CN107561408B - Method for improving accuracy rate of small current ground fault line selection - Google Patents

Method for improving accuracy rate of small current ground fault line selection Download PDF

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Publication number
CN107561408B
CN107561408B CN201710751482.8A CN201710751482A CN107561408B CN 107561408 B CN107561408 B CN 107561408B CN 201710751482 A CN201710751482 A CN 201710751482A CN 107561408 B CN107561408 B CN 107561408B
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fault
circuit breaker
bus
phase
current
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CN201710751482.8A
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CN107561408A (en
Inventor
黄坛坛
郑志华
张慧芬
高志鹏
王士新
朱玉波
杨海涛
姚继荣
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Power Service Center Of China Petroleum Chemical Co Shengli Oil Field Branch
University of Jinan
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Power Service Center Of China Petroleum Chemical Co Shengli Oil Field Branch
University of Jinan
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Abstract

The invention discloses a method for improving the accuracy of small-current ground fault line selection. The method solves the problem of low line selection accuracy caused by small electric fault amount of the current steady state line selection method utilizing fault steady state quantity, and has the advantages that after a single-phase earth fault occurs in a low-current grounding system, the fault current steady state component is obviously increased when a bus sectionalized circuit breaker is closed, so that the sensitivity of line selection and positioning protection based on the fault steady state quantity is improved, and the purposes of reliable line selection and positioning are achieved, and the structure is as follows: the bus comprises a bus of a protected power distribution system, wherein the bus is a single bus sectional system, a bus sectional switch adopts a circuit breaker, the circuit breaker is connected with a measurement and control device, the measurement and control device is connected with a voltage transformer, and the voltage transformer is connected with the bus; the measurement and control device detects whether the small current grounding system has a single-phase grounding fault or not, and controls the connection of the two sections of buses through the circuit breaker to increase the grounding current.

