CN105790251A - Method for determining transient current of key equipment of +/-10 kV flexible direct-current power distribution network - Google Patents

Abstract

The invention provides a method for determining the transient current of key equipment in a ±10kV flexible DC distribution network, which includes determining the access load of the ±10kV flexible DC distribution network and obtaining a system formed by connecting the ±10kV flexible DC distribution network with an AC grid Topological structure: Divide the system topology into areas to obtain the main converter area and the access equipment area, and determine the key equipment in the main converter area and the access equipment area and the corresponding decisive fault work of each key equipment conditions; through the preset simulation software, simulate the decisive fault conditions of all key equipment, and obtain the corresponding transient currents flowing through each key equipment. The implementation of the invention can provide a reference for the design and selection of key equipment of the ±10kV flexible direct current distribution network, and greatly promote the development of the flexible direct current distribution network.

Description

Method for Determination of Transient Current of Key Equipment in ±10kV Flexible DC Distribution Network

technical field

The invention relates to the technical field of smart distribution network access, in particular to a method for determining the transient current of key equipment in a ±10kV flexible DC distribution network.

Background technique

The transient current of equipment in the power system refers to the maximum fault current that electrical equipment may withstand under various fault conditions in the power system. However, the transient current of key equipment is the main basis for verifying the electrodynamic stability of equipment. It is also an important parameter for equipment selection and manufacture.

With the development of flexible DC transmission technology, the research on the determination method of transient current of key equipment in flexible DC transmission network has also been carried out one after another. The determination method of the transient current of key equipment in the flexible DC transmission network, on the basis of considering its unique topology, key equipment, fault conditions, and protection configuration, refers to the determination method and steps of the transient current of the HVDC transmission network However, the determination method of the transient current of the HVDC grid is only applicable to the HVDC grid based on the thyristor converter valve, so the determination method of the transient current of the key equipment in the flexible HVDC grid has not yet formed a unified standard, and the existing scheme The validity and reliability of this method need to be further verified.

Since the ±10kV flexible DC distribution network is connected to AC sensitive loads, AC microgrids, DC microgrids, and large-capacity energy storage devices on its DC lines, the topology, key equipment, and protection configurations are different from traditional high-voltage DC transmission grids, The HVDC flexible grid is quite different. Therefore, the method for determining the transient current level of key equipment in the ±10kV flexible DC distribution network still needs systematic and in-depth research.

Contents of the invention

The technical problem to be solved by the embodiments of the present invention is to provide a method for determining the transient current of key equipment in a ±10kV flexible DC power distribution network, which can provide a reference for the design and selection of key equipment in a ±10kV flexible DC power distribution network. Dadi promotes the development of flexible DC distribution network.

In order to solve the above technical problems, an embodiment of the present invention provides a method for determining the transient current of key equipment in a ±10kV flexible DC distribution network, the method comprising:

a. Determine the access load of the ±10kV flexible DC distribution network, and obtain the system topology formed by connecting the ±10kV flexible DC distribution network to the AC grid;

b. Divide the obtained system topology into regions to obtain the main converter region and the access device region, and determine the key equipment in the main converter region and the decisive fault work corresponding to each key device conditions, and determine the key equipment in the access equipment area and the decisive failure conditions corresponding to each key equipment;

c. Through the preset simulation software, simulate the decisive fault conditions of all key equipment, and obtain the corresponding transient currents flowing through each key equipment.

Wherein, the step a specifically includes:

When it is determined that the connected load of the ±10kV flexible DC distribution network is one or more of AC sensitive loads, AC microgrids, DC microgrids, and large-capacity energy storage devices, the determined connected The AC sensitive load and/or AC microgrid in the input load is connected to the DC line of the ±10kV flexible DC distribution network through a converter; and/or

Connecting the DC microgrid and/or large-capacity energy storage device in the determined access load to the DC line of the ±10kV flexible DC distribution network through a DC transformer;

After the DC line of the ±10kV flexible DC distribution network is connected to the determined access load, it is further connected to the AC grid through a main converter to obtain a system topology.

