A photovoltaic voltage-boosting pot-type transformer substation grounding protection circuit and device
Patent Information
- Application Number
- CN202521753226.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-18
- Publication Date
- 2026-08-21
- Estimated Expiration
- 2035-08-18
AI Technical Summary
即，现有的光伏升压华式箱变只能依靠测控的过电压保护来实现接地保护，但是其中有很多情况导致线路过电压，如操作过电压、铁磁谐振等均可能导致过电压，靠测控无法区分是否为接地故障引发的过电压，易造成误判或漏判
[0013]本申请提供了一种光伏升压华式箱变的接地保护电路，通过针对性的结构设计，使得该电路既能精准识别接地故障，又能控制故障带来的危害，从而对光伏升压华式箱变的低压侧进行更有效的接地保护。其中，电压互感器的一次侧采用Y型接线，直接连到变压器低压侧的主回路母线上，将能感应三相电压的变化；二次侧设计成开口三角形接线，将能专门用来输出“零序电压”。同时，电阻型消谐器正常运行时是低阻抗，能保证电压互感器中性点接地，让开口三角形稳定测零序电压；一旦接地故障导致中性点电压升高，它的阻抗会变大，能限制回路电流，避免逆变器等设备过载损坏。并且，电阻型消谐器旁边并联的电感线圈，还能抵消部分接地电容电流，减少接地点的电弧，进一步降低了弧光过电压和相间短路的风险。
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Abstract
Description
Technical Field
[0001] This application relates to the field of photovoltaic step-up transformer substation technology, and more specifically, to a grounding protection circuit and device for a photovoltaic step-up transformer substation. Background Technology
[0002] With the large-scale development of the photovoltaic industry, photovoltaic step-up transformers, as core equipment connecting photovoltaic arrays and high-voltage power grids, directly affect the power generation efficiency and grid stability of power plants through their operational safety. Among them, Chinese-style transformer substations are widely used in photovoltaic power plants due to their compact structure and strong adaptability, but there are still technical bottlenecks that need to be solved in terms of low-voltage side grounding protection.
[0003] Currently, the grounding protection of photovoltaic step-up transformer substations generally adopts the following methods: (1) Grounding method: In order to avoid the formation of a short circuit loop when the DC side of the inverter is grounded, such as the formation of an AC / DC short circuit through the neutral point after the photovoltaic panel PV- is grounded, which will damage the internal relay of the inverter, the photovoltaic step-up transformer substation generally adopts the neutral point ungrounded operation mode; (2) Protection dependence mechanism: The existing photovoltaic step-up transformer substations rely on the overvoltage protection of the measurement and control device, that is, to judge the possible grounding fault by monitoring the line overvoltage. That is, the existing photovoltaic step-up transformer substations can only rely on the overvoltage protection of the measurement and control to achieve grounding protection, but there are many situations that cause line overvoltage, such as operation overvoltage, ferroresonance, etc., which may cause overvoltage. The measurement and control cannot distinguish whether the overvoltage is caused by the grounding fault, which is easy to cause misjudgment or missed judgment.
[0004] Therefore, there is an urgent need for a circuit that can effectively ground the low-voltage side of a photovoltaic step-up transformer to address the above problems. Utility Model Content
[0005] The purpose of this application is to provide a grounding protection circuit and device for a photovoltaic step-up transformer substation. Through targeted structural design, it can effectively protect the low-voltage side of the photovoltaic step-up transformer substation from grounding.
[0006] This application is implemented as follows:
[0007] In a first aspect, this application provides a grounding protection circuit for a photovoltaic step-up transformer substation, which is applied to a target photovoltaic step-up transformer substation comprising a high-voltage compartment, a transformer, and a low-voltage compartment connected in series. The circuit includes a voltage transformer, a resistive harmonic suppressor, and an inductor coil. The resistive harmonic suppressor is a nonlinear resistor whose impedance increases with voltage. The primary side of the voltage transformer is Y-connected for connection to the low-voltage side main circuit busbar of the target photovoltaic step-up transformer substation, and the secondary side is open delta-connected. One end of the resistive harmonic suppressor is connected to the neutral point of the primary side of the voltage transformer, and the other end is grounded. The inductor coil is connected in parallel with the resistive harmonic suppressor.
[0008] In some implementations, the transformer adopts a connection group of Dy11 or Yd11.
