CN110687403B - Power distribution network single-phase earth fault detection method and device - Google Patents

Power distribution network single-phase earth fault detection method and device Download PDF

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Publication number
CN110687403B
CN110687403B CN201911149612.6A CN201911149612A CN110687403B CN 110687403 B CN110687403 B CN 110687403B CN 201911149612 A CN201911149612 A CN 201911149612A CN 110687403 B CN110687403 B CN 110687403B
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phase
ground
distribution network
current
grounding
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CN110687403A (en
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丁超文
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Jinan Taijing Power Technology Co ltd
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Jinan Taijing Power Technology Co ltd
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08Locating faults in cables, transmission lines, or networks
    • G01R31/081Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04SSYSTEMS 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
    • Y04S10/00Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52Outage or fault management, e.g. fault detection or location

Abstract

The disclosure provides a power distribution network single-phase earth fault detection method and device. The method for detecting the single-phase earth fault of the power distribution network comprises the following steps of 1: when the ground resistance of the neutral point on the low-voltage side of the distribution network transformer is less than 150 ohmsConnecting the grounding down lead of the neutral point at the low-voltage side of the distribution network transformer to an independent grounding network, wherein the resistance to the ground of the independent grounding network is not less than 150 ohms; step 2: measuring the current I between a neutral point and a corresponding earth grid0Phase I of current AaAnd C phase current Ic(ii) a And step 3: synchronous sampling and comparison I0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity is the same and is larger than the preset threshold value, the phase A is judged to be grounded; if I0Variation of (2) andcif the variation is the same, the phase C is determined to be grounded. The current traditional measures such as an arc extinction coil, a high-resistance grounding device and the like can be eliminated, the complexity of the existing grounding device is greatly reduced, and the safety is higher.

Description

Power distribution network single-phase earth fault detection method and device
Technical Field
The disclosure belongs to the field of power distribution network fault detection, and particularly relates to a power distribution network single-phase earth fault detection method and device.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
At present, a power grid is divided into a direct grounding system and a non-direct grounding system according to a neutral point grounding mode of a main transformer of a power transmission line. In China, a high-voltage transmission line (more than 110 kV) belongs to a direct grounding system, and is also called a high-current grounding system. The low-voltage line (35kV and below) belongs to a transformer neutral point indirect grounding system, which is also called as a low-current grounding system. The low-current grounding system is responsible for distributing power to end users, and therefore is also called a power distribution network, which is called a distribution network for short. The distribution network is close to a residential area, so that accidents are easily caused by various interferences. According to the technical statistics of national power grids, single-phase earth faults account for about 80% of distribution network faults. However, the single-phase earth fault characteristics of the distribution network are not obvious, the detection and the processing of the single-phase earth fault are difficult, and the detection accuracy is not high, which is related to the current detection theory and method.
From the detection principle, the current small current grounding detection method mainly comprises a steady state component method, a harmonic component method, a transient state method, a wavelet method and the like, and parameters analyzed and detected by the methods are mainly line phase current and zero sequence current. The inventor finds that the existing single-phase earth fault detection needs to connect an arc suppression coil and a high-resistance grounding device, so that the grounding device is complicated, and the detection process is complicated.
Disclosure of Invention
In order to solve the problems, the present disclosure provides a method and an apparatus for detecting a single-phase ground fault of a power distribution network, which can replace the conventional measures such as the current arc suppression coil and the high-resistance grounding device, thereby greatly reducing the complexity of the existing grounding device and having higher safety.
In order to achieve the purpose, the following technical scheme is adopted in the disclosure:
a first aspect of the present disclosure provides a method for detecting a single-phase ground fault of a power distribution network, including:
step 1: when the ground resistance of the neutral point at the low-voltage side of the distribution network transformer is less than 150 ohms, the ground down lead of the neutral point at the low-voltage side of the distribution network transformer is connected to the independent grounding network, and the ground resistance of the independent grounding network is not less than 150 ohms;
step 2: measuring the current I between a neutral point and a corresponding earth grid0Phase I of current AaAnd C phase current Ic
And step 3: synchronous sampling and comparison I0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity is the same and is larger than the preset threshold value, the phase A is judged to be grounded; if I0Variation of (2) andcif the variation is the same, the phase C is determined to be grounded.
