A method for detecting single-phase grounding fault of collector line in photovoltaic distribution network

Abstract

The present invention is applicable to the field of photovoltaic distribution network detection technology, and provides a method for detecting single-phase grounding faults in the collector line of a photovoltaic distribution network, including detecting three-phase traveling waves at each detection point in the collector line of the photovoltaic distribution network through a traveling wave mutual inductor, and judging whether a sudden change in traveling wave current occurs in the collector line according to a set traveling wave current threshold; when it is judged that a sudden change in traveling wave current occurs in the collector line, the traveling wave current of each phase line in a set time period before and after the sudden change in traveling wave current of the collector line is obtained; the traveling wave current change amount of each phase line and the asymmetric amount of each phase traveling wave change are calculated according to the traveling wave current of each phase line in a set time period before and after the sudden change; judging whether a grounding fault occurs according to the traveling wave current change amount of each phase line and the asymmetric amount of each phase traveling wave change. The method identifies a grounding fault by calculating and judging based on the traveling wave change amount, does not rely on zero-sequence voltage and zero-sequence current, and improves detection efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic distribution network detection technology, and in particular relates to a method for detecting a single-phase grounding fault of a collector line of a photovoltaic distribution network. Background Art

[0002] Photovoltaic power generation lines occupy a large area, the internal collector line wiring is complex, and the cable overhead mixed frame collector line is affected by the harsh operating environment during operation. Various grounding faults and hidden discharges will occur, causing line tripping. In addition, photovoltaic collector cable lines are not directly observable, and it is extremely difficult to find the fault point. As the overhead collector line increases in service life, the accumulation and deterioration of insulators, broken wires, and trees that are too high will cause certain defects in line insulation and discharge. Cable collector lines are prone to failure due to their complex operating environment and long service life. At the same time, the internal collector line wiring is complex. When a photovoltaic collector cable line fails, it is often very difficult to find the fault point. The aging and defects of the main cable insulation and cable joints cause hidden defect discharges. If the hidden discharges are not handled in time, they will cause serious safety risks to the stable operation of the system.

[0003] The existing ground fault detection method for photovoltaic distribution networks mainly uses low-sampling steady-state data, which can only solve low-resistance faults; the corresponding hidden danger discharge fault detection adopts partial discharge means, and the offline detection efficiency is slow and requires power outage to solve, which is time-consuming and labor-intensive. Summary of the invention

[0004] The embodiment of the present invention provides a method for detecting single-phase grounding faults of a collector line of a photovoltaic distribution network, aiming to solve the problem that the detection of hidden discharge faults in the photovoltaic distribution network adopts partial discharge means, resulting in low offline detection efficiency.

[0005] The embodiment of the present invention is implemented as follows:

[0006] The present invention provides a method for detecting a single-phase grounding fault of a collector line of a photovoltaic distribution network, comprising:

[0007] Detecting the three-phase traveling waves at each detection point in the photovoltaic distribution network collector line through a traveling wave mutual inductor, and determining whether a sudden change in traveling wave current occurs in the collector line according to a set traveling wave current threshold;

[0008] When it is determined that a sudden change in the traveling wave current occurs in the collector circuit, the traveling wave current of each phase circuit in a set time period before and after the sudden change in the traveling wave current of the collector circuit is obtained;

[0009] Calculate the travel wave current variation of each phase line and the asymmetry of each phase travel wave variation according to the travel wave current of each phase line in the set time period before and after the mutation moment;

[0010] A judgment is made based on the change in the traveling wave current of each phase line and the asymmetry of the traveling wave change of each phase to determine whether a ground fault has occurred.

