor.
In order to judge whether the actual fault of the line disappears, the resistance value of the adjustable resistor is adjusted after a certain time delay, a plurality of time delays can be set, the first time delay can be set to be 5 seconds in consideration of high proportion of instantaneous faults, and the subsequent time delay can be determined according to the first adjusting condition of the adjustable resistor.
And S1042, collecting the current value of the adjustable resistor branch, and preliminarily judging whether the actual fault of the line disappears.
Specifically, after each time delay, the current value I of the adjustable resistance branch is collectedmComparing the current value I of the adjustable resistance branchmAnd the calculated system maximum capacitance current threshold value I0Size, if I0-Im|≥10％|I0If yes, preliminarily judging that the actual fault of the line does not disappear, keeping a grounding switch connected with the fault of the bus in the transformer substation closed, waiting for a long time delay (10 minutes in the embodiment), and judging again until the fault disappears; if after the first delay I0-Im|<10％|I0And I, preliminarily judging that the actual fault of the line disappears.
And S1043, after preliminarily judging that the actual line fault disappears, adjusting the resistance value of the adjustable resistor again after a certain time delay according to the sequence from small to large, and judging whether the actual line fault disappears again.
Specifically, if I is present after the first delay in step 10410-Im|<10％|I0Initially determining that the actual fault of the line disappears, continuously adjusting the resistance value of the adjustable resistor in the order from small to large with a small delay (set to 1 minute in this embodiment), and continuously collecting the current values I of the adjustable resistor branches under three resistance valuesmIf the current value of the adjustable resistance branch circuit under three continuous resistance values is ImAll satisfy | I0-Im|<10％|I0If yes, the actual fault of the line disappears, at the moment, a bus grounding switch in the transformer substation is disconnected, and the system recovers to a normal operation state.
When the A phase is judged to be a fault phase, after the A phase grounding switch is closed for 5 seconds, the measured value I of the CT on the adjustable resistance branch is calculatedmAnd is combined withmAnd a threshold value I0Comparing the amplitudes, and determining the time delay of next adjustment of the adjustable resistance value according to the comparison result.
According to the method for judging the disappearance of the single-phase ground fault of the neutral point non-effective grounding system, whether the actual fault point disappears or not can be judged quickly and reliably by regulating the resistance value of the grounding resistor at the position of the bus in the transformer substation and analyzing and comparing the current amplitude of the adjustable resistor branch, the system can be prevented from running for a long time with a fault, and the impact on the running of power supply equipment and a power grid caused by blind probing through the operation of a grounding switch in the station can be avoided; after the fault occurs, the resistance value is adjusted in a short time delay mode to preliminarily judge whether the fault disappears; for some faults with longer discharge time and longer required time for system insulation recovery, whether the faults disappear or not is judged again by setting a plurality of longer delays, and the ground switch in the station can be tripped as soon as possible after the faults disappear, so that the system recovers to a normal operation state.
EXAMPLE III
The embodiment provides an example for analyzing two situations of a permanent single-phase earth fault and an instantaneous single-phase earth fault respectively by adopting the method for judging disappearance of the single-phase earth fault of the neutral point non-effective earthing system provided by the embodiment.
(1) And analyzing the permanent single-phase earth fault by adopting a neutral point non-effective earthing system single-phase earth fault disappearance judgment method.
At 3 minutes on a 7km long line L1Permanent single-phase grounding through a 3 omega transition resistor is generated, and after the control system detects the change of three-phase voltage of the bus, the A phase of the three-phase switch is rapidly controlled to be closed, so that a fixed grounding point in the transformer substation is formed. And calculating the current of the adjustable resistance branch circuit 5 seconds after the fault, and adjusting the resistance value according to a preset delay and mode, wherein the current variation trend of the adjustable resistance branch circuit corresponding to various resistance values is shown in figure 3.
As can be seen from FIG. 3, in the event of a permanent fault, there is a shunting action at the fault point F1 on the line, and as the adjustable resistor increases step by step, the current I flowing through the adjustable resistor branch in the stationmIt will be reduced step by step. In this case, when the resistance is adjusted to the second level R ═ 5 Ω, Im＝13.4A，|I0-Im9.94 is more than or equal to 0.1 multiplied by 23.34, the fault is preliminarily judged to exist, the adjustable resistor is suspended and adjusted according to the step 7), and the current I is continuously monitoredmAfter a longer delay (10 minutes) the pair I is repeatedmCalculating to judge whether I is satisfied0-Im|≥10％|I0L. If the condition is still met, the judgment is carried out again after continuously waiting for 10 minutes. FIG. 3 shows the branch current I when the adjustable resistance takes different values in the case of a permanent faultmIs intended to fully demonstrate I in the event of a permanent earth faultmThe change rule of (2).
