Method for quickly identifying short-circuit fault based on current change rate

Abstract

The invention, which belongs to the technical field of the power system, provides a method for rapidly identifying a short-circuit fault based on a current change rate, comprising the following steps: S1, monitoring a current value Ig of a monitored point in the power system and a change rate di / dt of the current in real time; s2, a current amplitude criterion Ig is set to be larger than or equal to 2Ie, wherein Ie is rated current of the monitored equipment or line; a current change rate criterion di / dt is set to be greater than or equal to 25kA / s; s3, when the current amplitude criterion and the current change rate criterion are met at the same time, it is judged that the power system has a short-circuit fault; according to the method, the current amplitude criterion and the current change rate criterion are adopted, and the two criteria cooperate with each other and are combined for use, so that faults can be accurately identified within several milliseconds to dozens of milliseconds, and time is bought for subsequent protection actions; the two are combined for use, so that misjudgment can be avoided, and only real short-circuit faults are identified.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system, in particular to a method for quickly identifying short-circuit fault based on current rate of change. BACKGROUND

[0002] In the long-term operation of power system, if a short-circuit occurs in a branch, the voltage on the bus connected with the branch will be sharply reduced, and the residual voltage (hereinafter referred to as residual voltage) of the bus is generally lower than 20% of the rated voltage. Only when the circuit breaker of the branch is tripped to cut off the short-circuit fault, the voltage of the bus can be restored. The time from the sharp reduction to the restoration of the bus voltage is the time for the circuit breaker to trip the short-circuit fault, which is about 0.1 second, that is, the time for the microcomputer comprehensive protection to judge the fault (20-30 ms), plus the inherent action time of the circuit breaker (40-80 ms), plus the arc zero-crossing time (about 16 ms). During the time when the bus voltage appears to be concave, the enterprise power supply system is called "flicker". During the occurrence of "flicker", the residual voltage of the bus is very low, which will affect the normal work of the remaining normal feeder circuits, cause some loads without short-circuit fault to lose power, and cause the generator to trip. At the same time, the concave of the bus voltage at the high-voltage side is also transmitted to the low-voltage side, which causes great loss to the normal production of the enterprise.

[0003] As can be seen from the above, the judgment of short-circuit fault is the first step and a key step for the repair of power grid system. However, the current fault judgment time is about 20-30 ms, and there is a possibility of misjudgment. Therefore, how to shorten the time for judging short-circuit fault is the key to shorten the time from the sharp reduction to the restoration of the bus voltage. SUMMARY

[0004] The present application provides a method for quickly identifying short-circuit fault based on current rate of change to solve the technical problems in the prior art.

[0005] To solve the above problems, the method for quickly identifying short-circuit fault based on current rate of change provided by the present application adopts the following technical scheme, which comprises the following steps:

[0006] S1. Real-time monitoring of the current value I of the monitored point in the power system g and the rate of change di / dt of the current;

[0007] S2. Setting current amplitude criterion I g ≥2I e , wherein I e is the rated current of the monitored device or line; and setting current rate of change criterion di / dt≥25kA / s;

[0008] S3. When the current amplitude criterion and the current rate of change criterion are both satisfied, it is determined that a short-circuit fault occurs in the power system.

[0009] As a further improvement, the monitored point comprises a line, a device current monitoring point in the power system.

[0010] The application also provides a bus residual voltage maintaining system based on distributed reactive power compensation, which adopts the above-mentioned method for quickly identifying short-circuit faults based on current change rate and comprises:

[0011] a short-circuit fault identification module for monitoring the current of the power system, determining that a short-circuit fault occurs when the current amplitude criterion I g ≥2I e and the current change rate criterion di / dt≥25kA / s are met;

[0012] a field current switching module comprising a normal field current loop and a residual voltage regulation field current loop, which are switched by a switch K, and the field current is switched to the residual voltage regulation field current when a short-circuit fault occurs;

