Alternating current leakage current fault diagnosis method

Abstract

The invention discloses an alternating current leakage current fault diagnosis method, which comprises the following steps that: a vehicle-mounted distribution box samples leakage current of a live wire and a zero wire of alternating current electric equipment to a shell through a zero sequence current transformer, determines a single sampling value and a sampling average value of the leakage current, and judges the stability of the sampling average value; setting safety protection current and corresponding duration of the instantaneous leakage current and the accumulated leakage current; executing accumulated leakage current detection logic according to the single sampling value of the leakage current, the accumulated leakage current safety protection current and the corresponding duration so as to judge whether the fault is an accumulated leakage current fault or not; the instantaneous leakage current detection logic is executed according to the difference value between the single sampling value of the leakage current and the sampling average value of the last period, the instantaneous leakage current safety protection current and the duration corresponding to the instantaneous leakage current safety protection current, so that whether an instantaneous leakage current fault occurs or not is judged; when an accumulated leakage current fault or an instantaneous leakage current fault is detected, the vehicle-mounted distribution box automatically cuts off power supply input and gives an alarm at the same time.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics, and in particular relates to an AC leakage current fault diagnosis method. Background Art

[0002] Conventional 380V AC power distribution designs for vehicles typically utilize the TN-S system, completely separating the neutral and neutral wires. 380V AC power is input to the onboard power distribution box via a four-wire system (three hot wires and one neutral wire), which distributes the AC power to the power consumers according to instructions. The cable's outer shield, the mounting bracket for the power consumer, and the grounding copper rod are connected through the vehicle's outer casing, and the grounding copper rod is inserted directly into the ground. A highly sensitive 30mA (operation time ≤ 0.1s) instantaneous electronic residual current device (RCD) is added to the input of the onboard power distribution box. Insulation faults in the equipment (cable) trigger the RCD to trip, preventing electric shock to the operator.

[0003] This design approach has several drawbacks: 1. The sensitivity and reliability of electronic leakage protectors are significantly affected by factors such as ambient temperature, humidity, and dust. Furthermore, the circuit breaker itself uses a mechanical tripping mechanism, resulting in high sensitivity but low reliability, making it prone to false tripping over extended periods of use. 2. Electrical equipment often incorporates power filters and feedthrough filters at the power input. The common-mode capacitance in the filter forms a loop with the housing, generating leakage current. Power devices are often placed in close proximity to the heat sink or device housing during heat dissipation design, creating distributed capacitance on the housing. This distributed capacitance also creates a loop with the housing, generating leakage current. Since leakage protectors are highly sensitive to weak leakage currents, the inherent leakage current of these devices may cause them to falsely trip. 3. The leakage protector only activates when the total leakage current exceeds 30mA. It cannot determine the actual leakage current value or detect the leakage current generated by individual devices, hindering fault diagnosis and troubleshooting. 4. The leakage protector is an off-the-shelf product, and its 30mA safety threshold and 0.1s trip time cannot be modified, making it difficult to adjust to the actual needs of the electrical equipment and load, resulting in limited flexibility.

[0004] It is necessary to design a new AC leakage current fault diagnosis method that can not only effectively detect the leakage current caused by equipment insulation failure or cable sheath damage, but also prevent the leakage protection from false operation due to the inherent leakage current of the electrical equipment, thereby ensuring the normal operation of the system. Summary of the Invention

[0005] The purpose of the present invention is to provide an AC leakage current fault diagnosis method to solve the problems of low reliability, poor flexibility and easy misoperation of traditional leakage protector methods.

[0006] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0007] A method for diagnosing an AC leakage current fault, comprising:

[0008] The onboard power distribution box samples the leakage current of the live and neutral wires of the AC electrical equipment to the housing through a zero-sequence current transformer, determines the single sampling value and sampling average value of the leakage current, and determines the stability of the sampling average value; sets the safety protection current and corresponding duration for the instantaneous leakage current and cumulative leakage current;

[0009] The accumulated leakage current detection logic is executed using the single sampling value of the leakage current, the accumulated leakage current safety protection current, and the corresponding duration to determine whether it is an accumulated leakage current fault;

[0010] The instantaneous leakage current detection logic is executed using the difference between the single sampling value of the leakage current and the sampling average value of the previous cycle, the instantaneous leakage current safety protection current, and the corresponding duration to determine whether it is an instantaneous leakage current fault;

[0011] When a cumulative leakage current fault or an instantaneous leakage current fault is detected, the on-board power distribution box automatically cuts off the power input and issues an alarm.

[0012] Furthermore, a dedicated grounding copper plate is designed on the vehicle, and the mounting rack or cabinet of the AC electrical equipment is connected to the vehicle's dedicated grounding wire. The vehicle's dedicated grounding wire is connected to a grounding copper rod on the grounding copper plate, and the grounding copper rod is inserted into the ground; so that in the event that the leakage current protection mechanism fails, the leakage current can quickly flow into the ground.

