CN109917230B - Grounding fault monitoring and protection integrated method for neutral point resistance-containing grounding power distribution network - Google Patents
Grounding fault monitoring and protection integrated method for neutral point resistance-containing grounding power distribution network Download PDFInfo
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Abstract
The invention discloses a grounding fault monitoring and protection integrated method for a neutral point resistance-containing grounding power distribution network, which is characterized in that when the current amplitude or waveform variation of a neutral point grounding resistance branch is in a threshold value interval and continuously exceeds a preset time length, the condition that the grounding insulation of the power distribution network is abnormal is judged and an alarm is given; when the current amplitude of the neutral point grounding resistor branch, the zero sequence current amplitude of the outgoing line branch and the phase difference between the zero sequence current and the current of the neutral point grounding resistor branch all meet preset conditions, the outgoing line branch is judged to have a ground fault so as to alarm or trip. By adopting the method disclosed by the invention, early warning can be realized when the insulation of the power distribution network is reduced and slight discharge occurs, so that the early warning is convenient to deal with in time, and more serious grounding or interphase faults are avoided; and for the generated discharge faults including high-resistance earth faults with fault resistance up to 1000 ohms, accurately identifying fault lines, and adopting rapid removal measures to isolate faults so as to realize sensitive and reliable protection of the earth faults of the power distribution network.
Description
Technical Field
The invention relates to the technical field of power distribution network monitoring and protection, in particular to a method for monitoring and protecting ground faults of a power distribution network with a neutral point and a resistance grounding.
Background
The neutral point grounding mode of the power distribution network comprises several main modes of non-grounding, grounding through an arc suppression coil, grounding through a parallel resistor of the arc suppression coil, grounding through a resistor and the like. In a grounding mode with a resistor at a neutral point, a zero sequence current protection is generally configured through an outgoing line connected to a bus to reflect a grounding fault on the outgoing line; the zero-sequence current protection takes the magnitude of zero-sequence current as an action basis, but must avoid capacitive zero-sequence current flowing through the line when other lines have faults, so the setting value is high, when the line has a ground fault through a transition resistor (fault resistor for short), the condition that the zero-sequence current value cannot reach the action value and action is rejected occurs, and in the engineering practice, the accident that the zero-sequence current protection is rejected due to the reasons has occurred for many times.
Because the outgoing line is only provided with the zero sequence current protection reaction ground fault, when the protection device or the switch fails to operate, the ground protection of other principles is not used as backup protection, and the single-phase fault can be converted into a multi-phase fault or cause the burning loss of large-area electrical equipment. In addition, ground faults in a large number of distribution lines, cables, switchgears and the like are caused by equipment aging and insulation level reduction, and the faults are manifested as leakage of a small current at an early stage and then progress to discharge of a large current. The distribution network has numerous electrical equipment and wide distribution range, a sensor is difficult to be arranged at each possible fault point to monitor leakage or discharge caused by insulation reduction on line, an economical and reliable early fault monitoring method is required to be adopted, leakage and discharge of the electrical equipment are found in time, a fault early warning signal is sent out, a corresponding countermeasure is adopted, and the condition that a slight fault is developed into a serious fault is avoided
Therefore, a highly sensitive, economical and reliable fault monitoring and protecting method is urgently needed, so that the ground fault can be timely found and corresponding measures can be taken, and the development of a slight fault into a serious fault can be avoided.
Disclosure of Invention
Therefore, the problem to be solved by the invention is how to find the grounding fault in time and take corresponding measures to avoid the development of a slight fault into a serious fault and provide a sensitive protection function when the existing zero-sequence current protection of high-resistance grounding is difficult to react.