[0013] a voltage recovery judgment module for monitoring the voltage change rate of the bus, dU M / dt, determining that the bus voltage enters the recovery stage when K=1 and dU M / dt>0;

[0014] a distributed reactive power compensation module comprising a distributed reactive power compensation bus residual voltage controller, a frequency converter and a conversion unit, the distributed reactive power compensation bus residual voltage controller can switch the residual voltage regulation reactive power Q 补 and the normal operation reactive power (0), and the compensation of the reactive power is realized through PI control, coordinate transformation and PWM output;

[0015] a feedback control module comprising a current transmitter LB and a PI controller, which form a closed-loop control to stabilize the bus voltage.

[0016] As a further improvement, the conversion unit comprises a three-phase / two-phase conversion unit, a two-phase conversion unit, a two-phase / three-phase conversion unit and a two-phase inverse conversion unit; the current sensor collects three-phase currents I a , I b , I c , and after being transformed by the three-phase / two-phase conversion unit and the two-phase conversion unit, active current components I p and reactive current components I q are obtained, which are used for feedback of subsequent control logic.

[0017] As a further improvement, it also comprises a phase-locked loop, which is used for tracking the phase of the bus voltage to provide a synchronous reference for subsequent control.

[0018] The application also provides a bus residual voltage maintaining method based on distributed reactive power compensation.

[0019] S1. The short-circuit fault recognition module monitors the current in real time, and when I g ≥2I e and di / dt≥25kA / s, it is determined that a short-circuit fault occurs.

[0020] S2. The excitation current switching module switches the excitation current to residual voltage regulation excitation current, and the distributed reactive power compensation module is switched to residual voltage regulation reactive power Q 补 mode.

[0021] S3. The voltage recovery judgment module monitors the bus voltage change rate dU M / dt, and when K=1 and dU M / dt>0, it is confirmed that the bus voltage enters the recovery stage.

[0022] S4. The feedback control module realizes the stable recovery of the bus voltage through PI control and current feedback in combination with the reactive power output of the distributed reactive power compensation module.

[0023] S5. When the bus voltage recovers to the normal range, the excitation current switching module switches back to the normal excitation current, and the distributed reactive power compensation module switches back to the normal operation reactive power mode.

[0024] The beneficial effects of the above technical solutions of the application are as follows:

[0025] 1. The application uses current amplitude criterion and current change rate criterion, which are used in combination, to accurately identify faults within a few milliseconds to tens of milliseconds, thereby gaining time for subsequent protection actions.

[0026] 2. In the step of improving the bus residual voltage, the synchronous motor and the frequency converter are used to complement each other in terms of technical characteristics, and have the characteristics of fast response speed, high regulation accuracy and high reliability, thereby significantly reducing power outages and equipment damage caused by voltage drop, and reducing the annual power outage loss and equipment maintenance cost of power enterprises and industrial users.

[0027] 3. This invention studies the influence of factors such as the amplitude and duration of different types of short-circuit currents on bus voltage, and analyzes transient faults under different fault types, including three-phase short circuits, two-phase short circuits, and single-phase ground faults. Simultaneously, based on power system transient analysis theory, a bus residual voltage calculation model incorporating distributed generation and load characteristics is established, deriving dynamic response formulas for bus residual voltage after different types of short-circuit faults. Furthermore, combined with power grid operation standards, the minimum threshold for bus residual voltage equipment operation is determined, and quantitative indicators for residual voltage maintenance are established, laying the foundation for research on bus residual voltage maintenance. Attached Figure Description

[0028] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein:

[0029] Figure 1 This is a flowchart of the synchronous motor reactive power regulation and lifting control of residual voltage on the plant busbar in this invention;

[0030] Figure 2 This is a diagram of the automatic control system for reactive power regulation of the frequency converter of the present invention;

