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There are many reasons that can cause flicker in the power supply. These include external forces such as lightning strikes, fluctuations in the voltage from the external power grid, and short-circuit faults, as well as human-induced factors such as the startup of unbalanced loads and changes in the power supply used by the facility. According to statistics, voltage sags caused by lightning account for over 60%. Due to the randomness and unpredictability of voltage sags, it can be said that voltage sags are inevitable. Fluctuations in power supply caused by external grid issues or internal faults can affect the reliability of power supply to the grid. This can lead to the tripping or damage of sensitive loads in manufacturing facilities, such as numerous contactors, frequency converters, PLCs, and various digital devices. It can also result in the loss of computer data and system crashes, thereby causing disruptions in production processes and imposing significant economic losses on the enterprise; in severe cases, it may even affect the safe and stable operation of the enterprise. Based on the existing protection configuration, in the event of a ground fault, the detection time by the protection device is approximately 60 ms; the tripping time of circuit breakers with conventional spring operating mechanisms is also 60 ms, while the duration of the voltage dip is at least 120 ms or more. Although voltage sags last for a short time, their consequences can be severe. The specific hazards are as follows: (1) When the voltage drops below 70% of its rated value and this condition persists for more than one cycle, the contactor will trip, resulting in a widespread power outage for users. For category I users, the losses caused by such sudden outages are extremely significant. (2) When the voltage drops below 50%, the motor loses its magnetism, and it restarts once the voltage is restored. Especially for users with a large number of high-voltage motors, the simultaneous re-acceleration of these motors exerts a significant strain on the power grid, and in severe cases, it can lead to power outages. (3) For programmable logic controllers (PLCs), when the voltage is below 50%, the PLC will stop operating ； Some I/O devices will be disconnected after just a few cycles once the voltage drops below 90%. This will lead to disruptions in the operation of production lines that use PLCs, resulting in significant economic losses. (4) Voltage sags can cause servers to become unusable and lead to data loss, having a significant impact on information security. Given that voltage sags pose serious safety risks to power grids and industrial customers, Nanjing Guogao Electrical Automation Co., Ltd. has developed the FBVP series of busbar voltage current-limiting protection devices based on rapid fault detection and fast mechanical switches. These devices are designed to address the issue of voltage fluctuations caused by short circuits in branch lines; they can detect such short circuits within 5 milliseconds, quickly disconnect the fast mechanical switches, and engage impedance elements to limit the short-circuit current. This helps to stabilize the voltage of the upstream busbars, ensuring that the voltage at all outlets connected to those busbars remains stable – at least 90% of the normal level. By doing so, the duration of voltage fluctuations in the power grid is reduced, minimizing the risk of disruptions and shutdowns in critical loads within the grid, thereby providing a stable and reliable power supply for industrial operations. The content of this solution: This series of products is designed to address the issue of voltage sags caused by circuit short circuits. Existing solutions require long detection times, and the opening and closing of circuit breaker devices also take time, which results in prolonged voltage sags; as a result, critical loads in the power grid are at risk of shutting down. Busbar fast protection devices can be installed on feeder branches where short-circuit faults are likely to occur. When a temporary short-circuit fault occurs on the feeder side, causing a significant drop in busbar voltage, the busbar protection device quickly detects the line fault and issues a tripping command to the fast-acting switch. The current-limiting reactor is then activated to limit the fault current, allowing the busbar voltage to remain above 90% of its rated value, thereby providing protection for the higher-level busbars. When the secondary fault is cleared, the main protection device will reset, and the system will return to normal operation. When a lower-level fault cannot be resolved properly, the backup regular circuit breaker in the main protection cabinet trips to isolate the fault point, as shown in Figure 1 below. Figure 1 Schematic diagram of a typical application solution for busbar protection in distribution networks. This product addresses the following issues: 1. Limiting short-circuit current to a reasonable level by restricting the system’s short-circuit current, thereby reducing the impact of such currents on critical loads, preventing widespread tripping accidents caused by temporary short-circuit faults, and enhancing the stability of power system operation. 2. Maintain stable bus voltage to prevent significant drops in voltage caused by voltage sags; by keeping the bus voltage stable, it is ensured that other loads on the same bus can operate properly, enabling important loads to withstand low-voltage conditions. 3. Reduce the active and reactive losses of the system. Under normal operation, the switching circuit operates at a low impedance; only in the event of a fault is the current-limiting reactor activated for a short period of time, thereby preventing an increase in system losses resulting from the use of high-impedance devices. This product is a complete set of busbar voltage current-limiting protection equipment. Advanced international technologies are employed in the research of power grid and enterprise auxiliary power systems, as well as in the design and manufacturing of main equipment and the development of control and protection systems, resulting in an excellent overall current-limiting protection performance for this busbar protection equipment and ensuring its reliable quality. The main components of the mother protection complete set include the following devices: 1. Ordinary circuit breakers; 2. Fast circuit breakers; 3. Trigger and drive system for fast switches; 4. Current-limiting reactors. The structure of the control and protection system is shown in Figure 2 below. Figure 2: Electrical system diagram of the mother protection equipment. The current-limiting reactor is connected in parallel across the fast circuit breaker, which is connected in series with the ordinary circuit breaker. The control and protection system collects bus voltage and current limiting values to enable rapid detection of faults. The entire equipment (10kV) is integrated within a metal-enclosed switchgear cabinet. The control and protection system operates the fast circuit breaker opening and closing via optical fiber. The quick switch is one of the core components of busbar protection systems. It operates through electromagnetic repulsion, and its advantages include fast opening and closing speeds: the opening time is less than 1.5 ms, and the rated insulation distance is achieved within 5 ms; the closing time is less than 10 ms, which is significantly lower than the several dozen milliseconds required by conventional circuit breakers for such