In order to solve the technical problems, the invention adopts the following technical scheme:
the method for monitoring and protecting the ground fault of the power distribution network with the neutral point grounded by the resistor comprises the following steps:
s101: collecting the current of a neutral point grounding resistor branch in real time and calculating the amplitude and the phase of the current;
s102, when the current amplitude or the waveform variation of the neutral point grounding resistance branch is within a threshold value interval and continuously exceeds a preset time length, judging that the ground insulation of the power distribution network is reduced or slightly discharged, and giving a grounding fault early warning signal;
s103: collecting and calculating power frequency amplitude and phase of each outlet zero sequence current connected on the bus in real time;
s104, calculating the phase difference between the zero sequence current of each outgoing line and the branch current of the neutral point grounding resistor;
s105, when the power frequency amplitude of the branch current of the neutral point grounding resistor, the power frequency amplitude of the branch current of the measured outgoing line, and the phase difference between the zero sequence current of the outgoing line and the branch current of the neutral point grounding resistor all meet preset conditions, judging that the outgoing line branch has a ground fault;
and S106, performing disconnection control on the outgoing line branch and giving an earth fault alarm.
Preferably, in step S2, the giving of the ground fault warning signal includes generating power distribution network ground fault warning information, and sending the power distribution network ground fault warning information to an operation and maintenance platform or a distribution network scheduling center.
Preferably, in step S6, giving a ground fault alarm includes generating fault information of the outgoing line branch, and giving an alarm based on the fault information of the outgoing line branch.
Preferably, the preset conditions in step S5 include:
the power frequency amplitude of the current of the neutral point grounding resistor branch is larger than a first amplitude setting threshold;
the current power frequency amplitude of the outgoing line branch is larger than a second amplitude setting threshold;
when the defined current direction is away from the bus as a positive direction, the phase difference between the outgoing line zero sequence current of the outgoing line branch and the neutral point grounding resistor branch current is larger than an angle setting threshold, or the phase difference between the negative value of the outgoing line zero sequence current of the outgoing line branch and the neutral point grounding resistor branch current is smaller than an absolute value (180 degrees-angle setting threshold);
and when the conditions are met and the duration time reaches a setting action time length threshold value, judging that the outgoing line branch circuit has a ground fault.
Preferably, a line at one end of the distribution network with a neutral point grounding resistor grounded passes through the induction areas of the first current transformer CT1 and the second current transformer CT2 to obtain current information of neutral point grounding resistor branches, each outgoing line branch of the distribution network passes through the induction area of one third current transformer CT3 to obtain zero-sequence current information of each outgoing line, and the output ends of the first current transformer CT1, the second current transformer CT2 and the third current transformer CT3 are connected with the input end of the ground fault monitoring protection device; the ground fault monitoring protection device comprises a processor and a trip control element, wherein a control command of the trip control element is connected with a circuit breaker trip loop, the processor is used for calculating the current amplitude and the phase of a neutral point grounding resistor based on current information output by a first current transformer CT1 and a second current transformer CT2, the processor is also used for judging that the power distribution network has ground faults when the current amplitude and the phase of a neutral point grounding resistor branch circuit are in a threshold value interval and the duration reaches a fault duration threshold value, the processor is also used for calculating the current power frequency amplitude and the phase of each outgoing line branch circuit based on the current information output by each third current transformer CT3, the processor is also used for calculating the outgoing line zero sequence current phase difference of each outgoing line branch circuit, and the processor is also used for judging that the outgoing line branch circuit has ground faults when the current amplitude of the neutral point grounding resistor, the current power frequency amplitude of the outgoing line branch circuit and the outgoing line zero sequence current phase, and the tripping control element is used for carrying out circuit breaking treatment on the outgoing line branch when the outgoing line branch has a ground fault.
Preferably, the processor is further configured to generate power distribution network ground fault early warning information when it is determined that a ground fault occurs in the power distribution network, and the ground fault monitoring and protecting device further includes a communication module, and the communication module is configured to send the power distribution network ground fault early warning information to an operation and maintenance platform or a distribution network scheduling center.
Preferably, the processor is further configured to generate fault information of any outgoing line branch when a ground fault occurs in the outgoing line branch, and the ground fault monitoring protection device further includes an alarm module configured to alarm based on the fault information of the outgoing line branch.
