A bus short circuit fault handling device for a frequency converter

Abstract

The utility model discloses a kind of bus short-circuit fault handling devices for frequency converter, belong to short-circuit monitoring protection technical field, the input side of frequency converter is connected to power bus through protection switch, the output side of frequency converter is connected to electric equipment, the device includes bypass device, current transformer, voltage transformer and controller, bypass device is parallel with frequency converter;Voltage transformer is used to monitor the voltage of power bus;Current transformer is connected between frequency converter and protection switch, for monitoring the current flowing through frequency converter;Controller is connected with protection switch, current transformer, voltage transformer and bypass device, controller is used to trigger bypass device when reaching current limit value and bus voltage drop specific percentage in the case of protection switch closing, to bypass frequency converter. Therefore, frequency converter protection shutdown and incoming line circuit breaker tripping can be prevented when bus short-circuit fault occurs, so as to avoid normal power supply area losing power supply.

Description

Technical Field

[0001] This utility model relates to the field of short circuit monitoring and protection technology, and more specifically, to a bus short circuit fault handling device for frequency converters. Background Technology

[0002] In the operation of power systems, short-circuit faults are a common hidden danger threatening the stability of power supply. When a short circuit occurs in the system, the equivalent impedance at the short-circuit point drops instantaneously, and a large amount of short-circuit current surges into the fault circuit in a very short time. According to Ohm's law, the bus voltage will drop sharply due to the voltage drop across the system impedance caused by the short-circuit current, resulting in a voltage sag.

[0003] For frequency converters connected to the bus, their normal operation depends on a stable bus voltage. When a bus voltage dip occurs, the DC-side voltage inside the frequency converter also drops. Due to inertia, the motor continues to rotate at a speed higher than the synchronous speed output by the frequency converter. According to the law of flux conservation, the flux must remain unchanged at the moment of the voltage drop. The stator windings induce a back electromotive force, and the motor transforms into a generator, converting mechanical energy into electrical energy and feeding it back to the DC bus, forming a reverse current. This reverse current may not only exceed the rated current capacity of the frequency converter itself, but also trigger a signal to its protection device. Once the reverse short-circuit current reaches the preset protection threshold of the frequency converter, the frequency converter will initiate a protection shutdown procedure and stop operation.

[0004] At the same time, the incoming circuit breaker will also be affected. Due to the presence of reverse short-circuit current, the waveform and magnitude of the current flowing through the circuit breaker will change, which may trigger the circuit breaker's overcurrent protection, instantaneous overcurrent protection, and other functions. Even if these currents do not originate from a genuine line short-circuit fault, the circuit breaker may still experience abnormal tripping without fault.

[0005] Once the frequency converter shuts down due to protection and the circuit breaker of the equipment's incoming line trips, the previously operating and healthy area will lose power. This will not only force the production equipment in that area to stop operating, causing production interruptions and economic losses, but may also trigger a series of chain reactions. For example, some equipment with extremely high requirements for power supply continuity, such as chemical production plants and medical equipment, may suffer serious consequences such as equipment damage, product scrapping, or even safety accidents if suddenly powered out, leading to a further expansion of the accident scope and bringing huge negative impacts to the entire power system and related industries. Utility Model Content

[0006] In response to the problem that when a short circuit occurs on the power supply bus of electrical equipment equipped with frequency converters, the voltage drop causes the frequency converter protection to stop and the incoming circuit breaker of the equipment to trip, resulting in the loss of power supply to the normal power supply area, this utility model proposes a bus short circuit fault handling device for frequency converters.

[0007] According to one embodiment of this utility model, a bus short-circuit fault handling device for a frequency converter is proposed. The input side of the frequency converter is connected to the power supply bus via a protection switch, and the output side of the frequency converter is connected to the electrical equipment. The bus short-circuit fault handling device includes a bypass device, a current transformer, a voltage transformer, and a controller. The bypass device is connected in parallel with the frequency converter. The voltage transformer is used to monitor the voltage of the power supply bus. The current transformer is connected between the frequency converter and the protection switch to monitor the current flowing through the frequency converter. The controller is electrically connected to the protection switch, current transformer, voltage transformer, and bypass device, and is configured to, when the protection switch is closed, The bypass device is activated when the current exceeds the limit and the bus voltage drops by a certain percentage.

[0008] In a more specific embodiment of the above implementation, the bypass device includes a bidirectional thyristor.

[0009] In a more specific embodiment of the above implementation, the controller is configured to: when the protective switch is closed, The bidirectional thyristor is turned on when the current exceeds the limit and the bus voltage drops by a certain percentage; the bidirectional thyristor is turned off when the protection switch is opened; and the bidirectional thyristor is turned off when the bus voltage recovers when the protection switch is closed.

[0010] In a more specific embodiment of the above implementation, the bypass device includes an ultra-high-speed closing mechanical switch, wherein the closing time of the ultra-high-speed closing mechanical switch is less than 3 milliseconds.