A second aspect of the present disclosure provides a single-phase ground fault detection device for a power distribution network, including:
a grounding down lead of a neutral point at the low-voltage side of the distribution network transformer;
a measurement module configured to measure a current I between the neutral point and the earth grid0Phase I of current AaAnd C phase current Ic
A sampling module configured to synchronously sample I0、IaAnd Ic
A processor configured to receive I of the synchronous samples0、IaAnd IcAnd compare I0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity is the same and is larger than the preset threshold value, the phase A is judged to be grounded; if I0Variation of (2) andcif the variation amounts of the two are the same, then the judgment is madeThe fixed phase C is grounded.
The beneficial effects of this disclosure are:
(1) according to the method for detecting the single-phase earth fault of the power distribution network, when the earth resistance of the neutral point at the low-voltage side of the distribution network transformer is smaller than 150 ohms, the earth down lead of the neutral point at the low-voltage side of the distribution network transformer is connected to the independent earth network, the earth resistance of the independent earth network is not smaller than 150 ohms, so that serious equipment damage accidents can not happen, the safety and stability of the power distribution network are guaranteed, and the I-phase earth fault of the power distribution network is synchronously sampled and compared0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity is the same and is larger than the preset threshold value, the phase A is judged to be grounded; if I0Variation of (2) andcif the variable quantity is the same, the phase C is judged to be grounded, and the method is simpler and more accurate than the existing known method;
(2) the single-phase earth fault detection method for the power distribution network can eliminate the traditional measures such as the current arc suppression coil, the high-resistance grounding device and the like, greatly reduces the complexity of the existing grounding device, and has higher safety.
(3) The method for detecting the single-phase grounding fault of the power distribution network is expected to thoroughly solve the worldwide problem of single-phase grounding of the power distribution network, and has important significance to power grid enterprises and society.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.
Fig. 1 is a schematic diagram of a single-phase ground fault detection of a power distribution network according to an embodiment of the present disclosure.
Fig. 2 is a schematic diagram of single-phase ground fault detection of a power distribution network according to another embodiment of the present disclosure.
Detailed Description
The present disclosure is further described with reference to the following drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The utility model provides a single-phase earth fault detection method of a power distribution network, which is a single-phase earth fault detection method of a power distribution network line based on a new earth theory; the present disclosure employs a neutral point current and phase current synchronous sudden change method based on the theory of "soft ground".
The term "soft ground" means that any grounding body is a parallel connection link of a ground resistance and a ground capacitance, when the appearance of the grounding body is standardized and the surrounding soil medium is controllable, the ground resistance is much larger than the ground resistance in the general sense (generally two orders of magnitude larger), when the neutral point of the distribution network transformer is grounded through the controllable independent grounding body, due to the effect of the ground resistance, even if the line is grounded in a single phase, the current to the ground is not more than tens of amperes (calculated by taking 35kV as an example), if the line is a general 10kV line, the current is reduced by 3.5 times, so the line is grounded in a small current, and the serious equipment damage is not caused. This neutral grounding body corresponds to the current high-resistance grounding device.
The neutral point current refers to a transformer current to be installed on a neutral point grounded down conductor defined in the present technology. When a single-phase earth fault occurs, fault phase current forms an additional current loop through a fault point and a grounding body, the current is still power frequency current, and the current needs to be collected and detected by a power frequency current transformer.
The synchronous sudden change means that the current flowing through the neutral point is actually the earth current flowing through the fault point of the fault phase, and the current and the earth current are equal in size and change simultaneously, so that the current can be used as a line selection criterion.
The method is a new method based on the recognition of the soft ground characteristic of a ground body, is different from the traditional steady-state component method, the harmonic component method, the transient state method, the wavelet method and other methods, has important theoretical and engineering values, is expected to thoroughly solve the worldwide problem of single-phase earth fault line selection in the field of power distribution networks, establishes the leading position of China in this respect, and has great economic and social benefits.
