Paper Mill Case Study in Safety Improvements for Generator On-Line Brush Changing

Many paper mills utilize steam turbine generators for electrical generation and extraction steam process demands. These generating units are critical to continuous mill operations. To avoid excessive utility power demand costs and for operations continuity of steam loads, turbine generator downtime must be kept to an absolute minimum. Consequently, at many mills with older, brush-type exciters, brushes are changed with the generator on-line. On-line brush changing is recognized by OSHA as a specific energized work task, with associated safety requirements and guidelines which are noted in the regulations. Both voltage and arc flash hazards for this DC system must be addressed to meet requirements of the 2004 edition of NFPA 70E, Standard for Electrical Safety in the Workplace. This paper describes a paper mill case study proceeding out of a hazards analysis of subject task with the goal of improving personnel safety through hardware enhancements, training and documented procedures. Specific improvements made to the collector housing system hardware, field ground relaying, over-current protection and alarming are noted and described in detail.