A method for improving the accuracy of relay protection devices for medium-voltage distribution networks containing photovoltaic power sources

Abstract

This invention belongs to the field of distribution network relay protection technology, and particularly relates to a method for improving the accuracy of relay protection devices in medium-voltage distribution networks containing photovoltaic (PV) power sources. The invention includes: determining the location where distributed PV power sources are connected to the medium-voltage distribution network, and configuring a deeply integrated primary and secondary pole-mounted circuit breaker at the point of common coupling (PCC); co-commissioning the PCC-configured PCC-configured circuit breaker with the main substation; and configuring setting parameters for each relay protection device on the grid according to the location of the distributed PV power source connected to the medium-voltage distribution network. This invention addresses the increasing number and capacity of distributed PV power sources connected to medium-voltage distribution networks, effectively improving the accuracy of relay protection at all levels of the medium-voltage distribution network, ensuring accurate operation of the distribution network during faults, and significantly improving the reliability of the distribution network.

Description

Technical Field

[0001] This invention belongs to the field of power distribution network relay protection technology, and particularly relates to a method for improving the accuracy of relay protection devices for medium-voltage power distribution networks containing photovoltaic power sources. Background Technology

[0002] Currently, most medium-voltage distribution networks adopt single-side power supply or dual-power open-loop operation mode. Urban and county-level distribution network structures mainly adopt single-radial, multi-segment, and multi-interconnection methods. With the large-scale integration of distributed photovoltaic power sources into medium-voltage distribution networks, the distribution network structure will become a complex structure with multiple power sources.

[0003] With the change in the power grid structure, the original relay protection schemes such as the three-stage overcurrent protection and grounding current protection configured in the distribution network will inevitably become unsuitable in terms of selectivity and sensitivity in the new distribution network structure.

[0004] Therefore, those skilled in the art urgently need to conduct further research and development to address the shortcomings of existing relay protection devices in adapting to new power distribution systems. Summary of the Invention

[0005] To address the shortcomings of the existing technology, this invention provides a method for improving the accuracy of relay protection devices in medium-voltage distribution networks containing photovoltaic power sources. The purpose is to ensure accurate operation of the distribution network during faults, thereby significantly improving the reliability of the distribution network.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0007] A method for improving the accuracy of relay protection devices for medium-voltage distribution networks containing photovoltaic power sources includes the following steps:

[0008] Determine the location where distributed photovoltaic power sources are connected to the medium-voltage distribution network, and configure a pole-mounted circuit breaker with deep integration of primary and secondary circuits at the point of common coupling;

[0009] The primary and secondary deeply integrated pole-mounted circuit breakers configured at the public connection points are jointly commissioned with the main station.

[0010] Based on the location of the distributed photovoltaic power source connected to the medium-voltage distribution network, setpoint parameters are configured for each relay protection device on the grid.

[0011] Furthermore, configuring setpoint parameters for each relay protection device on the grid based on the location of the distributed photovoltaic power source connected to the medium-voltage distribution network involves configuring anti-islanding protection on the feeder terminal line with the distribution automation master station as the common connection point.

[0012] Furthermore, the common connection point is outgoing line 3.

[0013] Furthermore, determining the location where the distributed photovoltaic power source is connected to the medium-voltage distribution network, if the distributed photovoltaic power source is connected to the middle of a 10kV main line, the directional protection function is configured for the upstream feeder terminal of the point of common coupling by the main substation, including the following steps:

[0014] Step 4.1: Reduce the reliability coefficient of the overcurrent stage II protection of the upstream feeder terminal of the common connection point to 1.2 using the main station line;

[0015] Step 4.2: Improve the reliability coefficient of the overcurrent stage I of the first outgoing feeder terminal of all feeders except those connected to the photovoltaic power supply line to 1.3-1.5 using the main station line;

[0016] Step 4.3: Configure directional protection on the feeder terminal line with the distribution automation master station as the common connection point. The current setting value should be less than the rated current of the distributed power source connected to it. At the same time, configure the synchronization detection and reclosing function to prevent islanding.

[0017] Furthermore, determining the location where the distributed photovoltaic power source is connected to the medium-voltage distribution network, if the distributed photovoltaic power source is connected to the end of a 10kV main line, and the reliability coefficient of the overcurrent stage II protection of the upstream adjacent feeder terminal at the point of common coupling is reduced to 1.2 by utilizing the main substation, includes the following steps:

[0018] Step 5.1: Utilize the main station to configure directional protection function for all feeder terminals upstream of the common connection point to ensure that overcurrent protection I and II are activated only when short-circuit current flows through the power supply of the substation, so as to prevent other feeder faults and prevent protection maloperation.

