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Fast switching devices originated from the auxiliary power systems of power plants, and are now widely used in industrial systems, especially in continuous manufacturing industries such as petrochemicals, steel metallurgy, biopharmaceuticals, and semiconductor manufacturing. The disturbance-free quick switching device is applied to dual-power supply systems. Its basic working principle involves rapid identification of the system’s operating status by the device; when a fault occurs in one of the power supplies, it quickly cuts off that faulty supply. Based on an assessment of the power disturbance pattern, it then rapidly connects the backup power supply, ensuring that the loads connected to the faulty section continue to operate without any interruptions or shocks. The application of fast switching technology is predicated on the presence of a large number of motor inductive loads connected to the busbar. When voltage fluctuations occur and the busbar voltage drops, many motors enter a \"free-running\" state; the energy stored in these motors then supplies power back to the busbar. At this point, the busbar retains a high residual voltage that decreases slowly, providing a time window for the fast switching device to act. This device uses the backup power source as a reference to determine in real time the frequency difference, phase difference, and voltage difference (vector difference) between the residual voltage of the busbar after a power loss and that of the backup power source. When these differences meet certain criteria, the device can safely and quickly switch the busbar from the lost power source to the backup power source. A fast switching device is required to enable seamless switching on-site. Currently, some manufacturers in the market have a misconception regarding what seamless switching entails; they believe that simply increasing the switching speed will suffice to achieve this. While speed is indeed important for fast switching devices, another equally crucial factor is switching safety. Achieving a situation in which the loaded equipment continues to operate without any interruptions or shocks during the switching process is what truly constitutes seamless switching. Once safety and speed are established as the criteria for unified switching, we can identify several key factors that determine the success of rapid switching: 1. The inherent initial phase angle difference between the main power supply and the backup power supply: In manufacturing enterprises with dual-circuit power inputs, there is inevitably a certain phase angle difference between the voltages of the two circuits. Experienced manufacturers conduct phase verification on the customer’s dual-input circuits prior to scheme configuration, ensuring that this phase angle difference remains within a specified range (typically 5–10°). Subsequently, the set values are optimized based on this initial phase angle difference data. 2. Starting method: Industrial field environments are becoming increasingly complex. When a power failure occurs, the affected section of the system operates as an isolated unit, and changes in bus voltage are the result of the combined effect of all loads. This requires that the device be able to start quickly and accurately in various complex operating conditions, in addition to starting in the event of a voltage loss. The DCM635G disturbance-free quick switching device includes seven startup modes: manual startup, protection startup, false trip startup, voltage loss startup, no-current startup, reverse power startup, and abnormal frequency and voltage startup. The specific logic is as follows: u is started manually. The manual start mode is primarily used for system switching, incoming line maintenance, and restoration of the incoming line after a fault; it triggers the switching function via a manual button through a digital input. The manual start function of the device is configured with corresponding switching logic for both the bus coupler operating mode and the incoming line operating mode. In the incoming line mode, manual start enables mutual switching between Incoming Line 1 and Incoming Line 2. In the bus coupler mode, “Manual Start 1” is used to initiate the switching between Infeed 1 and the bus coupler, while “Manual Start 2” is used to initiate the switching between Infeed 2 and the bus coupler. u Protection start. The fast main protection contact at the upstream stage on the power supply side is incorporated into the quick-switching device to initiate the switching process. Once the system is fully charged and operating normally, if a signal indicating activation of the upstream main protection is detected, the quick-switching device immediately initiates the switching, disconnects the faulty circuit, and activates the backup power supply. u Mistriggered start. When the system is operating normally after charging is complete, the switch that should remain in the closed position suddenly opens, and the incoming current on that side is below the no-current threshold; as a result, the device triggers an erroneous switching action to close the power supply on the other side, thereby ensuring power supply to the busbar. u file:///C:/Users/MARKET~1/AppData/Local/Temp/ksohtml816/wps10.png Under-voltage start. The device provides two criteria for detecting loss of voltage – line voltage and line current – for the user to choose from, with the selection being made through the “No voltage on line with voltage loss detection” control word. When the “No voltage on incoming line under voltage loss” control word is set to 1, if the device detects that the three-phase voltages of the busbar and the incoming line voltage are both below the preset value for voltage-loss activation, the switching function is activated after a configurable delay. When the control word “No voltage on the incoming line in case of voltage loss” is 0, and it is detected that the voltages of all three phases on the bus are below the voltage loss start threshold and there is no current on the incoming line, the switching function is activated via the preset delay device. This startup mode can be enabled or disabled via the control word in the set value. The voltage loss start logic is as follows: The logic diagram for voltage loss start is available at u file:///C:/Users/MARKET~1/AppData/Local/Temp/ksohtml816/wps11.png; start occurs in the absence of flow. When the device detects that the incoming current changes from a value with current (greater than the no-current start setting) to a value with no current (less than the no-current start setting), and the bus frequency is below the no-current start frequency setting, the device activates its start-switching function after a delay determined by the settings. The flow-free start mode is mainly used in situations where the protection on the incoming line side cannot be connected to the device. Its logic is as follows: flow-free start switching logic diagram u, reverse power start. When the fast protection contact starter without an incoming line is switched, this starting criterion enables rapid switching in the event of a fault. The logic is as follows: file:///C:/Users/MARKET~1/AppData/Local/Temp/ksohtml816/wps12.png Explanation of the reverse power start-up switching logic: 1. Reverse power direction: 225 > arg(Uab/Ic) > 45 or –225