Urban rail transit rectifier protection device and method

Abstract

The application provides a kind of urban rail transit rectifier protection method, comprising the following steps: S1: measuring the current value of all rectifier diodes of rectifier;S2: respectively calculate the current maximum value and the current effective value of the current value of each rectifier diode within the time setting value, and compare and distinguish with the current setting value respectively;S3: the result of discrimination meets the fault discrimination condition, then control the AC side circuit breaker and the DC side circuit breaker trip.And the device is characterized by: including current transformer and protector, the protector is connected with a plurality of current transformers, the current transformer is used to measure the current value of the rectifier diode of rectifier, the output of the protector is connected with AC side circuit breaker, DC side circuit breaker.The application fills the blank of grounding fault protection of rectifier transformer secondary side AC ungrounded system.

Description

Technical Field

[0001] This invention belongs to the field of urban rail transit, and specifically relates to a rectifier protection device and method for urban rail transit. Background Technology

[0002] The traction substation of urban rail transit rectifies the power from the medium-voltage AC network to obtain DC power, which is then supplied to the traction trains through the overhead contact line. A typical traction substation includes two medium-voltage AC power supplies, two 12-pulse rectifier units, two DC incoming circuit breakers, and four feeder circuit breakers. Two of the rectifier units are connected in parallel to form an equivalent 24-pulse circuit. The traction substation and the traction network together constitute the traction power supply system. Adjacent traction substations on the main line provide bilateral power supply to the main line's overhead contact line. The rectifier units are a critical component of the traction substation; faults during operation must be accurately identified and protected against.

[0003] Existing high-voltage side current protection devices for rectifier transformers cannot effectively identify certain faults, specifically: Fault 1: A single-phase ground fault occurs outside the equipment in the AC cable from the secondary side of the rectifier transformer to the rectifier; the 35kV side current protection cannot detect this fault. Fault 2: An open-circuit fault occurs in one of the rectifier bridge arms inside the rectifier; the 35kV side current protection cannot detect this fault. Fault 3: A short-circuit fault occurs in one of the rectifier bridge arms inside the rectifier; protection is provided by the fuses of each rectifier bridge arm, with the 35kV side current protection providing backup protection, but the protection time is relatively long, posing a risk of burning out the entire equipment. Therefore, the existing traction power supply system has relay protection blind spots; once such faults occur, the system operates with these defects, which is extremely dangerous. Summary of the Invention

[0004] This invention addresses the technical problems existing in the prior art by providing a protection device and method for rectifiers in urban rail transit, filling the gap in grounding fault protection for AC ungrounded systems on the secondary side of rectifier transformers. When used in conjunction with traditional fuses, it provides more comprehensive protection for rectifiers.

[0005] The technical solution adopted in this invention is: a method for protecting rectifiers in urban rail transit, comprising the following steps:

[0006] S1: Measure the current value of all rectifier diodes in the rectifier;

[0007] S2: Calculate the maximum current value and effective current value of each rectifier diode within the time setpoint, and compare them with the current setpoint respectively;

[0008] S3: If the judgment result meets the fault judgment condition, then control the AC side circuit breaker and the DC side circuit breaker to trip.

[0009] Furthermore, the fault detection conditions include:

[0010] (1) If the maximum current of one rectifier diode is less than the current setting I1, while the maximum current of the other rectifier diodes is greater than the current setting I1, it is determined that the rectifier diodes have an open circuit fault.

[0011] (2) If the effective current value of a certain rectifier diode exceeds the current setting value I2, it is determined that the rectifier diode has a short circuit fault; at the same time, calculate the effective current value of all lower bridge arm rectifier diodes in the rectifier bridge, and calculate the difference between the effective current value of two of the lower bridge arm rectifier diodes and the other rectifier diodes in the same group of rectifier bridges in the previous conduction period. When all the differences exceed the current setting value I3, it is determined that an AC side fault has occurred.

[0012] (3) The difference between the effective current values ​​of two rectifier diodes and the effective current values ​​of the other rectifier diodes exceeds the current setting value I3.

[0013] If the judgment result meets any of the aforementioned fault judgment conditions, then the AC side circuit breaker and the DC side circuit breaker will trip.

[0014] Specifically, I1 = 30A; I2 = 5kA; I3 = 80A.

[0015] The technical solution adopted in this invention is: a rectifier protection device for urban rail transit, including a current transformer and a protector. The protector is connected to multiple current transformers. The current transformers are used to measure the current value of the rectifier diodes of the rectifier. Each current transformer measures the current value of one rectifier diode. The output of the protector is connected to an AC side circuit breaker and a DC side circuit breaker.

[0016] Furthermore, the protector includes an analog input module, an A / D conversion module, a CPU, a memory, a digital output module, and a power supply module. The analog input module is connected to the CPU through the A / D conversion module. The CPU is connected to the memory and the digital output module respectively. The power supply module supplies power to the protector.

[0017] Furthermore, the protector also includes an Ethernet module and panel indicator lights, and the CPU is connected to the Ethernet module and panel indicator lights respectively.

