LIGHTNING, GROUNDING AND PROTECTION FOR CONTROL-SYSTEMS

Protection for installations that have been modernized or retrofitted presents a unique mix of problems that require a different perspective from a new installation. The paper addresses lightning, transients, a nd radiation that cause problems on programmable logic controllers, di stributed control systems, and remote electronic transducers. While co mplex grounding grids and networks were not required for analog system s, newer digital equipment requires a very effective means of maintain ing equal potential throughout the facility. Methods of protecting cir cuits include a variety of sophisticated and not-so-elegant techniques . Special consideration must be given to the impact that towers have o n a protection system. The investigation ranges from no air terminals to lightning arrays. The protection problem is compounded when differe nt soils such as clay and rock are encountered. Methods of calculating the grounding circuit resistance are identified. Although the paper i s based on a retrofit, the techniques are appropriate for any industri al installation using distributed control.