TABLE OF CONTENTS With the increase in size of industrial plant electrical systems, and the high short-circuit levels encountered on electricity power systems, it is essential that the electrical protection arrangements in any industrial installation are correctly designed and have the appropriate settings applied to ensure the correct functioning of the plant and continuity of supply within the installation. The importance of maintaining continuity of supply to industrial installations cannot be over emphasised and, in this respect, the interconnectors to the public supply system play a vital role. It is crucial that correct co-ordination is maintained between the protection on the main industrial supply infeeds and the power system supply feeders.
In addition to the overcurrent relay, which has been covered in Chapter 5, moulded-case circuit breakers (MCCBs) and thermal relay-contactor and fuse devices are frequently used to protect elements of the industrial electrical system and these will be covered in more detail in this chapter.
This type of relay is usually equipped with an instantaneous and/or time-delay unit. This latter unit can be inverse, very inverse or extremely inverse, and when it is necessary to prevent the relay from operating in one direction it should be provided with a directional element. This is required for ring systems or networks with several infeed sources, the latter being very common in industrial systems.
As their name indicates, these are devices that act directly on power breakers and...
