CN114414944A - Low-current grounding device based on phase current transient method and detection method - Google Patents

Low-current grounding device based on phase current transient method and detection method Download PDF

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CN114414944A
CN114414944A CN202210094046.9A CN202210094046A CN114414944A CN 114414944 A CN114414944 A CN 114414944A CN 202210094046 A CN202210094046 A CN 202210094046A CN 114414944 A CN114414944 A CN 114414944A
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季国鹏
史进宗
罗海波
姚舟华
赵春雷
刘斌斌
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Shanghai Daobo Electric Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing
    • 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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Abstract

The invention discloses a low-current grounding device based on a phase current transient method and a detection method. The device is arranged at the outlet and the branch of each line, when the system has ground fault, the three-phase current can have sudden change, the phase current transient method is characterized in that the relative magnitude of the three-phase current sudden change current amplitude of a sound line is higher than the consistency of the waveform, and the three-phase current sudden change difference of the fault line is very large, so that the device in front of the fault point sends out a fault signal after detecting the fault, and the section where the fault point is located is judged according to the signal. The technical scheme adopted by the device does not depend on a zero sequence voltage transformer and a zero sequence current transformer, and can effectively, accurately and quickly detect the small current grounding faults of various neutral point indirect grounding systems.

Description

Low-current grounding device based on phase current transient method and detection method
Technical Field
The invention belongs to the technical field of power distribution network fault detection, and particularly relates to a low-current grounding device and a detection method based on a phase flow transient method.
Background
The low-current grounding system has the advantage of high power supply reliability and is widely applied to domestic power distribution networks. When a low-current ground fault occurs in the system, the equipment in the system can be allowed to operate for a short time when the low-current ground fault occurs, because the fault current is small, the line voltages between three phases are still symmetrical, and the power supply of load equipment is not influenced. However, when one phase is grounded, the voltage to ground of the other two phases is raised to be several times of the phase voltage, which threatens the insulation performance of the equipment, and if the treatment is not timely, insulation damage, two-phase short circuit and arc discharge may be caused to cause system overvoltage, thereby affecting the safe and normal operation of the system and the reliability of power supply. However, when a low-current ground fault occurs, the detection of the low-current ground fault is still a world problem at present because a loop is not formed, the value of the ground current is much smaller than that of the load current, and the electrical characteristics of the fault are not obvious.
Existing low-current ground fault detection can be roughly classified into 3 types: external injection signal method, steady state quantity detection method and transient state quantity detection method.
(1) The external signal injection method is to inject a special signal into a system when a ground fault occurs, and then carry out ground detection according to the difference between a fault line and a non-fault line, but the method has the defect that line selection cannot be correctly carried out when the ground resistance is large;
(2) the steady state quantity detection method is characterized in that when a single-phase earth fault occurs in a system, the steady state electrical characteristics of a fault line are obviously different from those of a non-fault line, amplitude, phase, angle or comprehensive comparison is carried out according to the steady state electrical quantity after the fault occurs, and steady state quantity line selection is realized, and the method has the defect that the fault line is easily mistakenly selected due to the influence of interference signals (noise interference, system harmonic waves, zero sequence transformer precision, phase and angle);
(3) the transient state quantity detection method is characterized in that transient state signals generated instantly when a single-phase earth fault occurs in a system contain rich fault information, a mathematical model is established when each feeder line has a fault, model parameters are solved by utilizing voltage current data, parameters of a sound element do not change before and after the fault, parameters of a fault element change violently before and after the fault, and therefore fault judgment can be carried out through identifying the parameters. The method has the defects that in the case of high-resistance ground faults, particularly high-resistance ground faults above 2000 omega, the transient signal quantity is obviously reduced, the sensitivity of the protection action is influenced, the detection principle is complex, and the requirements on software and hardware of the detection device are high.