Wherein, the step b specifically includes:

Divide the area formed by the main converter and its peripheral equipment connected to the ±10kV flexible DC distribution network with the AC grid into the main converter area, and divide the ±10kV flexible DC distribution network The area formed by each access load and its corresponding converter or DC transformer is divided into the access equipment area;

Determine that the key equipment in the main converter area is one or more of AC bus, main converter, bridge arm reactor, converter valve unit, DC reactor, and DC circuit breaker, and further Determine the decisive fault conditions of each key equipment in the main converter area;

Determine that the key equipment in the access equipment area is one or more of converters and DC transformers, and further determine the decisive fault conditions of each key equipment in the access equipment area.

Wherein, when it is determined that the key equipment in the main converter area is an AC bus, the decisive fault condition of the AC bus is a three-phase ground short circuit.

Wherein, when it is determined that the key equipment in the access equipment area is a DC transformer, the decisive fault condition of the DC transformer is a bipolar short circuit of the DC bus of the DC transformer.

Wherein, the method further includes:

Combined with the system protection action situation formed by the connection between the ±10kV flexible DC distribution network and the AC grid, screen out the key equipment whose current amplitude of the transient current exceeds the preset condition, and select any key equipment in the screened key equipment A current-limiting reactor is connected in series on the line connected to the system topology.

Wherein, the method further includes:

Re-simulate the key equipment connected in series with a current-limiting reactor in its corresponding decisive fault condition to obtain the transient current of the key equipment connected in series with a current-limiting reactor, and to detect the obtained After the current amplitude of the transient current of the key equipment connected in series with the current-limiting reactor exceeds the preset condition, replace the series-connected current-limiting reactor until the critical The current magnitude of the transient current of the device is within the preset condition.

Implementing the embodiment of the present invention has the following beneficial effects:

1. In the embodiment of the present invention, since the determination of the transient current of the key equipment of the ±10kV flexible DC distribution network is based on the conventional system protection configuration, combined with the system topology, the main converter area and the access equipment area are divided , determine the transient current decisive fault conditions of each key equipment in the two areas, and then specifically calculate the transient current amplitude flowing through each equipment under the decisive fault conditions, which will help to more efficiently and accurately determine the critical fault conditions. The decisive fault conditions of equipment and key equipment can provide a reference for the design and selection of key equipment in the ±10kV flexible DC distribution network, which greatly promotes the development of flexible DC distribution network;

2. In the embodiment of the present invention, due to the combination of the protection action of the system, effective current limiting measures (such as series connection of current limiting reactors) are proposed, so that the protection device of the system can isolate or cut off the fault within a specified time, avoiding Key equipment is impacted by excessive transient current, which fully guarantees the tolerance of key equipment to transient current in actual engineering, making the equipment in actual engineering safer and more reliable.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those of ordinary skill in the art, obtaining other drawings based on these drawings still belongs to the scope of the present invention without any creative effort.

Fig. 1 is a flowchart of a method for determining the transient current of key equipment in a ±10kV flexible DC distribution network provided by an embodiment of the present invention;

Fig. 2 is a schematic diagram of the system topology formed by the ±10kV flexible DC distribution network and the AC grid in the method for determining the transient current of key equipment in the ±10kV flexible DC distribution network provided by the embodiment of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, in the embodiment of the present invention, a method for determining the transient current of key equipment in a ±10kV flexible DC distribution network is provided, and the method includes:

Step S1. Determine the access load of the ±10kV flexible DC distribution network, and obtain the system topology formed by connecting the ±10kV flexible DC distribution network to the AC grid;

The specific process is that the ±10kV flexible DC distribution network has the functional characteristics of high power supply reliability, high power quality, convenient distributed power access, and convenient DC load access. Among them, the system access load includes: AC sensitive load, AC microgrid, DC microgrid, and large-capacity energy storage device.

Therefore, when the access load of the ±10kV flexible DC distribution network is one or more of AC sensitive loads, AC microgrids, DC microgrids, and large-capacity energy storage devices, the AC in the loads will be connected Sensitive loads and/or AC microgrids are connected to the DC lines of the ±10kV flexible DC distribution network through converters; and/or the DC microgrids and/or large-capacity energy storage devices connected to the loads are connected to ± The DC line of the 10kV flexible DC distribution network is connected; and, after the DC line of the ±10kV flexible DC distribution network is connected to the determined access load, the system topology is further connected to the AC grid through the main converter.

As an example, as shown in Figure 2, it is a schematic diagram of the system topology formed by the ±10kV flexible DC distribution network and the AC grid with access loads including AC sensitive loads, AC microgrids, DC microgrids and large-capacity energy storage devices.