[0018] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention does not alter the original rectifier structure. It utilizes a current transformer to collect current data from the rectifier diodes. By distinguishing between the maximum and effective current values, it achieves protection against AC side faults, rectifier bridge arm open-circuit faults, and internal short-circuit faults in the rectifier. The protection output directly trips the high-voltage AC side circuit breaker and the DC side circuit breaker, interrupting the fault in a short time and preventing the accident from escalating. This invention fills the gap in grounding fault protection for AC ungrounded systems on the secondary side of rectifier transformers. Combined with traditional fuses, it provides more comprehensive rectifier protection. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the external connections of the protection device according to an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram showing the connection between the protection device and the current transformers of each rectifier bridge arm in an embodiment of the present invention.

[0021] Figure 3 This is a structural block diagram of the protector of the protection device according to an embodiment of the present invention;

[0022] Figure 4 This is a flowchart of the protection method according to an embodiment of the present invention;

[0023] Figure 5 This is a waveform diagram of the rectifier diode current under normal conditions according to an embodiment of the present invention;

[0024] Figure 6 This is a waveform diagram of the rectifier diode current when the rectifier bridge arm V11 is open-circuited according to an embodiment of the present invention.

[0025] Figure 7 This is a waveform diagram of the rectifier diode current when the rectifier bridge arm V11 has an internal short-circuit fault according to an embodiment of the present invention.

[0026] Figure 8 This is a waveform diagram of the rectifier diode current when there is an AC side fault (C relative to ground) according to an embodiment of the present invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Embodiments of the present invention provide a rectifier protection device for urban rail transit, such as... Figure 1-2As shown, it includes current transformers and protectors. The input terminal of the rectifier transformer TB is connected to the 35kV bus via the AC 35kV side circuit breaker 101, and the output terminal is connected to the input terminal of the rectifier R. The positive output of the rectifier R is connected to the positive bus via the DC side circuit breaker 201, and the negative output is connected to the DC negative bus. The output terminal of the protector is connected to the tripping circuits of the AC 35kV side circuit breaker 101 and the DC side circuit breaker 201. The input terminal of the protector is connected to 12 current transformers TA11-TA16 and TA21-TA26. The current transformers are used to measure the current value of the rectifier diodes of the rectifier R. Each current transformer measures the current value of one rectifier diode. Specifically, current transformers TA11-TA16 and TA21-TA26 measure the current values ​​of rectifier diodes V11-V16 and V21-V26, respectively.

[0029] like Figure 3 As shown, the protector includes an analog input module, an A / D conversion module, a CPU, a memory, a digital output module, a power supply module, an Ethernet module, and panel indicator lights. The analog input module is connected to the CPU through the A / D conversion module. The CPU is connected to the memory, the digital output module, the Ethernet module, and the panel indicator lights. The power supply module supplies power to the protector.

[0030] The analog current values ​​collected by current transformers TA11-TA16 and TA21-TA26 are converted by an A / D conversion module and then calculated and logically judged by the CPU. When the judgment result meets the fault judgment conditions, the CPU controls the AC 35kV side circuit breaker 101 and the DC side circuit breaker 201 to trip, thereby achieving protection.

[0031] The protection method adopted by the aforementioned urban rail transit rectifier protection device, taking the commonly used 35 / 1.18 / 1.18kV rectifier transformer TB in urban rail transit systems as an example, illustrates the logical judgment process, such as... Figure 4 As shown, it includes the following steps:

[0032] Measure the current values ​​of all rectifier diodes in the rectifier. Each rectifier bridge arm of the rectifier transformer TB conducts for 1 / 3 of the entire cycle. At any given moment, two diodes in a single rectifier bridge are simultaneously conducting, forming an equivalent 6-pulse rectification. Four diodes in two rectifier bridges are simultaneously conducting, forming an equivalent 12-pulse rectification. The rectifier diode current waveforms are as follows: Figure 5 As shown.

[0033] Calculate the maximum and effective current values ​​of each rectifier diode within the time setpoint, and compare them with the current setpoint respectively. If the judgment result meets the fault judgment condition, control the AC side circuit breaker and DC side circuit breaker to trip.

[0034] (1) Identification of open circuit faults in rectifier bridge arms:

[0035] When one of the rectifier diodes is open-circuited, the current flowing through the current transformer will remain zero, while the other rectifier diodes will continue to conduct normally. Taking the open-circuit condition of rectifier diode V11 as an example, the current waveforms of the corresponding rectifier diodes measured by current transformers TA11-TA16 are as follows: Figure 6 As shown.

[0036] Therefore, by monitoring the current waveforms of the 12 rectifier bridge arms and recording the maximum current value of each bridge arm within 100ms, the open-circuit rectifier diode can be identified and protection can be implemented. The specific fault identification conditions and protection are shown in Table 1.

[0037] Table 1. Fault identification conditions and protection table for rectifier bridge arm open circuit faults.

[0038]

[0039]

[0040] (2) Identification of internal short-circuit faults in bridge arms:

[0041] Taking the breakdown of rectifier diode V11 as an example, at this time, rectifier diodes V11, V13, and V15 all experience reverse current at different times, with waveforms as follows: Figure 7 As shown.