[0019] Step 5.2: Increase the reliability coefficient of the overcurrent stage I of the feeder terminal of the first outgoing feeder line (excluding the feeder line connected to the photovoltaic power source) to 1.3-1.5 on the main station line to prevent protection malfunction.

[0020] Step 5.3: Configure directional protection on the feeder terminal line with the distribution automation master station as the common connection point. The current setting value should be less than the rated current of the distributed power source connected in parallel. At the same time, configure the synchronization detection and reclosing function to prevent islanding.

[0021] Furthermore, when determining the location where the distributed photovoltaic power source is connected to the medium-voltage distribution network, if the distributed photovoltaic power source is connected to a certain 10kV branch line or sub-branch line, a directional protection function is configured for the upstream feeder terminal of the common connection point to ensure that the overcurrent stage III protection is activated only when the short-circuit current supplied by the substation power source flows through it.

[0022] Directional protection is configured on the feeder terminal line using the distribution automation master station as the common connection point. The current setting value is not greater than the rated current of the distributed power source connected in parallel. At the same time, a synchronization detection and reclosing function is configured to prevent islanding.

[0023] Furthermore, the overcurrent protection stage I is set according to the principle of avoiding the maximum three-phase short-circuit current at the end of the protected section of the line; the overcurrent protection stage II is set according to the principle of coordinating with the overcurrent protection stage I of the adjacent downstream line; the overcurrent protection stage III is set according to the principle of avoiding the overload current of the protected section of the line; the directional protection is achieved by using the directional element of the corresponding feeder terminal to determine the direction and magnitude of the current flowing through the line protected by the feeder terminal.

[0024] Furthermore, the common connection point is outgoing node B', and the upstream feeder terminals are outgoing nodes A and B.

[0025] Furthermore, the common connection point is outgoing node C', the upstream adjacent feeder terminal is outgoing node C; all feeder terminals upstream of the common connection point are outgoing nodes A, B, and C; the first outgoing feeder terminal of the remaining feeders is outgoing node A; and the feeder terminal of the common connection point is outgoing node C'.

[0026] Furthermore, the common connection is outgoing node D'; the upstream feeder terminal is outgoing node D; and the feeder terminal of the common connection point is outgoing node D'.

[0027] The present invention has the following beneficial effects and advantages:

[0028] This invention addresses the increasing number and capacity of distributed photovoltaic (PV) systems connected to medium-voltage distribution networks. By incorporating protection schemes for each feeder terminal at different locations of distributed PV connections, it effectively improves the accuracy of relay protection at all levels of the medium-voltage distribution network, ensuring accurate operation of the distribution network during faults and thus significantly enhancing the reliability of the distribution network.

[0029] This invention is applicable to any situation where distributed photovoltaic (PV) power sources are connected to a 10kV medium-voltage distribution network. It modifies the original relay protection scheme and formulates a protection scheme for the newly connected common connection point based on the corresponding connection point. This invention considers various situations where distributed PV power sources are connected to medium-voltage distribution lines, making its application value more considerable and its feasibility stronger. Attached Figure Description

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0031] Figure 1 This is a diagram of the protection scheme for the distributed power source when it is connected to the 10kV side bus of the substation according to the present invention.

[0032] Figure 2 This is a diagram of the protection scheme for distributed photovoltaic power generation when connected to the end of a 10kV main line according to the present invention;

[0033] Figure 3 This is a flowchart of the steps of the method of the present invention;

[0034] Figure 4 This is a flowchart illustrating the specific steps of the protection configuration for distributed photovoltaic systems at different locations according to the present invention. Detailed Implementation

[0035] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0037] The following reference Figures 1-4 The technical solutions of some embodiments of the present invention are described below.

[0038] Example 1

[0039] This invention provides an embodiment of a method for improving the accuracy of relay protection devices in medium-voltage distribution networks containing distributed photovoltaic power sources. For example... Figure 3 As shown, Figure 3 This is a flowchart of the steps of the method of the present invention.

[0040] A method for improving the accuracy of relay protection devices in medium-voltage distribution networks containing distributed photovoltaic power sources includes the following steps:

[0041] Step 1: First, determine the location where the distributed photovoltaic power source is connected to the medium-voltage distribution network, and configure a pole-mounted circuit breaker with deep integration of primary and secondary circuits at the point of common coupling.

[0042] Step 2: Connect the primary and secondary deeply integrated pole-mounted circuit breakers configured at the common connection point to the main station for joint commissioning to ensure accurate location.

[0043] Step 3: Configure setting parameters for each relay protection device on the grid according to the location of the distributed photovoltaic power source connected to the medium voltage distribution network.

[0044] Specifically, anti-islanding protection is configured on the feeder terminal line of the common connection point (outgoing line 3) using the distribution automation master station.

