Residual current protection method for active power distribution network
By installing current detection and communication devices in the active distribution network, the total residual current in each branch line is comprehensively judged, and the problem of leakage failure expansion caused by distributed roof photovoltaic access is solved, timely residual current protection is achieved, and fire risk is eliminated.
Patent Information
- Application Number
- CN202510312192.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-17
- Publication Date
- 2025-07-29
AI Technical Summary
In the existing rural distribution network, in a multi-end, multi-source, and reversible active distribution network environment, distributed roof photovoltaic access causes the residual current protector to refuse to move, and the lines cannot be cut off in time, resulting in an expansion of leakage faults and a fire risk.
The current detection device and communication device are installed at the T contacts of each branch line outlet of the transformer and the distributed roof photovoltaic. By calculating the total residual current in each branch line, comprehensively judging and sending an alarm signal and a shutdown signal when the preset threshold is reached, the timely operation of the residual current protector is realized.
The timely operation of the residual current protector is achieved to avoid leakage failures and fire, ensure personnel safety, and there is no need to change the existing protection structure, which is simple to operate and low cost.
Smart Images
Figure CN120389367A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of photovoltaic active agricultural distribution networks, and in particular relates to a residual current protection method for active distribution networks. Background Art
[0002] With the proposal of "carbon peak and carbon neutrality", rural distributed rooftop photovoltaics have developed on a large scale, and a large number of distributed rooftop photovoltaics have been connected to the 380V rural distribution network. The rural distribution network has been transformed from a traditional one-way radial tree network to a multi-terminal, multi-source, and flow-reversible active distribution network, which has brought huge challenges to the residual current protection of the rural distribution network.
[0003] Existing residual current protection for rural power distribution relies on traditional, single-source distribution networks, primarily employing a hierarchical, local protection strategy. According to GBT 13955-2017, "Installation and Operation of Residual Current Operated Protective Devices," to minimize the scope of power outages caused by electric shock accidents and ground faults, RCD (residual current device) protection should be implemented in a hierarchical manner within low-voltage power supply and distribution systems. The choice of hierarchical protection should be tailored to the power load, specific line conditions, and the protected equipment and location, resulting in a two- or three-tiered approach consisting of general protection, intermediate protection, and terminal protection. Rural power lines in my country are long, and rural distribution networks remain relatively weak. Based on field research, many rural areas currently utilize 300mA general protection and 30mA terminal protection at transformer branch outlets for leakage protection, without installing intermediate protection. Among rural electrical line leakages that can cause serious injuries and short-circuit fires, fires caused by ground fault arcs are the most dangerous. Arc energy above 300mA can easily ignite nearby combustible materials. Therefore, installing a 300mA leakage protection device at the transformer branch line outlet can ensure line safety overall.
[0004] According to NB / T32004-2018 "Technical Specifications for Photovoltaic Grid-Connected Inverters", photovoltaic inverters should provide residual current detection to monitor excessive continuous residual current and excessive residual current mutations. If the continuous residual current exceeds the following limits, the inverter should be disconnected from the grid within 300ms and issue a fault signal: 1) 300mA for inverters with rated output power ≤30kVA; 2) 10mA / kVA for inverters with rated output power >30kVA.
