Ship dc line protection method based on leakage current and low voltage

Abstract

A kind of ship DC line protection method based on leakage current and low voltage, after leakage current sensor detects that single pole ground fault occurs in DC load line, according to bus voltage and balance branch resistance and current, the insulation resistance value of the branch to ground, i.e.the ground resistance value is converted, at the same time, ground protection system sends warning signal, after time delay, the fault branch is tripped, and for single pole ground fault of load line, ground fault is discriminated by detecting the size of line leakage current.The present application does not add any signal to the DC system, so it will not cause interference;When calculating the resistance value of ground resistance, it will not be affected by the system distribution capacitor;When single pole of DC bus appears ground fault, the leakage current value is small, which will not cause misoperation;It can detect the situation that multiple branches are grounded at the same time.

Description

Technical Field

[0001] This invention relates to a technology in the field of power systems, specifically a method for protecting ship DC lines based on leakage current and low voltage. Background Technology

[0002] Shipboard integrated power systems employ a hybrid AC / DC power system, integrating DC and AC power, which significantly increases the complexity of the power system. Effective protection against various grounding faults is crucial to ensuring the normal operation of the ship. Existing technologies mostly address protection strategies and methods for AC system grounding faults and are not applicable to shipboard medium-voltage DC integrated power systems. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, this invention proposes a shipboard DC line protection method based on leakage current and low voltage. This method does not introduce any signals into the DC system, thus avoiding interference. When calculating the grounding resistance, it is not affected by the system's distributed capacitance. When a single pole of the DC bus experiences a grounding fault, the leakage current is small and will not cause malfunctions. It can also detect situations where multiple branches are grounded simultaneously.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for protecting a ship's DC line based on leakage current and low voltage. After the leakage current sensor detects a single-pole grounding fault in the DC load line, it calculates the insulation resistance value of the branch to ground, i.e., the grounding resistance value, based on the bus voltage, the resistance value of the balanced branch, and the current. At the same time, the grounding protection system issues an alarm signal, and after a time delay, it trips the faulty branch and identifies the single-pole grounding fault in the load line by detecting the magnitude of the line leakage current.

[0006] Technical effect

[0007] This invention addresses the topology of shipboard DC lines by employing combined criteria to detect and locate grounding faults, and by using time-limited coordination to coordinate grounding protection in different zones. Compared to existing technologies, this invention enables grounding fault protection for shipboard DC lines without additional communication devices, while not affecting the normal operation of other protection systems. Attached Figure Description

[0008] Figure 1 This is a fault diagram for a DC line.

[0009] Figure 2 This is a flowchart of the present invention. Detailed Implementation

[0010] like Figure 2As shown in the figure, this embodiment relates to a ship DC line protection method based on leakage current and low voltage, including:

[0011] Step 1, as follows Figure 1 As shown, when a leakage current sensor installed on a branch with a ground fault detects the difference between the current I+ flowing out of the positive terminal of the power supply and the branch current I- returning to the negative terminal of the power supply, the insulation resistance value to ground of that branch, i.e., the grounding resistance value R, is calculated based on the bus voltage, the resistance value of the balanced branch, and the current. k .

[0012] Step 2: After detecting a single-pole ground fault in the DC load line, the grounding protection system issues an alarm signal and trips the faulty branch after a time delay. Since the protection range of the DC line grounding protection is only the line itself, the remaining lines on the busbar can still operate normally after the faulty branch is disconnected.

[0013] Step 3: For a single-pole ground fault in the load line, the ground fault is identified by detecting the magnitude of the leakage current (the direction of leakage current flowing out of the distribution board busbar is taken as positive). This specifically includes:

[0014] ① The fault operation criterion for a ground fault is that the load current leakage current exceeds the leakage current operating current: ,in: For the operating current threshold, For load current and leakage current;

[0015] ② The current flowing through the grounding resistor exceeds the operating current of the grounding resistor: ,in: The grounding operating current threshold, This is the grounding resistance current;

[0016] ③ The criterion for positive grounding fault is: ,in: The operating voltage threshold. The current is the negative terminal grounding resistance. Positive voltage;

[0017] ④ The criterion for determining a negative grounding fault is: ,in: The current is the positive grounding resistance. It is the negative terminal voltage;

[0018] To prevent maloperation of the grounding protection, ① the leakage current operating current threshold is set and calculated based on the fault current during a typical arc grounding event: ,in: These are the tuning coefficients. This represents the maximum leakage current during a fault.

[0019] In this embodiment Take 0.8; calculate the typical leakage current value when a ground fault occurs through simulation. The operating current threshold is approximately 6.2A. It is 4.9A.

[0020] To prevent maloperation of the grounding protection, the grounding resistance operating current threshold in section ② is set and calculated based on the fault current during a typical arc grounding event: ,in: These are the tuning coefficients. DC rated voltage, This is the grounding resistance value.

[0021] In this embodiment Take 0.8, The voltage is 4000V, and the grounding resistance value is R. k If we take 450Ω, then the grounding operating current threshold is... It is 7.1A.

[0022] Therefore, when a ground fault occurs on a line, the protection system detects that the fault voltage and leakage current meet the fault criteria. The direction of the fault current can then be used to determine the fault pole. During the fault, the load voltage and current of other lines remain almost unchanged, but the leakage current of the faulty line reaches the threshold value. The ground fault protection system then issues a fault alarm signal and trips to clear the fault. The ground fault protection operating current threshold for the load line is... The protection operates at 4.9A, disconnecting the load line circuit breaker after no delay.

