An active full-compensation harmonic elimination method for preventing resonance faults induced by grounding disconnection

Abstract

This invention discloses an active full-compensation harmonic suppression method for preventing resonant faults induced by ground fault disconnection. The method includes the following steps: S1. Installing an active full-compensation harmonic suppression device in the system; S2. Real-time acquisition of system bus voltage and zero-sequence voltage, determining if a fault has occurred, identifying whether the fault type is a single-phase ground fault when a fault occurs, and monitoring the time when the fault disappears; S3. When the single-phase ground fault disappears, the active full-compensation harmonic suppression device immediately outputs a clamping zero-sequence voltage, slowly reducing the amplitude of the clamping zero-sequence voltage to the normal operating value before shutting off the output, and continuing to monitor the system's operating status. This invention achieves the purpose of preventing various resonant faults such as ferroresonance and phantom grounding by controlling the injected zero-sequence voltage, completely suppressing resonant faults in their nascent stage, improving the power grid operating environment, and enhancing the operational stability of the power system.

Description

Technical Field

[0001] This invention relates to the field of safe operation technology for 6-66kV power supply systems, and in particular to an active full-compensation harmonic elimination method. Background Technology

[0002] Currently, common harmonic suppression devices include two types: secondary harmonic suppression and primary harmonic suppression. Secondary harmonic suppression involves acquiring and analyzing the voltage signal of the open delta of the PT (potential transformer). When ferroresonance occurs in the system, zero-sequence voltages with different frequency components appear in the open delta of the PT. The device automatically identifies and distinguishes between ferroresonance and grounding, as well as whether it is a sub-frequency resonance or a high-frequency resonance, based on different frequencies and voltage values. Generally, calculations are required before the device can take action and output its output. Primary harmonic suppression involves adding a harmonic suppressor to the primary neutral point of the PT. The neutral point voltage and current act on the harmonic suppressor to limit the current flowing through it, thereby protecting the PT.

[0003] For neutral-point grounded systems with arc-suppression coils, PT resonance is unlikely to occur. However, the arc-suppression coil is an inductive load, making it prone to series resonance with the capacitive load of the system lines to ground. As system capacity increases, the system capacitive current also increases. After a single-phase ground fault disappears, if the damping resistor of the arc-suppression coil is not engaged in time, illusory grounding caused by series resonance can frequently occur, such as... Figure 4 As shown, there is currently no more effective way to deal with illusory grounding; the only solution is to remove the arc suppression coil and then re-engage the coil after the fault disappears.

[0004] Both single and double harmonic suppression methods address faults after resonance has occurred. However, resonance requires specific triggering conditions, such as resonance caused by the disappearance of grounding (the voltage waveform at this time is as follows). Figure 3 As shown), the resonance during switching operations and the disappearance of grounding trigger "phantom grounding" (the voltage waveform at this time is as shown). Figure 4 As shown in the image, oscillations (such as those caused by the transition from one state to another, where the system fails to effectively release excess energy during the transition) are generally triggered. Therefore, if measures are taken before resonance occurs to prevent it from happening, the stable operation of the system can be reliably guaranteed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an active full compensation method for preventing resonance faults induced by grounding disconnection, so as to destroy the resonance occurrence conditions and improve the stability and reliability of power system operation.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0007] An active full-compensation harmonic elimination method for preventing resonance faults induced by grounding disconnection specifically includes the following steps:

[0008] S1. An active full-compensation harmonic elimination device is installed in the system;

[0009] S2. Real-time acquisition of system bus voltage and zero-sequence voltage, and determination of whether a fault has occurred. When a fault occurs, identify whether the fault type is a single-phase ground fault, and monitor the time when the fault disappears.

[0010] S3. When the single-phase ground fault disappears, the active full-compensation harmonic elimination device immediately outputs the clamping zero-sequence voltage, and slowly reduces the amplitude of the clamping zero-sequence voltage to the normal operating value before shutting down the output, and continues to monitor the system operating status.

[0011] In the above-mentioned active full compensation harmonic elimination method for preventing grounding failure-induced resonance faults, in step S2, the active full compensation harmonic elimination device uses a fast fault identification algorithm to monitor the zero-sequence voltage change and identify the occurrence of the fault.

[0012] In the above-mentioned active full-compensation harmonic elimination method for preventing resonance faults induced by grounding failure, the method of slowly reducing the amplitude of the clamping zero-sequence voltage in step S3 is as follows: when the single-phase grounding fault disappears, the active full-compensation harmonic elimination device first gradually reduces the output clamping zero-sequence voltage Us from the calculated value by 20% within tens of milliseconds for the fault exit verification to prevent the fault from recurring; then, the clamping zero-sequence voltage Us is gradually reduced to the normal operating value or equal to 0V within hundreds of milliseconds, so that the system can smoothly recover from the fault state to the normal operating state.

