D.1 Why Protect The Automation System Against Overvoltage? - Siemens SIMATIC S5 Manual

The ET 200 distributed I/O system and lightning protection
D.1 Why protect the automation system against overvoltage?
Introduction
In-depth literature
Principle of zoned
lightning
protection
D-2
Overvoltage is one of the most frequent causes of failure. These dangerous
voltage surges can be caused by:
switching operations in power-supply networks
atmospheric discharges, or
electrostatic discharges
In this context, it is important to understand the theory of overvoltage
protection, in other words the concept of zoned lightning protection.
This chapter contains an outline of this concept, plus a discussion of the rules
governing the measures to be adopted at the interfaces between the individual
zones.
Note
This chapter merely indicates how to protect an automation system against
overvoltage.
Bear in mind that complete protection against overvoltage can be ensured
only if the entire structure which houses the system incorporates adequate
overvoltage-protection measures. This is especially significant for structural
measures intended for buildings in planning.
If you would like comprehensive information on overvoltage protection, we
strongly recommend that you consult your Siemens contact partner or a
company which specializes in lightning protection.
The proposals advanced in this chapter are based on the concept of zoned
lightning protection as described in IEC standard 1024-2 Protection against
LEMP.
The principle of zoned lightning protection requires that the volume (a
factory building, for example) to be protected against overvoltage be
subdivided into zones by the application of EMC criteria (see Fig. D-1).
The individual lightning-protection zones are formed by
The external lightning protection of the
building (field side)
The shielding of:
Buildings
Rooms and/or
Devices
Lightning-protection zone 0
Lightning-protection zone 1
Lightning-protection zone 2
Lightning-protection zone 3
ET 200 Distributed I/O System
EWA 4NEB 780 6000-02a