|Surge Protection Device (SPD) is intended to Limit transient Over-Voltages and Divert Surge Current. It contails at Least one Non-Linear component Viz., Spark Gap, Gas Discharge tube (GDT), MetaL Oxide Varistor (MOV), Silicon Avalanche Diode (SAD) or Surge Diode orTranszorb.Difference between SPDs & Fuse, MCB, RFI Filter, Isolation Transformer, Stabilizers, UPS, Under/ Over Voltage relays
All the above products are meant for problems from STEADY STATE ERROR, which are present for long duration. SPD is meant for TRANSIENT ERROR, which is micro second duration. SPD is a VOLTAGE OPERATED DEVICE, Which hasto be connected in parallelto the Load.
Other names of SPD
TVSS: Transient Voltage Surges Suppressor (IEEE used earlier, but has changed to SPD from 2009) LPU : Lightning Protection Unit Decades old names still followed by some consultants Lightning barrier/Surge barrier: Name given by some Manufacturers
Mainly it is to avoid increasing cost of failures of Electrical & Electronics System caused by Electromagnetic effect of lightning. Of Particulars important are Electronis System used in data processing, process control and safety for plants of considerable capital cost, Size and complexity for which plant outages are very undesirable for cost and Safety reasons.