[0031] Figure 3 This is a schematic diagram of the distributed reactive power compensation principle for improving bus residual voltage according to the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Those skilled in the art should understand that the embodiments described below are only some, not all, of the embodiments disclosed. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] In existing technologies, during long-term operation of a power system, if a short circuit occurs in a branch, the voltage on the busbar connected to that branch drops sharply. The residual voltage on the busbar is generally less than 20% of the rated voltage. The busbar voltage can only recover when the circuit breaker of that branch breaks the short circuit. The time from the voltage drop to its recovery is the time it takes for the circuit breaker to break the short circuit, which is approximately 0.1 seconds. This period of voltage dip on the busbar is referred to as "voltage slump" in the enterprise power supply system. During the "voltage slump," the low residual voltage on the busbar affects the normal operation of other normal feeder circuits, causing some loads without short circuit faults to lose power and generators to trip. At the same time, this voltage slump on the high-voltage side is also transmitted to the low-voltage side, causing significant losses to normal production. It also hinders the grid connection of some clean energy sources.

[0034] The core issue mentioned above lies in the rapid identification of short circuits. Research has found that using the rate of change of current to determine short circuit faults is faster and more effective than using instantaneous value changes. Therefore, the rate of change of current is adopted as the primary method for rapid identification of whether a short circuit fault has occurred in a system, combined with current amplitude criteria, to quickly and accurately determine whether a short circuit has occurred.

[0035] After quickly identifying a short circuit, a crucial issue is how to rapidly increase the residual voltage of the bus. Synchronous motors operate with two types of current: magnetizing current and armature current. Armature current refers to the rated operating current of the synchronous motor. As long as the load remains constant, the operating current and active power remain unchanged. Research has shown that adjusting the magnetizing current of the synchronous motor can alter its reactive power, thereby increasing the bus voltage. Substations typically contain numerous devices controlled by frequency converters. The core component of a frequency converter is an IGBT (bipolar transistor), so reactive power can also be supplied to the system through the frequency converter's rectifier feedback unit. This method can be performed simultaneously with the reactive power regulation of the synchronous motor, allowing the power system to recover to normal operating conditions more quickly and effectively.

[0036] After introducing the basic principles of the present invention, various non-limiting embodiments of the present invention are described in detail below. Any number of elements in the accompanying drawings is for illustrative purposes only and not for limitation, and any naming is for distinction only and has no limiting meaning.

[0037] The principles and spirit of the present invention will be explained in detail below with reference to several representative embodiments.

[0038] Example 1 of the method for rapidly identifying short-circuit faults based on the rate of change of current provided by this invention:

[0039] like Figures 1-3 As shown, the method for rapidly identifying short-circuit faults based on the rate of change of current includes the following steps:

[0040] S1. Real-time monitoring of the current value at the monitored point in the power system. g and the rate of change of the current, di / dt;

[0041] S2. Set current amplitude criterion I g ≥2I e , where I e The rated current of the monitored equipment or line is used; at the same time, the current change rate criterion is set to di / dt≥25kA / s;

[0042] S3. When both the current amplitude criterion and the current change rate criterion are satisfied, it is determined that a short-circuit fault has occurred in the power system.

[0043] The monitored points include current monitoring points of lines and equipment in the power system.

[0044] This embodiment also provides a bus residual voltage maintenance system based on distributed reactive power compensation, employing the aforementioned method for rapid short-circuit fault identification based on current change rate, including:

[0045] The short-circuit fault identification module is used to monitor the power system current. When the current amplitude criterion I is met... g ≥2I e Furthermore, a short-circuit fault is determined to have occurred when the rate of change of current di / dt ≥ 25 kA / s.

[0046] The excitation current switching module includes a normal excitation current circuit and a residual voltage regulating excitation current circuit. By switching via switch K, the excitation current is switched to the residual voltage regulating excitation current when a short circuit fault occurs.

