CN113899985A - Intelligent detection method for state of grounding wire of distribution line - Google Patents
Intelligent detection method for state of grounding wire of distribution line Download PDFInfo
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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
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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
- G01R31/088—Aspects of digital computing
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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
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
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- Y04S10/52—Outage or fault management, e.g. fault detection or location
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Abstract
The invention discloses an intelligent detection method for the state of a grounding wire of a distribution line, which simulates the state of the grounding wire by injecting three-phase voltage signals, deduces an impedance formula of a power transmission line of a power distribution network, and obtains an optimal frequency point of the injected three-phase voltage signal source by analysis; firstly, a probe of a high-voltage insulating rod is contacted with a power transmission line, a current clamp is used for clamping a leading-out wire of the insulating rod, then a portable grounding wire detection instrument is used for directly injecting an alternating-current voltage signal, detecting the current flowing through a grounding wire, deducing a threshold current calculation formula, setting a threshold current, comparing the current flowing through the grounding wire with the threshold current, and judging the hanging state of the grounding wire; based on an impedance distance measurement method, harmonic impedance is calculated through measured voltage and current, then line parameters are consulted, and finally the position of the missed disconnection ground wire is positioned according to the position of a signal injection point.
Description
Technical Field
The invention belongs to the technical field of power systems, and particularly relates to an intelligent detection method for the state of a grounding wire of a distribution line.
Background
With the rapid development of economy in China, the demand and dependence of people on electricity are continuously increasing. Therefore, how to effectively guarantee the safety of the power grid system is increasingly important, and higher standards and requirements are provided for the control of safety problems in the power grid system.
The hanging of the ground wire is a crucial link in the transformation and maintenance work of the distribution network. In the transformation and maintenance of the distribution network, a power failure line or equipment determined by the connection of a work ticket or a telephone and power dispatching is scheduled, an operation switch and a grounding switch closing command are issued to an operator according to the requirement of the work ticket or the emergency call, and the operator fills an operation ticket according to the command to finish operation reporting and scheduling. After receiving the command that the dispatching can work, the operating personnel hang the ground wire according to the working condition of the construction site and start to operate on the line or the equipment, and after the operation is finished and all safety measures are removed, the power dispatching is reported, and the power dispatching and power transmission system restores the power supply. In the operation process of 10-35kV distribution line operation and inspection, the existing management mode mainly depends on the execution degree of a work ticket system and field operation personnel on safety regulations, and when the distribution line is transformed and the number of maintenance work points is large, the occurrence probability of accidents such as ground wire loss, missed disconnection and the like is high.
At present, a microcomputer five-prevention device is adopted by a domestic power grid to inhibit some misoperation behaviors through a series of logic judgment, electrical interlocking and mechanical lock locking, but serious hidden dangers exist for the misoperation behavior of closing a switch with a ground wire of a power transmission line. The existing five-prevention system cannot be used for safety monitoring of line maintenance, so that the grounding wire may not be completely detached after the line maintenance is finished, and the power transmission line maintenance process and the working state cannot be automatically fed back to an operation manager, so that related responsible personnel cannot fully master the field condition, and possibly command mistake is caused. Meanwhile, in the traditional power line patrol process, a worker personally visits a field patrol line, records patrol conditions in a paper medium mode and then manually records the patrol conditions into a computer. However, because the manual entry data volume is large, errors are easy to occur in the manual entry process of the data; whether the staff patrols in place can not carry out effectual management, and the quality of patrolling can not be ensured.
Therefore, the invention aims to provide an intelligent detection method for the state of a grounding wire of a distribution line, which simulates the state of the grounding wire by injecting three-phase voltage signals, deduces an impedance formula of a power transmission line of a power distribution network, and obtains an optimal frequency point of the injected three-phase voltage signal source by analysis; firstly, a probe of a high-voltage insulating rod is contacted with a power transmission line, a current clamp is used for clamping a leading-out wire of the insulating rod, then a portable grounding wire detection instrument is used for directly injecting an alternating-current voltage signal, detecting the current flowing through a grounding wire, deducing a threshold current calculation formula, setting a threshold current, comparing the current flowing through the grounding wire with the threshold current, and judging the hanging state of the grounding wire; based on an impedance distance measurement method, the harmonic impedance is calculated by measuring voltage and current, then line parameters are consulted, and finally the position of the missed-disconnection grounding wire is positioned according to the position of a signal injection point.