[0005] It can be seen from this that for continuous residual current, the set action value of the PV inverter is at least 300 mA. A considerable proportion of rural households have rooftop PV installations of 50 - 80 kW, and the built-in residual current protection threshold of the PV inverter is between 0.5 - 0.8 A. The residual current protection in the distributed rooftop PV power station is controlled by the residual current protector integrated in the PV inverter. The leakage in the residential household is controlled by a 30 mA household residual current protector, while the leakage protection of the line between the rooftop PV power station and the substation transformer depends on the total residual current protector at the outlet of the transformer, posing a huge risk of leakage failure
[0006] When multiple distributed rooftop PV power stations are connected to the same transformer through a 380V line, multiple power sources are equivalent to being connected in parallel within the same transformer substation area. With the fluctuations of the electrical load and the changes in the light intensity, the current flow in the substation area may either go down or reverse upward. When the current flow in the substation area does not reverse upward, in the event of a leakage fault at a certain point on the branch line within the substation area, both the distribution network and the rooftop PV power station will inject leakage current into the fault point. However, the total residual current protector device at the distribution outlet and the residual current protector integrated in the PV power station inverter can only detect the leakage current injected by themselves into the fault point, resulting in a relatively small detected current value by the residual current protector, causing the protector to malfunction and triggering a fire. Within the same substation area, the larger the number and capacity of the distributed rooftop PV power stations, the higher the risk of leakage protection malfunction Summary of the Invention
[0007] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a residual current protection method for active distribution networks, solving the problems in the above background technology
[0008] The purpose of the present invention is achieved as follows: A residual current protection method for active distribution networks, which includes the following steps:
[0009] Step 1: Set a current detection device A and a main communication device B at the distribution outlet. The main communication device B is connected to the total residual current protector and the current detection device A respectively through communication lines
[0010] Step 2: Set a residual current detection device C and a slave communication device D at the T - connection point of each distributed rooftop PV. The slave communication device D is connected to the residual current detection device C through a communication line
[0011] Step 3: Perform calculation and processing on the leakage information I G of the distribution branch line of the transformer and the leakage information I pn (n = 1, 2…) at each distributed rooftop PV power station in the branch line to obtain the sum I 总 ;
[0012] Step 4: The sum I of the total residual current in the branch line总 is compared with the preset residual current threshold I of this branch line set If I 总 ≥I set , and the set time is exceeded, the main communication device B sends an alarm signal to the operation and maintenance unit, and sends a shutdown signal to the total residual current protector through the communication line. The residual current protector operates to prevent the leakage fault from developing into a fire.
[0013] Furthermore, the communication line interface uses I 2 C or RS485 that supports fiber optic communication.
[0014] Furthermore, the specific operation of step one is to install the current detection device A and the main communication device B at the total residual current protection of each distribution outlet of the transformer in the substation area. The main communication device B is connected to the total residual current protection of the branch line and the current detection device A respectively through the communication line.
[0015] Furthermore, the specific operation of step two is to install the residual current detection device C and the slave communication device D at the T-junction of each distributed rooftop photovoltaic. The slave communication device D is connected to the residual current detection device C through the communication line.
[0016] Furthermore, the specific operation of step three is to send the residual current information of each distributed rooftop photovoltaic power station installed on the rural distribution network branch line to the main communication device B through the slave communication device D. The current detection device A sends the branch line outlet current direction and the branch line residual current information to the main communication device B. The main communication device B calculates and processes the received leakage information I G of the transformer distribution branch line and the leakage information I pn (n = 1, 2…) of each distributed rooftop photovoltaic power station in the branch line to obtain the sum I 总 of the total residual current in the branch line; after the rooftop distributed photovoltaic is connected, with the fluctuations of the electricity load and the changes in the photovoltaic power generation, the branch line power flow in the substation area changes, and the branch line current direction goes down or up;
[0017] If it goes down, the residual current in the branch line is provided jointly by the photovoltaic power station and the transformer,
[0018] then I 总 =I G +I p1 +I p2 +…I pn ;
[0019] If it goes up, all the residual current in the branch line is provided by the photovoltaic power station,
[0020] I 总 =I p1 +I p2 +…I pn .
[0021] Further, step four is specifically that the residual current threshold I set is set to 200 mA, 300 mA, 500 mA or a dynamic value. If I 总 ≥I set , and the set time is exceeded, the main communication device B sends an alarm signal to the operation and maintenance unit, and sends a shutdown signal to the total residual current protector through the communication line, and the residual current protector operates to avoid the development of a leakage fault into a fire.
[0022] Further, the current detection device A is integrated with a current direction identification module and a residual current detection module, and the current direction identification module is used to detect the current direction. The current direction identification module is a Hall effect current sensor module or a fluxgate current sensor module or other current detection modules that can identify the current direction. The residual current detection device is used to measure the magnitude of the residual current value, and can be a detection element in a type B residual current protector that can detect DC residual current or other detection modules that can detect DC and harmonic residual current.
[0023] Further, the main communication device B is used to receive information and perform calculation and identification on the information, and can be a 5G communication module or an ultra-wideband power line carrier communication and other communication modules possessed by low-voltage devices.
