Metal-Clad Unit-Type Switchgear for 33-Kv Service

The experience of the Public Service Company of Northern Illinois with metal-clad switchgear has been outstanding, both from the standpoint of reliability of operation and safety to personnel, two of the principal objectives sought by the engineers of the company when they pioneered this type of equipment. This equipment has been applicable not only to the voltage classes up to and including 15,000 volts, but also in the 33,000-volt class, of which the company has seven major installations which have been in service from 13 to 16 years. This report of experience with 33-kv metal-clad switchgear is offered as proof that development and use should be resumed and continued in what is undoubtedly a fertile field for the application of principles which are now generally accepted. It is not a detailed discussion of the design and construction of metal-clad equipment, but rather a factual record of progress already made and proved by 13 years of operating experience. Conclusions drawn from this report are that the main objectives sought after in the development of metal-clad type of switchgear have been obtained satisfactorily. Experience has demonstrated clearly its outstanding operating reliability as compared with the conventional open type, and its perfect safety record for operating and maintenance personnel has been made possible by the inherent safety features which are practical only in metal-clad equipment.