Distributed photovoltaic power distribution section neutral point ungrounded protection system and method
By using leakage transformers and smart relays made of new materials in distributed photovoltaic systems, combined with real-time monitoring of the display, the problem that traditional protection configurations cannot detect faults quickly and accurately, and accurate measurement of milliampere level current is achieved and rapid handling of faults improves the safety and stability of the system.
Patent Information
- Application Number
- CN202411263103.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-10
- Publication Date
- 2024-12-27
AI Technical Summary
In distributed photovoltaic systems, traditional neutral point ground protection configurations cannot quickly and accurately detect fault currents, resulting in the expansion of faults and damage to the photovoltaic inverter and cannot accurately detect fault currents at milliamper levels.
The leakage transformer, intelligent current relay and voltage relay made of new materials are connected to the display screen through communication to achieve accurate measurement and real-time monitoring of milliampere current, quickly judge the fault circuit, and disconnect the fault feeder when operating.
It realizes fast and accurate fault detection and protection of distributed photovoltaic neutral point non-grounding systems, avoids the expansion of grounding faults and damages the photovoltaic inverter, and improves the safety and stability of the system.
Smart Images
Figure CN119209428A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of photovoltaic power distribution, and in particular to a distributed photovoltaic power distribution section neutral point ungrounding protection system and method. Background Art
[0002] In recent years, with the development and promotion of new energy, my country's photovoltaic system has developed rapidly. As an important link in the photovoltaic system, the safe and reliable operation of photovoltaic inverters directly affects the development of the entire photovoltaic system.
[0003] When the low-voltage distribution section to which the photovoltaic inverter is connected adopts the TN-S wiring method, the negative pole on the DC side of the photovoltaic inverter is grounded, and the grounding current flows back to the photovoltaic inverter through the neutral point of the coal shed photovoltaic 500V low-voltage section, causing accidents such as burning of the internal capacitor of the photovoltaic inverter and damage to the inverter module. During the period of inverter damage, the photovoltaic power generation is reduced, causing economic losses. The occurrence of this accident directly affects the safe operation of the photovoltaic system.
[0004] Therefore, eliminating the risk of inverter damage caused by DC grounding is of great practical significance for the stable operation of the photovoltaic system. To solve the above-mentioned problems existing in distributed photovoltaic systems, it is necessary to change the distributed photovoltaic system from TN-S (neutral point grounding) wiring method to IT (neutral point ungrounded) method.
[0005] However, after changing to IT wiring mode, the traditional grounding protection configuration cannot quickly and accurately cut off the fault. The protection configuration for distributed photovoltaic systems with ungrounded neutral points is usually implemented by configuring a small current line selection device or using the protection of the molded case switch itself. The current measured by the small current line selection device is usually several amperes, and the measurement deviation is large. The device may malfunction. When a grounding fault occurs in the distributed photovoltaic distribution section, the fault current of tens of milliamperes cannot be accurately detected and the grounding position cannot be determined. When the protection of the molded case itself is used, it cannot act immediately when a single-phase fault is grounded. The fault needs to continue for a period of time until it develops into a two-phase fault before the protection will act, causing the equipment to operate in a faulty state for a long time, which will also lead to further expansion of the fault.
[0006] A new type of protection configuration for the neutral point ungrounded system of a distributed photovoltaic distribution section used this time utilizes the sensitivity of the leakage transformer made of a new material (Bomalloy) to milliampere-level currents, the stability of the intelligent current relay, and the reliability of the voltage relay. The current relay and the voltage relay are connected to the intelligent operation panel in a communication manner to achieve accurate monitoring of the data, which is used to quickly and accurately determine the fault circuit of the distribution section of the neutral point ungrounded system. Compared with the small current line selection device and the molded case circuit breaker protection, it can quickly and accurately determine the fault. Summary of the invention
[0007] The purpose of the present invention is to provide a distributed photovoltaic distribution section neutral point ungrounded protection system and method, which solves the configuration difficulties of the existing photovoltaic system distribution section protection, the inability to quickly and accurately detect the fault current, which causes the fault to further expand and damage the photovoltaic inverter. At the same time, the accuracy is not enough and the fault current at the milliampere level cannot be detected.