Preferably, the current transformers on the neutral point resistance branch comprise a first current transformer CT1 and a second current transformer CT2, and the upper limit of the accurate measurement range of the first current transformer CT1 is the lower limit of the accurate measurement range of the second current transformer CT 2.
In conclusion, the invention discloses an integrated method for monitoring and protecting the ground fault of a neutral point resistance-containing grounding power distribution network, which is used for collecting the current of a neutral point grounding resistance branch in real time and calculating the amplitude and the phase of the current; when the current amplitude or the waveform variation of the neutral point grounding resistance branch is within a threshold value interval and continuously exceeds a preset time length, judging that the ground insulation of the power distribution network is reduced or slightly discharged, and giving a grounding fault early warning signal; collecting and calculating power frequency amplitude and phase of each outlet zero sequence current connected on the bus in real time; calculating the phase difference between each outgoing line zero sequence current and the neutral point grounding resistance branch current; when the power frequency amplitude of the branch current of the neutral point grounding resistor, the power frequency amplitude of the branch current of the measured outgoing line, and the phase difference between the zero sequence current of the outgoing line and the branch current of the neutral point grounding resistor all meet preset conditions, judging that the outgoing line branch has a grounding fault; and performing disconnection control on the outgoing line branch and giving an earth fault alarm. By adopting the method disclosed by the invention, fault early warning can be timely sent out when all other equipment connected to the power distribution network bus generates insulation leakage to the ground or slightly discharges to the ground, so that operation and maintenance personnel can timely handle the equipment, and more serious ground fault is avoided; for metallic or low-resistance (less than 100 ohms) single-phase earth faults or high-resistance (100 ohms to 1000 ohms) single-phase earth faults which are slightly converted or suddenly generated, fault outgoing lines are identified, and control commands are sent to remove the lines with faults, so that the reliability and the sensitivity of single-phase earth protection of the power distribution network are improved.
Drawings
For purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made in detail to the present invention as illustrated in the accompanying drawings, in which:
fig. 1 is a flowchart of an embodiment of a method for monitoring and protecting ground faults of a distribution network with a neutral point grounded by resistors according to the present invention;
FIG. 2 is a schematic diagram of the connection of a distribution network in which a neutral point is directly grounded via a resistor when the integrated method for monitoring and protecting the ground fault of the distribution network in which the neutral point includes the resistor and is grounded disclosed by the invention is adopted;
FIG. 3 is a schematic diagram of the connection of a distribution network with a neutral point grounded by a parallel resistor of an arc suppression coil when the integrated method for monitoring and protecting the ground fault of the distribution network with the neutral point grounded by the resistor disclosed by the invention is adopted;
FIG. 4 is a schematic diagram of one embodiment of a ground fault monitoring and protection apparatus of the present invention;
FIG. 5 shows a line fault resistance RfGrounding zero sequence equivalent diagram。
Description of reference numerals: distribution transformer DT, grounding transformer GT, neutral grounding resistor R0A first current transformer CT1, a second current transformer CT2, a third current transformer CT3, a ground fault monitoring and protecting device GMP and an arc suppression coil LOEqual-value-to-ground capacitance C of power distribution system0Fault resistance RfZero sequence voltage 3U0。
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, the invention discloses a method for monitoring and protecting the ground fault of a power distribution network with a neutral point grounded by a resistor and containing an arc suppression coil, which is applied to the application scene of the method and comprises a power distribution network with a neutral point grounded by a resistor connected in parallel with the arc suppression coil and a power distribution network with a neutral point directly grounded by a resistor (as shown in fig. 2 or fig. 3), and comprises the following steps:
s101: collecting the current of a neutral point grounding resistor branch in real time and calculating the amplitude and the phase of the current;
in the invention, a current transformer can be used for acquiring an analog signal from a line, and the analog signal is converted into a digital signal by adopting digital-to-analog conversion, so that the amplitude and the phase are calculated.
