Surge protection device, referred to as SPD, is a device that limits transient overvoltage and discharge surge current. It can divert the lightning surge current into the ground and protect the instrument from the impact of lightning surge current. It is one of the effective measures to provide lightning protection.
People often ask how does the surge protection device SPD protect against lightning? Generally speaking, surge protection devices are generally divided into two types: signal surge protection devices and power surge protection devices. It is enough to figure out the working principles of these two commonly used surge protection devices!
The signal surge protection device must meet the standard requirements of GB/T 18802.21/IEC 61643.21 "Low Voltage Surge Protection Device Part 21: Surge Protective Device (SPD) for Telecommunications and Signal Networks - Performance Requirements and Test Methods".
When the surge voltage is applied to the input terminal of the protection circuit of signal surge protection device, the transient suppression diode (TVS) with the fastest response will act first;
By selecting appropriate coupling element parameters, the signal surge protection device changes the line design so that the voltage drop on L2 plus the voltage drop on TVS will reach the breakdown voltage of the metal oxide varistor (MOV) as the discharge current increases before the transient suppression diode may be damaged., at which point the MOV starts to discharge;
Similarly, as the discharge current increases further, the voltage drop on L1 plus the breakdown voltage of the MOV reaches the action voltage of the gas discharge tube (GDT), and finally a larger surge current is released by the GDT.
When the power grid has an instantaneous pulse surge due to lightning strikes, the power surge protection device will be turned on within nanoseconds, and the lightning surge will be released to the ground instantly, so as not to affect the power supply of user equipment;
When the lightning current passes through the protected line, most of the lightning current will leak into the ground through the power surge protection device, and a small amount of residual lightning current will still reach the protected equipment, but the energy is small and the protected equipment can bear it.
The power surge protection device is applied at the entrance of each lightning protection zone of the power distribution system, while the signal surge protection device is applied in the machine room of the subsequent protection area.
The purpose of dividing the lightning protection zone in international standards and national standards is to reduce the surge protection device to a harmless level step by step before it reaches the terminal equipment and causes damage, so as to play an effective protective role.
The entire protection space of the building is divided into several lightning protection zones, and surge protection devices are installed where the line routes from one zone to another, and corresponding SPDs are installed according to the specific requirements of different zones.