Page 286 - 35_DS702_E_2014_Lightning_Protection_Guide

A more efficient use of drinking water is growing in significance, solution is not binding in any way and can be substituted by
especially against a backdrop of increasingly scarce drinking other equivalent solutions. In the following, only the essential
water resources. Therefore, sewage plants are a key element of characteristics of the example will be shown. At first, a ques-
the drinking water cycle. The necessary high efficiency of sew- tionnaire with important questions on the structure and its use
age plants (Figure 9.4.1) requires that the operating procedure was discussed and filled in together with the operator. This
be optimised and the operating costs be reduced at the same procedure allows to prepare a lightning protection concept
time. For this purpose, high investments were made in electronic that is comprehensible for all parties involved. The concept
measuring equipment and distributed electronic control and includes the minimum requirements which, however, can be
automation systems over the last years. However, these new technically improved at any time.
electronic systems only provide a low resistance to transients
compared to conventional technology. The structural conditions Plant description
of the widespread outdoor wastewater treatment systems with The complete process control system of the sewage plant is
measuring equipment and control units extending over large ar- centrally located in the operations building. In case of a light-
eas additionally increase the risk of interference caused by light- ning strike, substantial partial lightning currents and surges
ning discharges or surges. Thus, it is most likely that the com- are injected into the switch rooms via the extended cables
plete process control system or parts thereof fail if no protection leading to measuring stations and substations. In the past,
measures are taken. The consequences of such a failure can be this caused destruction and failure of the plant over and over
serious ranging from costs for re-establishing the availability of again. The same applies to the power supply and telephone
the sewage plant to the unknown costs for eliminating ground line. The operations building itself must be protected against
water contamination. Consequently, external and internal light- damage resulting from fire (caused by a direct lightning strike)
ning protection measures must be taken to efficiently eliminate and the electrical and electronic systems (control and automa-
this threat and to increase the availability of the systems. tion system, telecontrol system) from the effects of the light-
ning electromagnetic pulse (LEMP).
Assessment of the risk for the operations building
The example described in the following was calculated based Additional conditions:
on the IEC 62305-2 (EN 62305-2) standard. We expressively ¨ Protection measures against lightning effects have already
point out that the procedure shown is only an example. This been taken (external lightning protection system accord-

rainwater overflow basin pump / lift station
coarse / fine screen

ventilator / sand filter and grease trap
black water basin
operations building
primary clarifier

final clarifier precipitant tank
aeration tank /
effluent
nitrification – denitrification

river

Figure 9.4.1 Schematic diagram of a sewage plant

www.dehn-international.com LIGHTNING PROTECTION GUIDE 285