[0009] In some implementations, the circuit further includes a frame circuit breaker, which is disposed in the low-voltage side main circuit of the transformer and located between the transformer and the primary side of the voltage transformer. The output terminal of the frame circuit breaker is connected to the Y-connection input terminal of the primary side of the voltage transformer.
[0010] In some implementations, the circuit further includes at least one molded case circuit breaker and at least one leakage current transformer. The molded case circuit breaker is used to install on the low-voltage side branch circuit of the target photovoltaic step-up transformer, and the molded case circuit breaker is equipped with an electric operating mechanism. The leakage current transformer is installed at the output terminal of the molded case circuit breaker and is a zero-sequence current transformer with leakage function.
[0011] Secondly, this application provides a grounding protection device for a photovoltaic step-up transformer substation, which includes a grounding protection circuit for any of the photovoltaic step-up transformer substations described in the first aspect.
[0012] Compared with the prior art, this application has at least the following advantages or beneficial effects:
[0013] This application provides a grounding protection circuit for a photovoltaic step-up transformer substation. Through targeted structural design, this circuit can accurately identify grounding faults and control the hazards they cause, thus providing more effective grounding protection for the low-voltage side of the photovoltaic step-up transformer substation. Specifically, the primary side of the voltage transformer uses a Y-connection, directly connected to the main circuit busbar on the low-voltage side of the transformer, enabling it to sense changes in the three-phase voltage. The secondary side is designed with an open delta connection, specifically for outputting "zero-sequence voltage." Simultaneously, the resistive harmonic suppressor operates with low impedance during normal operation, ensuring the neutral point of the voltage transformer is grounded and allowing the open delta connection to stably measure the zero-sequence voltage. If a grounding fault causes the neutral point voltage to rise, its impedance increases, limiting the loop current and preventing overload damage to equipment such as inverters. Furthermore, the inductor coil connected in parallel next to the resistive harmonic suppressor can also offset part of the grounding capacitance current, reducing arcing at the grounding point and further lowering the risk of arc overvoltage and phase-to-phase short circuits. Attached Figure Description
[0014] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0015] Figure 1 This is a structural schematic diagram illustrating why grounding is not allowed at the neutral point of a transformer in one embodiment of this application;
[0016] Figure 2 This is a schematic diagram of a grounding fault in a photovoltaic neutral point ungrounded system according to an embodiment of this application;
[0017] Figure 3 This is a schematic diagram of the circuit structure of an embodiment of a grounding protection circuit for a photovoltaic step-up transformer substation according to this application. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of the embodiments clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.
[0019] Example
[0020] To facilitate understanding of the technical solutions provided in this application, some concepts will be introduced below.
[0021] 1. Why is grounding not allowed for the neutral point of the transformer in a photovoltaic step-up transformer substation?
[0022] For example, Figure 1 As shown, in the entire system, the DC 1500V of the photovoltaic panel passes through the inverter → filter → output relay → photovoltaic step-up transformer. If the neutral point of the low-voltage side (800V) of the photovoltaic step-up transformer is directly grounded, during the grid-connected operation of the inverter, when the DC side PV- of the photovoltaic panel is grounded, a loop will be formed through the PV cable → ground → neutral bus → AC phase A (or phase B, C) → internal circuit of the inverter → PV cable, causing an overcurrent fault in the Q4 relay inside the inverter. As a result, the inverter will be damaged due to the DC side insulation fault.
[0023] 2. Why can't traditional photovoltaic neutral point ungrounded systems achieve grounding protection?
[0024] For example, Figure 2 As shown, assuming current location is collected only through the frame circuit breaker, when a single-phase ground fault occurs in phase C, the ground capacitance currents of phases A and B are IA and IB, respectively. Taking phase A as an example, the current IA flows through phase A → ground → grounding point → phase C → neutral point → phase A. Therefore, from... Figure 2It can be seen that the vector sum of the three-phase currents is 0, so the frame circuit breaker will be unable to collect the zero-sequence current, thus failing to achieve grounding protection.
