Coordinated SPD System
The protection of internal systems against surges requires a systematic approach consisting of coordinated SPDs for both power and signal lines. The rules for the selection and installation of a coordinated SPD system are similar in both cases.
SPDs used as part of the fixed building installation are classified into:
- Type 1 surge protective devices.
- Type 2 surge protective devices.
- Type 3 surge protective devices.
Type 1 Surge Protective Devices(SPD)
The highest requirements with respect to the discharge capacity are placed on type 1 SPDs. These are used as part of the lightning and surge protection system at the boundary from LPZ 0A to LPZ 1 and higher. These surge protective devices must be capable of repeatedly carrying lightning currents of 10/350µs waveform without destructing the equipment. These type 1 SPDs are called lightning current arresters. Their function is to prevent destructive partial lightning currents from entering the electrical installation of a building.
Type 2 Surge Protective Devices(SPD)
To protect against surges, type 2 SPDs with a discharge capacity of about some 10 kA (8/20 µs) are used at the transition from LPZ 0B to LPZ 1 and higher or LPZ 1 to LPZ 2 and higher.
Type 3 Surge Protective Devices(SPD)
The last link in the lightning and surge protection system for power supply systems is the protection of terminal devices (transition from LPZ 2 to LPZ 3 and higher). The main function of a type 3 surge protective device installed at this point is to protect against overvoltage’s arising between the conductors of an electrical system, in particular switching overvoltage’s.