Disclosure of Invention
The invention provides a small current grounding device based on a phase current transient method and a detection method. The core detection method of the invention is PTM (phase transition method, phase flow transient method), which is characterized in that obvious difference exists according to the transient characteristics of phase current abrupt change before and after a fault point, after the fault occurs, the fault is judged according to the phase current transient method, and the device sends a fault alarm or a tripping outlet. The technical scheme can effectively, accurately and quickly detect the small current grounding faults of various neutral point indirect grounding systems without depending on a zero sequence voltage transformer and a zero sequence current transformer.
In order to realize the invention, the invention is realized by the following technical scheme:
the invention provides a low-current grounding device based on a phase current transient method, which comprises:
the sampling module is used for acquiring a three-phase current real-time sampling value of a line;
the operation module is used for the operation of transient sudden change of phase current and the operation of a similarity coefficient;
the judging module is used for judging the small current grounding fault based on a phase flow transient method;
and the output module is used for judging the output of the result and positioning the fault point.
The sampling module is characterized in that each grounding device is externally provided with three current transformers, the current transformers can be provided with buckle type transformers, and the current transformers can be directly clamped on a three-phase line under the condition that the line is not powered off and are used for collecting real-time current of the line.
Preferably, the detection method in the operation module and the determination module includes the following steps:
s1, collecting the AD sampling values of the three-phase current of each line in real time by using a current transformer, and calculating whether transient sudden change of the phase current occurs or not;
s2, if transient sudden change of the phase current is detected, carrying out low-pass filtering on the AD sampling value of each phase current in a fixed time period from the sudden change moment;
s3, according to the AD sampling values of the filtered currents of each phase, similarity comparison is carried out on the data of the two phases, so that whether the position of the device has a ground fault or not is determined, if the position is determined to be a fault part, a fault signal is sent, and if the position is determined to be a sound part, no signal is sent;
and S4, detecting each device on the line in real time according to the steps S1 to S3, and determining a fault section, namely the area from the grounding device which sends the signal farthest from the substation to the substation according to the signals sent by the grounding devices and the network topology of the line.
Preferably, the step of determining whether a transient sudden change of the phase current occurs further comprises the steps of:
s11, calculating instantaneous break variable delta I of three-phase current in real timeA(t)、ΔIB(t)、ΔIC(t) and three-phase synthesized zero-sequence current transient variable delta I0And (t) t is the current time.
Wherein, the formula of the transient mutation is as follows:
Figure BDA0003490381460000031
in the formula: n is the number of sampling points in the power frequency period, the value is related to the sampling frequency of a grounding device, and the device N is 128; Δ i (n) is a discrete value of the current step change amount.
S12, condition 1: max [ Delta ] IA(t),ΔIB(t),ΔIC(t)]Greater than phase current sudden change constant value delta IsetAnd condition 2: Δ i0(t) is greater than zero sequence current sudden change definite value delta I0set. The two conditions are simultaneously satisfied at the moment t, and judgment is madeAnd if the current is disconnected, the current is transient sudden change of the phase current, and t is the transient sudden change moment of the current phase current, otherwise, the current is not considered to be the transient sudden change of the current phase current.
Preferably, in step S2, fir (finite impulse response) finite impulse response filtering algorithm is used for filtering the AD samples in the abrupt change interval, and the algorithm can effectively remove the noise.
Preferably, in step S3, a similarity coefficient is defined to represent the degree of coincidence of the abrupt change waveforms of the phase currents, and the similarity coefficient is calculated according to the following formula:
Figure BDA0003490381460000032
