Generation of inrush current
  A Surge Current is a transient peak current that occurs in a circuit, usually for a short duration, but much higher than the normal operating current. Inrush current is commonly seen in the switching of electrical equipment, the start and stop of power equipment and lightning strikes. The main reasons are as follows:
      Electrical equipment switch operation:
  In the switching process of electrical equipment, especially when high-power equipment (such as motors, transformers, etc.) is started, sudden changes in current can cause surge current. When the device is just started, the voltage is usually not immediately stable, and the current will rise sharply in an instant, resulting in a surge current.
  Power supply voltage fluctuation:
  The fluctuation or sudden change of power grid voltage, especially frequent switching operation, load change, short-circuit recovery, etc., may lead to the generation of inrush current. For example, when a device's load is suddenly disconnected or reconnected, the current will change dramatically for a short period of time, forming a surge.
  Lightning strikes or electrostatic discharge:
  When lightning strikes equipment through the grid or directly through the electrical line, it produces a strong voltage pulse, which in turn causes a surge current. Electrostatic discharge (ESD) is also a common source of inrush current, especially in the operation of electronic products.
  Start and stop of power equipment:
  When some power equipment (such as high-power transformers, distribution switches, etc.) is started and stopped, due to the capacitance and inductance characteristics of the electrical equipment, the current will change instantaneously, resulting in a large surge current.
  Transient load change:
  The sudden start or close of the device in the circuit (such as the start of power tools, electrical equipment) may also cause instantaneous current fluctuations, forming a surge current.
  
Inrush current solution
  Inrush current can have serious effects on electrical equipment, such as damaging sensitive components, shortening equipment life, and even causing system failure. Therefore, it is very important to deal with the inrush current effectively. The following are common inrush current solutions:
  Surge Protector (SPD) :
  The surge protector is a common surge current protection device, which can guide the surge current to the ground when the voltage rises instantaneously, so as to protect the electrical equipment from the damage of overvoltage. SPD is widely used in power system, communication equipment, household appliances and other fields.
  
Types of surge protectors are:
  Surge protector: Used to protect low-voltage electrical equipment, such as household appliances.
  Lightning surge protector: Device for lightning sweep.
  Distribution surge protector: Protects the entire distribution system.
  Current limiting resistors and inductors:
  The current limiting resistor or inductor in series in the circuit can effectively limit the amplitude of the surge current and reduce the impact of the surge on the equipment. Inductors help smooth out current fluctuations, while resistors limit current increases.
  Soft starter:
  For some electric motors or large power equipment, the use of a Soft Starter can smooth the starting process of the equipment and reduce the generation of surge current when starting. The soft starter controls the current surge by adjusting the voltage and the time of the starting process.
  Transformer isolation:
  The use of transformer isolation is a common means of restraining inrush current. By isolating the transformer, the power equipment is isolated from the grid, which can reduce the conduction of inrush current in the grid, while providing a more stable power supply for the equipment.
  Capacitor filter:
  In power systems or electrical equipment, capacitors can be used for filtering to smooth current fluctuations and reduce the impact of inrush current. Capacitors can mitigate sudden changes in voltage and current and reduce fluctuations in system load.
  Suitable grounding system:
  A good grounding of the equipment and the power grid can effectively introduce the surge current to the ground, thereby reducing its impact on the equipment. Especially in power systems, ground wires must be designed to be strong enough to handle possible surge currents.
  Component selection for surge resistant design:
  When designing electrical equipment, the selection of components with surge resistance (such as resistors, capacitors and semiconductor devices with high surge resistance) can effectively reduce the damage of surge current to components.
  Power grid regulation and balance:
  Power companies can also reduce the inrush current to some extent by adjusting the load of the grid, increasing the energy storage system, optimizing the design of the grid and other measures. These adjustment measures can improve the stability of the power grid and reduce the surge caused by the power grid fluctuation.