[0008] To achieve the above-mentioned purpose, the present invention provides a distributed photovoltaic distribution section neutral point ungrounded protection system, comprising an inverter, and also comprising a leakage transformer, a current relay, a voltage relay, a voltage transformer and a display screen. The leakage transformer is connected to the inverter and connected to the low-voltage distribution section. The leakage transformer, the current relay, the voltage relay and the voltage transformer are connected in sequence. The voltage transformer is connected to the low-voltage distribution section. The display screen is respectively connected to the current relay and the voltage relay. Through the coordinated use of the leakage transformer, the current relay, the voltage relay and the display screen, accurate monitoring of data is achieved, so as to achieve the purpose of quickly and accurately judging the fault circuit of the distribution section in the system.
[0009] Wherein, a circuit breaker is also provided between the inverter and the connected low-voltage distribution section, and the circuit breaker is used for connecting and disconnecting the inverter and the photovoltaic distribution section.
[0010] The distributed photovoltaic power distribution section neutral point ungrounded protection system further comprises a photovoltaic monitoring subsystem, and the photovoltaic monitoring subsystem is connected to the display screen and is used to receive display data of the display screen to realize remote monitoring of the data.
[0011] The present invention also provides a distributed photovoltaic power distribution section neutral point ungrounding protection method, comprising the following steps:
[0012] First, change the grounding mode of the low-voltage side of the distributed photovoltaic system from direct neutral point grounding to ungrounded neutral point, and then connect the voltage transformer to the voltage relay to determine whether there is single-phase grounding in the system;
[0013] When a single-phase grounding occurs in the system, the voltage relay transmits the switch signal to the current relay, so that the current relay compares the data with the set value;
[0014] When the data exceeds the set value, the current relay is activated to disconnect the fault feeder circuit;
[0015] At the same time, the current relay and the voltage relay jointly transmit the data to the display screen to achieve real-time monitoring of the data.
[0016] The specific method of connecting the voltage transformer to the voltage relay is: connecting the open triangle voltage of the voltage transformer to the voltage relay.
[0017] When a single-phase grounding occurs in the system, the open triangle voltage of the voltage transformer changes from 0V to 100V, the voltage relay operates, and generates an output node, which is then sent to the current relay;
[0018] When the current relay receives the output node of the voltage relay, the output node is converted into a position change signal, and the leakage current value of the current relay itself is detected according to the position change signal;
[0019] After the current relay detects the leakage current value, the current relay compares the leakage current value with a set value of the leakage current.
[0020] Among them, when the data exceeds the set value, the current relay is activated to disconnect the fault feeder loop. The specific method is: when the leakage current value exceeds the set value, the current relay is activated to trip the circuit breaker of the fault feeder loop to disconnect the fault feeder loop.
[0021] The present invention discloses a distributed photovoltaic power distribution section neutral point ungrounded protection system and method. Through the coordinated use of the leakage transformer, the current relay and the voltage relay, the distributed photovoltaic neutral point ungrounded system is protected to avoid the expansion of grounding faults and damage to photovoltaic inverters. At the same time, the leakage transformer made of new glass-malloy material is used to replace the traditional steel-silicon current transformer, which can meet the measurement of milliampere-level grounding current and achieve accurate measurement. In addition, the current relay and the voltage relay are connected to the display screen in a communication manner to realize accurate monitoring of data, so as to achieve the purpose of real-time monitoring and early prediction of degradation trends. Based on the above three points, the problems of difficult configuration, low sensitivity, insufficient reliability and even no protection operation equipment of the traditional protection device for the distributed photovoltaic power distribution section neutral point ungrounded system are effectively solved, thereby improving the safety and stability of the operation of the distributed photovoltaic system. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.