[0024] The residual current detection device C can be a detection element in a type B residual current protector that can detect DC residual current or other detection modules that can detect DC and harmonic residual current.
[0025] The slave communication device D is used to send information, including a 5G communication module, an ultra-wideband power line carrier communication and other communication modules possessed by low-voltage devices.
[0026] Advantages of the present invention:
[0027] 1. Aiming at the problem that the transformation of rural distribution networks into active distribution networks with a large number of distributed rooftop PV access causes the original residual current protectors to malfunction, fail to cut off the line in time, and cause the expansion of leakage faults, it is proposed to comprehensively judge the residual current at the outlets of each branch of the transformer and the residual current of each distributed rooftop PV power station in the substation area, so as to realize the timely operation of the residual current protector and eliminate personal injuries and fires.
[0028] 2. The method of this patent does not need to change the existing residual current protection structure of rural distribution networks, and only needs to install corresponding equipment on the line, and the operation is simple.
[0029] 3. Each device used in this patent has a low cost and is popularizable. Description of the Drawings
[0030] Figure 1 is the structure diagram of residual current protection and current flow direction of the existing rural active distribution network;
[0031] Figure 2 is the schematic diagram of the downward flow of transformer power flow in the existing rural active distribution network;
[0032] Figure 3 is the structure schematic diagram of the present invention;
[0033] Figure 4 is the process schematic diagram of the present invention;
[0034] Figure 5 is the application schematic diagram of the present invention. Detailed implementation manners
[0035] The following further describes the present invention in detail with reference to the accompanying drawings. It should be noted that this is only for a clearer description and explanation of the present invention.
[0036] Embodiment 1
[0037] As Figure 3-5 shown, this embodiment discloses a residual current protection method for an active distribution network, which includes the following steps: Step 1, a current detection device A and a main communication device B are arranged at the distribution outgoing line outlet, and the main communication device B is respectively connected to the residual current total protector and the current detection device A through communication lines; Step 2, a residual current detection device C and a slave communication device D are arranged at the T-junction of each distributed rooftop photovoltaic, and the slave communication device D is connected to the residual current detection device C through a communication line; Step 3, perform calculation and processing on the leakage current information I G of the transformer distribution branch line and the leakage current information I pn at each distributed rooftop photovoltaic power station in the branch line (n = 1, 2...), and obtain the sum I 总 of the total residual current in the branch line; Step 4, compare the sum I 总 of the total residual current in the branch line with the preset residual current threshold I set of this branch line. If I 总 ≥I set , and it exceeds the set time, the main communication device B sends an alarm signal to the operation and maintenance unit, and sends a shutdown signal to the residual current total protector through the communication line.
[0038] The technical solution of this method aims at the problem that when a large number of distributed rooftop photovoltaics are connected to transform the rural distribution network into an active distribution network, the original residual current protector fails to operate, cannot cut off the line in time, and leads to the expansion of leakage faults. It proposes to comprehensively judge the residual current at the outlet of each transformer branch line and the residual current of each distributed rooftop photovoltaic power station in the substation area, so as to realize the timely action of the residual current protector and eliminate personal injuries and fires.
[0039] Example 2
[0040] As Figure 3-5 shown, this embodiment discloses a residual current protection method for an active distribution network, which includes the following steps: Step 1, a current detection device A and a main communication device B are arranged at the distribution outgoing line outlet, and the main communication device B is connected to the residual current total protector and the current detection device A respectively through communication lines; Step 2, a residual current detection device C and a slave communication device D are arranged at the T-joint of each distributed rooftop photovoltaic, and the slave communication device D is connected to the residual current detection device C through a communication line; Step 3, perform calculation and processing on the leakage current information I G of the distribution transformer branch line and the leakage current information I pn (n = 1, 2...) at each distributed rooftop photovoltaic power station in the branch line to obtain the sum I 总 of the total residual current in the branch line; Step 4, compare the sum I 总 of the total residual current in the branch line with the preset residual current threshold I set of this branch line. If I 总 ≥I set , and it exceeds the set time, the main communication device B sends an alarm signal to the operation and maintenance unit, and sends a shutdown signal to the residual current total protector through the communication line, and the total residual current protector acts to prevent the leakage fault from developing into a fire.