[0011] Furthermore, the calculation of the travel wave current variation of each phase line and the travel wave variation asymmetry of each phase according to the travel wave current of each phase line in the set time period before and after the mutation moment includes:

[0012] According to the traveling wave current of each phase line in the set time period before and after the traveling wave current mutation moment, the difference of the change amount of the traveling wave current sampling value between any two phases is calculated, including the AB phase difference current, the BC phase difference current and the CA phase difference current;

[0013] Calculate the effective value RMS of the amplitude change of any two-phase traveling wave current according to the difference of the variation of the sampling values ​​of the traveling wave current of any two phases;

[0014] The asymmetry of the traveling wave change of each phase is calculated according to the effective value RMS of the amplitude change of the traveling wave current of any two phases.

[0015] Furthermore, judging based on the variation of the traveling wave current of each phase line and the asymmetry of the traveling wave variation of each phase to determine whether a ground fault occurs includes:

[0016] If the asymmetry of the traveling wave change of at least any one phase is greater than the preset phase traveling wave change asymmetry threshold, the maximum value of the three-phase traveling wave current change is selected; determine whether the maximum value is greater than the other two phase traveling wave current changes multiplied by the preset phase traveling wave change asymmetry threshold. If so, it is determined that the phase with the maximum value of the traveling wave current change is the grounding fault phase, and the other two phases are non-fault phases.

[0017] Furthermore, judging whether a ground fault occurs based on the change amount of the traveling wave current of each phase line and the asymmetry amount of the traveling wave change of each phase, further includes:

[0018] If the asymmetry of any phase traveling wave change is not greater than the preset asymmetry threshold of the phase traveling wave change, then reset is performed.

[0019] Furthermore, the three-phase current traveling waves of each detection point in the photovoltaic collection line are collected by the traveling wave mutual inductor, specifically:

[0020] When the traveling wave sensor is used for the line selection device in the substation of the photovoltaic distribution network, the detection point is located at the head end of each feeder in the substation, and the three-phase current traveling wave at the head end of each feeder in the substation is collected through the traveling wave transformer;

[0021] When the traveling wave sensor is used for the external collection line of the substation of the photovoltaic distribution network, the detection point is located at the distribution terminal on the external collection line of the substation, and the three-phase current traveling wave of the distribution terminal on the external collection line of the substation is collected through the traveling wave transformer.

[0022] Beneficial effects of the present invention:

[0023] The photovoltaic distribution network collector line single-phase grounding fault detection method of the present invention detects the three-phase traveling waves of each detection point in the photovoltaic distribution network collector line through a traveling wave mutual inductor, and determines whether the collector line has a traveling wave current mutation according to the set traveling wave current threshold; when it is determined that the collector line has a traveling wave current mutation, the traveling wave current of each phase line in the set time period before and after the traveling wave current mutation moment of the collector line is obtained; the traveling wave current change of each phase line and the asymmetry of each phase traveling wave change are calculated according to the traveling wave current of each phase line in the set time period before and after the mutation moment; and the traveling wave current change of each phase line and the asymmetry of each phase traveling wave change are judged to determine whether a grounding fault occurs. The method identifies the grounding fault by calculating and judging based on the traveling wave change, has a simple scheme, is easy to implement, does not rely on the limiting conditions of zero-sequence voltage and zero-sequence current, and improves the detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the steps of a method for detecting a single-phase grounding fault of a collector line of a photovoltaic distribution network provided by an embodiment of the present invention;

[0025] Figure 2 is a schematic diagram of the variation of three-phase traveling waves provided by an embodiment of the present invention;

[0026] Figure 3 It is a schematic diagram of the steps of a method for detecting a single-phase grounding fault of a collector line of a photovoltaic distribution network provided by another embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] The single-phase grounding fault detection method of the collector line of the photovoltaic distribution network of the present invention identifies the grounding fault by calculating and judging based on the traveling wave variation. Compared with the prior art, the scheme is simple and easy to implement. It only needs to collect the current or voltage traveling wave in real time through the traveling wave sensor unit installed on the three-phase line. It does not need to master the characteristics of the calculation of zero mode or line mode signals, and does not rely on the restriction conditions of zero-sequence voltage and zero-sequence current, thereby improving the detection efficiency.