[0047] The voltage recovery judgment module is used to monitor the bus voltage change rate, dU M / dt, when K=1 and dU M When / dt>0, the bus voltage is determined to have entered the recovery phase;

[0048] The distributed reactive power compensation module includes a distributed reactive power compensation bus residual voltage controller, a frequency converter, and a conversion unit. The distributed reactive power compensation bus residual voltage controller can switch the residual voltage to regulate the reactive power Q. 补 The reactive power (0) during normal operation is compensated by PI control, coordinate transformation and PWM output.

[0049] The feedback control module, consisting of a current transmitter LB and a PI controller, forms a closed-loop control to stabilize the bus voltage.

[0050] The conversion unit includes a three-phase / two-phase conversion unit, a two-phase conversion unit, a two-phase / three-phase conversion unit, and a two-phase / two-phase conversion unit; the current sensor collects the three-phase current I. a I b I c After transformation by the three-phase / two-phase conversion unit and the two-phase conversion unit, the active current component I is obtained. p and reactive current component I q It is used for feedback in subsequent control logic.

[0051] It also includes a phase-locked loop (PLL), which is used to track the phase of the bus voltage and provide a synchronization reference for subsequent control.

[0052] This embodiment also provides a bus residual voltage maintenance method based on distributed reactive power compensation, which adopts the above-mentioned bus residual voltage maintenance system based on distributed reactive power compensation and includes the following steps:

[0053] S1. The short-circuit fault identification module monitors the current in real time, and when I is satisfied... g ≥2I e A short-circuit fault is determined to have occurred when di / dt ≥ 25 kA / s;

[0054] S2. The excitation current switching module switches the excitation current to residual voltage regulated excitation current, while the distributed reactive power compensation module switches to residual voltage regulated reactive power Q. 补 model;

[0055] S3. Voltage Recovery Judgment Module monitors the bus voltage change rate dU M / dt, when K=1 and dU M When / dt>0, it is confirmed that the bus voltage has entered the recovery phase;

[0056] S4. The feedback control module achieves stable recovery of bus voltage through PI control and current feedback, combined with the reactive power output of the distributed reactive power compensation module.

[0057] S5. When the bus voltage returns to the normal range, the excitation current switching module switches back to normal excitation current, and the distributed reactive power compensation module switches back to normal reactive power mode.

[0058] The working principle of the present invention will be described in detail below with reference to the accompanying drawings:

[0059] Figure 1 This is a flowchart of the reactive power regulation and boosting control of the residual voltage of the plant auxiliary busbar for synchronous motors. The left side represents the 10kV three-phase voltage U. a U b U c This is the high-voltage bus voltage; L1, L2, L3, and 380V below are the low-voltage bus voltages. Motor M is the load device in the system, I... f It is the excitation current of the motor (which will be adjusted later). Siemens represents the control or converter in the system, which is responsible for the conversion and control of power.

[0060] The trigger core is located on the right side of motor M, used to identify short-circuit faults and switch the excitation current adjustment strategy. g ≥2I e That is, the actual current I being monitored g ≥Rated current I e If the current is more than twice the normal value, it is considered an overload / short circuit; if di / dt ≥ 25 kA / s, i.e., the rate of change of current is ≥ 25 kA / s, it is considered a short circuit fault (because the short circuit current rises extremely rapidly). When these two conditions are met, the system identifies a short circuit fault and triggers subsequent logic.

[0061] The excitation current switching logic works as follows: Under normal conditions, switch K is connected to the normal excitation current, and the motor operates under conventional excitation. Under fault conditions, after the short-circuit criterion is triggered, switch K switches to the residual voltage regulation excitation current, and at the same time, the "0→1" logic signal is triggered to start the excitation regulation strategy under residual voltage.

[0062] Voltage recovery control and feedback, achieved through voltage change rate criterion and PI control, realizes bus voltage recovery control. M / dt>0, that is, the bus voltage U M The rate of change is positive, meaning the voltage is in the recovery phase, and K=1, meaning the coefficient is 1, indicating that the raw data of the voltage change rate is used directly without proportional correction. When these two conditions are met, a "1→0" logic signal is output to participate in subsequent control. After switching, the logic signal enters the PI controller (proportional-integral controller, used for precise voltage regulation). The current transmitter (LB) collects the current signal and feeds it back to the PI controller, forming a closed-loop control, ultimately achieving stable recovery of the bus voltage.