[0041] For better effect, the communication line interface adopts I 2 C or RS485 supporting fiber optic communication. Specifically, Step 1 is to install a residual current detection device A and a main communication device B at the residual current total protector at each distribution outgoing line outlet of the substation transformer, and the main communication device B is connected to the residual current total protector and the current detection device A respectively through communication lines.
[0042] For better effect, Step 2 is to install a residual current detection device C and a slave communication device D at the T-joint of each distributed rooftop photovoltaic, and the slave communication device D is connected to the residual current detection device C through a communication line.
[0043] For better effect, Step 3 is to send the residual current information of each distributed rooftop photovoltaic power station installed in the rural distribution network branch line to the main communication device B through the slave communication device D. The current detection device A sends the branch line outlet current direction and the branch line residual current information to the main communication device B. The main communication device B performs calculation and processing on the received leakage current information I G of the distribution transformer branch line and the leakage current information I pn (n = 1, 2...) at each distributed rooftop photovoltaic power station in the branch line to obtain the sum I 总After the rooftop distributed PV is connected, with the fluctuations of the electricity load and the changes in the PV power generation, the branch line power flow in the substation area changes, and the current direction is downward or upward. If it is downward, the residual current in the branch line is jointly provided by the PV power station and the transformer.
[0044] Then I 总 = I G + I p1 + I p2 +…I pn ; If it is upward, all the residual current in the branch line is provided by the PV power station, I 总 = I p1 + I p2 +…I pn .
[0045] For better effect, in step four, the residual current threshold I set is set to 200 mA, 300 mA, 500 mA or a dynamic value. If I 总 ≥ I set , and it exceeds the set time, the main communication device B sends an alarm signal to the operation and maintenance unit, and sends a shutdown signal to the total residual current protector through the communication line, and the residual current protector operates to avoid the development of a leakage fault into a fire.
[0046] For better effect, a current direction identification module and a residual current detection module are integrally arranged in the current detection device A. The current direction identification module is used to detect the current direction, and it can be a Hall effect current sensor module or a fluxgate current sensor module or other current detection modules that can identify the current direction. The residual current detection device is used to measure the magnitude of the residual current value, and it can be a detection element in a type B residual current protector that can detect DC residual current or other detection modules that can detect DC and harmonic residual current.
[0047] For better effect, the main communication device B is a 5G communication module or an ultra-wideband power line carrier communication and other communication modules of low-voltage equipment, which is used to receive information, calculate and identify the information, and perform calculation and processing on the received data information.
[0048] Embodiment 3
[0049] As Figure 1As shown, for continuous residual current, the set action value of the PV inverter is at least 300 mA. A considerable proportion of rural households have rooftop PV installations of 50 - 80 kW. The built-in residual current protection threshold of the PV inverter is between 0.5 - 0.8 A. The residual current protection in the distributed rooftop PV power station is controlled by the residual current protector integrated in the PV inverter. The leakage in the residential household is controlled by a 30 mA household residual current protector. However, the leakage protection of the line between the rooftop PV power station and the substation transformer depends on the total residual current protector at the outlet of the transformer, resulting in a huge risk of leakage refusal to operate.
[0050] As Figure 2 shown, when the transformer power flow is downward and a leakage fault occurs at point Q (such as a large resistance grounding), both the transformer and the distributed rooftop PV will inject leakage current into the fault point. The leakage current I Q at point Q is the sum of the leakage currents from the power grid and the distributed rooftop PV power stations on the same branch line. Temporarily disregarding the system leakage current, then I Q = I G + I P1 + … + I Pn where I G is the leakage current generated by the power grid through the transformer at point Q, and I Pn is the leakage current generated by the distributed rooftop PV on the branch line at point Q (n represents the number of distributed rooftop PV power stations on this branch line). When the leakage current I Q > 300 mA, the leakage current values detected by the total residual current protector at the distribution outlet and the residual current protector built into the PV inverter may still be less than 300 mA, thus refusing to operate and causing the leakage accident to continue to expand and resulting in a fire.
