How is the overcurrent protection mechanism of an electromagnetic heating furnace triggered and restored?
Release Time : 2025-11-06
The overcurrent protection mechanism of an electromagnetic heating furnace is one of its core design features for safe operation. It primarily prevents damage from overloads or short circuits by real-time monitoring of current changes, triggering protective actions, and implementing automatic recovery. This mechanism involves four key stages: current sampling, comparison and judgment, protection execution, and state recovery. These stages work together to ensure the stable operation of the electromagnetic heating furnace under abnormal conditions.
The current sampling stage is the foundation of overcurrent protection. It collects the current value of the main circuit of the electromagnetic heating furnace in real time through a current transformer or a resistor divider network. The current transformer uses the principle of electromagnetic induction to proportionally convert a large current into a small current signal, facilitating subsequent circuit processing. The resistor divider network divides the voltage from the main circuit using a series precision resistor, resulting in a voltage signal proportional to the current. Both sampling methods must have high accuracy and linearity to ensure accurate acquisition of the current value, providing a reliable basis for subsequent comparison and judgment.
The comparison and judgment stage is the core of overcurrent protection. It uses a dedicated comparator chip or a comparator module built into the main control chip to compare the sampled current signal with a preset overcurrent threshold in real time. When the current exceeds the threshold, the comparator outputs a high-level signal, triggering the protection circuit. If the current is within the safe range, it outputs a low-level signal, and the equipment operates normally. The overcurrent threshold setting needs to comprehensively consider the rated power, load characteristics, and safety margin of the electromagnetic heating furnace, and is typically set to 1.2-1.5 times the rated current to balance equipment efficiency and safety.
The trigger protection stage is the execution phase of overcurrent protection. When the comparator outputs a high-level signal, the protection circuit immediately activates. Common protection methods include: cutting off the IGBT (Insulated Gate Bipolar Transistor) drive signal to turn off the IGBT and stop energy transfer; reducing the PWM (Pulse Width Modulation) duty cycle to reduce output power; or employing multiple protection measures simultaneously to ensure the equipment quickly recovers from the overcurrent state. Some high-end electromagnetic heating furnaces also have graded protection functions, adopting different protection strategies according to the severity of the overcurrent, such as reducing power for minor overcurrent and shutting down directly for severe overcurrent.
The automatic recovery stage is an intelligent design of overcurrent protection, implemented through delay circuits or software algorithms. When the protection mechanism is triggered, the equipment does not restart immediately but enters a delay state, typically lasting several seconds to tens of seconds. During this period, the protection circuit continuously monitors the current value. If the current returns to normal, it automatically resumes operation after the delay; if the current still exceeds the limit, it maintains the protection state or triggers a higher level of protection. This design prevents the equipment from repeatedly restarting while the overcurrent fault remains, reducing mechanical stress damage to components.
The overcurrent protection mechanism of an electromagnetic heating furnace also needs to consider interference immunity. In practical applications, factors such as power grid fluctuations and sudden load changes may cause instantaneous current exceedances, but these are not actual faults. Therefore, the protection circuit typically integrates a filter module and a hysteresis comparator. The filter module filters out high-frequency noise, while the hysteresis comparator sets upper and lower thresholds, triggering protection only when the current consistently exceeds the upper threshold or falls below the lower threshold, avoiding false triggering due to instantaneous interference.
The reliability of the overcurrent protection mechanism also depends on the selection and layout of components. The current transformer must possess high precision and low phase error characteristics; the comparator must be selected as a model with low offset voltage and high response speed; the IGBT drive circuit must integrate overcurrent protection to ensure IGBT turn-off within microseconds. Furthermore, the circuit board layout must adhere to electromagnetic compatibility principles, separating high-current paths from sensitive signal paths to reduce parasitic coupling and improve the stability of the protection mechanism.
The overcurrent protection mechanism of the electromagnetic heating furnace achieves accurate identification and rapid handling of overcurrent faults through the close coordination of current sampling, comparison and judgment, protection execution, and automatic recovery. This mechanism not only ensures the safe operation of the electromagnetic heating furnace but also enhances the user experience through intelligent recovery functionality, making it an indispensable core technology for modern electromagnetic heating equipment.