[0063] The overall logic can be summarized as follows: When a short-circuit fault occurs in the system, i.e., when I is satisfied... g ≥2I e And when di / dt ≥ 25 kA / s, the excitation current switches to residual voltage regulation mode; subsequently, the bus voltage change rate dU is monitored. M When / dt>0 and K=1, the voltage is confirmed to have entered the recovery phase. Through PI control and current feedback, the bus voltage is eventually restored quickly and stably, avoiding the continuous impact of voltage fluctuations on the system.

[0064] Figure 2 This is a diagram of an automatic reactive power regulation control system for a frequency converter. The 10kV busbar is the high-voltage busbar of the system and a core node in power distribution; voltage dips can cause a sudden voltage drop. The frequency converter branch uses current sensors to collect the three-phase current I. a I b I c After passing through the three-phase / two-phase conversion unit and the two-phase conversion unit, the active current component I is obtained. p and reactive current component I q This is used for feedback in subsequent control logic. The frequency converter achieves frequency conversion control of electrical energy through IGBT modules.

[0065] The distributed reactive power compensation bus residual voltage controller is used to detect faults and switch reactive power compensation strategies. When a voltage dip occurs, it triggers the residual voltage to regulate the reactive power Q. 补 During normal operation, it switches to normal reactive power (0, i.e., no additional compensation), and the switching between the two modes is achieved by an electronic switch.

[0066] A phase-locked loop (PLL) is used to track the phase of the bus voltage, providing a synchronization reference for subsequent control.

[0067] PI controller: Reactive power loop, adjusts reactive power Q according to residual voltage. 补 The deviation from the actual reactive power outputs a reactive current command; the voltage loop outputs an active current command based on the deviation between the bus voltage U and the rated voltage.

[0068] Coordinate transformation (two-phase / three-phase transformation): This transforms the current command (I0) in the rotating coordinate system into a single phase. α I β ) is converted into a current command in a three-phase stationary coordinate system (I) a I b I c This provides a basis for PWM output.

[0069] PWM (Pulse Width Modulation) generates switching signals based on the three-phase current command after coordinate transformation, which drive the IGBT module of the frequency converter.

[0070] Final control: The frequency converter outputs corresponding reactive current according to the PWM signal to supplement the reactive power deficit of the bus, thereby improving and stabilizing the residual voltage of the bus and realizing voltage recovery after power fluctuation.

[0071] The overall logic is as follows: When a voltage dip occurs on the 10kV bus (low residual voltage), the distributed reactive power compensation bus residual voltage controller switches to "residual voltage regulation mode" and outputs reactive power compensation commands. After PI control and coordinate transformation, the reactive current is output through the PWM-driven frequency converter to supplement the reactive power deficit of the bus, ultimately achieving rapid and stable recovery of the bus voltage. During normal operation, the system automatically switches to a no-additional-compensation mode to ensure economy and stability.

[0072] Figure 3 This diagram illustrates the application principle of a bus residual voltage maintenance device based on distributed reactive power compensation. The core concept involves centralized control of reactive power compensation devices for various loads via a distributed reactive power compensation bus residual voltage controller. This maintains bus residual voltage and ensures system stability during power outages and other fault scenarios. Multiple control lines connect the reactive power compensation devices for various loads, enabling unified scheduling of the distributed compensation units.

[0073] Residual voltage maintenance logic: When the residual voltage of the bus drops due to faults such as short circuits, the controller will quickly instruct each distributed compensation device to output reactive power to supplement the reactive power deficit of the bus, thereby preventing the voltage from dropping further and maintaining the stability of the residual voltage.