Disclosure of Invention
In view of the problems raised by the above background art, the present invention is directed to: the intelligent detection method for the state of the grounding wire of the distribution line is provided.
In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:
an intelligent detection method for the state of the grounding wire of a distribution line comprises the following steps,
s1, injecting three-phase voltage signals, and selecting an optimal frequency point for detecting the grounding state;
the derivation process for determining the optimal frequency point is as follows,
the alternating current electrical parameters of the overhead lines in the distribution line are mainly divided into four, namely resistance (a physical quantity representing the thermal effect generated by active power loss when current passes through the resistance), reactance (a physical quantity representing the magnetic field effect generated around the electrified overhead line), conductance (a physical quantity representing the leakage current generated by the electrified overhead line in an insulating medium and the active power loss generated by air dissociation near the conducting wire) and susceptance (a physical quantity representing the electric field effect generated around the electrified overhead line),
in a single-phase equivalent circuit, the parameter is the unit resistance r0Unit inductance L0Unit conductance g0And a unit capacitance C0
Neglecting conductance, the impedance per unit length ZLAnd capacitive reactance ZCRespectively shown by formula 1 and formula 2,
ZL＝R0+jωL0 (1)
the whole line can be seen as a series connection of unit length impedance and capacitive reactance:
Z1＝ZL+ZC (3)
when n tends to infinity, then
ZnIt is possible to obtain, as shown by formula 6,
because of ZC＞＞ZL、R0Equation 6 can be simplified to equation 7
When the line length is L, the line impedance vector
Comprises the following steps:
the mode for obtaining the line impedance from equation 8, equation 9
The line impedance is related to the line length and frequency, and because the distributed capacitance exists in the power transmission line, the capacitance capacitive reactance is related to the frequency, the impedance is smaller when the frequency is higher, and when the total capacitance capacitive reactance is larger than the line resistance of the grounding line, the current is still large when the grounding line does not exist, so the optimal frequency point needs to be determined, and reasonable margin is considered, so the optimal frequency point is selected as a low-frequency signal;
s2, injecting an alternating voltage signal into the power transmission line, calculating a current threshold value and judging the grounding line hanging state;
the formula of the detected current is shown by the formula 10,
after simplification:
when a temporary grounding wire exists in a distant place, the detected current signals are larger than a threshold value and almost equal; when no grounding wire exists in a distant place, only a small capacitance current can be detected, and the hanging state of the grounding wire can be judged according to the magnitude of the current;
s3, deducing and determining the distance from the grounding wire to the voltage injection signal by using a line impedance distance measurement method;
the ranging formula is derived as follows,
l represents the distance from the ground line to the voltage injection signal point, and Z represents the positive sequence harmonic per kilometer of the lineWave impedance, UABThe phase-to-phase voltage of the signal injection point has the following relation:
UAB＝IAZL-IBZL＝(IA-IB)ZL (12)
the harmonic impedance is calculated through the measured voltage and current, and the distance between the grounding wire and the signal injection point is calculated by looking up the line parameters, so that the purpose of positioning the grounding wire can be achieved.
Further, the specific operation method for determining the grounding wire hanging state in step 2 is as follows,
contacting a probe of a high-voltage insulating rod with the power transmission line;
the current clamp is clamped on the lead-out wire of the insulating rod;
the alternating voltage signal is directly injected through a portable grounding wire detection instrument.
Further limiting, the principle of the impedance ranging method in step 3 is as follows,
after the grounding wire exists, the position of the grounding wire needs to be further determined, and as the distributed capacitance exists in the circuit, and the distributed capacitance and the frequency are related to the length of the circuit, the impedance value is in direct proportion to the length of the circuit aiming at the distributed parameter circuit. The length of the line is determined by measuring the loop impedance, and then the position of the grounding wire is determined according to the position of the signal injection point.
