The Surge Protection Device (SPD) is a component of the electrical installation protection system.
This device is connected in parallel on the power supply circuit of the loads that it has to protect. It can also be used at all levels of the power supply network.
This is the most commonly used and most efficient type of over voltage protection.
SPD connected in parallel has a high impedance. Once the transient over voltage appears in the system, the impedance of the device decreases so surge current is driven through the SPD, bypassing the sensitive equipment.
SPD is designed to limit transient over voltages of atmospheric origin and divert current waves to earth, so as to limit the amplitude of this over voltage to a value that is not hazardous for the electrical installation and electric switch gear and control gear.
SPD eliminates over voltages
- in common mode, between phase and neutral or earth;
- in differential mode, between phase and neutral.
- In the event of an over voltage exceeding the operating threshold, the SPD
- conducts the energy to earth, in common mode;
- distributes the energy to the other live conductors, in differential mode.