operations. Thanks to its extremely fast opening speed, it enables the rapid activation of the current-limiting reactor during the first half-wave; moreover, its tolerance to short-circuit currents and its performance in breaking short circuits are superior to those of conventional switches. Fast circuit breakers use a fast mechanism based on electromagnetic repulsion, as shown in Figure 3. It mainly includes a vacuum arc extinguisher chamber, an insulating pull rod K, a moving contact G, a stationary contact H, a opening coil C, a closing coil D, a metal disc (including the pull rod), and a buffering device L, etc. Its main working principle relies on the application of instantaneous currents to the opening coil C and the closing coil D to generate magnetic fields; the eddy current effect of these magnetic fields produces a repulsive force F, thereby enabling rapid movement of the mechanism. The fast switching drive system employs a design based on the combination of capacitor energy storage and power electronics control, and it holds independent intellectual property rights. This control system eliminates the conventional switching operation circuit; signal transmission between it and the protection devices is carried out via optical fibers. The control delay is less than 300 us, which is significantly lower than that of conventional node controls, and it also boasts strong interference resistance. The switching control system receives commands from the protection device and activates the thyristor in the capacitor discharge circuit, enabling the discharge of the energy storage capacitor within just a few dozen microseconds after receiving the command, thus facilitating rapid actuation of the fast switch. The current-limiting reactor is an important component of busbar protection equipment. It features a hollow cast structure; the overall insulation and heat resistance rating required is grade F, while the insulation materials used for the gaps between winding turns and between wire strands must have a heat resistance rating of grade H. The support insulators are of solid rod shape and consist of non-magnetic porcelain. The impedance value can be flexibly configured according to different current-limiting depth requirements, to meet the demands regarding dynamic and thermal stability currents as well as duration. The capacity parameters of the reactor need to be determined through simulation based on the system design parameters. The control and protection device utilizes the mature and stable 32-bit platform provided by Guogao Electric. This platform is widely used in various products such as protection systems, fast switching control systems, and digital substation control and protection systems. This platform is a high-performance, decentralized and distributed system with a user-friendly interface that facilitates functional expansion and supports remote maintenance. Thanks to the use of a 32-bit high-performance CPU and DSP, an internal high-speed bus, and intelligent I/O in the control unit, the system features fast response times and high control precision, enabling it to meet the requirements of the main protection control system for rapid adjustment. A multi-criterion fast fault identification method for short data windows, based on a combination of instantaneous values, slopes, and amplitudes, enables fault detection in less than 5 ms, with accurate results and high reliability. The fast mechanical switch and control protection device feature an integrated design of primary and secondary systems: it abandons the traditional node control method (with transmission delay times of up to 8-10ms) and uses fiber optic Ethernet-based encoding for communication in order to control the opening and closing of the fast switch; the control delay time is less than 300us, granting it strong resistance to interference. The quick switch features a compact design that matches the dimensions of existing conventional switches; it can be integrated with these switches within the same switchgear cabinet. It is compatible with existing conventional switchgear cabinets, offering a compact design and reducing space requirements. It meets users’ personalized needs, and can be used in both new installations and the renovation and expansion of existing stations. The working principle of the fast-acting switch-type bus voltage current-limiting protection device consists mainly of a conventional vacuum circuit breaker, a fast mechanical switch, and a current-limiting reactor. As shown in Figure 3, during normal operation both the ordinary switch and the fast switch are in the closed state and carry out the task of conducting current, resulting in the entire switching circuit being in a low-impedance state. When a short circuit occurs in the system, the fast switch completes the action of achieving the rated insulation clearance within 5 milliseconds, allowing the current to be diverted to the current-limiting reactor within the first cycle and thus serving to limit the current. Thereafter, if the fault disappears within 300 ms (the value can be adjusted according to the actual reactor configuration), a closing command is sent to the fast switch, the current-limiting reactor is disengaged, and the system returns to normal operation ； If the fault persists after 300 ms, a trip command is sent to the ordinary switch to isolate the fault point. Figure 3 shows the diagram of the bus voltage current-limiting protection device, while Figure 4 illustrates the operating waveforms of the bus protection device at different fault moments. After a short-circuit fault occurs, and before and after the current-limiting reactor of the main protection device is activated, the short-circuit current undergoes significant changes. Depending on the timing of the short circuit, the time at which the current-limiting reactor is activated varies. Since the initial stage of a short-circuit fault often contains a large DC component, if the fault occurs within the first 1/2 cycle of a half-wave, it is possible to activate the current-limiting reactor at the end of the first half-wave in order to achieve current limitation ； If a fault occurs at the end of the upper half-wave, the reactor is connected at the next zero point of current in the lower half-wave to achieve current limiting. Figure 5 shows a schematic diagram of the process of a fast switch breaking a short-circuit current. The control and protection device monitors the system current in real time; upon detecting a short-circuit fault in the circuit, it issues a switching-off command after a fault detection delay. After passing the inherent switching time and arcing time, the switch operates to disconnect at the zero crossing of the short-circuit current, at which point the current-limiting reactor is activated, initiating the current-limiting phase. Figure 4: Schematic diagram of the operating waveforms of the main protection and backup protection devices at different fault moments. Figure 5: Schematic diagram of the waveforms during the process of a fast switch breaking a short-circuit current. Summary: This current-limiting protection device limits the system’s short-circuit current, reduces the impact of such currents on critical loads, prevents widespread tripping accidents caused by temporary short-circuit faults, and enhances the operational stability of the power system. At the same time, it prevents significant drops in bus voltage caused by voltage sags, maintains stable bus voltage, ensures that other loads on the same bus can operate normally, and enables important loads to withstand low voltages.