The invention has the beneficial effects that:
1. the hanging state of the grounding wire can be effectively judged;
2. the distance between the leakage disconnection grounding wire and the signal injection point can be effectively measured.
Drawings
The invention is further illustrated by the non-limiting examples given in the accompanying drawings;
FIG. 1 is a single-phase equivalent circuit diagram of a unit long line in an embodiment of an intelligent detection method for the state of a grounding wire of a distribution line according to the invention;
FIG. 2 is a schematic diagram of measuring a direct injection voltage in an embodiment of an intelligent detection method for a state of a ground wire of a distribution line according to the present invention
FIG. 3 is a design drawing of a simulated hanging grounding wire in an embodiment of an intelligent detection method for the state of a grounding wire of a distribution line according to the invention
FIG. 4 is a diagram of different frequency signal detection current waveforms in an embodiment of an intelligent detection method for the state of a grounding line of a distribution line
FIG. 5 is a flowchart illustrating an embodiment of a method for intelligently detecting states of grounding wires of a distribution line according to the present invention
FIG. 6 shows the calculation results of the capacitance current and the threshold current
FIG. 7 shows the results of the impedance-based ranging
Detailed Description
In order that those skilled in the art can better understand the present invention, the following technical solutions are further described with reference to the accompanying drawings and examples.
As shown in fig. 1-7, in the implementation of the intelligent detection method for the state of the grounding line of the power distribution line according to the present invention, based on the above theoretical support, it can be known from formula 9 that the line impedance is related to the frequency, and since the power transmission line has distributed capacitance, the capacitance is related to the frequency, the higher the frequency is, the smaller the impedance is, when the total capacitance is larger than the line resistance of the grounding line, the current is still large when there is no grounding line, and therefore an optimal frequency point needs to be found;
the method is characterized in that a probe of a high-voltage insulating rod is firstly contacted into a power transmission line, the current is clamped on a lead-out wire of the insulating rod, an alternating voltage signal is directly injected through a portable grounding wire detection instrument, a current threshold value can be calculated according to the formula 11, and when a temporary grounding wire exists in a distance, a larger current signal flows through the circuit and is larger than the threshold value and almost equal; when the far distance does not have the grounding wire, only small capacitance current exists in the line; after the grounding wire exists, the position of the grounding wire needs to be further determined, the distance from the injection signal to the grounding wire is located based on an impedance ranging method, and as the distributed capacitance exists in the circuit, the frequency and the length of the circuit are related, and for the distributed parameter circuit, the impedance value is in direct proportion to the length of the circuit. Determining the length of a line by measuring loop impedance, and determining the position of a grounding wire according to the position of a signal injection point;
step 1: fixing the total distance between a three-phase voltage signal injection point and a grounding wire to be 50Km, and injecting a three-phase voltage signal;
step 2: in order to distinguish whether the grounding wire exists or not, a three-phase grounding fault is utilized for simulation at 0.1s, the frequency of an injection voltage signal is sequentially changed, and a design schematic diagram of the simulated hanging grounding wire is shown in fig. 3;
and step 3: analyzing the detected current waveforms obtained under different frequencies, as shown in fig. 4, it can be clearly seen that when the frequency is very high, even if there is a ground wire, the detected current value is very small, which is similar to the current value detected without the ground wire, even the latter is larger than the former;
and 4, step 4: selecting an optimal frequency point by considering reasonable margin, and selecting a low-frequency signal with f being 200 Hz;
and 5: calculating threshold current, as shown in fig. 6, when a temporary grounding wire exists in a distant place, a large current signal flows through the line, and the current signals are larger than the threshold value and almost equal; when the far distance does not have the grounding wire, only small capacitance current exists in the line;
step 6: after the grounding wire is determined to exist, the position of the grounding wire is positioned, an impedance distance measurement method is used for calculation, and the calculation result is compared with the actual distance, as shown in fig. 7, the calculation result is high in precision;
and 7: a set of complete detection methods for judging the hanging state of the grounding wire and positioning the grounding wire in a missing disassembly mode are formed.