[0051] As Figure 3 and 4 shown, a residual current protection method for an active distribution network is disclosed, including:
[0052] 1) Install current detection device A and main communication device B at the total residual current protector at each distribution outlet of the substation transformer. The main communication device B is connected to the total residual current protector and the current detection device A respectively through communication lines;
[0053] 2) Install residual current detection device C and slave communication device D at the T - connection point of each distributed rooftop PV. The slave communication device D is connected to the residual current detection device C through a communication line;
[0054] 3) Each residual current detection device C sends the residual current information of each distributed rooftop photovoltaic power station installed on the rural distribution network branch line to the main communication device B through the slave communication device D. The current detection device A sends the branch line outlet current direction and branch line residual current information to the main communication device B. The main communication device B processes the received leakage current information I of the transformer distribution branch line G and the leakage current information I at each distributed rooftop photovoltaic power station in the branch line pn (n = 1, 2…) for calculation to obtain the sum I of the total residual current in the branch line 总 . After the rooftop distributed photovoltaic is connected, with the fluctuations of the electricity load and the changes in the photovoltaic power generation, the branch line power flow in the substation area changes, and the current direction goes downward or upward. If it goes downward, the residual current in the branch line is provided jointly by the photovoltaic power station and the transformer, then I 总 = I G + I p1 + I p2 + … I pn ; if it goes upward, all the residual current in the branch line is provided by the photovoltaic power station, I 总 = I p1 + I p2 + … I pn .
[0055] 4) Compare I 总 with the preset residual current threshold I set of this branch line. If I 总 ≥ I set , and it exceeds the set time, I set can be set to 200 mA, 300 mA, 500 mA or a dynamic value according to the actual situation on site. If I 总 ≥ I set , then the main communication device B sends an alarm signal to the operation and maintenance unit and sends a shutdown signal to the residual current main protector through the communication line. The residual current main protector acts to avoid the development of a leakage fault into a fire, and can achieve a high-level protection for instant response protection of small current grounding, ensuring the safety of people's lives and property.
[0056] The current detection device A integrates a residual current detection device and a current direction identification device, which can measure the magnitude of the residual current value and also detect the current direction. Among them, the residual current detection device can be the detection element in the B-type residual current protector that can detect the DC residual current or other detection modules that can detect the DC and harmonic residual currents; the current direction identification device can be a Hall effect current sensor module, a fluxgate current sensor module or other current detection modules that can identify the current direction..
[0057] The residual current detection device C can be a detection element capable of detecting DC residual current in a type B residual current protector or other detection modules that can detect residual current including DC and harmonics.
[0058] The main communication device B is used to receive information and perform calculation and identification on the information. It includes a 5G communication module, an ultra-wideband power line carrier communication, and other communication modules that can communicate quickly, and can perform calculation and processing on the received data information.
[0059] The slave communication device D is used to send information, including a 5G communication module, an ultra-wideband power line carrier communication, and other communication modules that can communicate quickly.
[0060] As Figure 5 shown, for a 200KVA transformer in a certain village, there are two distribution branches. The threshold I set of the total residual current protector is 200mA. There are 3 distributed photovoltaic power stations installed in one of the branches, with capacities of 90kW, 20.7kW, and 27.2kW respectively. When the light intensity is insufficient (such as in the morning and evening), the current at the port of this branch drops. When a ground fault occurs at point M, the detected I G is 41.2mA, I P1 is 98.8mA, I P2 is 47.2mA, I P3 is 30.7mA, I 总 = I G + I P1 + I P2 + I P3 = 217.9 > I set , then the total residual current protector will act, cut off the line, and notify the operation and maintenance personnel to conduct a fault investigation. The method of the present invention aims at the problem that the rural distribution network is transformed into an active distribution network with a large number of distributed rooftop photovoltaics connected, resulting in the refusal of the original residual current protector to act, the inability to cut off the line in time, and the expansion of leakage faults. It proposes to comprehensively judge the residual current at the outlets of each branch of the transformer and the residual current of each distributed rooftop photovoltaic power station in the substation area, so as to achieve the timely action of the residual current protector, eliminate personal injuries and eliminate fires. Without changing the existing residual current protection structure of the rural distribution network, only corresponding equipment needs to be installed on the line, and the operation is simple. The various devices used have low costs and are popularizable.