S102, when the current amplitude or the waveform variation of the neutral point grounding resistance branch is within a threshold value interval and continuously exceeds a preset time length, judging that the ground insulation of the power distribution network is reduced or slightly discharged, and giving a grounding fault early warning signal;
in specific implementation, a current transformer with sensitivity in milliampere level can be used for collecting current information of the neutral point grounding resistor, and specifically, a current transformer CT1 with accurate measurement range of 10 milliampere to 2 amperes can be used. When the current amplitude or the mutation quantity of the neutral point grounding resistance is within a threshold value interval or the grounding current waveform characteristic meets the discharge characteristic matching degree and the duration reaches the fault duration threshold, the early stage earth discharge defect of the power distribution network is judged.
The grounding current of the electrical equipment grounding fault in the early insulation reduction stage of the fault is very small, and the bus can measure zeroThe sequence voltage is very small, and the early hidden danger cannot be found by means of protection or line selection of zero sequence voltage starting. Therefore, the invention can accurately measure milliampere level small current by adopting a neutral point resistance current measuring method through CT1, realize early monitoring of the ground fault and judge whether the ground fault occurs. Calculating the current amplitude I of the neutral point resistance branch obtained by CT1CT1When the current I isCT1In a threshold interval (the lower limit of the threshold interval is a preset current threshold I)CT1ZD1With an upper limit of a predetermined current threshold ICT1ZD2) The duration reaches the fault duration threshold TCT1ZDAnd judging that the power distribution network has a ground fault.
I in the present inventionCT1ZD1The value range is 10 milliampere to 500 milliampere, ICT1ZD2Taking the value as a ground fault identification threshold value, taking the value as 500 milliamperes to 2 amperes, and pressing TCT1ZDRanging from 1 second to 10 minutes or more.
The invention adopts the neutral point grounding resistance branch current to form the function of judging the early-stage fault of the grounding fault of the power distribution network, can realize the continuous monitoring on whether all the power distribution equipment has insulation leakage to the ground by only utilizing the current information of the neutral point resistance branch, avoids arranging insulation monitoring devices on a large amount of power distribution equipment and electric wires and cables, and has high reliability and economy.
S103: collecting and calculating power frequency amplitude and phase of each outlet zero sequence current connected on the bus in real time;
the invention can arrange a current transformer CT3 on each outgoing line branch for collecting the current information of each outgoing line branch and calculating the current power frequency amplitude and phase of each outgoing line branch after analog-to-digital conversion.
S104, calculating the phase difference between the zero sequence current of each outgoing line and the branch current of the neutral point grounding resistor;
here, the purpose is to determine whether a specific outgoing line has a fault and to determine whether a disconnection process needs to be performed. When the circuit breaking treatment is needed, the current which can be collected by the current transformer is larger no matter the neutral point grounding resistance branch or the outlet branch, so that the current transformer can accurately respond to the large currentAnd a transformer CT2 with a large current accurate measurement range is also arranged, for example, a current transformer with an accurate measurement current of 2-1000A is arranged for acquiring the current amplitude and the phase of the neutral point grounding resistor branch in real time. The two current transformers with different accurate measurement ranges can be respectively used for the insulation reduction or slight earth fault judgment stage of the whole power distribution network and the judgment of a specific certain outgoing line earth fault, and compared with the current transformer, the method can better ensure the measurement accuracy of small current and the measurement of large current. Only one current transformer capable of ensuring the full-scale precision can be adopted, namely the CT1 and the CT2 are the same current transformer. In the specific implementation, the amplitude and the phase of the current of the neutral point grounding resistor branch calculated by the current information measured by the CT2 are respectively set as IRM、PRSetting the current power frequency amplitude and phase of the outgoing line branch calculated by the information measured by CT3 as IL0、PL0。
S105, when the power frequency amplitude of the branch current of the neutral point grounding resistor, the power frequency amplitude of the branch current of the measured outgoing line, and the phase difference between the zero sequence current of the outgoing line and the branch current of the neutral point grounding resistor all meet preset conditions, judging that the outgoing line branch has a ground fault;
and S106, performing disconnection control on the outgoing line branch and giving an earth fault alarm.
And each outgoing line branch is provided with a breaker, and the breaker can realize the breaking control of a certain outgoing line branch.