Fig. 1 shows a single-phase ground fault detection principle of a power distribution network according to the present embodiment, and in fig. 1, 1 is a distribution network transformer; y is a star connection neutral point at the low-voltage side of the transformer; x is a ground fault point; g0The ground is the ground (zero potential) at the public grounding grid of the transformer substation, and G is the ground (zero potential) at the neutral point independent grounding body; r, C are neutral grounding network resistance to ground and capacitance to ground respectively; rx is the internal resistance of the grounding object of the fault point; r1、C1The resistance to ground and the capacitance to ground of the grounding object of the fault point are respectively; i isaIs the current of the current transformer of phase A; i iscIs a C-phase current transformer current; i is0A neutral grounding network to ground current.
The method for detecting the single-phase earth fault of the power distribution network comprises the following steps:
step 1: when the ground resistance of the neutral point at the low-voltage side of the distribution network transformer is less than 150 ohms, the ground down lead of the neutral point at the low-voltage side of the distribution network transformer is connected to the independent grounding network, and the ground resistance of the independent grounding network is not less than 150 ohms.
When the resistance to ground of the neutral point on the low-voltage side of the distribution network transformer is not less than 150 ohms, the neutral point on the low-voltage side of the distribution network transformer is directly connected to the public grounding network, as shown in fig. 2. As shown in fig. 2, 1 is a distribution network transformer; y is a star connection neutral point at the low-voltage side of the transformer; the grounding of the neutral point is connected to the public grounding grid, and G is the ground (zero potential) at the public grounding grid; r, C are respectively the resistance to ground and the capacitance to ground of the public grounding network; rx is the internal resistance of the grounding object of the fault point; r1、C1The resistance to ground and the capacitance to ground of the grounding object of the fault point are respectively; i isaIs the current of the current transformer of phase A; i iscIs a C-phase current transformer current; i is0A neutral grounding network to ground current.
Specifically, whether extra equipment such as an arc suppression coil, a small-resistance grounding box, a high-resistance grounding box and the like exists between the existing transformer neutral point down lead and the public grounding grid or not is checked, and if the extra equipment exists, the extra equipment is uniformly removed.
As shown in figure 1, the low-voltage side of the distribution network transformer is connected in a star connection mode, wherein a neutral point Y is connected to an independent grounding device through a grounding down lead, and the independent grounding device has a ground resistance R and a ground capacitance C. The resistance to ground is controlled within a preset range (in the present embodiment, not less than 150 ohms) to improve the sensitivity of the device. When single-phase grounding occurs at the far end (X), the grounding object also has resistance (R) to the ground1) And a capacitance to ground (C)1) Thus, the current of the whole grounding loop of the C phase is R and R1The current is limited and is very small, so that serious equipment damage accidents can not happen.
The reason for setting the 150 ohm threshold is: in order to limit the single-phase grounding current below 33A; wherein, the formula I of the calculation of the ground current is 10000V/(ground network ground resistance 150 Ω + fault point ground resistance 150 Ω). Therefore, serious equipment damage accidents can not occur, and the safety of the whole power distribution network is improved.
Step 2: measuring the current I between neutral and earth grids0Phase I of current AaAnd C phase current Ic
In the specific implementation, a precise current transformer is adopted to measure the current I between the neutral point and the corresponding grounding grid0
And a grounding down lead of a neutral point at the low-voltage side of the transformer is used as a primary side to pass through the straight-through precision current transformer, and a secondary side of the current transformer is connected into a measurement loop.
The precise current transformer series transformer core is formed by rolling a high-permeability soft magnetic material, is subjected to high-temperature protective heat treatment, and is wound by a secondary coil made of a high-strength insulating material, so that stable performance, safe and reliable operation are ensured.
Measuring A-phase current I by using current transformer for measurementaAnd C phase current Ic
Using a current transformer for A-phase measurement as A-phase current IaUsing a current transformer for C-phase measurement as C-phase current IcThe source of (a).
The current transformer for measurement is a current transformer for providing current for an indicating instrument, an integrating instrument and other similar electric appliances, and has higher precision than the current transformer for protection. Current transformers for measurement are widely used for measuring the current of low-voltage distribution systems, mainly for the purpose of the precision (given rating of the current transformer) level: 0.2, 0.5, 1, 3, 5, etc., convenient installation and various types and specifications, and the most economical and reasonable current transformer can be selected according to the busbar or the cable with different specifications.