Description

Method for improving accuracy rate of small current ground fault line selection
Technical Field
the invention relates to a ground fault detection technology in a power system, in particular to a method for improving the accuracy of small-current ground fault line selection.
Background
In an electric power system, the common grounding method for a neutral point mainly includes: the neutral point is in a non-grounding mode, the neutral point is in a grounding mode through an arc suppression coil, and the neutral point is in a direct grounding mode, wherein the first two grounding modes are in a low-current grounding mode.
the distribution network of 6-35kV in China mainly adopts a low-current grounding mode, the probability of single-phase grounding faults is the highest in the faults of a low-current grounding system, and more than 80% of the faults in the distribution network are counted to be single-phase grounding faults. When a single-phase earth fault occurs, the power supply system can still ensure the line voltage symmetry, and the line voltage symmetry does not form a fault loop, so that the current is very small, the continuous power supply to the load is not influenced, and the line voltage symmetry fault can continue to operate for 1-2h according to regulation. However, as the power grid becomes more complex and more lines are used, if the fault cannot be timely cleared and the fault operation is continued for a long time, the fault is easily deteriorated and enlarged, and a more serious short-circuit fault is caused, so that the system is tripped, and under a certain condition, overvoltage of the whole power grid may be caused, which is harmful to equipment and affects the normal operation of the power system. Therefore, when a single-phase earth fault occurs, although the power supply to the user is not affected for a short time, the faulty line must be found as soon as possible to prevent the fault from adversely affecting the grid.
At present, the single-phase earth fault line selection technology of the low-current grounding system is mainly divided into the following four types: the method comprises the steps of firstly, selecting a line in a steady state based on fault steady state quantity; secondly, a transient line selection method based on fault transient quantity; thirdly, a line selection method based on an external diagnosis signal; and fourthly, a line selection method based on the modern information fusion technology. The technical defects of the first two line selection methods are as follows: the fault steady-state quantity-based steady-state line selection method has the problems that the steady-state electrical fault quantity is small, and line selection failure is easily caused; the transient state line selection method based on the fault transient state quantity has the defects that the transient state electrical fault quantity is short in existing time and not easy to collect.
Disclosure of Invention
The invention aims to solve the problem that the line selection accuracy is low due to small electric fault amount of the current steady-state line selection method based on fault steady-state amount, and provides a method for improving the line selection accuracy of a low-current ground fault, when a single-phase ground fault of a low-current ground system occurs, if a bus sectional breaker (the circuit breakers are all bus sectional circuit breakers) before the fault is in an open state, the bus sectional circuit breakers are closed by a measurement and control device after the fault occurs; if the breaker is in a closed state before the fault, the measurement and control device is firstly disconnected and then closed after the fault. The method aims to put a line connected with another section of bus into a fault system when the system has single-phase earth fault, increase the fault current of the fault line, and keep the fault current of the non-fault line unchanged, thereby enlarging the difference of the fault current between the fault line and the non-fault line and improving the accuracy of line selection.
In order to achieve the purpose, the invention adopts the following technical scheme.
A method for improving the accuracy of small current ground fault line selection comprises a bus of a protected power distribution system, wherein the bus is a single bus sectional system, a bus sectional switch adopts a circuit breaker, the circuit breaker is connected with a measurement and control device, the measurement and control device is connected with a voltage transformer, and the voltage transformer is connected with the bus; the measurement and control device monitors whether the small current grounding system has single-phase grounding fault, and when the single-phase grounding fault occurs, if the circuit breaker is in an open state before the fault, the measurement and control device controls the circuit breaker to be closed after the fault; if the breaker is in a closed state before the fault, the measurement and control device controls the breaker to be opened firstly and then to be closed after the fault; the method aims to put a line connected with another section of bus into a fault system when the system has single-phase earth fault, increase the fault current of the fault line, and keep the fault current of the non-fault line unchanged, thereby enlarging the difference of the fault current between the fault line and the non-fault line and improving the accuracy of line selection.
The measurement and control device consists of a three-phase voltage and zero-sequence voltage acquisition module, a circuit breaker state detection module, a circuit breaker switch driving module, a man-machine conversation module and a CPU (central processing unit), and is used for monitoring the three-phase voltage and the zero-sequence voltage of the low-current grounding system to judge whether the system has a single-phase grounding fault or not so as to control the action of the circuit breaker; the three-phase voltage and zero sequence voltage acquisition module consists of a voltage transmitter, an RC low-pass filter, a preprocessing circuit consisting of an operational amplifier and an A/D conversion circuit; the circuit breaker state detection module consists of a circuit breaker auxiliary contact and a detection circuit; the circuit breaker switch driving module consists of a relay driving circuit and a control relay; the man-machine conversation module consists of a key and a liquid crystal display module; the CPU is composed of an STC12C5A60S2 singlechip and mainly realizes the functions of judging whether a single-phase grounding fault occurs or not according to three-phase voltage and zero-sequence voltage, storing the state of the circuit breaker before the fault is acquired by the circuit breaker state detection module, sending an opening and closing instruction of the circuit breaker to the circuit breaker switch driving module when the single-phase grounding fault occurs, selecting a fault line and carrying out man-machine conversation.
a method for improving the accuracy of line selection of low-current ground fault comprises,
(1) When the low-current grounding system normally operates, the circuit breaker is in an open or closed state according to the requirement of an operation mode, and the measurement and control device monitors the three-phase voltage, the zero-sequence voltage and the state of the circuit breaker of the system in real time and judges whether the system has a single-phase grounding fault or not;
(2) when no single-phase earth fault occurs, repeating the step (1); when a single-phase earth fault occurs, if the circuit breaker is in an open state before the fault, the circuit breaker is controlled to be closed by the measurement and control device after the fault, then a fault line is selected, and the circuit breaker is controlled to be opened after the line selection is finished; if the breaker is in a closed state before the fault, the measurement and control device controls the breaker to be disconnected and then to be closed after the fault, and then a fault line is selected;