The prior patents and documents provide methods for transforming a neutral point non-grounding or arc suppression coil grounding mode into a neutral point grounding mode through a resistor or a parallel resistor, and adopt different methods in aspects of neutral point resistor resistance value selection, different grounding mode selection, grounding line selection principle, electrical equipment temperature monitoring, partial discharge monitoring and the like, but documents for realizing integration of grounding fault monitoring and protection by using the matching of neutral point resistor branch current and outlet zero-sequence current are not found.
By adopting the method disclosed by the invention, the earth fault can be accurately judged when insulation leakage occurs on the outgoing line connected with the power distribution network bus, and when metallic or resistive single-phase earth fault occurs, the faulty outgoing line is identified and a control command is sent to remove the faulty line, so that safety accidents are avoided.
According to the invention, two current transformers with different accurate measurement ranges can be adopted to acquire the current amplitude and the phase of the neutral point grounding resistor in real time, wherein the accurate measurement range of the first current transformer CT1 is 10-2 amperes. The grounding current of most grounding faults in the early insulation descending stage of the fault is very small, the zero sequence voltage measurable by the bus is very small, and the early hidden danger of the fault cannot be found by means of protection or line selection started by the zero sequence voltage, so that the method can accurately detect the small current of the neutral point grounding resistor by using the first current transformer CT1, judge that the early insulation descending or discharging defect occurs in the power distribution network when the current amplitude of the neutral point grounding resistor is located in a threshold value interval or the waveform characteristic of the grounding current meets the matching degree of the discharging characteristic and the duration reaches the fault duration threshold value, and can give an early warning to a worker, and the worker can check the power distribution network according to the early warning to see that the insulation weak point exists, deal with the found defect and avoid the defect from developing into a serious fault. When the fault is serious, the current which can be collected by the current transformer is large no matter the neutral point grounding resistor branch or the outgoing line branch, therefore, the current transformer CT2 which meets the requirement of large-current accurate measurement is also arranged, the range can be set to be 2-1000 amperes, the current information of the neutral point grounding resistor at the moment is collected, the fault of the specific outgoing line branch is judged, and whether the open circuit processing is needed or not is judged.
It should be noted that, in the present invention, the first current transformer CT1 and the second current transformer CT2 are independent from each other. Only the information collected by the first current transformer CT1 may satisfy the condition in step S2, but the information collected by the second current transformer CT2 may not satisfy the preset condition in step S5, which indicates that the distribution network has only an early earth discharge defect, and at this time, the disconnection process is not needed, and only an early warning needs to be sent out to notify a worker to perform the overhaul. It is also possible that the information collected by the second current transformer CT2 satisfies the preset condition in step S5 before the worker completes the inspection after a while after the information collected by the first current transformer CT1 satisfies the condition in step S2, and at this time, it is necessary to perform the disconnection process when it is determined that the fault has deteriorated. It is also possible that the first current transformer CT1 and the second current transformer CT2 detect current information satisfying respective conditions at the same time, which indicates that the failed outlet branch needs to be disconnected when a fault occurs.
In specific implementation, in step S2, the giving of the ground fault early warning signal includes generating power distribution network ground fault early warning information, and sending the power distribution network ground fault early warning information to an operation and maintenance platform or a distribution network scheduling center.
After the power distribution network is judged to have a fault, early warning can be carried out firstly, when the fault is not deteriorated yet and the power distribution network can also work reluctantly, workers are reminded to overhaul in time, or corresponding countermeasures are made within sufficient time of the workers.
In specific implementation, in step S6, giving a ground fault alarm includes generating fault information of the outgoing line branch, and giving an alarm based on the fault information of the outgoing line branch.
In the present invention, the alarm device includes, but is not limited to, lighting a fault indicator on a control panel of the operation and maintenance platform or the dispatch center, popping up fault information on a display screen, and the like.