And step 3: synchronous sampling and comparison I0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity of the phase A is the same and is larger than a preset threshold value (the preset value is known when the threshold value is used), the phase A is judged to be grounded; if I0Variation of (2) andcif the variation is the same, the phase C is determined to be grounded.
Wherein, there are two kinds of modes in the sampling, be direct current sampling and interchange sampling respectively, both kinds of modes can, but any kind all must synchronous acquisition just can, must guarantee I0And Ia、IcThe signal sampling is done in as short a time as possible.
In the case of fig. 1, due to the earth current I flowing through the neutral point0And IcThe increment parts caused by grounding at the X position are equal, so that the C phase is judged to be subjected to single-phase grounding, and the rest phases are analogized. Of course, there may be three-phase unbalance caused by some suddenly increased user load, resulting in earth current, but the load access has continuous characteristic and is different from the intermittent development characteristic of fault earth, so that the method can still distinguish three-phase unbalance current from fault earth current.
When the ground resistance of the neutral point on the low-voltage side of the distribution network transformer is less than 150 ohmsThe grounding down lead of the neutral point at the low-voltage side of the distribution network transformer is connected to the independent grounding network, the resistance to the ground of the independent grounding network is not less than 150 ohms, so that serious equipment damage accidents can not occur, the safety and the stability of the distribution network are guaranteed, and the sampling and the comparison I are synchronized0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity is the same and is larger than the preset threshold value, the phase A is judged to be grounded; if I0Variation of (2) andcthe variation is the same, the phase C is judged to be grounded, and the method is simpler and more accurate than the existing known method.
The single-phase earth fault detection device of distribution network of this embodiment, it includes:
(1) a grounding down lead of a neutral point at the low-voltage side of the distribution network transformer;
when the ground resistance of the neutral point at the low-voltage side of the distribution network transformer is less than 150 ohms, the grounding down line of the neutral point at the low-voltage side of the distribution network transformer is connected to the independent grounding network, and the ground resistance of the independent grounding network is not less than 150 ohms.
When the resistance to ground of the neutral point on the low-voltage side of the distribution network transformer is not less than 150 ohms, the neutral point on the low-voltage side of the distribution network transformer is directly connected to the public grounding network.
(2) A measurement module configured to measure a current I between the neutral point and a respective ground net0Phase I of current AaAnd C phase current Ic
Wherein the measuring module comprises a precision current transformer for measuring the current I between the neutral point and the corresponding earth grid0
The measuring module comprises a current transformer for measuring A phase current IaAnd C phase current Ic
(3) A sampling module configured to synchronously sample I0、IaAnd Ic
Wherein, there are two kinds of modes in the sampling, be direct current sampling and interchange sampling respectively, both kinds of modes can, but any kind all must synchronous acquisition just can, must guarantee I0And Ia、IcIn the shortest possible timeAnd completing signal sampling.
The sampling module is a synchronous direct current sampling circuit or a synchronous alternating current sampling circuit, and the synchronous direct current sampling circuit and the synchronous alternating current sampling circuit are both of the existing circuit structure.
(4) A processor configured to receive I of the synchronous samples0、IaAnd IcAnd compare I0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity is the same and is larger than the preset threshold value, the phase A is judged to be grounded; if I0Variation of (2) andcif the variation is the same, the phase C is determined to be grounded.
In the embodiment, the grounding down lead of the neutral point at the low-voltage side of the distribution network transformer is directly connected to the independent grounding network, the grounding resistance of the neutral point at the low-voltage side of the distribution network transformer is checked and controlled to be not less than 150 ohms, so that serious equipment damage accidents can not occur, the safety and stability of the distribution network are guaranteed, and the sampling and comparison I are performed synchronously0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity is the same and is larger than the preset threshold value, the phase A is judged to be grounded; if I0Variation of (2) andcthe variation is the same, the phase C is judged to be grounded, and the method is simpler and more accurate than the existing known method.