Step S2. Divide the obtained system topology into regions to obtain the main converter region and the access device region, and determine the key devices in the main converter region and the decisive faults corresponding to each key device Working conditions, and determining the key equipment in the access equipment area and the decisive failure conditions corresponding to each key equipment;

The specific process is to divide the area formed by the main converter and its peripheral equipment connected to the ±10kV flexible DC distribution network with the AC power grid into the main converter area, and divide the ±10kV flexible DC distribution The area composed of the load and its corresponding converter or DC transformer is divided into the access equipment area;

Determine that the key equipment in the main converter area is one or more of the AC busbar, main converter, bridge arm reactor, converter valve unit, DC reactor, and DC circuit breaker, and further determine the main The decisive fault conditions of each key equipment in the converter area;

Determine that the key equipment in the access equipment area is one or more of converters and DC transformers, and further determine the decisive fault conditions of each key equipment in the access equipment area.

In the embodiment of the present invention, the possible faults of the AC bus include: single-phase ground short circuit, two-phase ground short circuit, two-phase short circuit, and three-phase ground short circuit; the possible faults of the bridge arm of the main converter include: valve bottom Ground short circuit, bridge arm short circuit; The possible faults of the DC bus of the converter and DC transformer are: single pole ground short circuit, double pole short circuit.

As an example, when the key equipment in the main converter area is the AC bus, the decisive fault condition of the AC bus is a three-phase ground short circuit; when the key equipment in the access equipment area is a DC transformer, the decisive fault condition of the DC transformer is The fault condition is a bipolar short circuit of the DC bus of the DC transformer.

Step S3, using the preset simulation software to simulate the decisive fault conditions of all key equipment, and obtain the corresponding transient currents flowing through each key equipment.

The specific process is to establish the electromagnetic transient model of each component of the system in PSCAD/EMTDC software, and determine all key equipment and their decisive fault conditions in the simulation model. Thus, the corresponding transient currents flowing through each key equipment are obtained.

Considering the maximum short-circuit current that the circuit breaker of the system can cut off and the opening time of the circuit breaker after a decisive fault condition occurs, and to protect the safety of the ±10kV flexible DC distribution network to the maximum extent, it is necessary to determine the installation of a current-limiting reactor and its corresponding position, so the method further includes:

Combined with the system protection actions formed by the connection between the ±10kV flexible DC distribution network and the AC grid, screen out the key equipment whose current amplitude of the transient current exceeds the preset condition, and place any of the screened key equipment in the A current-limiting reactor is connected in series with the line connected by the system topology.

In order to ensure that the series-connected current-limiting reactor can prevent key equipment from being impacted by excessive transient currents, making the key equipment in actual engineering safer and more reliable, it is necessary to replace unreasonable current-limiting reactors, so the method Further includes:

Re-simulate the key equipment connected in series with a current-limiting reactor in its corresponding decisive fault condition to obtain the transient current of the key equipment connected in series with a current-limiting reactor, and to detect the above-mentioned series-connected current-limiting reactor After the current amplitude of the transient current of the key equipment of the reactor exceeds the preset condition, replace the above-mentioned series-connected current-limiting reactor until it is detected that the current amplitude of the transient current of the key equipment after the current-limiting reactor is replaced is within the preset condition. Until the conditions are set.

As an example, in the access equipment area, the decisive fault condition of the DC transformer is the bipolar short-circuit fault of the DC bus of the DC transformer. Through the simulation results, it can be obtained that when the fault occurs, the transient current flowing through the DC bus of the DC transformer Sudden increase, reaching thousands of amperes within 1ms, while the maximum shut-off current of the DC circuit breaker is only 3.6-5kA, and the shut-off time is 3ms, so a current-limiting reactor needs to be connected in series with the DC bus of the DC transformer to limit the transient state The magnitude and rate of rise of the current.

However, the current-limiting reactors connected in series may not be able to limit the transient current, so it is necessary to further try to connect current-limiting reactors of 1mH, 5mH, and 8mH in series, and compare the effects of current-limiting reactors with different resistance values on transient currents. To limit the effect, select a current-limiting reactor that can limit the transient current amplitude within 5kA, and the time to rise to the peak value is less than 3ms.