[0013] In the above-mentioned active full compensation harmonic elimination method for preventing resonance faults induced by grounding failure, in step S3, when the active full compensation harmonic elimination device detects that a single-phase grounding fault still exists during the process of reducing the output clamping zero-sequence voltage, it immediately restores the voltage signal to the compensation value output.

[0014] The above-mentioned active full compensation harmonic elimination method for preventing resonance faults induced by grounding disconnection includes an active full compensation harmonic elimination device comprising a grounding transformer, a voltage transformer, an active full compensation device, an active power compensator, and a step-up transformer. The grounding transformer and the voltage transformer are respectively connected to the busbar. The input terminal of the active full compensation device is connected to the output terminal of the voltage transformer. The secondary side of the step-up transformer is connected in series between the neutral point of the grounding transformer and the ground. The primary side of the step-up transformer is connected in parallel to both sides of the active power compensator. The controlled terminal of the active power compensator is connected to the output terminal of the active full compensation device. The active power compensator is also connected to the secondary side of the grounding transformer.

[0015] In the above-mentioned active full-compensation harmonic elimination method for preventing resonance faults induced by grounding disconnection, a high-voltage switch is also connected in series between the secondary side of the step-up transformer and the neutral point of the grounding transformer.

[0016] Due to the adoption of the above technical solutions, the technical progress achieved by this invention is as follows.

[0017] This invention employs a voltage clamping output method to provide energy conversion for the system transitioning from one state to another. Using an active power compensator as the output device, it absorbs remaining capacity by controlling the system's recovery speed during fault recovery, thus resolving resonance problems that may occur during PT resonance, phantom grounding, and other fault recovery processes. It fundamentally eliminates the conditions for resonance to occur, completely resolving the ferroresonance caused by PT saturation, series resonance caused by the disappearance of a single-phase ground fault in a neutral point grounded system via an arc suppression coil, and system bus voltage oscillation caused by the disappearance of a single-phase ground fault. This also prevents PT burnout due to resonance problems and avoids the problem of controlling primary equipment due to phantom grounding, reducing maintenance costs, purifying the power grid operating environment, and improving the stability and reliability of the power system. Attached Figure Description

[0018] Figure 1 This is the electrical schematic diagram of the present invention;

[0019] Figure 2 This is a flowchart of the method described in this invention;

[0020] Figure 3 This is an abnormal waveform diagram of the bus voltage when the fault disappears in a traditional system.

[0021] Figure 4 This is a waveform diagram of a virtual ground fault that occurs when a fault disappears in a traditional system.

[0022] Figure 5 The waveform diagram of the PT resonant fault caused when the fault disappears in a traditional system;

[0023] Figure 6 This is a waveform diagram of the voltage state when the fault disappears during the operation of this invention.

[0024] Among them: JDB. Grounding transformer, PT. Voltage transformer, KZQ. Active full compensation device, KM. High voltage switch, APC. Active power compensator, SYB. Step-up transformer. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] An active full-compensation method for preventing resonance faults induced by grounding disconnection is applicable to 6-66kV distribution networks, including systems with ungrounded neutral points and systems where the neutral point is grounded via an arc-suppression coil and equipped with active intervention arc-suppression devices and active full-compensation arc-suppression devices. The specific method is as follows: Figure 2 As shown, it includes the following steps.

[0027] S1. An active full-compensation harmonic elimination device is installed in the system.

[0028] The active full-compensation harmonic suppression device includes a grounding transformer JDB, a voltage transformer PT, an active full-compensation device KZQ, an active power compensator APC, a step-up transformer SYB, and a high-voltage switch KM. The connection relationships between these components are as follows: Figure 1 As shown, specifically: the grounding transformer JDB and voltage transformer PT are connected to the busbar respectively; the input terminal of the active full compensation device KZQ is connected to the output terminal of the voltage transformer PT; the secondary side of the step-up transformer SYB is connected in series between the neutral point of the grounding transformer JDB and ground; the high-voltage switch is connected in series between the secondary side of the step-up transformer and the neutral point of the grounding transformer; the primary side of the step-up transformer SYB is connected in parallel to both sides of the active power compensator APC; the controlled terminal of the active power compensator APC is connected to the output terminal of the active full compensation device KZQ; and the active power compensator APC is also connected to the secondary side of the grounding transformer.

[0029] Among them, the active full compensation device KZQ is the core equipment of this invention. It can collect the system bus voltage and zero-sequence voltage in real time through the voltage transformer PT, and can control the operation and deactivation of the active power compensator APC, as well as control the clamping zero-sequence voltage change output by the active power compensator APC. The active power compensator APC is connected between the system neutral point and ground through the step-up transformer SYB.

[0030] S2. Real-time acquisition of system bus voltage and zero-sequence voltage, and determination of whether a fault has occurred. When a fault occurs, identify whether the fault type is a single-phase ground fault, and monitor the time when the fault disappears.

[0031] During normal system operation, the KZQ active full compensation device collects bus voltage and zero-sequence voltage in real time and records normal operation data. A fast fault identification algorithm is used to monitor changes in zero-sequence voltage and identify fault occurrences.

