Method for representing short circuit current of ship closed loop power supply network based on distribution coefficient

Abstract

The technical solution of this invention discloses a method for representing short-circuit current in a ship's closed-loop power supply network based on a current distribution coefficient. The method includes the following steps: calculating the total current of the faulty branch; and calculating the current flowing through each protected branch using the current distribution coefficient. This invention introduces the concept of a distribution coefficient to decompose and represent the short-circuit current in the closed-loop network, decomposing it into current components of each branch, thereby achieving a fast, accurate, and intuitive representation of the short-circuit current. The method disclosed in this invention enables efficient modeling and analysis of short-circuit current, effectively simplifies the modeling process of the closed-loop network, reduces computational complexity, and improves computational efficiency. It is applicable to complex ship power supply systems with multiple power sources and multiple branches, providing technical support for the safe operation and intelligent management of ship power systems.

Description

Technical Field

[0001] This invention relates to a method for representing short-circuit current in a ship's closed-loop power supply network, belonging to the fields of power system analysis and design and short-circuit current technology. Background Technology

[0002] In shipboard electrical systems, closed-loop power supply networks are a crucial choice for improving power supply reliability and system stability. However, when a short-circuit fault occurs, the calculation of the short-circuit current becomes complex due to the presence of multiple power supply paths within the closed-loop network. Traditional short-circuit calculation methods based on symmetric component methods or nodal admittance matrices are difficult to apply directly to closed-loop networks, especially in complex structures with multiple power sources and branches. These methods suffer from high computational complexity, poor convergence, and difficulty in quickly and accurately reflecting the distribution characteristics of the short-circuit current.

[0003] Furthermore, existing technologies lack a method to quickly and accurately represent the distribution of short-circuit current in closed-loop power supply networks. This is especially true in complex ship power supply systems with multiple power sources and branches, where real-time analysis and evaluation of short-circuit current are difficult to achieve, limiting fault diagnosis and protection configuration optimization of ship power systems.

[0004] Therefore, there is an urgent need for a method to represent the short-circuit current in a ship's closed-loop power supply network, to overcome the problems of complex short-circuit current calculation, inaccurate current distribution, and low computational efficiency in existing technologies under complex closed-loop structures. This method should be able to quickly and accurately represent the short-circuit current distribution of each branch in the closed-loop power supply network, providing reliable technical support for fault analysis, protection configuration optimization, and operation control of ship power systems. Summary of the Invention

[0005] The present invention aims to solve the problems of complex calculation of short-circuit current and difficulty in accurately representing current distribution in the prior art in closed-loop power supply networks.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention discloses a method for representing the short-circuit current of a ship's closed-loop power supply network based on a distribution coefficient, characterized by comprising the following steps:

[0007] Calculate the total current of the faulty branch; The current flowing through each protection branch is calculated using the current distribution coefficient. When calculating the current distribution coefficient of each protection branch, the ship's power supply network after the fault is decomposed into the normally operating protection branch and the fault-addition fault branch. In the fault branch, there is only one fault-addition potential at the fault point.

[0008] Preferably, the fault branch and the protection branch are respectively denoted as... and Then the current distribution coefficient Defined by the following formula:

[0009] In the formula, and These are the currents for the protection branch and the fault branch, respectively.

[0010] Preferably, when the ship's power supply network is operating in a closed loop, the allocation coefficient of the protection branch is... Calculated by the following formula:

[0011] In the formula: To protect the equivalent generator impedance of the branch away from the faulty branch; This is the closed-loop current shunting coefficient for jumper cables. It is set to 2 only when the protection branch is a jumper cable under closed-loop conditions; otherwise, it is set to 1. The system's equivalent impedance, , and The numbers of large-capacity and small-capacity generators are respectively. Let be the equivalent impedance of the i-th large-capacity generator. Let be the equivalent impedance of the j-th small-capacity generator.

[0012] This invention proposes a method for representing short-circuit current in a ship's closed-loop power supply network based on a distribution coefficient. By introducing the concept of a distribution coefficient, the short-circuit current in the closed-loop network is decomposed and represented, breaking it down into current components of each branch. This enables a fast, accurate, and intuitive representation of the short-circuit current. The method disclosed in this invention achieves efficient modeling and analysis of short-circuit current, effectively simplifies the modeling process of closed-loop networks, reduces computational complexity, and improves computational efficiency. It is applicable to complex ship power supply systems with multiple power sources and multiple branches, providing technical support for the safe operation and intelligent management of ship power systems. Attached Figure Description