in the formula: i.e. ix(n) and iyAnd (n) corresponds to a certain two-phase current sampling value.
The range of the similarity coefficient is-1 ≤ CorrxyNot more than 1, if CorrxyWhen the waveform is 1, the two waveforms are in a positive linear relation; corr et alxyWhen the waveform is equal to-1, the two waveforms are in a negative linear relation; corr et alxyIf 0, the two waveforms are completely dissimilar, | CorrxyThe greater the | value, the higher the similarity of the two-phase waveforms.
Preferably, in step S3, the method for determining whether the device has a ground fault is to calculate the similarity coefficient Corr between two phases of the three-phase abrupt currentAB、CorrBC、CorrCAWhen min (Corr)AB、CorrBC， CorrCA)>Corrset1Or min (Corr)AB、CorrBC，CorrCA)<Corrset2And judging as a sound part, otherwise, judging that the position of the device has a ground fault. Corrset1The constant value is a decimal number within the interval of (0,1), generally 0.6, Corrset2The constant value is a decimal fraction within the range of (-1,0), and is generally-0.3.
Preferably, the output module is configured to:
according to the result of the judging module, if the low-current grounding fault is judged to occur at the downstream of the position of the device, the device can be switched out in a serial communication mode or a direct hard contact, and is accessed to an existing feeder terminal or station terminal without single-phase grounding processing capacity, and the terminal forwards grounding fault information to a distribution network main station.
Compared with the existing small current grounding detection technology, the invention adopts the technical scheme, and has the following beneficial effects: the method provides the low-current ground fault detection which is simple and feasible, does not depend on a voltage transformer and a zero sequence current transformer, can be completed only by detecting three-phase current, and has simple detection method and reliable judgment result for the reconstruction of urban networks and rural networks.
The grounding device can be applied to all domestic indirect grounding systems, including a neutral point direct grounding system, a neutral point grounding system through an arc suppression coil, a neutral point grounding system through a high resistance and a neutral point grounding system through a small resistance. The detection of the device is not influenced by load current, line capacitance to ground, length of the detection line and system tuning.
The novel current transformer has the advantages of small size, convenience in installation and the like, the buckle current transformer can be installed under the condition that a circuit is not powered off, and the construction difficulty is effectively reduced.
Drawings
Fig. 1 is a schematic diagram of a low-current grounding device installed on a line based on a phase current transient method according to an embodiment of the present invention.
Detailed description of the preferred embodiments
The embodiments of the present invention will be described in detail below, and the embodiments described by referring to the drawings are exemplary only for the purpose of illustrating the present invention and are not to be construed as limiting the present invention.
The embodiment provides a low-current grounding device based on a phase current transient method, which comprises the following parts:
the sampling module is used for acquiring a three-phase current real-time sampling value of a line;
the operation module is used for the operation of transient sudden change of phase current and the operation of a similarity coefficient;
the judging module is used for judging the small current grounding fault based on a phase flow transient method;
and the output module is used for judging the output of the result and positioning the fault point.
The sampling module is characterized in that each grounding device is externally provided with three current transformers, the current transformers can be provided with buckle type transformers, and the current transformers can be directly clamped on a three-phase line under the condition that the line is not powered off and are used for collecting real-time current of the line.
The detection method in the operation module and the judgment module comprises the following specific processes:
s1, acquiring the AD sampling values of the three-phase current of each line in real time by using a current transformer and calculating whether transient sudden change of the phase current occurs or not;
s2, if transient sudden change of the phase current is detected, the device carries out low-pass filtering on the AD sampling value of each phase current in a fixed time period from the sudden change moment;
s3, according to the AD sampling values of the filtered currents of each phase, similarity comparison is carried out on the data of the two phases, so that whether the position of the device has a ground fault or not is determined, if the position is determined to be a fault part, a fault signal is sent, and if the position is determined to be a sound part, no signal is sent;