[0032] When the active full compensation device KZQ detects a single-phase ground fault, it identifies the fault type by collecting the bus voltage and activates the active power compensator APC output.

[0033] When a single-phase ground fault occurs, the KZQ active full compensation device collects the bus voltage and zero-sequence voltage in real time, and uses a fast fault identification algorithm to monitor the change of zero-sequence voltage and identify when the fault disappears.

[0034] S3. When the active full compensation device KZQ detects that the single-phase ground fault has disappeared, the active full compensation device KZQ immediately adjusts the output of the active power compensator APC to clamp the zero-sequence voltage Us, and slowly reduces the amplitude of the clamping zero-sequence voltage to the normal operating value before shutting down the output, and continues to monitor the system operating status.

[0035] In this step, the method of slowly reducing the clamping zero-sequence voltage amplitude is as follows: when the single-phase ground fault disappears, the active full compensation device KZQ first controls the clamping zero-sequence voltage Us output by the active power compensator APC to gradually reduce it by 20% from the calculated value within tens of milliseconds for the fault exit verification and to prevent the fault from recurring; then the clamping zero-sequence voltage Us is gradually reduced to the normal operating value or equal to 0V within hundreds of milliseconds, so that the system can smoothly recover from the fault state to the normal operating state.

[0036] When the active full compensation harmonic elimination device detects that a single-phase ground fault still exists during the process of reducing the zero-sequence voltage of the output clamping device, it immediately controls the active power compensator (APC) to restore the output voltage signal to the compensation value for output.

[0037] The active full compensation device of the present invention controls the active power compensator and the step-up transformer. Using the active power compensator as the output device, it absorbs the remaining capacity by controlling the recovery speed of the system during the system fault recovery time, so as to prevent the occurrence of various resonance faults such as ferroresonance and phantom grounding, and completely suppress the resonance fault in the bud, improve the power grid operating environment, and improve the stability of the power system operation.

[0038] After the application of this invention, the voltage state waveform diagram when a single-wire grounding fault is cleared is as follows: Figure 6 As shown. With Figures 3 to 5 In comparison, the waveform voltage output by the system is very stable. It can be seen that the present invention can effectively prevent the occurrence of various resonance problems caused by single-wire grounding faults and reliably ensure the normal operation of the system.

Claims

1. An active full compensation resonance mitigation method for preventing ground exit induced resonance fault, characterized in that, Specifically, the following steps are included: S1. An active full-compensation harmonic elimination device is installed in the system; S2. Real-time acquisition of system bus voltage and zero-sequence voltage, and determination of whether a fault has occurred. When a fault occurs, identify whether the fault type is a single-phase ground fault, and monitor the time when the fault disappears. S3. When the single-phase ground fault disappears, the active full-compensation harmonic elimination device immediately outputs the clamping zero-sequence voltage, and slowly reduces the amplitude of the clamping zero-sequence voltage to the normal operating value before shutting off the output and continuing to monitor the system operating status. In step S3, the method for slowly reducing the clamping zero-sequence voltage amplitude is as follows: when the single-phase ground fault disappears, the active full-compensation harmonic elimination device first gradually reduces the output clamping zero-sequence voltage Us from the calculated value by 20% within tens of milliseconds for the fault exit verification and to prevent the fault from recurring; then, the clamping zero-sequence voltage Us is gradually reduced to the normal operating value or equal to 0V within hundreds of milliseconds, so that the system can smoothly recover from the fault state to the normal operating state.

2. The active full compensation resonance avoidance method according to claim 1, wherein, In step S2, the active full-compensation harmonic elimination device uses a fast fault identification algorithm to monitor zero-sequence voltage changes and identify fault occurrences.

3. The active full compensation resonance avoidance method of claim 1, wherein, In step S3, when the active full compensation harmonic elimination device detects that a single-phase ground fault still exists during the process of reducing the zero-sequence voltage of the output clamping device, it immediately restores the voltage signal to the compensation value output.

4. The active full compensation resonance avoidance method of claim 1, wherein, The active full compensation harmonic elimination device includes a grounding transformer (JDB), a voltage transformer (PT), an active full compensation device (KZQ), an active power compensator (APC), and a step-up transformer (SYB). The grounding transformer (JDB) and the voltage transformer (PT) are respectively connected to the busbar. The input terminal of the active full compensation device (KZQ) is connected to the output terminal of the voltage transformer (PT). The secondary side of the step-up transformer (SYB) is connected in series between the neutral point of the grounding transformer (JDB) and the ground. The primary side of the step-up transformer (SYB) is connected in parallel to both sides of the active power compensator (APC). The controlled terminal of the active power compensator (APC) is connected to the output terminal of the active full compensation device (KZQ). The active power compensator (APC) is also connected to the secondary side of the grounding transformer.

5. The active full compensation resonance avoidance method of claim 4, wherein, A high-voltage switch (KM) is also connected in series between the secondary side of the step-up transformer (SYB) and the neutral point of the grounding transformer (JDB).

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