[0023] Figure 1 It is a system schematic diagram of a neutral point ungrounded protection system for a distributed photovoltaic distribution section according to a first embodiment of the present invention.
[0024] Figure 2It is a flow chart of the ungrounded neutral point protection method of the distributed photovoltaic distribution section according to the second embodiment of the present invention.
[0025] Figure 3 It is a specific process step diagram for comparing data and set values of the distributed photovoltaic distribution section neutral point ungrounding protection method according to the second embodiment of the present invention.
[0026] In the figure: 101 - inverter, 102 - leakage transformer, 103 - current relay, 104 - voltage relay, 105 - voltage transformer, 106 - display screen, 107 - photovoltaic monitoring subsystem, 108 - circuit breaker. DETAILED DESCRIPTION
[0027] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.
[0028] First embodiment:
[0029] See also Figure 1 , Figure 1 It is a system schematic diagram of a distributed photovoltaic distribution section neutral point ungrounded protection system of the first embodiment of the present invention. The present invention provides a distributed photovoltaic distribution section neutral point ungrounded protection system, including an inverter 101, a leakage transformer 102, a current relay 103, a voltage relay 104, a voltage transformer 105, a display screen 106 and a photovoltaic monitoring subsystem 107.
[0030] In this embodiment, the present invention realizes the protection of the distributed photovoltaic neutral point ungrounded system through the coordinated use of the leakage mutual inductor 102, the current relay 103 and the voltage relay 104, and avoids the expansion of the grounding fault to damage the photovoltaic inverter 101. At the same time, the leakage mutual inductor 102 made of the new glass-malloy material replaces the current mutual inductor made of the traditional steel-silicon material, which can meet the measurement of milliampere-level grounding current and achieve accurate measurement. In addition, the current relay 103 and the voltage relay 104 are connected to the display screen 106 in a communication manner to realize accurate monitoring of data, so as to achieve the purpose of real-time monitoring and early prediction of degradation trends. Based on the above three points, the traditional protection device effectively solves the problems of difficult configuration, low sensitivity, insufficient reliability and even no protection operation equipment for the protection of the neutral point ungrounded system of the distributed photovoltaic distribution section, thereby improving the safety and stability of the operation of the distributed photovoltaic system.
[0031] Among them, the inverter 101 is connected to the low-voltage distribution section, the leakage transformer 102, the current relay 103, the voltage relay 104 and the voltage transformer 105 are connected in sequence, the voltage transformer 105 is connected to the low-voltage distribution section, and the display screen 106 is connected to the current relay 103 and the voltage relay 104 respectively. Through the coordinated use of the leakage transformer 102, the current relay 103, the voltage relay 104 and the display screen 106, accurate monitoring of data is achieved, so as to achieve the purpose of quickly and accurately judging the fault circuit of the distribution section in the system.
[0032] Secondly, the leakage current transformer 102 is made of a new material, Permalloy, and can measure milliampere-level current.
[0033] Meanwhile, the display screen 106 is an HMI display screen 106 , and the current relay 103 and the voltage relay 104 are connected to the display screen 106 in a communication manner.
[0034] In addition, a circuit breaker 108 is provided between the inverter 101 and the low-voltage power distribution section, and the circuit breaker 108 is used to switch the inverter 101 on and off.
[0035] Finally, the photovoltaic monitoring subsystem 107 is connected to the display screen 106 to receive display data of the display screen 106 and realize remote monitoring of the data.
[0036] When using a distributed photovoltaic distribution section neutral point ungrounded protection system of the present embodiment, the distributed photovoltaic low-voltage side grounding method is changed from direct neutral point grounding to a neutral point ungrounded system, the voltage transformer 105 of the low-voltage distribution section is modified, and the open triangle voltage of the voltage transformer 105 is connected to the voltage relay 104 to determine whether there is single-phase grounding in the entire system.