[0011] In a more specific embodiment of the above implementation, the controller is configured to: when the protective switch is closed, The ultra-high-speed closing mechanical switch is closed when the current exceeds the limit and the bus voltage drops by a certain percentage; the ultra-high-speed closing mechanical switch is opened when the protection switch is opened; and the ultra-high-speed closing mechanical switch is opened when the bus voltage recovers while the protection switch is closed.

[0012] In embodiments of this invention, the specific percentage of bus voltage drop is in the range of 15% to 30%.

[0013] The beneficial effects of this utility model are as follows:

[0014] The bus short-circuit fault handling device for frequency converters of this utility model can control the bypass device connected in parallel with the frequency converter when a short-circuit fault occurs on the power supply bus of the equipment with frequency converter. This bypasses the frequency converter to avoid the frequency converter protection shutdown and the equipment incoming circuit breaker tripping due to voltage dips, thus preventing the normal power supply area from losing power.

[0015] The bus short-circuit fault handling device for frequency converters of this utility model can disconnect the bypass device when the bus voltage is restored, thereby enabling the frequency converter to operate normally. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the bus short-circuit fault handling device for frequency converters according to this utility model.

[0017] Figure 2 This is a schematic diagram of one embodiment of the bus short-circuit fault handling device for frequency converters according to the present invention.

[0018] Figure 3 This is a flowchart of the control logic of the controller of the bus short-circuit fault handling device for frequency converters according to this utility model. Detailed Implementation

[0019] like Figure 1 As shown, this is a primary system diagram of a substation. A three-phase short-circuit fault occurs on one of the outgoing lines, and the protection switch SS1 trips quickly. However, the bus voltage still experiences a temporary drop. This drastic voltage change will cause a change in magnetic flux in the relevant circuits and windings of the outgoing line where the frequency converter is located, according to the law of electromagnetic induction, thereby generating an induced electromotive force. When the circuit is in a closed state, this induced electromotive force forms a feedback current. This feedback current is greater than the protection setting value of the outgoing line where the frequency converter is located, thus causing the circuit breaker of that outgoing line to trip. Even if the bus voltage recovers, the frequency converter will eventually stop operating.

[0020] See also Figure 1 In one embodiment of this utility model, a bus short-circuit fault handling device for frequency converters is proposed. The input side of the frequency converter is connected to the power supply bus via a protection switch BK. This protection switch BK is typically a circuit breaker with overload and short-circuit protection functions, which can provide preliminary protection for the circuit to a certain extent. The output side of the frequency converter is connected to electrical equipment, such as various industrial motors, fans, etc. The bus short-circuit fault handling device of this utility model mainly consists of four core components: a bypass device, a current transformer CT2, a voltage transformer PT, and a controller.

[0021] In one embodiment of this utility model, the bypass device is connected in parallel with the frequency converter. Its core function is to quickly establish a new current path when a short circuit fault occurs on the bus, isolate the frequency converter from the system, and ensure that the power transmission between the power supply bus and the electrical equipment is not affected.

[0022] In different embodiments of this utility model, the bypass device has multiple implementations. For example... Figure 2 As shown, in one embodiment, the bypass device uses a bidirectional thyristor, which is a semiconductor device with advantages such as small size, fast response speed, and no contacts, and can complete the conduction and cut-off actions in a very short time; another embodiment uses an ultra-high speed closing mechanical switch. With its special mechanical structure design, this mechanical switch can quickly complete the closing operation when a short circuit fault occurs, and has high current carrying capacity and reliability.

[0023] Preferably, the closing time of the ultra-high-speed closing mechanical switch is less than 3 milliseconds. On the one hand, in a typical industrial power supply system, the time from the occurrence of a short-circuit current to its peak value is usually within 5-10 milliseconds. A closing time of less than 3 milliseconds ensures that the frequency converter is isolated from the faulty circuit by the bypass device before the short-circuit current reaches its destructive peak value, reducing the risk of equipment damage. On the other hand, the protection switch on the input side of the frequency converter, as the main protection of the system, has an inherent mechanical delay in its opening action (usually on the order of tens of milliseconds, such as 10-50 milliseconds). If the closing time of the bypass device is too long, a situation may occur where the protection switch has not yet opened, but the frequency converter has already been damaged by the continuous short circuit. Setting the closing time of the ultra-high-speed closing mechanical switch to less than 3 milliseconds ensures that the bypass device has been activated before the protection switch operates, forming a timing coordination where the bypass operates before the main protection, providing early protection for the frequency converter.

[0024] In one embodiment of this invention, a voltage transformer is used to monitor the voltage of the power supply bus. Its working principle is based on the law of electromagnetic induction, proportionally converting the high voltage of the power supply bus into a low voltage signal, facilitating subsequent acquisition and analysis by the controller. Real-time monitoring of changes in the bus voltage provides crucial information for determining whether a short-circuit fault has occurred in the system.

[0025] In one embodiment of this utility model, a current transformer is connected between the frequency converter and the protection switch to monitor the current flowing through the frequency converter. Current transformers, also based on the principle of electromagnetic induction, convert large currents into small current signals. Their accuracy and reliability directly affect the accurate monitoring of inverter current. Through continuous monitoring... It can promptly detect abnormal increases in current.

