Why upgrade the protection and grounding of generators at pulp and paper mills?

Significant changes have occurred in the protection and grounding of generators in the past 15 years, which impact generators at pulp and paper mills. This paper updates the author´s earlier paper on the subject of generator protection upgrade [1] and highlights areas of protection that continue not to be address by some generator owners as well as new protection areas not previously addressed. New generator protection changes are reflected in recent IEEE standards such as C37.102-2006 [2]. This paper discusses these changes as they apply to industrial generators as well as the risks of not addressing them. The paper addresses the risks in several functional areas where old generator electromechanical relay protection is inadequate. In addition, the paper discusses hybrid grounding of the generator stator windings, which substantially reduces stator ground fault damage avoiding lengthy generator outages to repair. This type of grounding is a relatively new concept in generator grounding introduced in a series of IAS Working Group papers publicized in 2002 [3]. This grounding scheme has been installed on a number of generators but must be coupled with proper relay as well as transient overvoltage protection. The paper also highlights the major new protection requirements for gas turbine starting and protection advances made possible by the use of digital technology which have foster new methods not possible with older technologies.