[0013] Furthermore, the single sampling value and the sampling average value of the leakage current are determined as follows:

[0014] The leakage current sampling module of the onboard power distribution box reads the leakage current value collected by the zero-sequence current transformer once every T1 time, and sends it to the AD chip for calculation. This leakage current value is recorded as a single sampling value;

[0015] After the sampling module continuously reads the single sampling values of a cycle N1 times, it calculates the sampling average value of the current N1 single sampling values and compares it with the single sampling values of these N1 times. If the difference is less than or equal to the sampling value threshold, the sampling average value is recorded; if there is a difference greater than the sampling value threshold, the sampling average value is not recorded.

[0016] Furthermore, the T1 is 10ms, N1 is 32 times, and the sampling threshold is 4mA.

[0017] Furthermore, the stable sampling average value is the inherent leakage current generated during the design process of the electrical equipment, excluding the leakage current caused by equipment insulation failure; by reducing the number and capacity of the common-mode capacitors of the electrical equipment and reducing the distributed capacitance of the system, the purpose of reducing the inherent leakage current is achieved.

[0018] Furthermore, the cumulative leakage current safety protection current is set to 100mA, and the cumulative leakage current safety protection duration is set to 200ms; the instantaneous leakage current safety protection current is set to 25mA, and the instantaneous leakage current safety protection duration is set to 150ms.

[0019] Furthermore, the cumulative leakage current detection logic is:

[0020] When it is detected that the single sampling value of the current leakage current is greater than the cumulative leakage current safety protection current, the filter timing starts; during the filter timing process, sampling is continuously performed in the form of a sliding window to obtain single sampling values. If each single sampling value is greater than the cumulative leakage current safety protection current when the filter timing reaches the cumulative leakage current safety protection duration, it is determined to be a cumulative leakage current fault and the output is cut off.

[0021] Furthermore, the instantaneous leakage current detection logic is:

[0022] When it is detected that the difference △I between the current leakage current single sampling value and the sampling average value of the previous cycle is greater than the instantaneous leakage current safety protection current, the filter timing begins. During the filtering timing process, single sampling values are continuously acquired in the form of a sliding window, and the sampling average value of each cycle and the difference △I between the two are calculated. If each difference △I is greater than the instantaneous leakage current safety protection current during the process of filtering timing reaching the instantaneous leakage current safety protection duration, it is recorded as a fault sampling result. The single sampling value is acquired again and the above process is repeated. If the sampling results for three consecutive times are all faults, it is determined to be an instantaneous leakage current fault and the output is cut off.

[0023] Furthermore, when the difference ΔI is calculated for the first time, the sampling average value of the previous cycle is calculated as 0.

[0024] A terminal device includes a processor, a memory, and a computer program stored in the memory; when the processor executes the computer program, the AC leakage current fault diagnosis method is implemented.

[0025] A computer-readable storage medium stores a computer program; when the computer program is executed by a processor, the AC leakage current fault diagnosis method is implemented.

[0026] Compared with the prior art, the present invention has the following technical features:

[0027] The present invention has a novel design, high reliability, and flexible use, and has been implemented in a certain project. The results show that this method can detect leakage currents caused by equipment or cable insulation faults in real time, and can effectively prevent false operations caused by the high sensitivity of traditional methods, thus meeting the application requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the logic flow for cumulative leakage current detection;

[0029] Figure 2 This is the logic flow for instantaneous leakage current detection. DETAILED DESCRIPTION

[0030] The present invention provides an AC leakage current fault diagnosis method applicable to a vehicle TN-S system, comprising: an on-board power distribution box samples the leakage current of the live wire and neutral wire of a 380V AC electrical device to the housing (earth) through a zero-sequence current transformer, determines a single sampling value and a sampling average value of the leakage current, and determines the stability of the sampling average value; and sets the safety protection current and corresponding duration of the instantaneous leakage current and the cumulative leakage current through the display interface of the on-board power distribution box;

[0031] The single sampling value of the leakage current, the cumulative leakage current safety protection current, and the corresponding duration are used to perform cumulative leakage current detection logic to determine whether it is a cumulative leakage current fault;

[0032] The instantaneous leakage current detection logic is performed using the difference between the single sampling value of the leakage current and the sampling average value of the previous cycle, the instantaneous leakage current safety protection current, and the corresponding duration to determine whether it is an instantaneous leakage current fault;

[0033] When a cumulative leakage current fault or an instantaneous leakage current fault is detected, the onboard power distribution box automatically cuts off the power input and sounds a buzzer alarm to achieve the purpose of leakage protection;

[0034] The vehicle is equipped with a dedicated grounding copper plate. The mounting rack (or cabinet) for AC electrical equipment is bolted to the vehicle's dedicated grounding wire. The vehicle's dedicated grounding wire is securely bolted to a grounding copper rod on the grounding copper plate, and the grounding copper rod is then inserted into the ground. If the leakage current protection mechanism fails, the leakage current can quickly flow into the ground, avoiding the risk of electric shock and effectively protecting the operator's personal safety.