[0026] In one embodiment of this utility model, the controller is connected to a protective switch, a current transformer, a voltage transformer, and a bypass device. It is responsible for receiving data collected by each sensor and making judgments and decisions based on preset logic. Preferably, the controller is a 6U controller conforming to the 6U standard size. Specifically, the controller is configured to, when the protective switch is closed, When the current exceeds the limit and the bus voltage drops by a certain percentage, the bypass device is triggered to bypass the frequency converter.

[0027] The current over-limit values ​​described in this article are determined comprehensively based on the parameters of the specific electrical equipment and frequency converter. They are generally set at a certain multiple of the frequency converter's rated current, for example, 1.2 to 1.5 times the rated current. If this value is exceeded, it indicates that the frequency converter may experience abnormal conditions such as protection shutdown.

[0028] This invention sets a specific percentage of bus voltage drop within the range of 15% to 30%. This is because when a short circuit fault occurs, the rapid increase in short circuit current will cause a significant drop in the power supply bus voltage. By setting a reasonable voltage drop percentage threshold, it is possible to effectively distinguish between short circuit faults and normal voltage fluctuations, and avoid false triggering of the bypass device.

[0029] like Figure 3 As shown, when a bidirectional thyristor is used as a bypass device, the controller will send a conduction signal to the bidirectional thyristor when the above triggering conditions are met, so that it quickly conducts, thereby bypassing the frequency converter and stabilizing the DC side voltage of the frequency converter without feedback current. When the protection switch is tripped, it means that the system is in an abnormal operating state or is undergoing maintenance. At this time, the controller will turn off the bidirectional thyristor to prevent accidental current surges. When the bus voltage returns to normal, the controller will turn off the bidirectional thyristor, so that the bidirectional thyristor automatically turns off at the zero-crossing point, allowing the frequency converter to return to normal operation.

[0030] If the bypass device uses an ultra-high-speed closing mechanical switch, the controller will close the protection switch and meet the requirements. When the current exceeds the limit or the bus voltage drops by a certain percentage, the controller will control the ultra-high-speed closing mechanical switch to close quickly and establish a bypass path. When the protection switch opens, the controller will cause the ultra-high-speed closing mechanical switch to open and disconnect the bypass. When the bus voltage recovers, the controller will also control the ultra-high-speed closing mechanical switch to open so that the inverter can be checked and restored.

[0031] This utility model's busbar short-circuit fault handling device, through the coordinated operation of a bypass device, current transformer, voltage transformer, and controller, can respond rapidly when a short-circuit fault occurs on the power supply busbar, minimizing the impact of the fault and effectively improving the system's reliability and stability. Furthermore, the design of different types of bypass devices provides diverse options to meet various application scenarios and needs.

[0032] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited to this. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the inventive spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A bus short-circuit fault handling device for a frequency converter, wherein the input side of the frequency converter is connected to the power supply bus via a protection switch, and the output side of the frequency converter is connected to the electrical equipment, characterized in that, It includes bypass devices, current transformers, voltage transformers, and controllers, among which, The bypass device is connected in parallel with the frequency converter; The voltage transformer is used to monitor the voltage of the power supply bus; The current transformer is connected between the frequency converter and the protection switch to monitor the current flowing through the frequency converter. ; The controller is electrically connected to the protection switch, current transformer, voltage transformer, and bypass device, and is configured to, when the protection switch is closed, The bypass device is activated when the current exceeds the limit and the bus voltage drops by a certain percentage.

2. The bus short-circuit fault handling device for frequency converters according to claim 1, characterized in that, The bypass device includes a bidirectional thyristor.

3. The bus short-circuit fault handling device for frequency converters according to claim 2, characterized in that, The controller is configured to: When the protection switch is closed, The bidirectional thyristor is activated when the current exceeds the limit and the bus voltage drops by a certain percentage. The bidirectional thyristor is turned off when the protection switch is tripped. When the protection switch is closed, the bidirectional thyristor is turned off when the bus voltage is restored.

4. The bus short-circuit fault handling device for frequency converters according to claim 1, characterized in that, The bypass device includes an ultra-high-speed closing mechanical switch, wherein the closing time of the ultra-high-speed closing mechanical switch is less than 3 milliseconds.

5. The bus short-circuit fault handling device for frequency converters according to claim 4, characterized in that, The controller is configured to: When the protection switch is closed, The ultra-high-speed closing mechanical switch is closed when the current exceeds the limit and the bus voltage drops by a certain percentage. In the event that the protection switch is tripped, the ultra-high-speed closing mechanical switch is also tripped. When the protection switch is closed, the ultra-high-speed closing mechanical switch is opened when the bus voltage is restored.

6. The bus short-circuit fault handling device for frequency converters according to any one of claims 1 to 5, characterized in that, The specific percentage decrease in bus voltage is in the range of 15% to 30%.

Images