In specific implementation, the preset conditions in step S5 include:
(1) current amplitude I of neutral point grounding resistor branchRGreater than a first amplitude setting threshold IRMZDThe first amplitude setting threshold is larger than a preset current threshold;
current amplitude I of neutral point grounding resistorRMIs zero when the line is not faulted, so the first amplitude setting threshold IRMZDAccording to the ratio of I to ICT1ZD2The setting is only needed, and an overlapping relation is formed between the setting and the ground fault early warning range, for example, the setting is 500 milliamperes, so that the sensitivity of the reaction fault is very high.
The neutral point grounding resistor current amplitude is adopted as one of the protection action conditions, and the neutral point grounding resistor branch current is zero before only the arc suppression coil is connected to the arc suppression coil and the resistor is not put into use in the arc suppression coil and resistor mode, and the protection device does not meet the action condition and is locked, so that the possible misoperation of the protection device during the arc suppression period is avoided, and the reliability of the protection action under the condition is ensured.
(2) Current power frequency amplitude I of outgoing line branchCT3Greater than a second amplitude setting threshold ICT3ZD；
Second amplitude setting threshold ICT3ZDCalculating the error of the zero-sequence current transformer when the maximum load current flows through the corresponding outgoing line branch, for example, calculating the error of 10% conversion of the zero-sequence current transformer, and then obtaining the maximum load current of (0.1 line);
(3) the outgoing zero-sequence current phase difference of the outgoing branch is smaller than an angle setting threshold;
angle setting threshold PZD0＝arctan(R0/XLC)-θk，XLC＝XLXC/(XL-XC)，XLIs the neutral point arc suppression coil reactance, XCIs the total capacitive reactance formed by the capacitance to ground of other equipment except the protection installation line; r0Is a neutral point ground resistance; thetakIs a setting margin angle.
The judgment condition is only related to arc suppression coil parameters, line distributed capacitance parameters and neutral point grounding resistance values, but is not related to the grounding resistance values of fault points, so that the judgment condition has high reliability when a high-resistance grounding fault occurs in a line.
Under the compensation action of arc suppression coil, XLIs approximately equal to XCThe phase difference between the fault branch current and the neutral point resistance branch current is close to 180 degrees, and the setting angle P can be reliably metZD0. The method is therefore suitable for very high-value ground faults.
(4) And when the conditions are met and the duration time reaches a setting action time length threshold value, judging that the outgoing line branch circuit has a ground fault.
Setting action duration threshold TCT1ZDAccording to the zero sequence of the circuitAnd calculating in a matched manner of current protection, and adding an interval time larger than 0 on the basis of the zero sequence current protection action time of the line, for example, 0.3-0.5 second.
In the above judgment conditions, only the condition (1) is related to the condition (2) and the current amplitude, and the calculation only needs to consider the error of the current transformer, and the calculated value is small, so that the threshold value satisfying the two conditions is low. The protection principle ensures that the fault can be sensitively judged when the high fault grounding resistance, namely zero-sequence current, is small. Namely, the open circuit protection in the invention can realize the high-resistance grounding protection of the distribution line.
In specific implementation, a line at one end of a neutral point grounding resistor of a power distribution network passes through the induction areas of a first current transformer CT1 and a second current transformer CT2 to obtain current information of neutral point resistor branches, each outgoing line branch of the power distribution network passes through the induction area of a third current transformer CT3 to obtain zero-sequence current information of each outgoing line, the output ends of the first current transformer CT1 and the second current transformer CT2 and the third current transformer CT3 are connected with the input end of a grounding fault monitoring protection device, the grounding fault monitoring protection device comprises a processor and a tripping control element, wherein a control command of the tripping control element is connected with a tripping circuit of a circuit breaker, the processor is used for calculating the current amplitude and the phase of the neutral point grounding resistor based on the current information output by the first current transformer CT1 and the second current transformer CT2, and the processor is further used for calculating the current amplitude and the phase of the neutral point grounding resistor when the current amplitude and the phase are within a threshold interval and the duration reaches a, the processor is further used for calculating the current power frequency amplitude and the phase of each outgoing line branch based on the current information output by each third current transformer CT3, calculating the outgoing line zero sequence current phase difference of each outgoing line branch, judging that the outgoing line branch has a ground fault when the neutral point ground resistance current amplitude, the current power frequency amplitude of the outgoing line branch and the outgoing line zero sequence current phase difference meet preset conditions, and enabling the outgoing line branch to be subjected to open circuit processing due to the fact that the outgoing line branch has the ground fault.
