The only severe transmission line outage in Vermont occurred near the Canadian border. The
46-kV line on the causeway over the Missisquoi Bay between West Swanton and Alburg was
down for several days. The weight of ice caused two poles and between 40 and 50 crossarms to
break. Ice-laden trees caused two other 46-kV lines to trip out at times during the storm (Doug
Best, CVPS, personal communication). One of these went from New Haven to Lincoln and the
other from Middlebury to Weybridge.
In New Hampshire a single non-tree-related problem in the transmission system occurred to
the 450-kV DC line (designed for 1.5 in. of ice) where it crosses the summit of Sentinel Moun-
tain at about 2100 ft in Warren (Richard Holmes, Granite State Electric, personal communica-
tion). The ice load on a static wire caused the pin in a Y-shackle to pull out and the wire to drop.
The line was subsequently brought back up at two-thirds power before the location of the break
was found and repaired about two days later. Metallurgical tests on the Y-shackle indicated that
its performance was within the specified strength tolerance limits. David Plante, Reggie Lang,
and Kevin Cote of Public Service of New Hampshire (PSNH) supplied information on outages in
PSNH's 2000 miles of transmission lines all over the state. PSNH experienced a number of tree-
related problems to its 34- and 115-kV lines, which are in fairly narrow right-of-ways. In New
Hampton it lost eight to ten sections of a 1920s vintage line. The two problems in its 115-kV
system were caused by tall white pines, well out of its right-of-way, falling on the wires. Its
transmission lines are designed to NESC, except the 345-kV lines, which are engineered to with-
stand 1.5 in. of ice, in addition to the NESC-specified loads.
In Maine, Bangor Hydro's 115-kV line east of Deblois failed (Ken Miller, Larry Billings, Jeff
Fenn, George Baker, Bangor Hydro, personal communication). That radial line, built in 1955, is
the only line serving the Calais region in eastern Maine. The cascade failure of six miles of H-
frame structures (Fig. 17) was initiated by a single conductor breaking from the heavy (~1 in.)
ice load. The cascade was stopped at one end by a corner tower, and at the other by a long span
that absorbed the load. Power was restored to the region, while a new line was under construc-
tion, by routing electricity along existing 33-kV lines, and using local generation (diesel and
wood). There were a number of problems in CMP's power transmission system, primarily in its
34-kV system, with only a few
problems in the 115-kV system
(Tom Bragg, CMP, personal com-
munication). The 34-kV lines are
particularly vulnerable to tree
damage, because the wires are on
relatively short poles (35 to 40
feet tall), and the lines are in nar-
row right-of-ways or near the
edge of wider right-of-ways for
115-kV lines. As redundancy is
incorporated in the system, many
of the problems caused no outag-
es. Other outages, generally limit-
ed to four hours, occurred during Figure 17. Six miles of Bangor Hydro's 115-kV H-frame trans-
mission line in the blueberry barrens east of Deblois failed
switching or sectionalizing of a
under the ice load (photo Larry Billings, Bangor Hydro).
line. There were, however, a
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