and S4, detecting each device on the line in real time according to the steps S1 to S3, and determining a fault section, namely the area from the grounding device which sends the signal farthest from the substation to the substation according to the signals sent by the grounding devices and the network topology of the line.
In step S1, the step of determining whether a transient sudden change of the phase current occurs further includes the steps of:
s11, calculating instantaneous break variable delta I of three-phase current in real timeA(t)、ΔIB(t)、ΔIC(t) and three-phase synthesized zero-sequence current transient variable delta I0And (t) t is the current time.
Wherein, the formula of the transient mutation is as follows:
Figure BDA0003490381460000051
in the formula: n is the number of sampling points in the power frequency period, the value is related to the sampling frequency of a grounding device, and the device N is 128; Δ i (n) is a discrete value of the current variation.
S12, condition 1: max [ Delta ] IA(t),ΔIB(t),ΔIC(t)]Greater than phase current sudden change constant value delta Iset，
Condition 2: Δ i0(t) is greater than zero sequence current sudden change definite value delta I0set。
The two conditions are simultaneously met at the moment t, the transient sudden change of the phase current is judged, the moment t is the transient sudden change moment of the current phase current, and otherwise, the transient sudden change of the phase current is not considered.
In step S2, fir (finite impulse response) finite impulse response filtering algorithm is used to filter the AD samples in the abrupt change interval, and the algorithm can effectively remove the noise.
In step S3, a similarity coefficient is defined to represent the degree of coincidence of the abrupt change waveforms of the phase currents, and the similarity coefficient calculation formula is as follows:
Figure BDA0003490381460000052
in the formula: i.e. ix(n) and iyAnd (n) corresponds to a certain two-phase current sampling value.
The range of the similarity coefficient is-1 ≤ CorrxyNot more than 1, if CorrxyWhen the waveform is 1, the two waveforms are in a positive linear relation; corr et alxyWhen the waveform is equal to-1, the two waveforms are in a negative linear relation; corr et alxyIf 0, the two waveforms are completely dissimilar, | CorrxyThe greater the | value, the higher the similarity of the two-phase waveforms.
In step S3, the method for determining whether the device has a ground fault is to calculate the similarity coefficient Corr between the three phases of the sudden change currentAB、CorrBC、CorrCAWhen min (Corr)AB、CorrBC，CorrCA)>Corrset1Or min (Corr)AB、CorrBC，CorrCA)<Corrset2And judging as a sound part, otherwise, judging that the position of the device has a ground fault.Corrset1The constant value is a decimal number within the interval of (0,1), generally 0.6, Corrset2The constant value is a decimal fraction within the range of (-1,0), and is generally-0.3.
The output module is used for:
according to the result of the judging module, if the low-current grounding fault is judged to occur at the downstream of the position of the device, the device can be switched out in a serial communication mode or a direct hard contact, and is accessed to an existing feeder terminal or station terminal without single-phase grounding processing capacity, and the terminal forwards grounding fault information to a distribution network main station.
In this example, as shown in fig. 1, each section switch on the line is configured with a grounding device (device I (1) … … device I (n), device II (1) … … device II (n), device III (1) … … device III (n)) having the detection algorithm, and the devices perform real-time detection according to steps S1 to S3, determine that the fault point is F according to the signal of the device I (1) that sends out the ground, and the other devices do not report the ground signal, and combine the network topology of the line, thereby locating the fault area quickly and accurately.
Further, the above-described embodiments of the apparatus are merely illustrative, and for convenience of description, the above-described apparatus is set forth in terms of the functionality of the various modules. Of course, in implementing the present application, the functions of the respective modules may also be implemented in one or more of hardware and/or software.
The modules, if in the form of software functional modules, when used and sold as relatively self-contained products, may be stored in a computer readable storage or computer usable medium having computer readable program code embodied therein for carrying out all or a portion of the steps of the methods described in the various embodiments of the present application by or in connection with an instruction execution system.
In addition, those skilled in the art or developers can make modifications and alterations to the present invention without departing from the spirit and scope of the invention. Such variations and modifications are also considered to be within the scope of the invention as defined by the appended claims.

