Letters

Letters to the editor.

09/01/2008


Protecting hospitals

In the cases described in the “Be prepared: Hospital protection for catastrophic events” article, June 2008 (page 32), the hospital's emergency power supply (EPS) was a medium voltage bank of generators. While the choice of medium over low voltage has its advantages for large systems, this design always leaves transformers normally de-energized, as is the case with the described systems.

The insulation system of dry type transformers is hygroscopic and the manufacturer's instructions recommend an insulation resistance measurement be taken when the unit is allowed to cool to ambient. ANSI/IEEE C57.94 paragraph 7.2, “IEEE Recommended Practice for Installation, Application, Operation, and Maintenance of Dry-Type General Purpose, Distribution, and Power Transformers” also makes the same recommendation. Both the instructions and the standard both recommend a drying out procedure should the measurement not meet specifications.

I would like to know of a transformer specification, preferably dry-type, which allows for a normally de-energized state, then a sudden application of full voltage and load.

Jim Hall , PE Electrical Engineer AKF Engineers Philadelphia

Author response:

This is definitely one of the pro/con discussions for medium-voltage systems. There are a few ways we address this concern:

  1. Use medium-voltage transfer switches where possible, allowing the step down transformers to be constantly energized. This is typically used for non-essential services, large equipment loads such as chillers, and for service loops, such as exists at Queens.

  2. Manufacturers typically recommend the use of cast coil transformers instead of dry type when periods of no-load conditions exist. These are designed to minimize moisture in the coils.

  3. Specify space heaters to minimize moisture buildup inside the transformer. In addition, you will need power from a separate source.

  4. In a healthcare facility code requires that the emergency system is tested weekly, which will energize all transformers at least once per week.

  5. Systems of this size will typically partake in utility load sharing programs, which will also increase the frequency that these transformers are energized.

Typically, the size of these facilities and the emergency power supply system (EPSS) require the use of medium-voltage systems. A 480-V system is limited from combined generator fault output, automatic transfer swtich size, cable quantity, and maximum switchgear current ratings.

James Ferris, PE Associate Electrical Project Engineer, TLC Engineering for Architecture Olando, FLA.

“Selecting & maintaining smoke detectors” July 2008 (page 60) correction

In the article, I believe they got the theory of operation of photo and ion detectors reversed. The difference of operation in a life safety situation, when installed according to their manufacturers' instructions, is non-consequential. My professional preference is to use Ionization unless problems with false alarming crops up after the installation. Then I replace those Ion detectors that are being problematic with photo detectors.

I would never use a heat detector in place of a smoke detector that is to be used for detection of fire in a life safety situation The only time a heat detector is applicable is when the heat detector is used in conjunction with a sprinkler fire protection system, i.e. detection for a pre-action style fire protection system, for property protection.

Joseph M. Crowley , Electrical Engineer Jaco Systems Stoddard, WIS

Author response:

Your reader was correct. The functional uses of the two detector types were inadvertently switched

A.J. Sevast , Set Consultant RJA Group Greenwood Village, COLO.

Suggested reading

I enjoyed the July 2008 issue of Consulting-Specifying Engineer, on page 52, there is a list of “Additional Reading” for grounding and bonding. Widely considered the most definitive work on the topic was omitted. “The Soares Book on Grounding and Bonding” by the International Assn. of Electrical Inspectors is used by inspectors and should be a reference on the bookshelf of every electrical engineer working with power.

Michael Beanland , PETriAxis Engineering Inc.Vancouver, Wash



Letters

Send your letters to Michael Ivanovich, editor-in-chief, Consulting-Specifying Engineer , 2000 Clearwater Drive, Oak Brook, IL 60523, or via e-mail tomichael.ivanovich@reedbusiness.com.

Letters should be no longer than 200 words, and may be edited for space, style, spelling, and grammar.



No comments
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 Leaders Under 40 program features outstanding young people who are making a difference in manufacturing. View the 2013 Leaders here.
The new control room: It's got all the bells and whistles - and alarms, too; Remote maintenance; Specifying VFDs
2014 forecast issue: To serve and to manufacture - Veterans will bring skill and discipline to the plant floor if we can find a way to get them there.
2013 Top Plant: Lincoln Electric Company, Cleveland, Ohio
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Bring focus to PLC programming: 5 things to avoid in putting your system together; Managing the DCS upgrade; PLM upgrade: a step-by-step approach
Balancing the bagging triangle; PID tuning improves process efficiency; Standardizing control room HMIs
Commissioning electrical systems in mission critical facilities; Anticipating the Smart Grid; Mitigating arc flash hazards in medium-voltage switchgear; Comparing generator sizing software

Annual Salary Survey

Participate in the 2013 Salary Survey

In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.

Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.

2012 Salary Survey Analysis

2012 Salary Survey Results

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.