Talking back between our readers

When David Loucks of Eaton wrote an article on selective coordination, he didn't have to wait a month for a reaction from Plant Engineering readers. The reaction came the next day, via the Talkback feature at www.PlantEngineering.com “In his article,” the reader wrote, “Mr. Loucks indicates that even when fault current falls within the instantaneous trip range of two circuit b...

11/15/2007


When David Loucks of Eaton wrote an article on selective coordination, he didn't have to wait a month for a reaction from Plant Engineering readers. The reaction came the next day, via the Talkback feature at www.PlantEngineering.com

“In his article,” the reader wrote, “Mr. Loucks indicates that even when fault current falls within the instantaneous trip range of two circuit breakers exposed to the same magnitude of fault current, the breaker closest to the fault could be the first breaker to open, as the breaker closest to the fault would likely be the smaller (lower amp frame and trip) of the two breakers and would have lower mass to overcome allowing it to start opening first and introducing arc impedance to the faulted circuit, thus reducing the fault current to a level lower than the instantaneous pickup of the upstream (and slower) breaker.

“My first question is once the instantaneous trip has been triggered on any circuit breaker, is this not the point of 'no return,' meaning that the breaker will trip, regardless of what happens to the fault current over time?”

And the reader added this thought: “Relying on the idea of a downstream breaker acting faster than a larger upstream breaker in the instantaneous trip range of both breakers to prevent the upstream breaker from tripping instantaneously sounds like something that would need testing to confirm such operation and not something that can be guaranteed.”

At PlantEngineering.com, Loucks was able to respond with a complete explanation, and a conversation had begun.

“Regarding the instantaneous tripping issue, yes, if in fact both breakers were in the process of opening, then you would have a point of no return; and while the smaller breaker might open first, the upstream breaker would still trip eventually,” wrote Loucks. “But what I was talking about was not the breaker contacts opening, but rather the tripping mechanism within the breaker that tells the breaker when to trip.

“The larger breaker will have a larger, heavier tripping mechanism that must be accelerated with a force and/or distance greater than what would be required on a smaller breaker. When that smaller breaker tripping mechanism operates a few milliseconds before the big one, you add arc impedance to the circuit.

“And I agree about your testing comment. You couldn't guarantee that this would work in all cases. Another interesting reason that could explain why we don't hear about selective coordination issues, at least from properly sized and set breakers, is this %%MDASSML%% the 2005 code mandates selective coordination on emergency systems.”

The Talkback feature at www.PlantEngineering.com is a great way to contact story authors and editors. It's also a great way to build a network of plant managers. That kind of dialogue is important today as plant managers around the world work to solve common problems on the plant floor.





No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 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...
Your leaks start here: Take a disciplined approach with your hydraulic system; U.S. presence at Hannover Messe a rousing success
Hannover Messe 2016: Taking hold of the future - Partner Country status spotlights U.S. manufacturing; Honoring manufacturing excellence: The 2015 Product of the Year Winners
Inside IIoT: How technology, strategy can improve your operation; Dry media or web scrubber?; Six steps to design a PM program
Getting to the bottom of subsea repairs: Older pipelines need more attention, and operators need a repair strategy; OTC preview; Offshore production difficult - and crucial
Digital oilfields: Integrated HMI/SCADA systems enable smarter data acquisition; Real-world impact of simulation; Electric actuator technology prospers in production fields
Special report: U.S. natural gas; LNG transport technologies evolve to meet market demand; Understanding new methane regulations; Predictive maintenance for gas pipeline compressors
Warehouse winter comfort: The HTHV solution; Cooling with natural gas; Plastics industry booming
Managing automation upgrades, retrofits; Making technical, business sense; Ensuring network cyber security
Designing generator systems; Using online commissioning tools; Selective coordination best practices

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

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.
This article collection contains several articles on the vital role that compressed air plays in manufacturing plants.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.
This article collection contains several articles on strategic maintenance and understanding all the parts of your plant.
click me