Surge Arresters (SPDs)

 Surge Arresters (SPDs)

When lightning strikes close to a powerline it induces a surge in the lines due to the electromagnetic pulse (EMP). 

EMPs are also called "transient electromagnetic disturbances". 

Surge arresters are designed to prevent surges caused by a "lightning flash" EMP or other transients from affecting large areas of the grid.  

They do not protect against a direct strike on your line, this device stops surges which have a slower rise than direct strikes, which have a rapid rise in voltage. 

Electromagnetic Compatibility Engineers specialize in understanding the phenomena and damage caused by EMPs.

The surge arrester became very important as consumer devices with semiconductors proved to be very sensitive to mild surges. 

Prior to the 1960s mild surges had always existed in the web but there was not the need to have as precise control of them. 

Most consumer electronics have some type of Zinc Metal Oxide surge protector.

ZnO technology is used in small surge protection systems on computers and appliances as well as in large surge arresters used in the grid. 

The surge arrester basically consists of a ceramic tube are filled with zinc oxide

"A distribution class surge arrester comprises a core formed of distributed zinc oxide varistor blocks, aluminum blocks acting as heat sinks and as spacers providing voltage grading and required arcing distances, and terminal blocks held in face to face contact by means of a glass reinforced epoxy shell which is formed by winding a pre-preg onto the assembled blocks and thermally curing under mould pressure within an evacuated mould."

Overvoltage is designed to go right down through the core of the device to ground.