(3) continuously monitoring the bus voltage and the zero sequence voltage of the system, and judging whether the single-phase earth fault is removed;
(4) if the fault is not removed, continuing to perform the operation of the step (3);
(5) and (5) if the fault is relieved, returning to the step (1) to perform the operation again.
the working process of the invention is as follows: for the operating low-current grounding system, the three-phase voltage, the zero-sequence voltage and the state of the circuit breaker of the system are monitored in real time by the measurement and control device, and whether the system has a single-phase grounding fault or not is judged in real time. When the system normally operates, the circuit breaker is opened or closed according to the requirement of an operation mode. When a single-phase earth fault occurs, if the circuit breaker is in an open state before the fault, the circuit breaker is closed by the measurement and control device after the fault; if the breaker is in a closed state before the fault, the measurement and control device is firstly disconnected and then closed after the fault. The method aims to put a line connected with another section of bus into a fault system when the system has single-phase earth fault, increase the fault current of the fault line, and keep the fault current of the non-fault line unchanged, thereby enlarging the difference of the fault current between the fault line and the non-fault line and improving the accuracy of line selection. After the line selection is finished, the circuit breaker is restored to the state of the original working requirement, and adverse effects on the operation of the system can be avoided.
the invention has the beneficial effects that: (1) according to the invention, after a single-phase earth fault occurs in a low-current earth system, the circuit connected with the other section of bus is put into the fault system through the breaker, so that the fault current of the fault circuit is increased, but the fault current of the non-fault circuit is unchanged, and thus the difference of the fault current between the fault circuit and the non-fault circuit is enlarged, and the stable state line selection and positioning protection based on the stable state quantity of the fault are more accurate. (2) The invention improves the anti-transition resistance capability of the steady state line selection and the positioning protection based on the fault steady state quantity, and enhances the fault degree of the fault point and correspondingly improves the anti-transition resistance capability because the invention increases the fault zero sequence current.
In a word, the invention can effectively improve the accuracy of steady-state line selection and positioning protection based on fault steady-state quantity.
Drawings
FIG. 1 is a schematic structural diagram of the present invention.
Fig. 2 is a functional block diagram of the measurement and control device.
FIG. 3 is a flow chart of the method of the present invention.
The system comprises a bus 1, a bus 2, a bus segmented circuit breaker 3, a measurement and control device, a three-phase voltage and zero-sequence voltage acquisition module 4, a circuit breaker state detection module 6, a circuit breaker switch driving module 7, a man-machine conversation module 8, a CPU 9 and a voltage transformer.
Detailed Description
In fig. 1, a bus-section breaker 2 is connected on each phase of a protected low-current grounding system bus 1. The measurement and control device 3 is used for monitoring whether a single-phase earth fault occurs in the low-current earth system, so as to control the action of the circuit breaker 2, as shown in fig. 2. The measurement and control device 3 consists of a three-phase voltage and zero-sequence voltage acquisition module 4, a circuit breaker state detection module 5, a circuit breaker switch driving module 6, a man-machine conversation module 7 and a CPU 8, and is used for monitoring the three-phase voltage and zero-sequence voltage of a small current grounding system and the state of the circuit breaker 2 in real time and judging whether the system has a single-phase grounding fault or not, so as to control the action of the circuit breaker 2; the three-phase voltage and zero sequence voltage acquisition module 4 consists of a voltage transmitter, an RC low-pass filter, a preprocessing circuit consisting of an operational amplifier and an A/D conversion circuit; the breaker state detection module 5 consists of a breaker auxiliary contact and a detection circuit; the breaker switch driving module 6 consists of a relay driving circuit and a control relay; the man-machine conversation module 7 consists of a key and a liquid crystal display module; the CPU 8 is composed of an STC12C5A60S2 single chip microcomputer, and mainly realizes the functions of judging whether a single-phase grounding fault occurs or not according to three-phase voltage and zero-sequence voltage, storing the state of the circuit breaker 2 before the fault is acquired by the circuit breaker state detection module 5, sending an instruction of opening and closing the circuit breaker 2 to the circuit breaker switch driving module 6 when the single-phase grounding fault occurs, selecting a fault line and realizing man-machine conversation. The measurement and control device 3 is also connected with a voltage transformer 9, and one end of the voltage transformer 9 is connected with the bus 1.
The method of the invention is shown in figure 3:
(1) When the low-current grounding system normally operates, the circuit breaker is in an open or closed state according to the requirement of an operation mode, and the measurement and control device monitors the three-phase voltage, the zero-sequence voltage and the state of the circuit breaker of the system in real time and judges whether the system has a single-phase grounding fault or not;
(2) When no single-phase earth fault occurs, repeating the step (1); when a single-phase earth fault occurs, if the circuit breaker is in an open state before the fault, the circuit breaker is controlled to be closed by the measurement and control device after the fault, then a fault line is selected, and the circuit breaker is controlled to be opened after the line selection is finished; if the breaker is in a closed state before the fault, the measurement and control device controls the breaker to be disconnected and then to be closed after the fault, and then a fault line is selected;
(3) continuously monitoring the bus voltage and the zero sequence voltage of the system, and judging whether the single-phase earth fault is removed;
(4) If the fault is not removed, continuing to perform the operation of the step (3);
(5) and (5) if the fault is relieved, returning to the step (1) to perform the operation again.
In fig. 1, it is assumed that a single-phase earth fault occurs in the phase C of the line ii, and if the circuit breaker 2 is in an open state before the fault, the measurement and control device 3 closes the circuit breaker after the fault; if the circuit breaker 2 is in a closed state before the fault, the measurement and control device 3 is firstly disconnected and then closed after the fault; the method aims to put a line III and a line IV connected with another bus into a fault system when a fault occurs, and the zero sequence current of the fault line is the sum of the zero sequence currents generated by the line I, the line III and the line IV. Therefore, after a single-phase earth fault occurs in a low-current earth system, the method puts a line connected with another section of bus into a fault system when the circuit breaker 2 is closed, increases the fault current of the fault line, but does not change the fault current of the non-fault line, so that the difference of the fault current between the fault line and the non-fault line is enlarged, and the judgment accuracy of steady-state line selection and positioning protection by utilizing the fault steady-state quantity can be improved.

