GE logo GE Consumer & Industrial
Electrical Specifier Link
Issue VII
Paralleling Switchgear

Paralleling is the operation in which multiple power sources, usually two or more generators, are synchronized and then connected to a common bus. Some applications require two or more generators to be paralleled with the Utility. The frequency, voltage, phase angle and phase rotation of all the sources must match within prescribed limits before they can be paralleled.

Paralleling multiple sources provides increased reliability, flexibility in load management, uninterruptible maintenance and cost savings during peak rate incentive periods. Multiple generators paralleled to a common bus better serve critical loads. The first generator that reaches the preset operating parameters will power the critical loads with the remaining generators synchronizing and then picking up the lower priority loads. Load management schemes are easier to manage when load demands match the individual generator capacities. It is easy to take one generator off line for maintenance and let the others pick up the slack, especially if a N+1 configuration was adopted. Generators run at their highest efficiency when near full load. Lightly loaded generators are prone to ‘wet stacking’ where the temperature at which the engine runs is not high enough to efficiently burn all the fuel, resulting in un-burnt fuel being deposited in the exhaust system.


Paralleling Switchgear
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.


Subscribe to E-mail List | Ask the engineer
© 2008 General Electric Company. 307 N. Hurstbourne Pkwy, Louisville, KY, 40222, USA.