Backup generation considerations for telecommunication / central office applications

Recent rulings by the FCC and the addition of Article 708 to the National Electrical Code are driving a greater focus on reliability of telecommunications services. Within the Telecommunications Industry, especially central office sites, backup power system design and failure mode operating philosophies are critical. These applications are often configured in an N or 2N structure, utilizing large kW generators. Though this approach offers simplicity and reliability, it does have some negatives. The large generator approach must incorporate full dark-office (dead battery) capacity plus future load growth into each design. This design results in extremely low generator utilization - less than 25% and represents a significant investment in capital with less than optimal value. This design approach is beginning to change as various telecommunication organizations are beginning to utilize integrated generator paralleling solutions in N+1 and N+2 configurations. Paralleled generator configurations have always been technically possible. Deployment by the Telecommunications Industry was often rejected in central office applications due to the complexity of traditional implementations and the uncertainty in failure mode operation. This paper will review the limitations of the large generator configuration and N+l configuration utilizing traditional paralleling equipment. This paper will then explore how integrated paralleling technology has overcome these limitations by reducing complexity and costly switching devices while offering highly reliable N+l and N+2 solutions. Also presented will be the design requirements for supporting system scalability, simple failure mode operation/repair and utilizing a commercially available solution with a cost effective design. Finally, load growth and power distribution philosophies will also be explored based on reliability and complexity criteria.