[0023] Based on the setting principles of different protection devices and according to the grounding time principle and the threshold values ​​of operating voltage and operating current, a grounding protection scheme for medium-voltage DC systems is formed. When a leakage current exceeding the threshold value is detected at the DC load line, the protection will trip the load line circuit breaker after 0.1 seconds. When a differential leakage current exceeding the threshold value is detected at the DC distribution board, the protection will trip all circuit breakers connected to the distribution board after 0.1 seconds. When the generator set protection detects a fault voltage below the threshold value, if a directional leakage current signal is detected, the protection will trip the generator set incoming line circuit breaker after a delay of 0.2 seconds. If only a low voltage signal is detected, the protection will trip the generator set incoming line circuit breaker after a delay of 0.3 seconds.

[0024] The timing principle of DC grounding protection

[0025] Through specific practical experiments, a shipboard medium-voltage DC integrated power system was built in MATLAB / SIMULINK. After a single-pole ground fault occurred in the load line, the operating status of each unit of the DC system is as follows:

[0026] DC system load line grounding fault

[0027] Based on the above simulation analysis results, when a single-pole ground fault occurs in a DC system and the fault transition resistance is 0.5Ω, 5Ω, and 50Ω, the fault characteristic current flowing through the protection exceeds the operating current threshold. The 4.9A leakage current protection can correctly reflect ground faults and promptly control the circuit breaker to clear the fault. This proves that the present invention can correctly operate when a single-pole ground fault with different transition resistances occurs under different operating conditions, isolate the fault, and ensure the safe operation of the system.

[0028] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for protecting ship DC lines based on leakage current and low voltage, characterized in that, When the leakage current sensor detects a single-pole ground fault in the DC load line, it calculates the insulation resistance value of that branch to ground (i.e., the grounding resistance value) based on the bus voltage, the resistance value of the balanced branch, and the current. Simultaneously, the grounding protection system issues an alarm signal, trips the faulty branch after a time delay, and determines the grounding fault based on the magnitude of the leakage current in the load line. Specifically, this includes: Step 1: When the leakage current sensor installed on the branch with a ground fault detects the difference between the current I+ flowing out of the positive terminal of the power supply and the branch current I- returning to the negative terminal of the power supply, the insulation resistance value to ground of that branch, i.e., the grounding resistance value R, is calculated based on the bus voltage, the resistance value of the balanced branch, and the current. k ; Step 2: After a single-pole ground fault is detected in the DC load line, the grounding protection system issues an alarm signal and trips the faulty branch after a time delay. Since the protection range of the DC line grounding protection is only the line, the remaining lines on the bus can still work normally after the faulty branch is disconnected. Step 3: For a single-pole ground fault in the load line, the ground fault is determined by detecting the magnitude of the line leakage current. Specifically, this includes: ① The fault action criterion for the ground fault is that the load current leakage current exceeds the leakage current operating current. ,in: For the operating current threshold, ① Load current leakage current; ② The current flowing through the grounding resistor exceeds the operating current of the grounding resistor: ,in: The grounding operating current threshold, The grounding resistance current; ③ The criterion for positive grounding fault is: ,in: The operating voltage threshold. The current is the negative terminal grounding resistance. The positive voltage is used as the criterion for the negative grounding fault. ,in: The current is the positive grounding resistance. This is the negative voltage.

2. The ship DC line protection method based on leakage current and low voltage according to claim 1, characterized in that, The leakage current operating current threshold in criterion ① is calculated and set based on the fault current during a typical arc grounding event: ,in: These are the tuning coefficients. This represents the maximum leakage current during a fault.

3. The shipboard DC line protection method based on leakage current and low voltage according to claim 1, characterized in that, The grounding resistance operating current threshold in criterion ② is calculated and set based on the fault current during a typical arc grounding event: ,in: These are the tuning coefficients. DC rated voltage, This is the grounding resistance.

4. The shipboard DC line protection method based on leakage current and low voltage according to claim 2, characterized in that, The aforementioned setting coefficient Take 0.8; calculate the typical leakage current value when a ground fault occurs through simulation. The operating current threshold is approximately 6.2A. It is 4.9A.

5. The ship DC line protection method based on leakage current and low voltage according to claim 3, characterized in that, The aforementioned setting coefficient Take 0.8, The voltage is 4000V, and the grounding resistance value is R. k If we take 450Ω, then the grounding operating current threshold is... It is 7.1A.

6. The ship DC line protection method based on leakage current and low voltage according to claim 1, characterized in that, when When a ground fault occurs on a line, the protection system detects that the fault voltage and leakage current meet the fault criteria. The direction of the fault current can then be used to determine the fault pole. During the fault, if the leakage current of the faulty line reaches a threshold value, the grounding protection system issues a fault alarm signal and trips to clear the fault. The grounding protection trip current threshold of the load line is then activated. The protection operates at 4.9A, disconnecting the load line circuit breaker after no delay.

7. The shipboard DC line protection method based on leakage current and low voltage according to claim 1, characterized in that, Based on the setting principles of different protection devices, and according to the grounding time principle and the threshold values ​​of operating voltage and operating current, a grounding protection scheme for medium-voltage DC systems is formed. When a leakage current exceeding the threshold value is detected at the DC load line, the protection will trip the load line circuit breaker after 0.1 seconds. When the DC distribution board detects that the differential leakage current exceeds the threshold value, the protection will disconnect all circuit breakers connected to the distribution board after 0.1 seconds. When the generator set protection detects that the fault voltage is lower than the threshold value, if a directional leakage current signal is detected, the protection will disconnect the generator set incoming circuit breaker after a delay of 0.2s. If only a low voltage signal is detected, the protection will disconnect the generator set incoming circuit breaker after a delay of 0.3s.

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