Surge Protective Device (SPD) is a device used to protect electronic equipment from power surges or transient voltages. They are connected in parallel with the load power circuit that needs protection and can also be used in power supply networks at all levels. This article will delve into the working principle of surge protective devices and their important role in electrical systems.
Surge protective devices control transient voltages by diverting or limiting surge currents, protecting sensitive electronic equipment connected to them, such as computers, televisions, washing machines, and safety circuits (such as fire detection systems and emergency lighting). These devices contain sensitive electronic circuits that are prone to damage from transient overvoltages; thus, surge protective devices play a crucial role in protecting electrical installation systems.
The primary function of the surge protective device (SPD) is to protect electrical systems and equipment from surge events by limiting transient voltages and diverting surge currents. Surges can come from external sources, the most intense usually being lightning; they can also come from internal electrical load switching. These internal surges (accounting for 65% of all transients) include sources such as load turning on and off, relay and circuit breaker operations, heating systems, motors, and office equipment.
Without proper SPD, transient events can damage electronic equipment and lead to costly downtime. Therefore, the importance of surge protective devices in protecting electrical equipment cannot be overstated.
In the most basic sense, when a transient voltage appears on the protected circuit, SPD will limit the transient voltage and divert the current back to its source or ground. To achieve this, the SPD must contain at least one nonlinear component that switches between high impedance and low impedance states under different conditions.
Under normal operating voltages, the SPD is in a high impedance state and does not affect the system. When a transient voltage appears on the circuit, the SPD switches to a conduction state (low impedance), diverting the surge current back to its source or ground, thus limiting or clamping the voltage to a safer level. After the transient transfers, the SPD automatically resets back to its high impedance state.
Working Principle of SPD
Surge protective devices contain at least one nonlinear component (such as a varistor or spark gap) whose resistance varies with the applied voltage. Their function is to divert discharge or pulse currents and limit overvoltages to downstream devices.
In the absence of a surge, the surge protection device has no effect on the system it is installed in. It acts as an open circuit, maintaining isolation between live conductors and ground.
When a voltage surge occurs, the surge protection device will reduce its impedance in nanoseconds and divert the surge current. At this point, the SPD behaves like a closed circuit, short-circuiting the overvoltage and limiting it to values acceptable to the electrically connected downstream equipment.
Once the pulse surge ceases, the surge protection device will restore its original impedance and return to the open circuit state, continuing to monitor the voltage conditions in the electrical system.
Selection Principle of Surge Protector in Distribution BoxJune 20, 2022(1) The voltage protection level Up of SPD should always be less than the impulse withstand voltage Uc of the protected equipment, and greater than the maximum operating voltage Us of the power grid o...viewAntenna Surge Protective Device for Cellular Base StationsJuly 3, 2024Currently, the world is experiencing significant changes, including planning and establishing new mobile radio sites, as well as revitalizing and expanding existing network infrastructure. In the era ...viewDo Surge Protectors Stop Electrical Fires?May 14, 2025Surge protectors (SPDs) can effectively reduce the risk of electrical fires caused by surges when designed, installed and maintained in accordance with international standards (such as the IEC 61643 s...viewThe role of ground potential counterattack protectorSeptember 28, 2021When the power distribution system is struck by lightning and when switching on or off inductive loads or large loads, it often produces high operating overvoltages, also called surge voltages. Surges...viewChoosing The Right Lightning Protection Device For Building ResilienceJanuary 10, 2024Ensuring the safety and resilience of buildings against lightning strikes is a paramount consideration in structural design and risk management. The choice of a lightning protection device for buildin...viewIs Surge Backup Protector the Same As Surge Protector?March 13, 20231.The Role of Surge Backup ProtectorBefore the advent of surge backup protectors, the backup protection devices of SPD surge protectors typically used fuses or circuit breakers to separate the short-c...view
EN
jp 
ko 
fr 
de 
es 
it 
ru 
pt 
ar 
vi 
th 
ro 
bg 
nl 
