IEEE Power & Energy Magazine - September/October 2014 - 8

letters to the editor

share your thoughts
send comments to molken@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, molken@ieee.org. Letters may be edited for publication.

Mercury-Arc Valves

deepak tiku's "History" article on
early HVdc power transmission in
the March/april 2014 issue of IEEE
Power & Energy Magazine ("dc
Power transmission: Mercury-arc to
thyristor HVdc Valves," vol. 12, no. 2,
pp. 76-96, March/april 2014) was
very informative. I, for one, had no
idea that so many early installations
were made in europe and elsewhere.
In 1932, the general electric company
(ge) installed such a pioneering transmission line between the ge plant in
schenectady, new York, and an 1898
hydroelectric station on the champlain
canal in Mechanicville, new York.
Mercury-arc valves were used, and
the line reportedly operated at 20 kV.
at the schenectady plant, the dc was
inverted to standard 60-Hz ac. However, the Mechanicville station operated
at 40 Hz, a frequency introduced by ge
during the 1890s in a failed attempt to
replace the evolving dual frequency
standard of 25 and 60 Hz. today, the
Mechanicville plant is restored and
still operating at 40 Hz (with frequency
changers to 60 Hz), but the 1932 dc

Digital Object Identifier 10.1109/MPE.2014.2329175
Date of publication: 18 August 2014

ieee power & energy magazine

transmission line operated only up to
the end of World War II.
this information appeared in an
article by James a. Besha, "the Historic Mechanicville Hydroelectric station- Part 3" in IEEE Industry Applications Magazine, vol. 13, pp. 9-11,
May/June 2007.
-Thomas J. Blalock

Author's Response
I express thanks to thomas J. Blalock
for having gone through my article
"dc Power transmission: Mercuryarc to thyristor HVdc Valves." there
were many more experimental dc systems
that existed and were
operational from early
in the 20th century to
1945 than those that
were discussed in some
detail in the article.
as rightly pointed out
by Mr. Blalock, one
of the important dc
links using mercury-arc
valves was Mechanicville-schenectady (united states), a
pilot project jointly owned by new
York Power and Light corporation and
ge and was reported to be commissioned in 1937. this dc link transmitted 4.7 MW of power over a distance of
17 mi (27.4 km) at a voltage of 27 kV
(pole to pole). the dc link was used to
connect ac systems that were operating
at different frequencies of 40 and 60 Hz.
Before that, in 1935 at schenectady,
ge had established an experimental dc

system operated in a "back-to-back"
mode with a power-handling capacity
100 kW at 15 kV. after the successful
operation of the Mechanicville-schenectady pilot project, in 1941 ge was
asked to undertake the supply of one
of the largest mercury-arc-valve-based
frequency converters (2 × 10 MW) at
the edgar thomson works of carnegieIllinois steel corporation. It was meant
for power exchange between carnegieIllinois steel corporation's two power
systems operating at 44 kV, 25 Hz and
69 kV, 60 Hz connected to a public utility. the frequency converter was commissioned in stages,
first a 10-MW unit in
december 1943 and a
second unit in February 1944.
as always, there
is a space constraint.
I had the option of
breaking up the article into two parts or
reducing the size of
the article by almost
half. I opted for the
latter. It was a difficult task, and I tried
to include the major milestones that
shaped the development of the valves
for dc transmission. In doing so, many
other experimental links that were
equally important could not be discussed. the author regrets the same.

Mercury-arc
valves were
used, and the
line reportedly
operated at
20 kV.

-Deepak Tiku
p&e

september/october 2014

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - September/October 2014