[0037] When single-phase grounding occurs in the entire system, the open triangle voltage of the voltage transformer 105 changes from 0V to 100V, the voltage relay 104 is actuated, and an open node is generated, and the generated open node is sent to the current relay 103. When the current relay 103 receives the open node of the voltage relay 104, the current relay 103 converts the open node into a displacement signal, and detects the leakage current value of the current relay 103 itself according to the displacement signal. After the current relay 103 detects the leakage current value, the current relay 103 compares the leakage current value with the set value of the leakage current.
[0038] When the leakage current value exceeds the set value of the leakage current, the current relay 103 is activated to trip the circuit breaker 108 of the faulty feeder circuit, disconnecting the faulty feeder circuit.
[0039] At the same time, the current relay 103 and the voltage relay 104 jointly transmit the detection data to the display screen 106 to realize real-time monitoring of the data of the entire system. While monitoring the data in real time, the display screen 106 will send an alarm signal to the photovoltaic monitoring subsystem 107 and display it on the photovoltaic monitoring subsystem 107 to realize remote monitoring of the data.
[0040] Second embodiment:
[0041] Based on the first embodiment, please refer to Figure 2 and Figure 3 , Figure 2 is a flowchart of a neutral point ungrounded protection method for a distributed photovoltaic power distribution section according to a second embodiment of the present invention. Figure 3 1 is a specific process step diagram of comparing data and set values of the neutral point ungrounded protection method of the distributed photovoltaic distribution section according to the second embodiment of the present invention. The present invention also provides a distributed photovoltaic distribution section neutral point ungrounded protection method, comprising the following steps:
[0042] S1. First, change the grounding mode of the low-voltage side of the distributed photovoltaic system from direct neutral point grounding to ungrounded neutral point, and then connect the voltage transformer 105 to the voltage relay 104 to determine whether there is single-phase grounding in the system.
[0043] Specifically, the grounding mode of the low-voltage side of the distributed photovoltaic system is changed from direct grounding of the neutral point to an ungrounded neutral point system, the voltage transformer 105 of the low-voltage distribution section is modified, and the open triangle voltage of the voltage transformer 105 is connected to the voltage relay 104 to determine whether there is single-phase grounding in the entire system.
[0044] S2. When a single-phase grounding occurs in the system, the voltage relay 104 transmits the switch signal to the current relay 103, so that the current relay 103 compares the data with the set value.
[0045] Specifically, when a single-phase grounding occurs in the system, the voltage relay 104 transmits a switch signal to the current relay 103. The signal is one of the necessary conditions for the current relay 103 to operate. At the same time, the current relay 103 compares the detected leakage current with the set value in the following specific manner:
[0046] S21, when a single-phase grounding occurs in the system, the open triangle voltage of the voltage transformer 105 changes from 0V to 100V, the voltage relay 104 operates, and generates an output node, and then sends the generated output node to the current relay 103;
[0047] S22, when the current relay 103 receives the output node of the voltage relay 104, the output node is converted into a position change signal, and the leakage current value of the current relay 103 itself is detected according to the position change signal;
[0048] S23. After the current relay 103 detects the leakage current value, the current relay 103 compares the leakage current value with a set value of the leakage current.
[0049] S3. When the data exceeds the set value, the current relay 103 is activated to disconnect the fault feeder loop.
[0050] Specifically, when the leakage current value data exceeds the set value of the leakage current, the current relay 103 is actuated to trip the circuit breaker 108 of the faulty feeder circuit, thereby disconnecting the faulty feeder circuit.
[0051] S4. At the same time, the current relay 103 and the voltage relay 104 jointly transmit the data to the display screen 106 to achieve real-time monitoring of the data.