[0035] Figure 1 shows the cumulative leakage current detection logic flow, Figure 2 The instantaneous leakage current detection logic flow is shown; two leakage current detection logic flows are detected simultaneously. When one of them meets the leakage current fault condition, it is determined to be a leakage current fault and the AC input is cut off.

[0036] Depend on Figure 1 、 Figure 2 It can be seen that the leakage current detection logic process is divided into the following parts:

[0037] (1) Leakage current sampling.

[0038] The leakage current sampling module of the onboard power distribution box reads the leakage current value collected by the zero-sequence current transformer every 10ms and sends it to the AD chip for calculation. This leakage current value is recorded as a single sampling value;

[0039] After the sampling module continuously reads 32 single sampling values in a cycle (a total of 320ms), it calculates the sampling average of the current 32 single sampling values and compares it with the 32 single sampling values. If the difference is less than or equal to 4mA (the leakage current is considered stable within 320ms), the sampling average is recorded; if the difference is greater than 4mA (the leakage current is considered unstable within 320ms), the sampling average is not recorded; the resolution of the single sampling value and the sampling average of the leakage current is 0.1mA.

[0040] A stable sampling average value, excluding leakage currents caused by insulation failures in equipment (or cables), is generally an inherent leakage current generated during the design of electrical equipment. This can be achieved by reducing the number and capacity of common-mode capacitors in electrical equipment and lowering the distributed capacitance of the system. However, changes related to product design are difficult to make. However, when the sampling average value reaches or even exceeds the safety protection current of the cumulative leakage current, it must be changed.

[0041] (2) Leakage current safety protection threshold setting.

[0042] According to the recommended band division diagram for the effects of electric current on the human body in GB / T 13870.1, "Effects of Electric Current on Humans and Domestic Animals - Part 1: General," when the current passing through the human body is less than 50 mA and the corresponding duration is within 100 ms, it will not cause harm to the human body. When the current passing through the human body is less than 50 mA and the corresponding duration is within 1 s, ventricular fibrillation generally will not occur. When the current passing through the human body is less than 100 mA and the corresponding duration is within 500 ms, ventricular fibrillation generally will not occur. However, if the current passing through the human body continues to increase and the current-on duration is very short (for example, 500 mA for 100 ms), there is still a risk of inducing ventricular fibrillation.

[0043] During the design, the actual operating conditions and the leakage current characteristics of the system electrical equipment are taken into consideration, and appropriate margins are left to reasonably set the safety protection thresholds; the cumulative leakage current safety protection current is set to 100mA, and the cumulative leakage current safety protection duration is set to 200ms, which is 2.5 times the safety rate compared to the human body current of 100mA and the ventricular fibrillation current with a duration of 500ms; the instantaneous leakage current safety protection current is set to 25mA (can be set to a maximum of 50mA), and the instantaneous leakage current safety protection duration is set to 150ms, which is 12 times the safety rate compared to the human body current of 50mA and the ventricular fibrillation current with a duration of 1s.

[0044] (3) Leakage current detection logic process judgment.

[0045] Cumulative leakage current protection is for the total value of leakage current, and instantaneous leakage current protection is for the leakage current growth change △I. Setting up these two protection mechanisms can ensure safe and reliable power use:

[0046] When it is detected that the single sampling value of the current leakage current is greater than the cumulative leakage current safety protection current of 100mA, the filtering timing starts; during the filtering timing, sampling is continuously performed in the form of a sliding window to obtain single sampling values. If, when the filtering timing reaches the cumulative leakage current safety protection duration of 200ms, each single sampling value is greater than the cumulative leakage current safety protection current of 100mA, it is determined to be a cumulative leakage current fault and the output is cut off.

[0047] When it is detected that the difference △I between the single sampling value of the current leakage current and the sampling average value of the previous cycle is greater than the instantaneous leakage current safety protection current of 25mA, the filtering timing starts; during the filtering timing, the single sampling value is continuously obtained in the form of a sliding window, and the sampling average value of each cycle and the difference △I between the two are calculated; if each difference △I is greater than the instantaneous leakage current safety protection current of 25mA when the filtering timing reaches the instantaneous leakage current safety protection duration of 150ms, it is recorded as a fault sampling result; the single sampling value is obtained again and the above process is repeated. If the sampling results for three consecutive times are all faults, it is determined to be an instantaneous leakage current fault and the output is cut off; among them, when the difference △I is calculated for the first time, the sampling average value of the previous cycle is calculated as 0.