[0029] Embodiment 1

[0030] See also Figure 1 and Figure 2 The embodiment of the present invention provides a method for detecting a single-phase grounding fault of a collector line of a photovoltaic distribution network, comprising:

[0031] S1. Detect the three-phase traveling waves of each detection point in the collector line of the photovoltaic distribution network through a traveling wave mutual inductor, and determine whether a sudden change of traveling wave current occurs in the collector line according to a set traveling wave current threshold;

[0032] Since the present invention performs calculation based on the traveling wave variation, in the photovoltaic distribution network, a traveling wave mutual inductor is used to detect each detection point in the photovoltaic distribution network collector line, and the three-phase traveling wave of each detection point is displayed. In this embodiment, the three-phase traveling wave of each detection point is displayed by an oscilloscope, and the current curve trend can be observed intuitively. In the three-phase traveling wave diagram, if the current curve changes greatly, such as Figure 2 It can be seen that, according to the set traveling wave current threshold, it is possible to clearly observe whether a sudden change of traveling wave current occurs in the collector line.

[0033] S2. When it is determined that a sudden change in the traveling wave current occurs in the collector circuit, the traveling wave current of each phase circuit in a set time period before and after the sudden change in the traveling wave current of the collector circuit is obtained;

[0034] After determining that a sudden change in traveling wave current has occurred, it is necessary to collect the traveling wave current of each phase line in a set time period before and after the sudden change in the traveling wave current of the power line. In this embodiment, the specific collection method can be selected by the data amplitude displayed by the oscilloscope. At the same time, the set time period before and after the sudden change can be set within a reasonable range according to actual conditions.

[0035] S3, calculating the travel wave current change amount of each phase line and the asymmetry amount of each phase travel wave change according to the travel wave current of each phase line in the set time period before and after the mutation moment;

[0036] S4. Determine whether a ground fault occurs based on the change in the traveling wave current of each phase line and the asymmetry of the traveling wave change of each phase.

[0037] It should be noted that in this embodiment, the three-phase traveling waves of each detection point in the photovoltaic distribution network collection line are detected by a traveling wave mutual inductor. In some embodiments, other collection devices can also be used for collection and acquisition, and the collection device has a waveform display function.

[0038] The single-phase grounding fault detection method of the collector line of the photovoltaic distribution network of the present invention performs real-time sampling and monitoring of the three-phase traveling waves on the distribution line; calculates the variation of the three-phase traveling waves; and detects the grounding fault by judging the imbalance of the variation of the three-phase traveling waves to determine whether the grounding fault occurs. The method identifies the grounding fault by calculating and judging based on the variation of the traveling waves. Compared with the prior art, the scheme is simple and easy to implement. It only needs to collect the current or voltage traveling waves in real time through the traveling wave sensor unit installed on the three-phase line. It does not need to master the characteristics of the calculation of zero mode or line mode signals, and does not rely on the limiting conditions of zero-sequence voltage and zero-sequence current, thereby improving the detection efficiency. At the same time, the method can be judged on the spot, and the collected data does not need to be transmitted to the data master station, which can well avoid the errors caused by the traditional signal positioning due to the problems of timing. It only needs to calculate the traveling wave amount collected on the spot to realize the detection of single-phase grounding faults and hidden dangers of the distribution network.

[0039] Embodiment 2

[0040] See also Figure 3 , according to the traveling wave current of each phase line in the set time period before and after the mutation moment, the present embodiment calculates the traveling wave current change amount of each phase line and the asymmetric amount of each phase traveling wave change, including:

[0041] S11, according to the traveling wave current of each phase line in the set time period before and after the traveling wave current mutation moment, calculate the difference of the change amount of the traveling wave current sampling value of any two phases, including the AB phase difference current, the BC phase difference current and the CA phase difference current;

[0042] In this embodiment, the waveform data of the set time period before and after the sudden change occurs (0.05 ms before and after the sudden change point) is taken for calculation, then:

