Reliability considerations in simple paralleling applications

When a decision is made to use paralleled generator sets, many considerations need to be addressed to ensure a reliable system.


Learning objectives

  1. Understand advantages and disadvantages associated with using paralleled generator sets as opposed to a single, larger generator set.
  2. Know the codes that govern generator on-site power generation systems.
  3. Identify best practices to maximize system reliability in simple paralleling applications.

Reliability in power generation systems, defined as the probability that power will be available at any point in time, is the primary reason standby generator sets are purchased. Using paralleled redundant generator sets is one method commonly used to enhance system reliability. Redundancy traditionally has been a requirement only in critical applications such as data centers and hospitals where an extended loss of power could result in loss of life or a substantial financial loss, as these were the only scenarios where the cost of a redundant generator and the associated paralleling switchgear could be justified. In recent years, however, the availability of lower cost power transfer devices and paralleling control systems has made redundant paralleled generators an attractive option in less critical standby power applications. 

The decision of whether to use a single generator set or multiple paralleled generator sets typically is based on reliability and cost. After a decision is made to use paralleled generator sets, many considerations must be addressed to ensure a reliable system. 

Reliability and redundancy

The purpose of redundancy is to eliminate a single point of failure from a system. While it is well documented that having redundant systems makes the overall system more reliable, this is based on the assumptions that single points of failure are truly eliminated and not just moved to another part of the system and that the controls enabling redundancy don’t introduce new failure modes that compromise reliability. Paralleled generator sets that rely on a single master control for signals to start and to close to a paralleled bus actually replace one failure point with two, as the master control and the communication link between the master and the generator sets each represent single points of failure. 

Investing in a reliable standby generator set and a robust maintenance program so the generator doesn’t fail is often a better investment than installing a more complex system to compensate for a failed generator set. 

Total system cost

In some instances, the cost of two small generator sets is less than the cost of one larger generator set. The total installed cost of the system is often overlooked in basic standby applications. Beyond the cost of the generator sets, the following factors must be evaluated: 

  • Foundation: A larger generator set may require additional structural support as its weight will be concentrated on one spot; however, smaller generator sets may require pouring multiple concrete slabs. 
  • Space requirements: Multiple generator sets and their associated switchgear will take up more space than a single larger generator set, although the smaller generator sets offer greater flexibility as they can be maneuvered into smaller spaces. 
  • Cabling: Smaller generator sets enable the use of smaller cables and easier termination. However, paralleled generator sets require additional cable runs, which is labor-intensive, particularly if cable is run underground. 
  • Commissioning costs: Start-up and testing costs of paralleled generator sets are substantially higher than those for a single generator set. 
  • Maintenance costs: Replacement parts for smaller generators are less expensive than replacement parts for a larger generator. However, that difference is more than offset by the labor costs of maintaining two generators and switchgear rather than one single generator set. 
  • Capital investment: When a facility’s power demand is expected to increase in the future, in some cases initial capital investment can be minimized by installing a smaller generator with the intent of adding paralleled generators in the future as demand increases. This will need to be balanced against the future investment required to add generators and switchgear and other required facility modifications. 

<< First < Previous 1 2 3 4 5 6 Next > Last >>

Anonymous , 05/08/13 10:25 AM:

Excellent Article.
VISH , CA, United States, 05/08/13 12:53 PM:

Some of the increased cost of the parallel system can be off-set by Peak Load shaving technique. Illustration of Pros and cons of the system will greatly help the engineers to make the right decision.
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2013 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
A cool solution: Collaboration, chemistry leads to foundry coat product development; See the 2015 Product of the Year Finalists
Raising the standard: What's new with NFPA 70E; A global view of manufacturing; Maintenance data; Fit bearings properly
Sister act: Building on their father's legacy, a new generation moves Bales Metal Surface Solutions forward; Meet the 2015 Engineering Leaders Under 40
Cyber security cost-efficient for industrial control systems; Extracting full value from operational data; Managing cyber security risks
Drilling for Big Data: Managing the flow of information; Big data drilldown series: Challenge and opportunity; OT to IT: Creating a circle of improvement; Industry loses best workers, again
Pipeline vulnerabilities? Securing hydrocarbon transit; Predictive analytics hit the mainstream; Dirty pipelines decrease flow, production—pig your line; Ensuring pipeline physical and cyber security
Upgrading secondary control systems; Keeping enclosures conditioned; Diagnostics increase equipment uptime; Mechatronics simplifies machine design
Designing positive-energy buildings; Ensuring power quality; Complying with NFPA 110; Minimizing arc flash hazards
Building high availability into industrial computers; Of key metrics and myth busting; The truth about five common VFD myths

Annual Salary Survey

After almost a decade of uncertainty, the confidence of plant floor managers is soaring. Even with a number of challenges and while implementing new technologies, there is a renewed sense of optimism among plant managers about their business and their future.

The respondents to the 2014 Plant Engineering Salary Survey come from throughout the U.S. and serve a variety of industries, but they are uniform in their optimism about manufacturing. This year’s survey found 79% consider manufacturing a secure career. That’s up from 75% in 2013 and significantly higher than the 63% figure when Plant Engineering first started asking that question a decade ago.

Read more: 2014 Salary Survey: Confidence rises amid the challenges

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.