LETTERS TO THE EDITOR

Share Your Thoughts

Send comments to m.olken@ieee.org

 
Readers are encouraged to share their views on issues affecting the electric power engineering profession. Send your letters to Mel Olken, editor in chief, m.olken@ieee.org. Letters may be edited for publication.

Hydro Plants

As usual, I enjoyed the history article in the January/February 2007 issue of IEEE Power & Energy Magazine. However it strikes me as unusual that both P&E and IEEE Industry Applications Magazine should run history articles on century-old hydro plants in the same issue.

The description of the Pinawa plant was fascinating, almost as much for things that weren't said as for things that were said. For instance, all the switching devices were referred to as simply oil switches. The term "circuit breaker" wasn't used, nor was any mention made of "interrupting capacity." Perhaps this concept wasn't yet understood in 1906. As I remember it, the General Engineering people in Schenectady were still trying to get users to understand interrupting capacity when I joined GE in the late 1940s.

Also missing was any reference to system grounding. Everything was delta connected at both generator and transmission voltages. The only ground mentioned was for the lightning arresters.

Further, there was no mention made of any kind of overcurrent or other system protection. Surely there must have been some kind of primitive overcurrent devices used at that time. Did the oil switches have series overcurrent devices like today's low voltage breakers? Maybe some of this information appeared in the part of the article that you omitted.

Anyway, good article and good magazine. I always enjoy reading it.

Baldwin Bridger, Jr.

Editor's note: Associate Editor Carl Sulzberger and I agreed that only Pinawa article author Lindsay Ingram could properly respond to Baldy Bridger's comments, and Lindsay was only too pleased to do just that. His response follows. Also, the coincidence of an article on old hydro facilities in both IEEE Power & Energy Magazine and IEEE Industry Applications Magazine is just that...a coincidence.

Author's Response

Mr. Bridger's assumption is right regarding "no grounding" on the transmission system. The arrangement was made by delta connections on the single phase power transformers and so arranged that in the event of a transformer failure the line could be operated at one third reduced capacity with the failed transformer disconnected. This emergency practice was called "open delta" operation.

The term "oil switches" would be described in todays world as oil circuit-breakers.

Westinghouse (and others, no doubt) introduced a new line of overcurrent relays in 1901 called the C relay. They used the secondary current from instrument transformers that also supplied meters such as ammeters and wattmeters for the control room operator to do his job. As mentioned in the Moody article that appeared in the 23 June 1906 issue of Electrical World, the "oil switches" were "motor operated," which meant that a dc motor was used to close the switch contacts against a spring, when initiated by the operator from a remote location. Tripping the switch was also done by the operator or a protection relay by means of a trip coil that released the spring and opened the breaker.

Lindsay Ingram

Many States of Distribution

In the July/August issue of IEEE Power & Energy Magazine, the article "Many States of Distribution" states that the increase of voltage from 2,400 V delta to 2.4/4.16 kV grounded wye gave an increase of 3X in capacity using the same conductors. Rather than 3 times it should be 1.732 times (square root of three).

It was also stated that the increase in voltage from 2,400 V delta to 7,200 V delta gave an increase of nine times. Rather than nine, it should be three times.

Brad Peaseley,
Life Member

Authors' Response

Brad Peaseley's comments would be correct for distribution circuits that are thermally limited. However, most primary feeders during the era of extensive voltage conversions, as well as even today, are limited in loading by permissible voltage regulation. Voltage conversions occurred due to the growth of load in a specified area, with the alternative being the costly addition of primary feeders. The increase in load carrying capacity of a feeder serving a fixed area created by an increase in primary voltage is related to the voltage-square factor: (new primary line-neutral voltage/old primary line-neutral voltage). To maintain the same voltage drop over existing conductors when tripling the primary voltage, the new feeder loading can be increased nine times. Or, as in the example where the primary voltage was increased from 2,400 V Delta to 2.4/4.16 kV Wye, the load could be increased three times with the same voltage drop.

A second factor could be introduced, increasing the feeder length to serve the additional load. While the authors were specific in addressing increased load and load densities, rather than increased length of the distribution feeders, this is addressed herein to attempt full coverage of the issue. The voltage-square rule can still be applied. As long as the product of the distance ratio (new distance/old distance) and the load ratio (new feeder loading/old feeder loading) equals the voltage-square factor, the same voltage drop will result. If the primary voltage was doubled on an existing distribution feeder, the voltage drop would be reduced by a factor of four. If the feeder length and configuration remained constant, the load could be increased four times with the same voltage drop. Or, if the load density in the area was constant, the length of the feeder could be doubled, thereby doubling the load, and the voltage drop on that feeder would remain the same.

This is explained much better and in greater detail in the Westinghouse "Electric Utility Engineering Reference Book, Volume 3, Distribution Systems," on pages 118-119.

The authors thank Mr. Peaseley for taking the time to address this issue that apparently was not presented in a clear manner. His effort has allowed us an opportunity to clarify a characteristic of distribution feeders, and the not-so-apparent effect of voltage increases on load carrying capability. Hopefully, this discussion will encourage the younger engineers in our industry to search for other unique factors that impact the design and operation of the largest, most complex, dynamic machine ever created.

James Bouford and
Cheryl Warren