CN103616615A - Single-phase earth fault locating method of power distribution network - Google Patents

Abstract

The invention discloses a method for locating a single-phase ground fault in a distribution network, which comprises the following steps: Step 1. Install a distribution network fault indicator on each node and branch line of the distribution network; A distribution network fault indicator compares the three-phase transient current information in real time to determine whether there is a fault; Step 2. Send the fault information of each line to the monitoring center to determine the location of the fault. The method of the invention is simple and can quickly judge the fault location.

Description

A single-phase-to-earth fault location method in distribution network

technical field

The invention relates to a positioning method, in particular to a single-phase grounding fault positioning method of a power distribution network.

Background technique

At present, most of the 6kV-35kV medium-voltage distribution networks in my country adopt the neutral point ungrounded method or the neutral point grounded method through the arc suppression coil, which is called the neutral point non-effectively grounded method, or the small current grounded system. After a single-phase ground fault occurs in the distribution network, the problem of fault location has not been well resolved for a long time, which affects the reliability and economy of power supply. Commonly used single-phase ground fault detection methods are as follows:

1) High-order harmonic zero-sequence component online measurement method

It is mainly used in substation for fault line selection, online detection of the direction of the zero-sequence component of the 5th or n-th harmonic current, and comparing the magnitude of the zero-sequence component of the harmonic current of each line. Non-linear factors such as fault points and line equipment will generate harmonic currents, of which the 5th and nth harmonic components are dominant. Since the compensation effect of the arc suppressing coil on the 5th harmonic is only equivalent to 1/25 of the power frequency, and the compensation effect of the nth harmonic is only equivalent to 1/120 of the power frequency, so under normal conditions the fault line is zero The 5th and 11th harmonic currents in the sequence current are larger than those of the non-faulty line and in the opposite direction, so the faulty line can be determined accordingly. However, the harmonic content in the zero-sequence current is small and fluctuates greatly, which cannot guarantee the reliability of protection. Generally, the magnitude and direction of the high-order harmonic components of zero-sequence current can be detected online in substations for fault line selection.

2) High-order harmonic zero-sequence component off-line measurement method

Using this principle, it can also be made into an off-line ground fault detector and a hand-held detector, which can detect the magnitude of the 5th and 11th harmonic magnetic field and the zero-sequence harmonic electric field of the zero-sequence current offline. When in use, stand under the overhead line to detect the 5th harmonic and 11th harmonic current magnetic field, and at the same time use the electric field potential gradient of the overhead wire to detect the zero-sequence high-order harmonic voltage component, so as to detect the power direction and compare different The magnitude and direction of the zero-sequence current high-order harmonic component of the outgoing line and different branch lines, so as to judge the faulty outgoing line and faulty branch. This kind of grounding detector has a good effect on overhead lines in rural and suburban areas, but it is not suitable for erecting multiple lines on the same pole in the urban network and other communication power lines erected on parallel poles, and manual detection along the line is required.

3) Active component method

Detect the active component in the zero-sequence current of each line at the outlet of the substation, and select the fault line. Sometimes it is necessary to connect a resistor in series under the coil or a resistor in parallel at both ends of the coil in a system where the neutral point is grounded through the arc suppression coil. to produce active components. This method is generally used in substation line selection. When used on the line, only a special measuring device or FTU can be used to detect the active component in the zero-sequence component, so the cost is high, it is not suitable for large-scale installation, and it is difficult to locate the fault. Branches and points of failure.

4) Power direction

Input zero-sequence current and zero-sequence voltage for Fourier analysis and calculation. The one with the largest zero-sequence active power is the fault line. It is generally used in substation line selection and cannot be used for fault location.

5) Transient signal measurement and calculation method

Using the transient process generated by the charging and discharging process of the distributed capacitance at the moment of grounding, measure the transient zero-sequence current and zero-sequence voltage, judge the fault direction and estimate the fault distance, there are first half-wave method, differential equation method, Fourier transform method, least squares multiplication method, etc. These methods still have a lot of error in calculating the fault distance, and it is difficult to locate the fault branch and fault point in the case of multiple branches.

6) Injection current method

After a single-phase ground fault occurs, a signal of a special frequency (higher than the power frequency, such as 80 Hz) is injected into the fault phase of the substation, and then detected by an offline device to determine the fault branch and fault point. But when the non-faulty line is very long and the faulty line is short, it is difficult to judge.

7) Zero sequence admittance method

According to the zero-sequence circuit in the normal operation of the power grid, using the appropriate detuning condition of the arc suppression coil and the corresponding change of the displacement voltage, the ground admittance and admittance coefficient of each outgoing line can be calculated, which can be used as the reference value of the corresponding outgoing line When it is stored, it is equivalent to adding an asymmetric power supply to the power grid when the fault occurs, which will cause a change in the admittance coefficient of the outgoing line. By comparing the change of the admittance coefficient before and after the fault of each line, the faulty line can be determined. This method has high sensitivity and has been used in European countries. However, it needs to be used in conjunction with the arc suppression coil, and the ungrounded system or the system that cannot automatically adjust the arc suppression coil is not suitable for use. This method is not suitable for locating the fault point on the line, and can only judge the faulty line according to the change of the zero-sequence admittance of the outgoing line.

