Service Capabilities for UPS
Uninterruptible Power Supplies, UPS equipment is used to maintain service to critical loads and improve uptime. Proper maintenance of the UPS should provide the owner with an Uninterrupted Revenue Stream, lower capital expenditures and lower long-term maintenance cost.
Let’s take a look at what “Service” is available to maintain the UPS. We will do this in two parts. First will be an overview and a look at best practices for UPS service and the second will be GE’s offering to accomplish this.
Critical Operations Power Systems
NEC 2008, Article 708
Over the last several years, the US has been challenged by both natural and human caused events that have made many people re-think the safety and reliability of our infrastructures and facilities. This prompted the US government to create the Department of Homeland Security in 2002 to implement plans and actions to maintain a safe environment in the US. In addition, the National Fire Protection Association (NFPA) established a task force (CMP-20) to review the existing codes and determine changes that could be added to increase the reliability, safety, and functionality of facilities. This task force met in August 2005 to review current NFPA 70-2005 National Electrical Code (NEC), and other NFPA documents, such as; NFPA 1600-2004 Standard on Disaster/Emergency Management, NFPA 110-2005 Standard for Emergency and Standby Power Systems, and NFPA 111-2005 Standard on Stored Electrical Energy Emergency and Standby Power Systems.
Resistance Grounding Systems Basics
Resistance Grounding Systems are used in industrial electrical power distribution facilities to limit phase-to-ground fault currents. IEEE Standard 142-1991 states: “The reasons for limiting the current by resistance grounding may be one or more of the following:
1. To reduce burning and melting effects in faulted electrical equipment, such as switchgear, transformers, cables, and rotating machines.
2. To reduce mechanical stresses in circuits and apparatus carrying fault currents.
3. To reduce electrical-shock hazards to personnel caused by stray ground fault currents in the ground return path.
4. To reduce the arc blast or flash hazard to personnel who may have accidentally caused or who happen to be in close proximity to the ground fault.
5. To reduce the momentary line-voltage dip occasioned by the occurrence and clearing of a ground fault.
6. To secure control of the transient over-voltages while at the same time avoiding the shutdown of a facility circuit on the occurrence of the first ground fault (high-resistance grounding).”
Generally speaking, there are two types of resistors used to tie an electrical system’s neutral to ground: low resistance and high resistance.