[0061] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.
Claims
1. A residual current protection method for an active power distribution network, characterized in that: Including the following steps: Step 1: Install a current detection device A and a main communication device B at the power distribution outlet. The main communication device B is connected to the residual current total protector and the current detection device A respectively through communication lines. Step 2: Install a residual current detection device C and a slave communication device D at the T-junction of each distributed rooftop photovoltaic. The slave communication device D is connected to the residual current detection device C through a communication line. Step 3: Detect leakage information of transformer distribution branch line I G The leakage information of each distributed rooftop photovoltaic power station in the branch line I pn (n=1,2…) Calculate and process to obtain the total residual current I in the branch line 总 ; Step 4: The sum of the total residual current in the branch line I 总 The residual current threshold I set For comparison, if I 总 ≥I set , and exceeds the set time, the main communication device B sends an alarm signal to the operation and maintenance unit, and sends a shutdown signal to the total residual current protector through the communication line. The residual current protector is activated to prevent the leakage fault from developing into a fire.
2. The residual current protection method for active distribution network according to claim 1, characterized in that: The communication line interface adopts I 2 C or RS485 supporting optical fiber communication.
3. The residual current protection method for an active distribution network according to claim 1, characterized in that: Specifically, Step 1 is to install a current detection device A and a main communication device B at the residual current total protector at each power distribution outlet of the substation transformer. The main communication device B is connected to the branch residual current total protector and the current detection device A respectively through communication lines.
4. The residual current protection method for active power distribution network according to claim 1, characterized in that: Specifically, Step 2 is to install a residual current detection device C and a slave communication device D at the T-junction of each distributed rooftop photovoltaic. The slave communication device D is connected to the residual current detection device C through a communication line.
5. The residual current protection method for an active distribution network according to claim 1, characterized in that: Specifically, in Step 3, the residual current information of each distributed rooftop photovoltaic power station installed on the rural distribution network branch line is sent from the communication device D to the main communication device B, and the current detection device A sends the branch line outlet current direction and the branch line residual current information to the main communication device B. The main communication device B calculates the leakage current information I of the transformer distribution branch line received G and the leakage current information I at each distributed rooftop photovoltaic power station in the branch line pn (n = 1, 2, …) to obtain the sum of the total residual currents I in the branch line 总 ; after the rooftop distributed photovoltaic power is connected, with the fluctuations of the electricity consumption load and the changes in the photovoltaic power generation, the branch line power flow in the substation area changes, and the branch line current direction goes downward or upward; If it is downward, the residual current in the branch line is provided jointly by the photovoltaic power station and the transformer. Then I 总 = I G + I p1 + I p2 + … I pn ; If it is upward, all the residual current in the branch line is provided by the photovoltaic power station. I 总 =I p1 +I p2 +…I pn 。 6. The residual current protection method for an active distribution network according to claim 1, characterized in that: Step 4 specifically refers to the residual current threshold I set which is set to 300 mA, 500 mA or a dynamic value. If I 总 ≥ I set , the main communication device B sends an alarm signal to the operation and maintenance unit, and sends a shutdown signal to the total residual current protector through the communication line. The total residual current protector operates to prevent the leakage fault from developing into a fire.
7. The residual current protection method for an active distribution network according to claim 3, characterized in that: The current detection device A integrates a current direction identification module and a residual current detection module. The current direction identification module is used to detect the current direction, which can be a Hall effect current sensor module or a fluxgate current sensor module or other current detection modules that can identify the current direction. The residual current detection device is used to measure the magnitude of the residual current value, which can be a detection element in a type B residual current protector that can detect DC residual current, or other detection modules that can detect DC and harmonic residual current.
8. The residual current protection method for an active distribution network according to claim 7, characterized in that: The main communication device B is used to receive information and perform calculation and identification on the information, and is a 5G communication module or an ultra-wideband power line carrier communication and other communication modules possessed by low-voltage devices. The residual current detection device C is a detection element in a type B residual current protector that can detect DC residual current or other detection modules that can detect DC and harmonic residual current. The slave communication device D is used to send information, including a 5G communication module, an ultra-wideband power line carrier communication, and other communication modules possessed by low-voltage devices.