To adapt to different load types and reduce false tripping, the intelligent overload protection of a low-voltage intelligent distribution cabinet (LVIC) requires precise load type identification, which forms the foundation for tailored protection strategies. The cabinet's built-in load signature acquisition module captures key parameters such as the connected load's current waveform, voltage phase difference, and harmonic content in real time. Resistive loads (such as electric heating equipment) exhibit a near-sine wave current waveform with a small phase difference between current and voltage. Inductive loads (such as motors) experience a brief, high-current surge during startup, with the current phase lagging the voltage. Capacitive loads (such as capacitor compensation devices) exhibit a current-voltage-voltage-voltage-voltage-voltage-voltage-voltage-voltage-voltage-compensation-system-leading-current characteristic. By analyzing these differentiated characteristics, the system automatically determines the current load type, avoiding misidentification of specific loads due to the use of a unified protection logic and providing a basis for subsequent precise protection.
To address the startup characteristics of inductive loads (especially motors), the LVIC's intelligent overload protection requires a dynamic delay mechanism to account for the normal inrush current during startup. During motor startup, the current draw can significantly exceed the rated current. However, this overload condition is brief and necessary, making it highly susceptible to false tripping if conventional instantaneous tripping logic is used. In this situation, the low-voltage intelligent distribution cabinet automatically switches to "motor-specific protection mode" based on load identification. It first records the starting current peak and decay trend, then sets a dynamic delay that matches the current decay rate. Initially, the current is allowed to remain high. As the motor speed increases and the current gradually falls back to the rated range, the delay is shortened until the overload protection threshold is restored. This on-demand delay prevents false tripping caused by startup shock while also ensuring timely protection in the event of sustained motor overloads (such as stalls or phase loss), ensuring equipment safety.
For resistive loads (such as resistance furnaces and lighting equipment), overloads often manifest as sustained overcurrent without noticeable surges. Therefore, the intelligent overload protection of the low-voltage intelligent distribution cabinet emphasizes real-time monitoring and filtering to mitigate interference. Resistive loads typically experience minimal current fluctuations, and overloads are often caused by load failures (such as short-circuited heating elements) or abnormal grid voltage. The system monitors current changes at a high sampling frequency and uses digital filtering algorithms to filter out false overload signals generated by transient grid fluctuations (such as short current spikes caused by the startup and shutdown of other equipment). These signals are extremely short-lived and represent no actual overloads. If left unchecked, they can trigger unnecessary tripping. Tripping protection is only initiated when the monitored current continuously exceeds the rated range and meets the overload characteristics of a resistive load, ensuring accurate protection.
For capacitive loads (such as power capacitors and electronic equipment rectifier and filter circuits), the intelligent overload protection of the low-voltage intelligent distribution cabinet (LVIC) requires a complex judgment condition based on voltage parameters to avoid false positives caused by temporary overcurrents caused by capacitor charging and discharging. Current changes in capacitive loads are often closely correlated with voltage changes. For example, when the grid voltage recovers after a sudden drop, capacitors experience a short period of high current charging. Although the current exceeds the rated value, this is a normal recovery process. The low-voltage intelligent distribution cabinet (LVIC) monitors both current and voltage trends. If the current exceeds the threshold but the voltage is recovering, and if the current falls rapidly and steadily with the voltage, it is considered normal charging and discharging, and no tripping is triggered. Only when the current exceeds the threshold and the voltage stabilizes, or when the current continues to rise accompanied by voltage anomalies, is it considered a true overload and protection is activated, eliminating normal fluctuations.
In mixed-load scenarios (where multiple load types are connected to the distribution cabinet simultaneously), the LVIC's intelligent overload protection utilizes a "zone protection + load priority coordination" strategy to prevent false tripping caused by load interactions. The system logically partitions the distribution circuits by load type, independently setting protection parameters for each zone. For example, dynamic delay protection is enabled for the motor circuit, filtering and anti-interference protection is enabled for the lighting circuit, and dual-parameter judgment protection is enabled for the capacitor circuit. This ensures that the protection strategies of each circuit do not interfere with each other. The system also prioritizes loads based on their importance. When multiple circuits show signs of minor overload (for example, when multiple printers in an office area are simultaneously activated, causing the lighting circuit current to slightly exceed the limit), priority is given to ensuring power supply to critical loads such as emergency lighting and key equipment. Overload signals from non-critical loads are temporarily buffered, and a trip decision is made after the fluctuations stabilize, minimizing false trips caused by the combined effects of multiple load fluctuations.
The intelligent overload protection of the low-voltage intelligent distribution cabinet also features adaptive learning capabilities. By recording load operating data over time, it continuously optimizes protection parameters to adapt to dynamic changes in load characteristics. For example, as a motor on a production line ages, its starting current decay rate slows. If the initial protection delay is retained, false trips may occur. The low-voltage intelligent distribution cabinet regularly analyzes the motor's historical startup data and automatically adjusts the dynamic delay time to consistently match the current startup characteristics. If the load type changes (for example, a small motor is connected to the original lighting circuit), the system identifies the load characteristic changes and automatically updates the protection strategy, eliminating the need for manual reconfiguration. This prevents false trips caused by unadjusted parameters after the load change.
Finally, the intelligent overload protection of the low-voltage intelligent distribution cabinet incorporates a fault prediction and early warning mechanism. This provides early warnings through abnormal trend analysis before overload reaches the tripping threshold, reducing tripping caused by non-emergency overloads. The system tracks the slope of load current changes in real time. If the motor current does not exceed the load threshold but shows a slow, continuous upward trend, this could be a sign of bearing wear or insufficient lubrication. In this case, the low-voltage intelligent distribution cabinet will issue a warning signal (flashing indicator light, background prompt) to alert maintenance personnel to investigate. Tripping protection is only triggered if the fault develops to the point where the current rapidly exceeds the threshold, potentially damaging equipment or posing a safety hazard. This "warning first, tripping as a backup" logic ensures equipment safety while minimizing unnecessary tripping and improving power supply continuity.