The case shown in fig. 2 is more risky than the case shown in fig. 1, in that if a ground fault occurs in the substation with a 10kV outgoing line, a metallic short circuit will be created and the short circuit current will be large, since the neutral point is directly connected to the common earth grid. Thus, the approach shown in fig. 1 (isolated grounding grid) is suggested, but fig. 2 still does not prevent the use of this method.
The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Claims (10)

1. A single-phase earth fault detection method for a power distribution network is characterized by comprising the following steps:
step 1: when the ground resistance of the neutral point at the low-voltage side of the distribution network transformer is less than 150 ohms, the grounding down lead of the neutral point at the low-voltage side of the distribution network transformer is wired to an independent grounding network based on the 'soft ground' theory, and R, C are the ground resistance and the ground capacitance of the neutral grounding network respectively; rx is the internal resistance of the grounding object of the fault point; r1、C1The resistance to ground and the capacitance to ground of the grounding object of the fault point are respectively; the resistance to ground of the independent grounding grid is not less than 150 ohms; the soft ground means that any grounding body is a parallel link of a resistance to ground and a capacitance to ground, and the resistance to ground is controllable under the conditions that the appearance of the grounding body is standardized and the surrounding soil medium is controllable;
step 2: measuring the current I between a neutral point and a corresponding earth grid0Phase I of current AaAnd C phase current Ic
And step 3: synchronous sampling and comparison I0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity is the same and is larger than the preset threshold value, the phase A is judged to be grounded; if I0Variation of (2) andcif the variation is the same, the phase C is determined to be grounded.
2. The method for detecting the single-phase ground fault of the power distribution network according to claim 1, wherein in the step 1, when the resistance to ground of the neutral point on the low-voltage side of the distribution network transformer is not less than 150 ohms, the neutral point on the low-voltage side of the distribution network transformer is directly connected to the public ground network.
3. The single-phase earth fault detection method for the power distribution network of claim 1, wherein in the step 2, a precision current transformer is used for measuring the current I between the neutral point and the corresponding grounding grid0
4. The single-phase earth fault detection method for power distribution network according to claim 1, wherein in step 2, measuring current is usedMutual inductor for measuring A-phase current IaAnd C phase current Ic
5. A single-phase earth fault detection device for a power distribution network, which is used in the single-phase earth fault detection method for the power distribution network according to any one of claims 1 to 4, and which comprises:
a grounding down lead of a neutral point at the low-voltage side of the distribution network transformer;
a measurement module configured to measure a current I between the neutral point and a respective ground net0Phase I of current AaAnd C phase current Ic
A sampling module configured to synchronously sample I0、IaAnd Ic
A processor configured to receive I of the synchronous samples0、IaAnd IcAnd compare I0And Ia、IcSize of (A), if I0Variation of (2) andaif the variable quantity is the same and is larger than the preset threshold value, the phase A is judged to be grounded; if I0Variation of (2) andcif the variation is the same, the phase C is determined to be grounded.
6. The single-phase ground fault detection device of the power distribution network of claim 5, wherein when the resistance to ground of the distribution network transformer low-voltage side neutral point is less than 150 ohms, the grounding down-lead of the distribution network transformer low-voltage side neutral point is wired to the independent grounding network, and the resistance to ground of the independent grounding network is not less than 150 ohms.
7. The single-phase ground fault detection device of the power distribution network of claim 5, wherein the neutral point on the low-voltage side of the distribution network transformer is directly connected to the common ground network when the resistance to ground of the neutral point on the low-voltage side of the distribution network transformer is not less than 150 ohms.
8. The single-phase ground fault detection device of a power distribution network of claim 5, wherein the measurement module comprises a precision current transformer for measuring a neutral point and a corresponding groundCurrent between nets I0
9. The single-phase ground fault detection device of the power distribution network of claim 5, wherein the measurement module comprises a current transformer for measurement for measuring the A-phase current IaAnd C phase current Ic
10. The single-phase ground fault detection device of the power distribution network according to claim 5, wherein the sampling module is a synchronous DC sampling circuit or a synchronous AC sampling circuit.
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JPH09145772A (en) * 1995-11-20 1997-06-06 Furukawa Electric Co Ltd:The Method and device for locating transmission/distribution line electric wire failure section
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