(2) And analyzing the transient single-phase earth fault by adopting a neutral point non-effective earthing system single-phase earth fault disappearance judgment method.
Simulating a certain 7km line L at 3 minutes1Transient single-phase grounding occurs through a transition resistance of 3 Ω, and the duration of the transient fault is set to 3 seconds. After the control system detects the change of the three-phase voltage of the bus, the A phase of the three-phase switch is rapidly controlled to be closed to form power transformationAnd fixing a grounding point in the station, and calculating the current of the adjustable resistance branch 5 seconds after the fault. The current variation trend of the corresponding adjustable resistance branch under various resistance values is shown in fig. 4.
Fig. 4 shows that when the actual fault point of the line disappears, the current I of the adjustable resistance branch circuitmAbout 23A, | I0-Im|＝0.01<0.1 multiplied by 23.34, and the failure is preliminarily judged to disappear. After a small delay (1 minute), the adjustable resistance value is adjusted from 0.5 omega to 5 omega, and the current I is measured and calculated againmAt this time ImThe value is still maintained at about 23A, and I is satisfied0-Im|≤10％|I0And adjusting the adjustable resistance to 10 omega after 1 minute of delay, wherein I is still satisfied0-Im|≤10％|I0L. Continuously adjusting three resistance values to satisfy I0-Im|≤10％|I0And l, judging that the actual fault of the line disappears, and at the moment, switching off the A-phase switch in the control station and recovering the normal operation of the system. FIG. 4 shows the branch current I when the adjustable resistance takes different values in the case of a transient faultmThe value of (A) shows completely the value of I in the case of a transient earth faultmThe change rule shows that the current I of the adjustable resistance branch circuit changes along with the change of the adjustable resistance value at the momentmBasically unchanged, and whether the actual fault point disappears or not can be judged timely and reliably.
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 (10)
1. A single-phase earth fault disappearance judgment system of a neutral point non-effective earthing system is characterized by comprising a three-phase switch, an adjustable resistor, a current transformer and a control system, wherein the three-phase switch is installed at a bus of a transformer substation;
one end of the three-phase switch is connected with a three-phase bus of the transformer substation, the other end of the three-phase switch is grounded through an adjustable resistor, the current transformer is arranged on the adjustable resistor branch, and the current transformer is used for collecting the current value of the adjustable resistor branch and transmitting the current value to the control system;
the control system comprises a maximum capacitance current calculation module, a fault phase judgment module and a fault point disappearance judgment module; wherein:
the maximum capacitance current calculation module is used for calculating the maximum capacitance current of the power supply system when single-phase grounding occurs according to the ground distribution capacitance values of all lines of the power distribution network;
the fault phase judging module is used for judging the fault phase according to the change condition of the three-phase voltage of the bus of the transformer substation when a single-phase earth fault occurs, and controlling the corresponding earth switch at the fault phase bus to be closed;
the fault point disappearance judgment module is used for obtaining the current value of the adjustable resistor branch after the resistance value is adjusted after a certain short time delay and the resistance value of the adjustable resistor is adjusted, and preliminarily judging whether the actual fault of the line disappears; if the actual fault of the line is preliminarily judged to disappear, the current values of the adjustable resistance branches under a plurality of different resistance values are continuously obtained after a certain long time delay and resistance value adjustment, and whether the actual fault of the line disappears or not is judged again.
2. The system for determining disappearance of single-phase earth faults in a neutral point non-actively grounded system as claimed in claim 1, wherein the fault phase determining module is specifically configured to:
acquiring three-phase voltage of a bus of the transformer;
if one phase voltage is reduced and the other two phase voltages are increased to generate zero sequence voltage, the voltage reduction phase is a fault phase;
and controlling the grounding switches corresponding to the fault phases at the bus of the transformer substation to be closed.
3. The system for determining the disappearance of single-phase earth faults in a neutral point non-active grounding system according to claim 1, wherein the module for determining the disappearance of fault points comprises a module for determining the disappearance of preliminary fault points and a module for determining the disappearance of long fault points.