During specific implementation, the processor is further used for generating distribution network ground fault early warning information when the distribution network is judged to have ground fault, the ground fault monitoring and protecting device further comprises a communication module, and the communication module is used for sending the distribution network ground fault early warning information to an operation and maintenance platform or a distribution network scheduling center.
During specific implementation, the processor is further used for generating fault information of the outgoing line branch when judging that any outgoing line branch has a ground fault, and the ground fault monitoring protection device further comprises an alarm module which is used for giving an alarm based on the fault information of the outgoing line branch.
During specific implementation, the first current mutual inductance device comprises a first current transformer and a second current transformer, and the upper limit of the accurate measurement range of the first current transformer is the lower limit of the accurate measurement range of the second current transformer.
As shown in fig. 4, the ground fault monitoring and protecting device, i.e. the GMP in the figure, the processor, i.e. the CPU, and the ground fault monitoring and protecting device further includes a digital-to-analog conversion module, a storage module, and the like. The ground fault monitoring protection device comprises an AC1 interface, an AC2 interface, an AC3 interface, an alarm module, a communication module and a trip module (the trip module is used for controlling the corresponding outgoing line branch to be broken), wherein the interfaces are respectively connected with the CT1 interface, the CT2 interface and the CT3 interface. In the invention, only one ground fault monitoring protection device can be adopted, and signals of CT1, CT2 and CT3 current transformers of all outlet branches need to be accessed; and each outlet branch can be respectively provided with a ground fault monitoring protection device, and only signals of the current transformers of the CT1, the CT2 and the CT3 of the selected outlet branch need to be accessed.
The first current transformer and the second current transformer correspond to CT1 and CT2, respectively.
Finally, it is noted that the above-mentioned embodiments illustrate rather than limit the invention, and that, while the invention has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (7)
1. The method for monitoring and protecting the ground fault of the power distribution network with the neutral point grounded by the resistor is characterized in that the application scene of the method comprises the power distribution network with the neutral point grounded by the arc suppression coil connected with the resistor in parallel and the power distribution network with the neutral point directly grounded by the resistor, and comprises the following steps:
s101: collecting the current of a neutral point grounding resistor branch in real time, calculating the amplitude and the phase of the current, and collecting the current information of the neutral point grounding resistor by adopting a current transformer CT1 with the sensitivity of milliampere level;
s102, when the current amplitude or the waveform variation of the neutral point grounding resistance branch is in a threshold value interval and continuously exceeds a preset time length, judging that the ground insulation of the power distribution network is reduced or slightly discharged, and giving a grounding fault early warning signal, wherein the lower limit of the threshold value interval is a preset current threshold value ICT1ZD1The value range is 10 milliamperes to 500 milliamperes, and the upper limit is a preset current threshold ICT1ZD2The value range is 500 milliampere to 2 ampere, and the fault duration threshold value TCT1ZDThe value range is 1 second to 10 minutes;
s103: collecting and calculating power frequency amplitude and phase of each outlet zero sequence current connected on the bus in real time;
s104, calculating the phase difference between the zero sequence current of each outgoing line and the branch current of the neutral point grounding resistor;
s105, when the power frequency amplitude of the branch current of the neutral point grounding resistor, the power frequency amplitude of the branch current of the measured outgoing line, and the phase difference between the zero sequence current of the outgoing line and the branch current of the neutral point grounding resistor all meet preset conditions, judging that the outgoing line branch has a ground fault; the preset conditions include: the power frequency amplitude of the current of the neutral point grounding resistor branch is larger than a first amplitude setting threshold; the current power frequency amplitude of the outgoing line branch is larger than a second amplitude setting threshold; when the defined current direction is away from the bus as a positive direction, the phase difference between the outgoing line zero sequence current of the outgoing line branch and the neutral point grounding resistor branch current is larger than an angle setting threshold, or the phase difference between the negative value of the outgoing line zero sequence current of the outgoing line branch and the neutral point grounding resistor branch current is smaller than an absolute value (180 degrees-angle setting threshold); when the conditions are all met and the duration time reaches a setting action time length threshold, judging that the outgoing line branch circuit has a ground fault;
and S106, performing disconnection control on the outgoing line branch and giving an earth fault alarm.
