The new emerging industries are now indulging more electronic facilities that are dependent on computer control of their processes, and also require an increase in cleanliness and reliability of the electrical power supply system. Electronic logics are now replacing the electromechanical subsystems. Lightning and other external disturbances rank on the top of the list of uncontrollable events that have switching off facilities in recent years. Every piece of electronic equipment in any industrial environment is prone to power surges generated on the utility grid either inside or outside of the plant and are transmitted to the equipment via incoming power lines.

Before coming to the surge protection devices, firstly we have to know what is surge. The term SURGE is used to describe a transient overvoltage on a power line that has duration of a few microseconds. A transient overvoltage can increase the insulation of electrical equipment causing degradation of insulation and immediate loss to the equipment. The result will be that equipment will have to be repaired more frequently.

In order to protect the equipment from surges, users are installing SPDs either at the main circuit breaker for the equipment or the branch circuit breaker depending on equipment ratings. Power surges can cause failure, permanent degradation or short term abnormal function of electronic devices and systems. The development of SPD is of paramount importance to manufacturers and users of industrial electronic equipment.

AC power Surge Protection Devices
There are several SPD’s available, utilizing different overvoltage protection topologies. The commercially available SPD’s significantly differ in terms of their surge handling capabilities and the level of protection they provide. Most of the electronic equipments are powered from AC source. There is a special range of SPD to secure AC powered Electronics. There is Class B/type I, Class C/type II and Class B+C/ type I+II AC powered surge protection device complying IEC 61643-1 & UL 1449. Class B lightning surge protector comes into zone from LPZ 0-1 to protect against lightning surge current discharge in 10/350µs. Class C switching surge protector is designed under the zone from LPZ 1-2 offering protection from switching surges or transient current discharge in 8/20µs. Class B+C  lightning cum switching surge protectors are the most upgraded version of SPD comes into zone from LPZ 0-2 combining 10/350µs and 8/20µs. This protection device is specially designed for highly sensitive ac power applications from both lightning and switching surges.