[0048] The instantaneous leakage current fault judgment is based on the fact that the three sampling results are exactly the same (maximum duration 450ms) when the instantaneous leakage current safety protection threshold is met, and the instantaneous leakage current fault can be concluded. This effectively avoids leakage current false protection caused by external interference signals generated on the detection line.

[0049] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for diagnosing AC leakage current faults, characterized in that: include: The onboard power distribution box samples the leakage current of the live and neutral wires of the AC electrical equipment to the housing through a zero-sequence current transformer, determines the single sampling value and sampling average value of the leakage current, and determines the stability of the sampling average value; sets the safety protection current and corresponding duration for the instantaneous leakage current and cumulative leakage current; The accumulated leakage current detection logic is executed using the single sampling value of the leakage current, the accumulated leakage current safety protection current, and the corresponding duration to determine whether it is an accumulated leakage current fault; The instantaneous leakage current detection logic is executed using the difference between the single sampling value of the leakage current and the sampling average value of the previous cycle, the instantaneous leakage current safety protection current, and the corresponding duration to determine whether it is an instantaneous leakage current fault; When a cumulative leakage current fault or an instantaneous leakage current fault is detected, the on-board power distribution box automatically cuts off the power input and issues an alarm.

2. The AC leakage current fault diagnosis method according to claim 1, characterized in that: A dedicated grounding copper plate is designed on the vehicle. The mounting rack or cabinet of the AC electrical equipment is connected to the vehicle's dedicated grounding wire. The vehicle's dedicated grounding wire is connected to a grounding copper rod on the grounding copper plate, and the grounding copper rod is inserted into the ground. This allows the leakage current to quickly flow into the ground if the leakage current protection mechanism fails.

3. The AC leakage current fault diagnosis method according to claim 1, characterized in that: The single sampling value and the sampling average value of the leakage current are determined as follows: The leakage current sampling module of the onboard power distribution box reads the leakage current value collected by the zero-sequence current transformer once every T1 time, and sends it to the AD chip for calculation. This leakage current value is recorded as a single sampling value; After the sampling module continuously reads the single sampling values of a cycle N1 times, it calculates the sampling average value of the current N1 single sampling values and compares it with the single sampling values of these N1 times. If the difference is less than or equal to the sampling value threshold, the sampling average value is recorded; if there is a difference greater than the sampling value threshold, the sampling average value is not recorded.

4. The AC leakage current fault diagnosis method according to claim 3, characterized in that: The T1 is 10ms, N1 is 32 times, and the sampling threshold is 4mA.

5. The AC leakage current fault diagnosis method according to claim 1, characterized in that: The stable sampling average value is the inherent leakage current generated during the design of the electrical equipment, excluding the leakage current caused by equipment insulation failure. The purpose of reducing the inherent leakage current is achieved by reducing the number and capacity of the common-mode capacitance of the electrical equipment and reducing the distributed capacitance of the system.

6. The AC leakage current fault diagnosis method according to claim 1, characterized in that: The cumulative leakage current safety protection current is set to 100mA, and the cumulative leakage current safety protection duration is set to 200ms; the instantaneous leakage current safety protection current is set to 25mA, and the instantaneous leakage current safety protection duration is set to 150ms.

7. The AC leakage current fault diagnosis method according to claim 1, characterized in that: The cumulative leakage current detection logic is: When it is detected that the single sampling value of the current leakage current is greater than the cumulative leakage current safety protection current, the filter timing starts; during the filter timing process, sampling is continuously performed in the form of a sliding window to obtain single sampling values. If each single sampling value is greater than the cumulative leakage current safety protection current when the filter timing reaches the cumulative leakage current safety protection duration, it is determined to be a cumulative leakage current fault and the output is cut off.

8. The AC leakage current fault diagnosis method according to claim 1, characterized in that: The instantaneous leakage current detection logic is: When it is detected that the difference △I between the single sampling value of the current leakage current and the sampling average value of the previous cycle is greater than the instantaneous leakage current safety protection current, the filtering timing starts; during the filtering timing process, the single sampling value is continuously obtained in the form of a sliding window, and the sampling average value of each cycle and the difference △I between the two are calculated; If, during the process of the filter timing reaching the instantaneous leakage current safety protection duration, each difference △I is greater than the instantaneous leakage current safety protection current, it is recorded as a fault sampling result; the single sampling value is obtained again and the above process is repeated. If the sampling results for three consecutive times are all faults, it is determined to be an instantaneous leakage current fault and the output is cut off.

9. The AC leakage current fault diagnosis method according to claim 8, characterized in that: When the difference △I is calculated for the first time, the sampling average value of the previous cycle is calculated as 0.

10. A terminal device comprising a processor, a memory, and a computer program stored in the memory; characterized in that: When the processor executes the computer program, the AC leakage current fault diagnosis method according to any one of claims 1 to 9 is implemented.

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