[0052] Specifically, at the same time, the current relay 103 and the voltage relay 104 jointly transmit the detection data to the display screen 106, so as to realize real-time monitoring of the data of the entire system. While monitoring the data in real time, the display screen 106 will send an alarm signal to the photovoltaic monitoring subsystem 107 and display it on the photovoltaic monitoring subsystem 107, so as to realize remote monitoring of the data.
[0053] What is disclosed above is only one or more preferred embodiments of the present application, and cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of implementing the above embodiments and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.
Claims
1. A distributed photovoltaic power distribution section neutral point ungrounding protection system, including an inverter, characterized in that: It also includes a leakage transformer, a current relay, a voltage relay, a voltage transformer and a display screen. The leakage transformer measures the current of the inverter. The leakage transformer is connected to the current relay, the voltage relay is connected to the voltage transformer, and the voltage transformer is connected to the low-voltage distribution section. The display screen is respectively communicated with the current relay and the voltage relay. Through the coordinated use of the leakage transformer, the current relay, the voltage relay and the display screen, accurate monitoring of data is achieved, so as to achieve the purpose of quickly and accurately judging the fault circuit of the distribution section in the system.
2. The distributed photovoltaic power distribution section neutral point ungrounded protection system according to claim 1, characterized in that: A circuit breaker is also provided between the inverter and the connected low-voltage power distribution section, and the circuit breaker is used for connecting and disconnecting the inverter and the photovoltaic power distribution section.
3. The distributed photovoltaic power distribution section neutral point ungrounded protection system according to claim 1, characterized in that: The distributed photovoltaic power distribution section neutral point ungrounded protection system also includes a photovoltaic monitoring subsystem, which is communicatively connected to the display screen and is used to receive display data of the display screen to achieve remote monitoring of the data.
4. A distributed photovoltaic distribution section neutral point ungrounding protection method, applied to the distributed photovoltaic distribution section neutral point ungrounding protection system according to any one of claims 1 to 3, characterized in that: The following steps are involved: First, change the grounding mode of the low-voltage side of the distributed photovoltaic system from direct neutral point grounding to ungrounded neutral point, and then connect the voltage transformer to the voltage relay to determine whether there is single-phase grounding in the system; When a single-phase grounding occurs in the system, the voltage transformer transmits the detected voltage value to the voltage relay, and the voltage relay compares it with the set value. When the voltage value reaches the set value of the voltage relay, the voltage relay transmits the switch value to the current relay; The current transformer transmits the detected current value to the current relay. When the data exceeds the set value of the current relay, the current relay operates to disconnect the fault feeder loop. At the same time, the current relay and the voltage relay jointly transmit the data to the display screen to achieve real-time monitoring of the data.
5. The distributed photovoltaic power distribution section neutral point ungrounding protection method as claimed in claim 4, characterized in that: The specific method of connecting the voltage transformer to the voltage relay is: connecting the open triangle voltage of the voltage transformer to the voltage relay.
6. The distributed photovoltaic power distribution section neutral point ungrounding protection method according to claim 4, characterized in that: When a single-phase grounding occurs in the system, the voltage relay transmits the switch signal to the current relay, and the current relay compares the data with the set value in the following specific manner: When a single-phase grounding occurs in the system, the open triangle voltage of the voltage transformer changes from 0V to 100V, the voltage relay operates, and generates an output node, which is then sent to the current relay; When the current relay receives the output node of the voltage relay, the output node is converted into a position change signal, and the leakage current value of the current relay itself is detected according to the position change signal; After the current relay detects the leakage current value, the current relay compares the leakage current value with a set value of the leakage current.
7. The distributed photovoltaic power distribution section neutral point ungrounding protection method according to claim 4, characterized in that: The specific method of the current relay being actuated to disconnect the faulty feeder loop when the data exceeds the set value is as follows: when the leakage current value exceeds the set value, the current relay is actuated to trip the circuit breaker of the faulty feeder loop to disconnect the faulty feeder loop.