8) Residual flow incremental method

In the case of a single permanent ground fault, if the detuning degree of the arc suppression coil (or the resistance value of the damping resistor) is changed, only the zero-sequence current (residual current at the fault point) in the fault line will change accordingly. Therefore, by comparing the zero-sequence current changes of each outgoing line before and after the detuning degree changes, the faulty line is the one with the largest change. This method has high sensitivity and reliability, and is suitable for ground fault line selection in substations. The disadvantage is that it is not applicable to systems that are not grounded and the arc suppression coil cannot be automatically adjusted, and the fault point cannot be located.

9) The neutral point is grounded with a small resistance

After a single-phase ground fault occurs, a small resistor is connected to the neutral point for a short time to generate a large zero-sequence component, and zero-sequence protection is configured on the outgoing line of the substation to ensure tripping of the faulty outgoing line. The instantaneous fault of arc extinguishing, on the contrary, produces unnecessary power outages and increases the power outage time.

10) Dynamic resistive load input method

The main principle of the dynamic resistive load input method is to install an automatic controllable resistive load device (i.e. signal source) in the substation. When a single-phase ground fault occurs, the neutral point of the substation (or the neutral point of the grounding When the neutral point can be connected to the busbar), the dynamic resistive load device is automatically put into operation for a short time, and a special small signal current (maximum not greater than 40A) is generated between the substation and the field grounding point. This signal current will be modulated to the fault On the load current on the phase, the ground fault indicator installed at the outgoing line of the substation and the branch point of the line can detect this current signal, and can automatically act and indicate to achieve the purpose of indicating the fault. This method works well, but requires the installation of median resistors and throwing devices.

Some of the above methods are only suitable for use in substations, some are less accurate or cost too much when used on the line, and some are only suitable for use in special systems and are not suitable for promotion in power distribution systems.

Contents of the invention

The purpose of the present invention is to provide a method for locating a single-phase ground fault in a power distribution network.

The technical solution to realize the object of the present invention is: a method for locating a single-phase ground fault in a distribution network, comprising the following steps:

Step 1. Install a distribution network fault indicator on each node and each branch line of the distribution network, and the distribution network fault indicator detects the current information on the corresponding node in real time;

Step 2, comparing the measured transient current directions of the three-phase nodes of the same line, if the three-phase transient current directions are different, it is judged that the three-phase nodes are faulty nodes;

Step 3. Determine the faulty line. If the three-phase nodes in the current inflow direction of a line are faulty nodes, and the three-phase nodes in the current outflow direction are all non-faulty nodes, then the line is a faulty line.

Compared with the prior art, the present invention has the remarkable advantages that the single-phase ground fault location method of the distribution network is simple and can quickly determine the fault location.

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Description of drawings

FIG. 1 is an example diagram of a distribution network circuit of the present invention.

Detailed ways

In combination with the accompanying drawings of the description, a method for locating a single-phase ground fault in a distribution network of the present invention includes the following steps:

Step 1. Install a distribution network fault indicator on each node and each branch line of the distribution network, and the distribution network fault indicator detects the current information on the corresponding node in real time;

Step 2, comparing the measured transient current directions of the three-phase nodes of the same line, if the three-phase transient current directions are different, it is judged that the three-phase nodes are faulty nodes;

Step 3. Determine the faulty line. If the three-phase nodes in the current inflow direction of a line are faulty nodes, and the three-phase nodes in the current outflow direction are all non-faulty nodes, then the line is a faulty line.

The specific description is as follows:

Combined with Fig. 1, Fig. 1 is a simple grounding distribution network diagram of arc suppressing coils. The fault indicator is installed at the front end of each line. Assuming that a single-phase grounding fault occurs in phase A of branch line 3, the transient state of the grounding current The process is basically that all the capacitors of phase A of the entire line are discharged through the grounding point, and the currents of all the capacitors of phase B and phase C flow to the direction of the power supply, and flow to the grounding point through the power supply side through the A phase line. Therefore, the direction of the transient capacitive current of phase B and phase C is the opposite direction of the power supply current, the direction of the transient current before the fault point of the A phase line is the direction of the power supply current, and the direction of the transient current after the fault is the opposite direction of the power supply current direction. Using the above method, it can be judged whether the three-phase node is a faulty node. If the three-phase node in the current inflow direction of a line is a faulty node, and the three-phase nodes in the current outflow direction are all non-faulty nodes, then the line is a faulty line. Therefore, by judging the direction of A, B, and C three-phase transient currents, it can be used to judge the fault area.

It can be seen from the above that the single-phase ground fault location method of the distribution network is simple and can quickly determine the fault location.

Claims (1)

1. A distribution network single-phase ground fault location method, is characterized in that, comprises the following steps: Step 1. Install a distribution network fault indicator on each node and each branch line of the distribution network, and the distribution network fault indicator detects the current information on the corresponding node in real time; Step 2, comparing the measured transient current directions of the three-phase nodes of the same line, if the three-phase transient current directions are different, it is judged that the three-phase nodes are faulty nodes; Step 3. Determine the faulty line. If the three-phase nodes in the current inflow direction of a line are faulty nodes, and the three-phase nodes in the current outflow direction are all non-faulty nodes, then the line is a faulty line.

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