The foregoing embodiments are merely illustrative of the principles of the present invention and its efficacy, and are not to be construed as limiting the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (3)
1. An intelligent detection method for the state of a grounding wire of a distribution line is characterized by comprising the following steps: comprises the following steps of (a) carrying out,
s1, injecting three-phase voltage signals, and selecting an optimal frequency point for detecting the grounding state;
the derivation process for determining the optimal frequency point is as follows,
the alternating current electrical parameters of the overhead lines in the distribution line are mainly divided into four, namely resistance (a physical quantity representing the thermal effect generated by active power loss when current passes through the resistance), reactance (a physical quantity representing the magnetic field effect generated around the electrified overhead line), conductance (a physical quantity representing the leakage current generated by the electrified overhead line in an insulating medium and the active power loss generated by air dissociation near the conducting wire) and susceptance (a physical quantity representing the electric field effect generated around the electrified overhead line),
in a single-phase equivalent circuit, the parameter is the unit resistance r0Unit inductance L0Unit conductance g0And a unit capacitance C0
Neglecting conductance, the impedance per unit length ZLAnd capacitive reactance ZCRespectively shown by formula 1 and formula 2,
ZL＝R0+jωL0 (1)
the whole line can be seen as a series connection of unit length impedance and capacitive reactance:
Z1＝ZL+ZC (3)
when n tends to infinity, then
ZnIt is possible to obtain, as shown by formula 6,
because of ZC＞＞ZL、R0Equation 6 can be simplified to equation 7
When the line length is L, the line impedance vector
Comprises the following steps:
the mode for obtaining the line impedance from equation 8, equation 9
The line impedance is related to the line length and frequency, and because the distributed capacitance exists in the power transmission line, the capacitance capacitive reactance is related to the frequency, the impedance is smaller when the frequency is higher, and when the total capacitance capacitive reactance is larger than the line resistance of the grounding line, the current is still large when the grounding line does not exist, so the optimal frequency point needs to be determined, and reasonable margin is considered, so the optimal frequency point is selected as a low-frequency signal;
s2, injecting an alternating voltage signal into the power transmission line, calculating a current threshold value and judging the grounding line hanging state;
the formula of the detected current is shown by the formula 10,
after simplification:
when a temporary grounding wire exists in a distant place, the detected current signals are larger than a threshold value and almost equal; when no grounding wire exists in a distant place, only a small capacitance current can be detected, and the hanging state of the grounding wire can be judged according to the magnitude of the current;
s3, deducing and determining the distance from the grounding wire to the voltage injection signal by using a line impedance distance measurement method;
the ranging formula is derived as follows,
l represents the distance from the ground line to the voltage injection signal point, Z represents the positive sequence harmonic impedance of the line per kilometer, UABThe phase-to-phase voltage of the signal injection point has the following relation:
UAB＝IAZL-IBZL＝(IA-IB)ZL (12)
equation 13 shows the harmonic impedance of a three-phase ground fault:
formula 13 can be ZKProportional to L, so that L can be represented by the harmonic impedance ZKAnd line per kilometer positive sequence harmonic impedance Z1Represents:
the harmonic impedance is calculated through the measured voltage and current, and the distance between the grounding wire and the signal injection point is calculated by looking up the line parameters, so that the purpose of positioning the grounding wire can be achieved.
2. The intelligent detection method for the state of the grounding wire of the distribution line according to claim 1, characterized in that: the specific operation method for determining the grounding wire hanging state in the step 2 is as follows,
contacting a probe of a high-voltage insulating rod with the power transmission line;
the current clamp is clamped on the lead-out wire of the insulating rod;
the alternating voltage signal is directly injected through a portable grounding wire detection instrument.
3. The intelligent detection method for the state of the grounding wire of the distribution line according to claim 1, characterized in that: the principle of the impedance ranging method in step 3 is as follows,
after the grounding wire exists, the position of the grounding wire needs to be further determined, and as the distributed capacitance exists in the circuit, and the distributed capacitance and the frequency are related to the length of the circuit, the impedance value is in direct proportion to the length of the circuit aiming at the distributed parameter circuit. The length of the line is determined by measuring the loop impedance, and then the position of the grounding wire is determined according to the position of the signal injection point.
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