[0045] like Figure 1 As shown, Figure 1This is a diagram illustrating the protection scheme when a distributed power source is connected to the 10kV busbar of a substation. When distributed photovoltaic power is connected to the 10kV busbar of a substation, this invention, based on the photovoltaic connection location (outgoing line 3), aims to ensure the selectivity of overcurrent protection for each outgoing line (i.e., each outgoing line node A). It utilizes the distribution automation master station line to increase the reliability coefficient of the overcurrent protection of outgoing line node A (outgoing line 1 node A and outgoing line 2 node A) from 1.2-1.3 to 1.3-1.5, thus ensuring that the overcurrent protection of node A does not malfunction when a fault occurs in the protected section of each outgoing line node B.

[0046] Example 2

[0047] This invention provides another embodiment, a method for improving the accuracy of relay protection devices in medium-voltage distribution networks containing photovoltaic power sources, and more specifically, a method for improving the accuracy of relay protection devices in medium-voltage distribution networks containing distributed photovoltaic power sources. For example... Figure 4 As shown, Figure 4 This is a flowchart illustrating the specific steps of the protection configuration for distributed photovoltaic systems at different locations according to the present invention.

[0048] If distributed photovoltaic power is connected to the middle of a 10kV main line, then this invention provides a protection scheme for such distributed photovoltaic power being connected to the middle of a 10kV main line.

[0049] By configuring directional protection function for the upstream feeder terminals (outgoing nodes A and B) of the common connection point (outgoing node B') at the main station, the overcurrent protection I and II stages are activated only when a short-circuit current flows through the power supply of the substation, so as to prevent the protection from malfunctioning due to faults in other feeders.

[0050] Specifically, the following steps are included:

[0051] Step 4.1: Reduce the reliability coefficient of the overcurrent stage II protection of the upstream feeder terminal (outgoing node B) of the common connection point on the main station line to 1.2 to ensure the selectivity of the protection.

[0052] Step 4.2: Increase the reliability coefficient of the overcurrent stage I of the feeder terminal (outgoing node A) of the feeders other than the feeder connected to the photovoltaic power source to 1.3-1.5 on the main station line to prevent protection malfunction.

[0053] Step 4.3: Configure directional protection on the feeder terminal (outgoing node B') with the distribution automation master station as the common connection point. The current setting value should not exceed the rated current of the distributed power source connected in parallel. At the same time, configure the synchronization detection and reclosing function to prevent islanding.

[0054] Example 3

[0055] The present invention provides another embodiment, which is a method for improving the accuracy of relay protection devices for medium-voltage distribution networks containing photovoltaic power sources.

[0056] If distributed photovoltaic power is connected to the end of a 10kV main line, such as Figure 2 As shown, Figure 2 This is a diagram of the protection scheme for distributed photovoltaic power generation when connected to the end of a 10kV main line.

[0057] By using the main station, the reliability coefficient of the overcurrent stage II protection of the upstream adjacent feeder terminal (outgoing node C) of the common connection point (outgoing node C') is reduced to 1.2 to ensure the sensitivity of the protection in this area.

[0058] Specifically, the following steps are included:

[0059] Step 5.1: Configure directional protection function for all feeder terminals (outgoing nodes A, B, and C) upstream of the common connection point using the main station to ensure that overcurrent protection I and II are activated only when short-circuit current flows through the power supply of the substation, so as to prevent other feeder faults and prevent protection maloperation.

[0060] Step 5.2: Increase the reliability coefficient of the overcurrent stage I of the feeder terminal (outgoing node A) of the feeders other than the feeder connected to the photovoltaic power source to 1.3-1.5 on the main station line to prevent protection malfunction.

[0061] Step 5.3: Configure directional protection on the feeder terminal (outgoing node C') with the distribution automation master station as the common connection point. The current setting value should not exceed the rated current of the distributed power source connected in parallel. At the same time, configure the synchronization detection and reclosing function to prevent islanding.

[0062] Example 4

[0063] The present invention provides another embodiment, which is a method for improving the accuracy of relay protection devices in medium-voltage distribution networks containing distributed photovoltaic power sources.

[0064] If the distributed photovoltaic system is connected to a 10kV branch line or a secondary branch line, then this invention provides a protection scheme for the distributed photovoltaic system connected to a 10kV branch line or a secondary branch line.

[0065] Configure directional protection function for the upstream feeder terminal (outgoing node D) of the common connection point (outgoing node D') to ensure that overcurrent stage III protection is activated only when a short-circuit current flows through the power supply of the substation.

[0066] Directional protection is configured on the feeder terminal (outgoing node D') with the distribution automation master station as the common connection point. The current setting value is not greater than the rated current of the distributed power source connected in parallel. At the same time, the synchronization detection and reclosing function is configured to prevent islanding.