Claims (3)

1. a method for improving the accuracy of small current ground fault line selection comprises a bus of a protected power distribution system, wherein the bus is a single bus sectional system, a bus sectional switch adopts a circuit breaker, the circuit breaker is connected with a measurement and control device, the measurement and control device is connected with a voltage transformer, and the voltage transformer is connected with the bus; the measurement and control device monitors whether the small current grounding system has single-phase grounding fault, and when the single-phase grounding fault occurs, if the circuit breaker is in an open state before the fault, the measurement and control device controls the circuit breaker to be closed after the fault; if the breaker is in a closed state before the fault, the measurement and control device controls the breaker to be opened firstly and then to be closed after the fault; the method aims to put a line connected with another section of bus into a fault system when the system has single-phase earth fault, increase the fault current of the fault line, and keep the fault current of the non-fault line unchanged, thereby enlarging the difference of the fault current between the fault line and the non-fault line and improving the accuracy of line selection.
2. The method for improving the accuracy of small-current ground fault line selection according to claim 1, wherein the method comprises the following steps: the measurement and control device consists of a three-phase voltage and zero-sequence voltage acquisition module, a circuit breaker state detection module, a circuit breaker switch driving module, a man-machine conversation module and a CPU (central processing unit), and is used for monitoring the three-phase voltage and the zero-sequence voltage of the low-current grounding system to judge whether the system has a single-phase grounding fault or not so as to control the action of the circuit breaker; the three-phase voltage and zero sequence voltage acquisition module consists of a voltage transmitter, an RC low-pass filter, a preprocessing circuit consisting of an operational amplifier and an A/D conversion circuit; the circuit breaker state detection module consists of a circuit breaker auxiliary contact and a detection circuit; the circuit breaker switch driving module consists of a relay driving circuit and a control relay; the man-machine conversation module consists of a key and a liquid crystal display module; the CPU is composed of an STC12C5A60S2 singlechip and mainly realizes the functions of judging whether a single-phase grounding fault occurs or not according to three-phase voltage and zero-sequence voltage, storing the state of the circuit breaker before the fault is acquired by the circuit breaker state detection module, sending an opening and closing instruction of the circuit breaker to the circuit breaker switch driving module when the single-phase grounding fault occurs, selecting a fault line and carrying out man-machine conversation.
3. The method for improving the accuracy of small-current ground fault line selection according to claim 1, wherein the method comprises the following steps: the method comprises the following steps of,
(1) When the low-current grounding system normally operates, the circuit breaker is in an open or closed state according to the requirement of an operation mode, and the measurement and control device monitors the three-phase voltage, the zero-sequence voltage and the state of the circuit breaker of the system in real time and judges whether the system has a single-phase grounding fault or not;
(2) When no single-phase earth fault occurs, repeating the step (1); when a single-phase earth fault occurs, if the circuit breaker is in an open state before the fault, the circuit breaker is controlled to be closed by the measurement and control device after the fault, then a fault line is selected, and the circuit breaker is controlled to be opened after the line selection is finished; if the breaker is in a closed state before the fault, the measurement and control device controls the breaker to be disconnected and then to be closed after the fault, and then a fault line is selected;
(3) Continuously monitoring the bus voltage and the zero sequence voltage of the system, and judging whether the single-phase earth fault is removed;
(4) if the fault is not removed, continuing to perform the operation of the step (3);
(5) and (5) if the fault is relieved, returning to the step (1) to perform the operation again.
CN201710751482.8A 2017-08-28 2017-08-28 Method for improving accuracy rate of small current ground fault line selection Expired - Fee Related CN107561408B (en)

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