[0043] AB phase difference current △i AB :

[0044] Δi AB =Δi A -Δi B

[0045] BC phase difference current △i BC :

[0046] Δi BC =Δi B -Δi C

[0047] CA phase difference current △i CA :

[0048] Δi CA =Δi C -Δi A

[0049] S12, calculating the effective value RMS (root mean square) of the change in the amplitude of the traveling wave current of any two phases according to the difference in the change in the sampling value of the traveling wave current of any two phases, expressed as:

[0050]

[0051] Where i is represented by (AB, BC, CA), and N is the number of sampling points in the set time period before and after the mutation occurs (0.05ms before and after the mutation point).

[0052] S13, calculating the asymmetry of each phase traveling wave change according to the effective value RMS of the traveling wave current amplitude change of any two phases, expressed as:

[0053]

[0054]

[0055]

[0056] It should be noted that in this embodiment, the waveform data of the set time period before and after the sudden change occurs (0.05ms before and after the sudden change point) is calculated, which is not specified as 0.05ms. In other embodiments, it can be formulated according to actual conditions.

[0057] In this embodiment, the difference between the changes in the sampling values ​​of the traveling wave currents of any two phases is calculated by taking the waveform data of 0.05ms before and after the mutation point, and the effective value RMS of the changes in the amplitudes of the traveling wave currents of any two phases is further calculated, and finally the asymmetry of the traveling wave changes of each phase is calculated. The calculation process is simple, and the data collection is convenient, accurate and efficient, which provides an accurate data source for subsequent ground fault judgment.

[0058] Embodiment 3

[0059] In this embodiment, judging whether a ground fault occurs based on the variation of the traveling wave current of each phase line and the asymmetry of the traveling wave variation of each phase includes:

[0060] If at least any one phase traveling wave change asymmetry is greater than a preset phase traveling wave change asymmetry threshold, for example, Max(P A ,P B ,P C )>k (and the value range of k is [2, 4]);

[0061] Select the maximum value of the three-phase traveling wave current change, counted as △Imax, and judge whether the maximum value is greater than the other two-phase traveling wave current change multiplied by the preset phase traveling wave change asymmetry threshold, as follows:

[0062] If |△Imax|>k*|△I1|} and |△Imax|>k*|△I2| are satisfied at the same time, it is determined that the phase with the maximum value of the phase traveling wave current change is the ground fault phase, and the other two phases are non-fault phases.

[0063] Among them, the value range of k is [2,4], △I1 and △I2 are the changes of the other two phase current traveling waves at the △Imax sampling time, and it is judged that a ground fault occurs.

[0064] In this embodiment, ΔImax=max{|ΔIA|, |ΔIB|, |ΔIc|}, and the maximum value ΔImax of the phase traveling wave current variation is the traveling wave current variation of one phase among the three phases.

[0065] In addition, in other embodiments, if the asymmetric amount of the traveling wave change of any phase is not greater than the preset asymmetric amount threshold of the traveling wave change of the phase, then reset is performed. Reset refers to the confirmation of the alarm signal generated by the protection action. In this embodiment, it means that the ground fault signal is generated. After the secondary system sends out the alarm signal, it has attracted the attention of the duty personnel and taken corresponding treatment measures. At this time, the duty personnel can manually eliminate the ground fault signal according to the work procedure.

[0066] Embodiment 4

[0067] In this embodiment, the three-phase current traveling waves of each detection point in the photovoltaic collection line are collected by the traveling wave mutual inductor, specifically:

[0068] When the traveling wave sensor is used for the line selection device in the substation of the photovoltaic distribution network, the detection point is located at the head end of each feeder in the substation, and the three-phase current traveling wave at the head end of each feeder in the substation is collected through the traveling wave transformer;

[0069] When the traveling wave sensor is used for the external collection line of the substation of the photovoltaic distribution network, the detection point is located at the distribution terminal on the external collection line of the substation, and the three-phase current traveling wave of the distribution terminal on the external collection line of the substation is collected through the traveling wave transformer.