[0067] Among them, the overcurrent protection stage I is set according to the principle of avoiding the maximum three-phase short-circuit current at the end of the protected section.

[0068] The overcurrent protection stage II is set according to the principle of coordinating with the overcurrent protection stage I of the adjacent downstream line. The overcurrent protection stage III is set according to the principle of avoiding overload current in the line protection section. The directional protection uses the directional element of the corresponding feeder terminal to determine the direction and magnitude of the current flowing through the line protected by the feeder terminal to achieve protection discrimination.

[0069] In this invention, the terms "connection" and "fixation" should be interpreted broadly. For example, "connection" can mean a fixed connection, a detachable connection, or an integral connection. Those skilled in the art can understand the specific meaning of these terms in this invention according to the specific circumstances.

[0070] In the description of this invention, it should be understood that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description, and is not intended to indicate or imply that the device or unit referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0071] In the description of this specification, the terms "one embodiment," "some embodiments," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for improving the accuracy of relay protection devices for medium-voltage distribution networks containing photovoltaic power sources, characterized in that: Includes the following steps: Determine the location where distributed photovoltaic (PV) power sources are connected to the medium-voltage distribution network, and configure a deeply integrated primary and secondary pole-mounted circuit breaker at the point of common coupling (PCC). Specifically, when determining the location for PV power source integration into the medium-voltage distribution network, if the PV power source is integrated into the middle of a 10kV main line, utilize the substation to configure directional protection functions for the upstream feeder terminals at the PCC. This includes: reducing the overcurrent stage II protection reliability coefficient of the upstream feeder terminals at the PCC to 1.2 on the substation line; and increasing the first outgoing feeder of all feeders except those connected to the PV power source on the substation line. The reliability coefficient of the overcurrent stage I protection of the terminal is reduced to 1.3-1.5; directional protection is configured on the feeder terminal line using the distribution automation master station as the point of common coupling, with the current setting value less than the rated current of the distributed power source connected to it, and a synchronization detection and reclosing function is configured to prevent islanding; the location of the distributed photovoltaic power source connected to the medium voltage distribution network is determined. If the distributed photovoltaic power source is connected to the end of a 10kV main line, the reliability coefficient of the overcurrent stage II protection of the upstream adjacent feeder terminal of the point of common coupling is reduced to 1.2 using the master station as the point of common coupling. All feeder terminals upstream of the connection point are equipped with directional protection to ensure that overcurrent protection stages I and II are activated only when short-circuit current flows through the substation power supply, thus preventing faults in other feeders and preventing maloperation of protection. The reliability coefficient of overcurrent stage I for feeder terminals on the main station line, excluding feeders connected to photovoltaic power sources, is increased to 1.3-1.5 to prevent maloperation of protection. Directional protection is configured on feeder terminals using the distribution automation master station as the point of common coupling, with a current setting value less than the rated current of the distributed power source, and a synchronization detection and reclosing function is configured to prevent islanding. The location of the distributed photovoltaic power source connected to the medium-voltage distribution network is determined. If the distributed photovoltaic power source is connected to a 10kV branch line or secondary branch line, directional protection is configured on the feeder terminals upstream of the point of common coupling to ensure that overcurrent protection stage III is activated only when short-circuit current flows through the substation power supply. Directional protection is configured on feeder terminals using the distribution automation master station as the point of common coupling, with a current setting value not exceeding the rated current of the distributed power source, and a synchronization detection and reclosing function is configured to prevent islanding. The primary and secondary deeply integrated pole-mounted circuit breakers configured at the public connection points are jointly commissioned with the main station. Based on the location of the distributed photovoltaic power source connected to the medium-voltage distribution network, setpoint parameters are configured for each relay protection device on the grid.

2. The method for improving the accuracy of relay protection devices for medium-voltage distribution networks containing photovoltaic power sources according to claim 1, characterized in that: The method of configuring setpoint parameters for each relay protection device on the grid based on the location of the distributed photovoltaic power source connected to the medium-voltage distribution network is to configure anti-islanding protection on the feeder terminal line with the distribution automation master station as the common connection point.

3. The method for improving the accuracy of relay protection devices for medium-voltage distribution networks containing photovoltaic power sources according to claim 1, characterized in that: The overcurrent protection stage I is set according to the principle of avoiding the maximum three-phase short-circuit current at the end of the protected section of the line. The overcurrent stage II protection is set according to the principle of coordination with the overcurrent stage I protection of the adjacent downstream line; The overcurrent protection stage III is set according to the principle of avoiding overload current in the line protection zone; Directional protection utilizes the directional element at the corresponding feeder terminal to determine the direction and magnitude of the current flowing through the protected line to achieve protection discrimination.

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