[0025] In summary, in conventional photovoltaic step-up transformer substations, to avoid short-circuit loops caused by DC-side grounding of the inverter, an ungrounded neutral point operation mode is required. However, the overvoltage protection system relied upon for this mode cannot provide adequate grounding protection. In other words, while the ungrounded neutral point design of the photovoltaic step-up transformer substation avoids the short-circuit risk to the inverter from DC-side grounding, it introduces the problem of ineffective grounding protection on the low-voltage side. Therefore, this application proposes a grounding protection circuit to provide effective grounding protection for the low-voltage side of the photovoltaic step-up transformer substation.
[0026] After introducing the basic principles of this application, various non-limiting embodiments of this application will be described in detail below with reference to the accompanying drawings. Unless otherwise specified, the various embodiments and features described below can be combined with each other.
[0027] Please see Figure 3 This grounding protection circuit for a photovoltaic step-up transformer substation is applied to a target photovoltaic step-up transformer substation comprising a high-voltage compartment, a transformer, and a low-voltage compartment connected in series. The circuit includes a voltage transformer, a resistive harmonic suppressor, and an inductor coil. The resistive harmonic suppressor is a nonlinear resistor whose impedance increases with voltage. The primary side of the voltage transformer is Y-connected, used to connect to the low-voltage side main circuit busbar of the target photovoltaic step-up transformer substation, and the secondary side is open delta-connected. One end of the resistive harmonic suppressor is connected to the neutral point of the primary side of the voltage transformer, and the other end is grounded. The inductor coil is connected in parallel with the resistive harmonic suppressor.
[0028] Existing photovoltaic step-up transformer substations rely solely on overvoltage protection for grounding protection. However, overvoltage can be caused by a multitude of factors, making it difficult to determine whether a ground fault is the cause. In the aforementioned embodiment, the primary side of the voltage transformer uses a Y-connection, directly connected to the main circuit busbar on the low-voltage side of the transformer (i.e., the A, B, and C phase lines), capable of sensing changes in the three-phase voltage. The secondary side is designed with an open delta connection (the three-phase windings are connected end-to-end but not closed, leaving two output terminals), specifically for outputting "zero-sequence voltage"—this voltage only occurs when there is three-phase imbalance (such as single-phase grounding) and is a "dedicated signal" for grounding faults. Therefore, this design can accurately identify grounding faults, avoiding misjudgments and missed detections.
[0029] In conventional photovoltaic step-up transformer substations, to avoid short-circuit loops caused by DC-side grounding of the inverter, an ungrounded neutral point operation mode is required. However, this can easily lead to high overvoltages and continuous arcing, damaging the equipment. In the above embodiment, the resistive harmonic suppressor operates with low impedance during normal operation, ensuring the neutral point of the voltage transformer is grounded and allowing the open delta to stably measure the zero-sequence voltage. Once a ground fault causes the neutral point voltage to rise, its impedance increases, limiting the loop current and preventing overload damage to the inverter and other equipment. In other words, the resistive harmonic suppressor is a nonlinear resistor whose impedance increases with voltage. The inductor coil connected in parallel next to the resistive harmonic suppressor can offset part of the grounding capacitance current, reducing the arc at the grounding point, thus reducing the risk of arc overvoltage and phase-to-phase short circuits, solving the problem of difficult-to-control fault hazards in existing technologies.
[0030] It should be noted that although the neutral point on the primary side of the voltage transformer is grounded through a resistive harmonic suppressor and an inductor, this is grounding the neutral point of the voltage transformer, not directly grounding the neutral point on the low-voltage side of the transformer—the two belong to different circuits. The neutral point on the low-voltage side of the transformer does not form a direct electrical connection with the ground. Therefore, when an event occurs... Figure 1 When the photovoltaic panel is grounded on the DC side (PV-), a loop of "PV cable → ground → neutral bus → AC A / B / C phases → inverter internal circuit" will not be formed. Furthermore, the resistive harmonic suppressor exhibits high impedance characteristics when the voltage rises, significantly limiting the loop current. At the same time, the inductor coil also hinders sudden current changes, making the overall loop current much lower than the inverter's tolerance value, which can further block overcurrent conditions in dangerous loops.
[0031] Therefore, in the above embodiments, through targeted structural design, grounding faults are accurately identified and the hazards caused by the faults are controlled, perfectly making up for the shortcomings of the existing technology, thereby enabling more effective grounding protection for the low-voltage side of the photovoltaic step-up transformer.
[0032] To enable those skilled in the art to understand this application more intuitively, its principles will be explained below in conjunction with specific working conditions.