[0070] In other embodiments, the detection point can be reselected. The detection point is not unique, but is the most preferred one and can be selected based on actual conditions.

[0071] It is understandable that those skilled in the art can, under the guidance of the above embodiments, combine various implementation methods in the above embodiments to obtain technical solutions of multiple implementation methods.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting single-phase grounding fault of a collector line of a photovoltaic distribution network, characterized in that: include: Detecting the three-phase traveling waves at each detection point in the photovoltaic distribution network collector line through a traveling wave mutual inductor, and determining whether a sudden change in traveling wave current occurs in the collector line according to a set traveling wave current threshold; When it is determined that a sudden change in the traveling wave current occurs in the collector circuit, the traveling wave current of each phase circuit in a set time period before and after the sudden change in the traveling wave current of the collector circuit is obtained; Calculate the travel wave current variation of each phase line and the asymmetry of each phase travel wave variation according to the travel wave current of each phase line in the set time period before and after the mutation moment; Determine whether a ground fault occurs based on the change in the traveling wave current of each phase line and the asymmetry of the traveling wave change of each phase; The calculation of the traveling wave current variation of each phase line and the traveling wave variation asymmetry of each phase according to the traveling wave current of each phase line in the set time period before and after the mutation moment includes: According to the traveling wave current of each phase line in the set time period before and after the traveling wave current mutation moment, the difference of the change amount of the traveling wave current sampling value between any two phases is calculated, including the AB phase difference current, the BC phase difference current and the CA phase difference current; Calculate the effective value RMS of the amplitude change of any two-phase traveling wave current according to the difference of the variation of the sampling values ​​of the traveling wave current of any two phases; The asymmetric amount of each phase traveling wave change is calculated according to the effective value RMS of the amplitude change of any two-phase traveling wave current, and the asymmetric amount of each phase traveling wave change is expressed as: Among them, I AB Indicates the effective value of the difference current between phases AB, I BC Indicates the effective value of the BC phase difference current, I CA Indicates the effective value of the CA phase difference current; The step of judging whether a ground fault occurs based on the variation of the traveling wave current of each phase line and the asymmetry of the traveling wave variation of each phase line comprises: If the asymmetry of the traveling wave change of at least any one phase is greater than the preset phase traveling wave change asymmetry threshold, the maximum value of the three-phase traveling wave current change is selected; determine whether the maximum value is greater than the other two phase traveling wave current changes multiplied by the preset phase traveling wave change asymmetry threshold. If so, it is determined that the phase with the maximum value of the traveling wave current change is the grounding fault phase, and the other two phases are non-fault phases.

2. The method for detecting single-phase grounding fault of a collector line of a photovoltaic distribution network according to claim 1, characterized in that: The step of judging whether a ground fault occurs based on the amount of change of the traveling wave current of each phase line and the amount of asymmetry of the traveling wave change of each phase line includes: If the asymmetry of any phase traveling wave change is not greater than the preset asymmetry threshold of the phase traveling wave change, then reset is performed.

3. The method for detecting single-phase grounding fault of a collector line of a photovoltaic distribution network according to claim 1, characterized in that: The three-phase current traveling waves of each detection point in the photovoltaic collection line are collected by the traveling wave mutual inductor, specifically: When the traveling wave sensor is used for the line selection device in the substation of the photovoltaic distribution network, the detection point is located at the head end of each feeder in the substation, and the three-phase current traveling wave at the head end of each feeder in the substation is collected through the traveling wave transformer; When the traveling wave sensor is used for the external collection line of the substation of the photovoltaic distribution network, the detection point is located at the distribution terminal on the external collection line of the substation, and the three-phase current traveling wave of the distribution terminal on the external collection line of the substation is collected through the traveling wave transformer.

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