2. The method for integrating monitoring and protection of the ground fault of the power distribution network with the neutral point grounded through the resistor in the claim 1 is characterized in that in the step S102, giving out the ground fault early warning signal comprises generating power distribution network ground fault early warning information and sending the power distribution network ground fault early warning information to an operation and maintenance platform or a distribution network dispatching center.
3. The method of claim 1, wherein the step S106 of giving an earth fault alarm includes generating fault information of the outgoing line branch and giving an alarm based on the fault information of the outgoing line branch.
4. The method of claim 1, wherein the line at the neutral point grounded resistance grounding end of the distribution network passes through the induction areas of a first current transformer CT1 and a second current transformer CT2 to obtain neutral point grounded resistance branch current information, each outgoing line branch of the distribution network passes through the induction area of a third current transformer CT3 to obtain outgoing line zero sequence current information, and the output ends of the first current transformer CT1, the second current transformer CT2 and the third current transformer CT3 are connected with the input end of the ground fault monitoring protection device; the ground fault monitoring protection device comprises a processor and a trip control element, wherein a control command of the trip control element is connected with a circuit breaker trip loop, the processor is used for calculating the current amplitude and the phase of a neutral point grounding resistor based on current information output by a first current transformer CT1 and a second current transformer CT2, the processor is also used for judging that the power distribution network has ground faults when the current amplitude and the phase of a neutral point grounding resistor branch circuit are in a threshold value interval and the duration reaches a fault duration threshold value, the processor is also used for calculating the current power frequency amplitude and the phase of each outgoing line branch circuit based on the current information output by each third current transformer CT3, the processor is also used for calculating the outgoing line zero sequence current phase difference of each outgoing line branch circuit, and the processor is also used for judging that the outgoing line branch circuit has ground faults when the current amplitude of the neutral point grounding resistor, the current power frequency amplitude of the outgoing line branch circuit and the outgoing line zero sequence current phase, and the tripping control element is used for carrying out circuit breaking treatment on the outgoing line branch when the outgoing line branch has a ground fault.
5. The integrated method for monitoring and protecting the ground fault of the distribution network with the neutral point including the resistor as recited in claim 4, wherein the processor is further configured to generate distribution network ground fault early warning information when it is determined that the distribution network has the ground fault, and the ground fault monitoring and protecting device further includes a communication module, and the communication module is configured to send the distribution network ground fault early warning information to an operation and maintenance platform or a distribution network scheduling center.
6. The integrated method for monitoring and protecting ground faults of the distribution network with the neutral point grounded through the resistor as claimed in claim 4, wherein the processor is further used for generating fault information of the outgoing line branch when judging that any outgoing line branch has the ground fault, and the ground fault monitoring and protecting device further comprises an alarm module which is used for giving an alarm based on the fault information of the outgoing line branch.
7. The method for integrating the ground fault monitoring and protection of the distribution network with the neutral point grounded through the resistor as claimed in claim 4, wherein the current transformers on the resistor branch of the neutral point include a first current transformer CT1 and a second current transformer CT2, and the upper limit of the accurate measurement range of the first current transformer CT1 is the lower limit of the accurate measurement range of the second current transformer CT 2.
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| CN112838610B (en) * | 2021-01-17 | 2023-12-15 | 昆明理工大学 | MMC converter station ground fault analysis method considering neutral point current based on two-port network |
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| CN101598761B (en) * | 2009-07-29 | 2011-01-26 | 江苏省电力公司常州供电公司 | Fault line selection method for small electric current grounding system of distribution network |
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