Implementing the embodiment of the present invention has the following beneficial effects:

1. In the embodiment of the present invention, since the determination of the transient current of the key equipment of the ±10kV flexible DC distribution network is based on the conventional system protection configuration, combined with the system topology, the main converter area and the access equipment area are divided , determine the transient current decisive fault conditions of each key equipment in the two areas, and then specifically calculate the transient current amplitude flowing through each equipment under the decisive fault conditions, which will help to more efficiently and accurately determine the critical fault conditions. The decisive fault conditions of equipment and key equipment can provide a reference for the design and selection of key equipment in the ±10kV flexible DC distribution network, which greatly promotes the development of flexible DC distribution network;

2. In the embodiment of the present invention, due to the combination of the protection action of the system, effective current limiting measures (such as series connection of current limiting reactors) are proposed, so that the protection device of the system can isolate or cut off the fault within a specified time, avoiding Key equipment is impacted by excessive transient current, which fully guarantees the tolerance of key equipment to transient current in actual engineering, making the equipment in actual engineering safer and more reliable.

Those of ordinary skill in the art can understand that all or part of the steps in the method of the above-mentioned embodiments can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable storage medium, and the storage Media such as ROM/RAM, magnetic disk, optical disk, etc.

The above disclosures are only preferred embodiments of the present invention, and certainly cannot limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (7)

1. A method for determining the transient current of key equipment in a ±10kV flexible DC distribution network, characterized in that the method comprises: a. Determine the access load of the ±10kV flexible DC distribution network, and obtain the system topology formed by connecting the ±10kV flexible DC distribution network to the AC grid; b. Divide the obtained system topology into regions to obtain the main converter region and the access device region, and determine the key equipment in the main converter region and the decisive fault work corresponding to each key device conditions, and determine the key equipment in the access equipment area and the decisive failure conditions corresponding to each key equipment; c. Through the preset simulation software, simulate the decisive fault conditions of all key equipment, and obtain the corresponding transient currents flowing through each key equipment. 2. The method according to claim 1, wherein said step a specifically comprises: When it is determined that the connected load of the ±10kV flexible DC distribution network is one or more of AC sensitive loads, AC microgrids, DC microgrids, and large-capacity energy storage devices, the determined connected loads The AC sensitive load and/or AC microgrid in the input load is connected to the DC line of the ±10kV flexible DC distribution network through a converter; and/or Connecting the DC microgrid and/or large-capacity energy storage device in the determined access load to the DC line of the ±10kV flexible DC distribution network through a DC transformer; After the DC line of the ±10kV flexible DC distribution network is connected to the determined access load, it is further connected to the AC grid through a main converter to obtain a system topology. 3. The method according to claim 1, wherein said step b specifically comprises: Divide the area formed by the main converter and its peripheral equipment connected to the ±10kV flexible DC distribution network with the AC grid into the main converter area, and divide the ±10kV flexible DC distribution network The area formed by each access load and its corresponding converter or DC transformer is divided into the access equipment area; Determine that the key equipment in the main converter area is one or more of AC bus, main converter, bridge arm reactor, converter valve unit, DC reactor, and DC circuit breaker, and further Determine the decisive fault conditions of each key equipment in the main converter area; Determine that the key equipment in the access equipment area is one or more of converters and DC transformers, and further determine the decisive fault conditions of each key equipment in the access equipment area. 4. The method according to claim 3, wherein when it is determined that the key equipment in the main converter area is an AC bus, the decisive fault condition of the AC bus is a three-phase ground short circuit. 5. The method according to claim 3, wherein when it is determined that the key equipment in the access equipment area is a DC transformer, the decisive fault condition of the DC transformer is a bipolar short circuit of the DC bus of the DC transformer . 6. The method of claim 1, further comprising: Combined with the system protection action situation formed by the connection between the ±10kV flexible DC distribution network and the AC grid, screen out the key equipment whose current amplitude of the transient current exceeds the preset condition, and select any key equipment in the screened key equipment A current-limiting reactor is connected in series on the line connected to the system topology. 7. The method of claim 6, further comprising: Re-simulate the key equipment connected in series with a current-limiting reactor in its corresponding decisive fault condition to obtain the transient current of the key equipment connected in series with a current-limiting reactor, and to detect the obtained After the current amplitude of the transient current of the key equipment connected in series with the current-limiting reactor exceeds the preset condition, replace the series-connected current-limiting reactor until the critical The current magnitude of the transient current of the device is within the preset condition.