[0033] (1) Normal operating condition (without grounding fault)
[0034] Voltage transformer: The primary side is Y-connected to induce a three-phase balanced voltage. Because the three-phase voltages are symmetrical, the potential of the Y-type neutral point is zero. The voltage at both ends of the open delta on the secondary side is zero (the vector sum of the three-phase voltages is zero), and there is no zero-sequence voltage output.
[0035] Resistive harmonic suppressor: At this time, the neutral point potential is zero, and the voltage across the resistive harmonic suppressor is extremely low, exhibiting low impedance characteristics, which is equivalent to reliably grounding the neutral point of the voltage transformer. This state ensures the normal operation of the voltage transformer (only when the neutral point is grounded can the open delta accurately sense the zero-sequence voltage during a fault).
[0036] Inductor: Since there is no grounding fault, there is no abnormal capacitive current in the circuit, there is no voltage difference across the inductor, and no canceling current is generated, so it is in a "standby" state.
[0037] (2) When a single-phase ground fault occurs
[0038] After a single-phase ground fault, the three-phase voltages become unbalanced (the faulty phase voltage is zero, while the non-faulty phase voltage rises to the line voltage), and the neutral point potential of the Y-connected circuit rises (no longer zero). At this time, the primary side of the voltage transformer will induce a three-phase unbalanced voltage, and the open delta secondary side will output a zero-sequence voltage signal (this is a characteristic signal specific to ground faults) because the vector sum of the three-phase voltages is not zero. Subsequently, the ground fault causes the neutral point potential of the voltage transformer to rise (typically to 1.732 times the phase voltage), and the voltage across the resistive harmonic suppressor rises accordingly. Because the harmonic suppressor is a nonlinear resistor (the higher the voltage, the greater the impedance), its impedance increases sharply at this time, significantly limiting the fault current passing through the neutral point (such as the AC / DC loop current that may be formed when the DC side of the inverter is grounded). Simultaneously, the ground fault generates a ground capacitance current (forming a loop through the earth), while the current generated by the inductor coil is opposite in phase and close in magnitude to the capacitance current (because the phase characteristics of inductance and capacitance are opposite). The two cancel each other out, reducing the arc energy at the grounding point.
[0039] That is, through the progressive coordination of "detection-current limiting-arc suppression" among the three devices—voltage transformer, resistive harmonic suppressor, and inductor coil—the problem of "difficulty in identifying grounding faults" in the existing technology (zero-sequence voltage output of the voltage transformer) is solved, and the hazards of the fault are controlled (current limiting by the harmonic suppressor + arc suppression by the inductor) to ultimately achieve accurate and reliable protection of the low-voltage side of the photovoltaic step-up Huashi box-type transformer.
[0040] Based on the aforementioned scheme, in some implementations of this application, the transformer adopts a Dy11 or Yd11 connection group. Dy11 refers to a delta (D) connection on the high-voltage side and a star (y) connection on the low-voltage side, with a phase difference of 330° between the high and low voltage line voltages at the 11 o'clock position. The neutral point of the star connection on the low-voltage side is not brought out, therefore there is no directly groundable neutral point. Yd11 refers to a star (Y) connection on the high-voltage side and a delta (d) connection on the low-voltage side, with the same 330° phase difference between the high and low voltage line voltages. The low-voltage side is delta-connected and has no neutral point, so it cannot be grounded. Therefore, by adopting a Dy11 or Yd11 connection group, the transformer structurally eliminates the risk of inverter damage due to DC-side grounding.
[0041] Based on the aforementioned scheme, in some implementations of this application, the circuit further includes a frame circuit breaker, which is disposed in the main circuit of the low-voltage side of the transformer and located between the transformer and the primary side of the voltage transformer. The output terminal of the frame circuit breaker is connected to the Y-type connection input terminal of the primary side of the voltage transformer.