[0013] Figure 1 The diagram shows the current, voltage, and composite sequence network at the point of a two-phase ungrounded short-circuit fault. Figure 2 The topology is illustrated; Figure 3 The fault-addition state network is illustrated; Figure 4 The diagram illustrates the topology of the AC dual power station with two generating units. Detailed Implementation

[0014] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0015] After calculating the total current of the faulty branch, this embodiment of the invention further utilizes current distribution coefficients to calculate the current flowing through each protection branch. When the ship's power supply network operates in a closed loop and contains multiple power sources, the calculation of the current distribution coefficients is complex. According to the superposition theorem, the post-fault network can be decomposed into a normal operating network and a fault-addition network. In the fault-addition network, there is only one fault-addition potential at the fault point. Based on this characteristic, the distribution coefficients of each protection branch can be quickly solved.

[0016] Specifically, the following assumptions are made: ignore the load current during normal operation; ignore the line impedance and only consider the generator impedance (transient or subtransient).

[0017] Shipboard power supply networks operate in various modes. For a specific topology under a particular mode, fault branches and protection branches can be denoted as follows: and Then the current distribution coefficient It can be defined as:

[0018] In the formula: and These are the currents of the protected branch and the faulty branch, respectively. This indicates the system's operating mode.

[0019] Closed-loop power supply network topology as follows Figure 2 As shown, in closed-loop operation mode, all circuit breakers are closed. In open-loop operation mode, bus tie switch B1 is open, and bus B1 is divided into left and right parts, named B11 and B12 respectively.

[0020] When the system is running in closed loop, if a three-phase short circuit occurs at F1, the fault-related network is as follows: Figure 3 As shown in the diagram. The fault branch is bus B2, and the protection branches are each generator G and cable L. to This is the positive sequence impedance of the generator. For the fault branch current, , To protect the branch current, The fault is supplemented with a power supply, which is equal in magnitude but opposite in direction to the voltage at point F1 during normal operation.

[0021] The distribution coefficient of the protection branch The calculation method is as follows:

[0022] In the formula: To protect the equivalent generator impedance of the branch away from the faulty branch, the calculation method is the same as... The calculation method This is the closed-loop current shunting coefficient for jumper cables. It is set to 2 only when the protection branch is a jumper cable under closed-loop conditions; otherwise, it is set to 1.

[0023]

[0024] In the formula: The equivalent impedance of the system; and The numbers represent the number of large-capacity and small-capacity generators, respectively.

[0025] Figure 3 Distribution coefficient at L1 of the middle cable It can be represented as: .

[0026] For example Figure 4 The example of current distribution coefficients in the power grid topology (AC dual power stations, two generating units per power station) further illustrates the present invention.

[0027] Table 1. Maximum current of the target branch for phase-to-phase fault in a dual AC power plant with two generating units.

[0028] Table 2. Minimum current of the target branch for phase-to-phase fault in AC dual-power station with two generating units.

[0029] The meanings of each item in the table above are as follows: Target branch: refers to the protected component; Target branch maximum / minimum current: refers to the maximum / minimum short-circuit current that may flow through this branch, which is equal to the maximum / minimum total fault current. Allocation coefficient; Calculation conditions: system operating mode and fault type when the target branch flows through the maximum / minimum current.

Claims

1. A method of representing short circuit current in a shipboard closed loop power supply network based on distribution factors, characterized by, Includes the following steps: Calculate the total current of the faulty branch; The current flowing through each protection branch is calculated using the current distribution coefficient. When calculating the current distribution coefficient of each protection branch, the ship's power supply network after the fault is decomposed into the normally operating protection branch and the fault-addition fault branch. In the fault branch, there is only one fault-addition potential at the fault point.

2. A method of representing short circuit current in a shipboard closed loop power distribution network based on distribution factors as claimed in claim 1, wherein, The faulty branch and the protection branch are respectively denoted as and The current distribution coefficient is defined by the following formula: wherein and are the currents of the protection branch and the fault branch, respectively.

3. A method of representing short circuit current in a shipboard closed loop power distribution network based on distribution factors as claimed in claim 2, wherein, the distribution factor of the protection branch when the ship power supply network is operated in closed loop is calculated from the formula: In the formula: Zeq is the equivalent generator impedance in the direction of the protected branch away from the fault branch direction; This is the closed-loop current shunting coefficient for jumper cables. It is set to 2 only when the protection branch is a jumper cable under closed-loop conditions; otherwise, it is set to 1. The system's equivalent impedance, , and The numbers of large-capacity and small-capacity generators are respectively. Let be the equivalent impedance of the i-th large-capacity generator. Let be the equivalent impedance of the j-th small-capacity generator.

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