As the name suggests, Surge Protective Devices are used to protect the Electrical Installations from transient over voltages what we called as voltage surges. These transient over voltages are defined as electrical surges lasts for short duration occurred due to sudden release of energy which is previously stored or induced either naturally occurring or man-made.

A voltage surge can result in either instant failure of the installation or cause an eventual failure only evident over a longer period of time. Despite that it can cause,

  • Serious injuries or loss of human life
  • Interruption of essential services or public services
  • Interruption of commercial or industrial functions

In short terms Surge Protective Devices are called as SPDs and these can protect our valuable electrical installations such as wiring, switchgears, wired equipment’s, fire detection systems and emergency lighting, sensitive electronic items and machineries from these voltage surges coming through our electrical supply.

Some SPDs are is connected parallel to your network and the basic operation of this is, it has a high impedance in normal conditions and once a transient overvoltage appears in the power lines due to lightning or switching of motors and transformers, the impedance of the surge protective device will be decreased and it allows to drive the surge current through it divert it to the earth. Hence the sensitive equipment in your system doesn’t get any damage.

Type 1:

Type 1 SPDs are installed at the installations where direct lightning can occurs. It can be at industrial buildings which consists a Lightning Protection System with lightning rod or a meshed cage or high lightning density area where the heavy surge currents can flow in the power lines. Type 1 SPD is intended locate between the secondary side of the service transformer and the Incoming of the Main Distribution Board of the installation.

Type 1 SPD is characterized for current impulses having 10/350 µs current wave that the SPD is capable of discharging at once.

Iimp= Impulse current having 10/350 µs current wave

Type 2:

Type 2 SPDs recommended at the installations where indirect lightning can occurs. Type 2 SPDs are normally located at sub distribution boards or in the main distribution board if there is no need of a type 1 SPD. It protects the sensitive loads from surge currents characterized with 8/20 µs current wave.

Imax= Maximum discharge current

In= Nominal discharge peak current value of an 8/20 µs waveform

Imax value is more dominant than the  value because it defines the surge peak that can handle without any damage.

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