[0042] It should be noted that the frame circuit breaker is a high-capacity main switching device with basic functions such as overload protection and short-circuit protection. It can quickly disconnect and cut off the main circuit power supply when a large current fault occurs in the circuit. Because the frame circuit breaker is located between the transformer and downstream equipment, it can quickly trip and cut off the power supply when a large current fault such as a phase-to-phase short circuit or severe overload occurs in the main circuit, preventing the fault from impacting core equipment such as the transformer and high-voltage compartment, thus reducing accident losses. Furthermore, the outgoing terminals of the frame circuit breaker are directly connected to the voltage transformer, meaning that it is in a conducting state during normal operation and will not obstruct the transmission of voltage signals from the low-voltage side of the transformer to the voltage transformer. This ensures that the voltage transformer can accurately sense the three-phase voltage changes in the main circuit. In the event of a single-phase ground fault, the open delta on the secondary side can normally output zero-sequence voltage, providing a reliable signal for ground fault detection and avoiding detection failure due to problems such as poor contact in the main circuit switch.
[0043] Based on the aforementioned scheme, in some implementations of this application, the circuit further includes at least one molded case circuit breaker and at least one leakage current transformer. The molded case circuit breaker is used to be installed on the low-voltage side branch circuit of the target photovoltaic step-up transformer, and the molded case circuit breaker is equipped with an electric operating mechanism. The leakage current transformer is installed at the output terminal of the molded case circuit breaker and is a zero-sequence current transformer with leakage function.
[0044] It should be noted that a molded case circuit breaker (MCCB) is a switching device used in low-voltage circuits (typically below 1000V). By installing a corresponding MCB on each branch circuit of the low-voltage side of the target photovoltaic step-up transformer substation, it can be used to control the on / off state of the corresponding branch. Furthermore, because the MCB has an electrically operated mechanism, it can automatically trip upon receiving external signals (such as commands from monitoring and control devices) without manual operation.
[0045] In addition, a leakage current transformer is a "zero-sequence current transformer with leakage function," installed at the outgoing terminal of a molded case circuit breaker (that is, after the current flows out of the molded case circuit breaker, it first passes through it before proceeding to subsequent lines). The function of the zero-sequence current transformer is to detect the "vector sum of the three-phase currents": under normal conditions, the three-phase currents are symmetrical, the vector sum is zero, and it has no signal output; once a single-phase ground fault occurs in this branch, the three-phase currents are asymmetrical, and the vector sum is not zero (that is, the zero-sequence current generated by the ground fault), it will transmit this current signal to the measurement and control device.
[0046] This application also provides a grounding protection device for a photovoltaic step-up transformer substation, which includes a grounding protection circuit as described above. This device can be constructed by encapsulating a circuit board with the grounding protection circuit of the photovoltaic step-up transformer substation into a housing, thus facilitating user operation and providing convenience.
[0047] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this application is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this application. No reference numerals in the claims should be construed as limiting the scope of the claims.
Claims
1. A grounding protection circuit for a photovoltaic step-up transformer substation, characterized in that, Applied to a target photovoltaic step-up transformer, which includes a high-voltage compartment, a transformer, and a low-voltage compartment connected in series, the circuit includes a voltage transformer, a resistive harmonic suppressor, and an inductor coil; the resistive harmonic suppressor is a nonlinear resistor whose impedance increases with increasing voltage. The primary side of the voltage transformer is Y-connected, used to connect to the low-voltage side main circuit busbar of the target photovoltaic step-up transformer, and the secondary side is open delta-connected; one end of the resistive harmonic suppressor is connected to the neutral point of the primary side of the voltage transformer, and the other end is grounded; the inductor coil is connected in parallel with the resistive harmonic suppressor.
2. The circuit according to claim 1, characterized in that, The transformer adopts either Dy11 or Yd11 connection group.
3. The circuit according to claim 1, characterized in that, The circuit also includes a frame circuit breaker, which is installed in the low-voltage side main circuit of the transformer and located between the transformer and the primary side of the voltage transformer. The output terminal of the frame circuit breaker is connected to the Y-type connection input terminal of the primary side of the voltage transformer.
4. The circuit according to claim 1 or 3, characterized in that, The circuit also includes at least one molded case circuit breaker and at least one leakage current transformer. The molded case circuit breaker is used to install on the low-voltage side branch circuit of the target photovoltaic step-up transformer, and the molded case circuit breaker is equipped with an electric operating mechanism. The leakage current transformer is installed at the output terminal of the molded case circuit breaker and is a zero-sequence current transformer with leakage function.
5. A grounding protection device for a photovoltaic step-up transformer substation, characterized in that, Including a grounding protection circuit for a photovoltaic step-up transformer as described in any one of claims 1-4.