[0042] The amplitude of the reverse current is approximately equal to the phase-to-phase short-circuit current on the 1.18kV side of the rectifier transformer. The theoretical calculated values ​​of the short-circuit current are shown in the table below.

[0043] Table 2. Theoretical Calculation Values ​​of Short-Circuit Current

[0044]

[0045] Therefore, by monitoring the current waveforms of the 12 rectifier bridge arms and determining whether the effective current value of each bridge arm reaches the short-circuit current, the short-circuited bridge arm can be identified and protection can be implemented. The specific fault identification conditions and protection measures are shown in Table 3.

[0046] Table 3. Criteria and Protection Measures for Short Circuit Faults Inside Bridge Arms

[0047]

[0048] (3) Identification of AC side faults:

[0049] Taking a ground fault on phase C of the rectifier's AC input side as an example, the current in the current transformers TA12 and TA14 corresponding to the rectifier bridge changes abruptly, while the current waveforms of other rectifier diodes are normal, as shown in the waveform below. Figure 8As shown. The reason is that when phase C of the AC circuit is short-circuited to ground, the current loop path changes, and part of the current flows as follows: phase C → ground → rail → negative pole (L-) → phase A or phase B.

[0050] At this time, the effective value of the current in the current transformer V14 is TA14 = In + In / (R2 x sin(π / 3))(A). For newly opened lines, the rail insulation to ground meets the standard, and R2 = 15Ω; for lines that have been in operation for a period of time, the rail insulation to ground is not ideal, and R2 = 1Ω; if the rail potential limiting device is closed, R2 is short-circuited, and R2 ≈ 0.1Ω. The theoretical calculations for different cases of R2 are shown in the table below.

[0051] Table 4. Theoretical calculation values ​​of R² for different cases.

[0052]

[0053] Therefore, by monitoring the current waveforms of the 12 rectifier bridge arms, recording the effective current value of each bridge arm, and subtracting it from the effective current value of the previous conduction period, if the difference is greater than a set value, the short-circuited bridge arm can be identified and protection can be implemented. The specific fault identification conditions and protection are shown in Table 5.

[0054] Table 5 Fault Judgment Criteria and Protection Measures for the AC Side

[0055]

[0056]

[0057]

[0058] The present invention has been described in detail above through embodiments, but the content described is only an exemplary embodiment of the present invention and should not be considered as limiting the scope of the present invention. The scope of protection of the present invention is defined by the claims. Any technical solutions designed by those skilled in the art using the technical solutions described in the present invention, or designed by those skilled in the art under the inspiration of the technical solutions of the present invention, within the substance and protection scope of the present invention, to achieve the above-mentioned technical effects, or any equivalent changes and improvements made to the scope of the application, should still fall within the patent protection scope of the present invention.

Claims

1. A method for protecting a rectifier of urban rail transit, characterized in that: The method comprises the following steps: S1: measuring the current value of all rectifier diodes of the rectifier; S2: calculating the current maximum value and the current effective value of each rectifier diode within a time limit, respectively, and comparing them with the current limit value, respectively; S3: if the result of the discrimination meets the fault discrimination condition, controlling the AC side circuit breaker and the DC side circuit breaker to trip; The fault discrimination condition comprises: (1) the current maximum value of a certain rectifier diode is less than the current limit value I1, and the current maximum value of the rest of the rectifier diodes is greater than the current limit value I1, which determines that the rectifier diode has a circuit breaking fault, (2) the current effective value of a certain rectifier diode exceeds the current limit value I2, which determines that the rectifier diode has a short circuit fault; meanwhile, the current effective values of all lower bridge arm rectifier diodes in the rectifier bridge are calculated, and the difference between the current effective values of two lower bridge arm rectifier diodes and the current effective values of other rectifier diodes in the same group of rectifier bridge in the previous conduction period is calculated, when all the differences exceed the current limit value I3, it is determined that an AC side fault has occurred; (3) the difference between the current effective values of two rectifier diodes and the current effective values of the rest of the rectifier diodes exceeds the current limit value I3; If the result of the discrimination meets any of the fault discrimination conditions, the AC side circuit breaker and the DC side circuit breaker are controlled to trip.

2. The method of claim 1, wherein: I1=30A; I2=5kA; I3=80A.

3. The urban rail transit rectifier protection device applied to the urban rail transit rectifier protection method of claim 1, characterized in that: The current transformer and the protector are connected, the current transformer is used to measure the current value of the rectifier diode, and the output of the protector is connected with the AC side circuit breaker and the DC side circuit breaker.

4. The urban rail transit rectifier protection device of claim 3, wherein: The protector comprises an analog input module, an A / D conversion module, a CPU, a memory, a switching output module and a power module, the analog input module is connected with the CPU through the A / D conversion module, the CPU is connected with the memory and the switching output module, respectively, and the power module supplies power to the protector.

5. The urban rail transit rectifier protection device of claim 4, wherein: The protector further comprises an Ethernet module and a panel indicator, and the CPU is connected with the Ethernet module and the panel indicator, respectively.

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