[0074] While various embodiments of the invention have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will occur to those skilled in the art without departing from the spirit and essence of the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in the practice of the invention. The appended claims are intended to define the scope of the invention and therefore cover any modular compositions, equivalents, or alternatives within the scope of these claims.

Claims

1. A method for rapidly identifying short-circuit faults based on the rate of change of current, characterized in that, Includes the following steps: S1. Real-time monitoring of the current value at the monitored point in the power system. g and the rate of change of the current, di / dt; S2. Set current amplitude criterion I g ≥2I e , where I e The rated current of the monitored equipment or line is used; at the same time, the current change rate criterion is set to di / dt≥25kA / s; S3. When both the current amplitude criterion and the current change rate criterion are satisfied, it is determined that a short-circuit fault has occurred in the power system.

2. The method for rapidly identifying short-circuit faults based on the rate of change of current as described in claim 1, characterized in that: The monitored points include current monitoring points of lines and equipment in the power system.

3. A bus residual voltage maintenance system based on distributed reactive power compensation, employing the method for rapid short-circuit fault identification based on current change rate as described in claim 1 or 2, characterized in that, include: The short-circuit fault identification module is used to monitor the power system current. When the current amplitude criterion I is met... g ≥2I e Furthermore, a short-circuit fault is determined to have occurred when the rate of change of current di / dt ≥ 25 kA / s. The excitation current switching module includes a normal excitation current circuit and a residual voltage regulating excitation current circuit. By switching via switch K, the excitation current is switched to the residual voltage regulating excitation current when a short circuit fault occurs. The voltage recovery judgment module is used to monitor the bus voltage change rate, dU M / dt, when K=1 and dU M When / dt>0, the bus voltage is determined to have entered the recovery phase; The distributed reactive power compensation module includes a distributed reactive power compensation bus residual voltage controller, a frequency converter, and a conversion unit. The distributed reactive power compensation bus residual voltage controller can switch the residual voltage to regulate the reactive power Q. 补 The reactive power (0) during normal operation is compensated by PI control, coordinate transformation and PWM output. The feedback control module, consisting of a current transmitter LB and a PI controller, forms a closed-loop control to stabilize the bus voltage.

4. The bus residual voltage maintenance system based on distributed reactive power compensation according to claim 3, characterized in that: The conversion unit includes a three-phase / two-phase conversion unit, a two-phase conversion unit, a two-phase / three-phase conversion unit, and a two-phase / two-phase conversion unit; the current sensor collects the three-phase current I. a I b I c After transformation by the three-phase / two-phase conversion unit and the two-phase conversion unit, the active current component I is obtained. p and reactive current component I q It is used for feedback in subsequent control logic.

5. The bus residual voltage maintenance system based on distributed reactive power compensation according to claim 4, characterized in that: It also includes a phase-locked loop (PLL), which is used to track the phase of the bus voltage and provide a synchronization reference for subsequent control.

6. A method for maintaining bus residual voltage based on distributed reactive power compensation, employing a bus residual voltage maintenance system based on distributed reactive power compensation as described in any one of claims 3 to 5, characterized in that, Includes the following steps: S1. The short-circuit fault identification module monitors the current in real time, and when I is satisfied... g ≥2I e A short-circuit fault is determined to have occurred when di / dt ≥ 25 kA / s; S2. The excitation current switching module switches the excitation current to residual voltage regulated excitation current, while the distributed reactive power compensation module switches to residual voltage regulated reactive power Q. 补 model; S3. Voltage Recovery Judgment Module monitors the bus voltage change rate dU M / dt, when K=1 and dU M When / dt>0, it is confirmed that the bus voltage has entered the recovery phase; S4. The feedback control module achieves stable recovery of bus voltage through PI control and current feedback, combined with the reactive power output of the distributed reactive power compensation module. S5. When the bus voltage returns to the normal range, the excitation current switching module switches back to normal excitation current, and the distributed reactive power compensation module switches back to normal reactive power mode.

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