Claims (10)

1. A low-current grounding device based on a phase current transient method is characterized by comprising the following parts:
the sampling module is used for acquiring a three-phase current real-time sampling value of a line;
the operation module is used for the operation of transient sudden change of phase current and the operation of a similarity coefficient;
the judging module is used for judging the small current grounding fault based on a phase flow transient method;
the output module is used for judging the output of the result and positioning a fault point;
each sampling module is provided with three current transformers which are connected with a small current grounding device, and each current transformer is a buckle type transformer and is clamped on a three-phase line.
2. The method for detecting the low-current grounding device based on the phase current transient method as claimed in claim 1, wherein the determining step is as follows:
s1, acquiring the AD sampling values of the three-phase current of each line in real time by using a current transformer and calculating whether transient sudden change of the phase current occurs or not;
s2, if transient sudden change of the phase current is detected, the device carries out low-pass filtering on the AD sampling value of each phase current in a fixed time period from the sudden change moment;
s3, according to the AD sampling values of the filtered currents of each phase, similarity comparison is carried out on the data of the two phases, so that whether the position of the device has a ground fault or not is determined, if the position is determined to be a fault part, a fault signal is sent, and if the position is determined to be a sound part, no signal is sent;
and S4, detecting each device on the line in real time according to the steps S1 to S3, and determining a fault section, namely the area from the grounding device which sends the signal farthest from the substation to the substation according to the signals sent by the grounding devices and the network topology of the line.
3. The method for detecting low-current grounding based on the phase current transient method of claim 2, wherein the step S1 for determining whether the transient sudden change of the phase current occurs further comprises the steps of: when the instantaneous break variable Delta I of the three-phase current is calculated in real timeA(t)、ΔIB(t)、ΔIC(t) and three-phase synthesized zero-sequence current transient variable delta I0(t), wherein t is the current moment; wherein, the formula of the transient mutation is as follows:
Figure FDA0003490381450000011
in the formula: n is the number of sampling points in the power frequency period, the value is related to the sampling frequency of a grounding device, the device N is 128, and delta i (N) is a discrete value of a current abrupt change.
4. The method for detecting low-current grounding based on the phase current transient method according to claim 3, wherein the condition 1: max [ Delta ] IA(t),ΔIB(t),ΔIC(t)]Greater than phase current sudden change constant value delta Iset，
Condition 2: Δ i0(t) is greater than zero sequence current sudden change definite value delta I0set，
And if the two conditions are simultaneously met at the moment t, judging that the transient sudden change of the phase current occurs, wherein t is the transient sudden change moment of the current phase current, otherwise, the transient sudden change of the phase current is not considered.
5. The method for detecting low-current grounding based on phase current transient method of claim 2, wherein in step S2, the filter algorithm for the AD samples in the abrupt change interval is FIR finite impulse response filter algorithm, which can effectively remove noise.
6. The method for detecting low-current grounding based on phase current transient method of claim 2, wherein in step S3, a similarity coefficient is defined to represent the consistency of the sudden change waveform of phase current, and the calculation formula of the similarity coefficient is as follows:
Figure FDA0003490381450000021
in the formula: i.e. ix(n) and iyAnd (n) corresponds to a certain two-phase current sampling value.
7. The phase current transient method-based small current ground detection method as claimed in claim 6, wherein the similarity coefficient is in the range of-1 ≦ Corrxy≤1，
Corr et alxyIf the waveform is 1, the two waveforms are in a positive linear relation;
corr et alxyIf the waveform is-1, the two waveforms are in a negative linear relationship;
corr et alxyIf 0, the two waveforms are completely dissimilar, | CorrxyThe greater the | value, the higher the similarity of the two-phase waveforms.
8. The method for detecting low-current grounding based on phase current transient method as claimed in claim 2, wherein in step S3, the method for determining whether the grounding fault occurs at the position of the device is to calculate the similarity coefficient Corr between two phases of three-phase abrupt currentAB、CorrBC、CorrCAWhen min (Corr)AB、CorrBC，CorrCA)>Corrset1Or min (Corr)AB、CorrBC，CorrCA)<Corrset2And judging as a sound part, otherwise, judging that the position of the device has a ground fault.
9. The phase current transient method-based low current ground detection method of claim 8, wherein Corr is a phase current transient methodset1The constant value is a decimal number within the interval of (0,1), generally 0.6, Corrset2The decimal fraction in the range of the fixed value (-1,0) is taken as-0.3.
10. The phase current transient method-based low-current grounding device of claim 2, wherein the output module is configured to: according to the result of the judging module, if the low-current grounding fault is judged to occur at the downstream of the position of the device, the device can be switched out in a serial communication mode or a direct hard contact, and is accessed to an existing feeder terminal or station terminal without single-phase grounding processing capacity, and the terminal forwards grounding fault information to a distribution network main station.
CN202210094046.9A 2022-01-26 2022-01-26 Low-current grounding device based on phase current transient method and detection method Pending CN114414944A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115267415A (en) * 2022-05-30 2022-11-01 江苏省电力试验研究院有限公司 Single-phase earth fault discrimination method for stock distribution network and terminal thereof

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115267415A (en) * 2022-05-30 2022-11-01 江苏省电力试验研究院有限公司 Single-phase earth fault discrimination method for stock distribution network and terminal thereof
CN115267415B (en) * 2022-05-30 2024-04-12 江苏省电力试验研究院有限公司 Method for discriminating single-phase earth fault of stock distribution network and terminal thereof

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