A Surge Protection Device (SPDs) is a component of the electrical installation protection system. This device is connected to the power supply in parallel with the loads (circuits)that it is intended to protect (see Figure 4). It can also be used at all levels of the power supply network.
Principle of Surge Protection Operation:
SPDs are designed to limit transient overvoltages due to lightning or switching and divert the associated surge currents to earth, so as to limit these overvoltages to levels that are unlikely to damage the electrical installation or equipment.
Types of surge protection devices:
There are three types of SPD according to international standards:Type 1 SPD
Protection against transient overvoltages due to direct lightning strokes. The Type 1 SPD is recommended to protect electrical installations against partial lightning currents caused by direct lightning strokes. It can discharge the voltage from lightning spreading from the earth conductor to the network conductors.
Type 2 SPD
Protection against transient overvoltages due to switching and indirect lightning strokes. The Type 2 SPD is the main protection system for all low voltage electrical installations. Installed in each electrical switchboard, it prevents the spread of overvoltages in the electrical installations and protects the loads.
Type 3 SPD
Type 3 SPD is used for local protection for sensitive loads. These SPDs have a low discharge capacity. They must therefore only be installed as a supplement to Type 2 SPD and in the vicinity of sensitive loads. They are widely available as hard wired’ devices (frequently combined with Type 2 SPDs for use in fixed installations).
However they are also incorporated in:
Surge protected socket outlets
Surge protected portable socket outlets
Telecoms and Data protection