4. The system of claim 3, wherein the preliminary fault point disappearance determination module is configured to:
after the resistance value of the adjustable resistor is adjusted in a delayed manner for a certain short time, the current value I of the adjustable resistor branch is obtainedm(ii) a Comparing the current value I of the adjustable resistance branchmAnd the calculated maximum system capacitance current value I0Size; if I0-Im|≥10％|I0If yes, preliminarily judging that the actual fault of the line does not disappear, keeping a grounding switch connected with the fault of the bus in the transformer substation closed, and judging again after waiting for a certain long time delay until the fault disappears; if I0-Im|<10％|I0And I, preliminarily judging that the actual fault of the line disappears.
5. The system for determining the disappearance of single-phase earth faults in a system with a non-effectively grounded neutral point as claimed in claim 3, wherein the long-term disappearance determination module is configured to:
after the resistance value of the adjustable resistor is adjusted according to the sequence from small to large after a certain long time delay, the current value I of the adjustable resistor branch under a plurality of different resistance values is continuously acquiredm；
If the current value I of the adjustable resistance branch under a plurality of continuous resistance valuesmAll satisfy | I0-Im|<10％|I0If yes, the actual fault of the fault line disappears, and a bus grounding switch in the transformer substation is disconnected.
6. A method for judging disappearance of single-phase earth fault of a neutral point non-effectively grounded system, which is implemented based on the system for judging disappearance of single-phase earth fault of the neutral point non-effectively grounded system as claimed in any one of claims 1 to 5, and which is characterized by comprising the steps of:
calculating the maximum capacitance current of the power supply system when single-phase grounding occurs according to the ground distribution capacitance values of all lines of the power distribution network;
when a single-phase earth fault occurs, judging the phase of the fault according to the change condition of the voltage of the bus of the transformer substation, and controlling the corresponding earthing switch at the bus of the fault phase to be closed;
after a certain short time delay and the resistance value of the adjustable resistor are adjusted, the current value of the adjustable resistor branch circuit after the resistance value is adjusted is obtained, and whether the actual fault of the circuit disappears or not is preliminarily judged;
if the actual fault of the line is preliminarily judged to disappear, the current values of the adjustable resistance branches under a plurality of different resistance values are continuously obtained after a certain long time delay is carried out again and the resistance values of the adjustable resistance are adjusted from small to large, and whether the actual fault of the line disappears is judged again.
7. The method for judging disappearance of single-phase earth faults of the neutral point non-effectively grounded system as claimed in claim 6, wherein the calculation formula of the maximum capacitance current of the power supply system when single-phase grounding occurs is as follows:
wherein, U0Is zero sequence voltage in case of fault, UNIs the effective value of the phase voltage, Z, in the normal operation state of the system0Is the zero sequence loop equivalent impedance, XCIs the equivalent capacitive reactance to the ground of the system.
8. The method for judging disappearance of single-phase earth faults of the neutral point non-effective earthing system as claimed in claim 6, wherein the step of judging the fault phase according to the change condition of the substation bus voltage comprises the following steps:
acquiring three-phase voltage of a bus of the transformer;
if one phase voltage is reduced and the other two phase voltages are increased to generate zero sequence voltage, the voltage reduction phase is a fault phase;
and controlling the grounding switches corresponding to the fault phases at the bus of the transformer substation to be closed.
9. The method for determining disappearance of single-phase earth fault of the neutral point non-effective earthing system as claimed in claim 6, wherein the step of preliminarily determining whether the actual fault of the line disappears comprises:
after a certain short time delay and the resistance value of the adjustable resistor are adjusted;
obtaining the current value I of the adjustable resistance branchm；
Comparing the current value I of the adjustable resistance branchmAnd the calculated maximum system capacitance current value I0Size;
if I0-Im|≥10％|I0If yes, preliminarily judging that the actual fault of the line does not disappear, keeping a grounding switch connected with the fault of the bus in the transformer substation closed, and judging again after waiting for a certain long time delay until the fault disappears;
if I0-Im|<10％|I0And I, preliminarily judging that the actual fault of the line disappears.
10. The method as claimed in claim 6, wherein the step of determining whether the actual line fault disappears again comprises:
after a certain long time delay and the resistance values of the adjustable resistors are adjusted according to the sequence from small to large, the current values I of the adjustable resistor branches under the three resistance values are continuously obtainedm；
If the current value I of the adjustable resistance branch under three continuous resistance valuesmAll satisfy | I0-Im|<10％|I0If yes, the actual fault of the line disappears, at the moment, a bus grounding switch in the transformer substation is disconnected, and the system recovers to a normal operation state.
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