POLYMER INSULATORS - Hubbell Power Systems

♦ INSULATORS ♦
BY JOHN M. BURCH
Director of Engineering
Florida Keys Electric Cooperative, Inc.
Tavernier, FL
POLYMER INSULATORS
For Florida Electric Company
“. . . Ohio Brass polymer insulators con-
tributed significantly to our ability to
complete the project about one year
ahead of schedule.”
®
POWER
SYSTEMS, INC.
Fax 573-682-8714 http://www.hubbellpowersystems.com
The history of electric service to the Florida
Keys is a bit unique. Initially it consisted of
a 50HP generator operated by H.S.
McKenzie in conjunction with Florida
Power and Light (FPL). His subscribers
were provided with service from 5 to 10 AM and
from 5 to 10PM - except on Saturday when the
service was extended to midnight. In 1935, President
Franklin Delano Roosevelt created the Rural
Electric Administration (REA) and in 1936 congress
passed the Rural Electrification Act. About
that same time, a hurricane wiped out the Flagler
Railway system to the Keys. The already developed
right of way and bridges provided the
surface over which the overseas highway (U.S. 1)
was later built.
In January 1940, the Florida Keys Electric
Cooperative (FKEC) was certified by the Florida
Secretary of State. Its service area was from the
Dade-Monroe county line on the north to the 7mile
bridge south of Marathon on the south.
Using REA funds made available to rural com-

munities, an electric distribution system was built. Progress
was slowed by the demand for war material although the
Keys benefited from the war when the Navy built a water line
all the way to Key West. The stage was set for rapid growth
with a roadway to access the Keys, an electric system and an
adequate water supply.
The FPL/McKenzie holdings were purchased in 1941 and
in 1942 a power plant was built in Tavernier. Marathon
relied on a portable generator. From this evolved the system
as it exists today. It is important to note that the FKEC is not
only a distribution cooperative but has 16.5MW of generation
and extensive transmission facilities.
The transmission system got started in 1956 when a 69kV
line was built from Tavernier to Florida City on the mainland.
The FKEC then purchased power from the city of
Homestead and later from FPL. The line paralleled U.S. 1
and FKEC built the line from Florida City to Jewfish, then
from Jewfish to Tavernier. In addition, a 69kV cable was
installed between Tavernier and Islamorada. The first effort
to establish overhead transmission between Marathon and
Tavernier met with disaster when a line to Coco Plum was
immediately destroyed by hurricane Donna in 1960.
To keep up with growing demand, construction for a new
138kV line began in 1975. The new line went from Key
Largo to the Card Sound Bridge on state route 905 where it
tied into FPL. About five years later, the old 69kV line from
Key Largo to Tavernier was upgraded to 138kV and a new
section was built from Tavernier to Marathon. This line was
designed for 217MW but voltage considerations limit us to
about 180MW. Capacitors have already been added.
Text continues ➥

The joint FKEC
— City Electric System
of Key West
(CES) transmission
system had its inception
in 1985 when the
CES built a 138kV line
and tied into the FKEC
at Marathon. An agreement
was reached
whereby CES could get
as much as 50MW if it
was available. However the
demand continued to grow
and it became clear that it
would be necessary to beef
up the transmission facilities
for the entire Florida
Keys. In 1991 a plan calling
for joint ownership of the
transmission system was
evolved. The percentage of
ownership and the allocation
of transferred energy were defined
in the contract.
The plan called for replacing
the 69kV line from Key Largo
to the county line with a new
138kV line. This line would
then proceed south to Tavernier
where a new four breaker ring
bus substation would be built.
The line would be designed for
230kV but operated at 138kV
and FPL agreed to upgrade their
tie line to 230kV. This would
provide FKEC with a loop feed
to Tavernier. All this was to be
completed by 1996.
In August 1992 hurricane Andrew
severely damaged the existing 138kV line and essentially
destroyed the old 69kV line. It was imperative that the whole
plan be put on a fast track with completion now scheduled for
early 1995. Expediting the permits presented special problems
because the line is in an area of environmentally sensitive
mangroves and adjacent to the Everglades National Park. The
switchyard in Tavernier was proposed for construction in the
area of a sensitive hardwood hammock. After much debate and
some compromise, the permits were finally issued. After
hurricane Andrew it was decided to design the line for a
maximum effective wind speed of 172 mph at the pole top!
The CES and FKEC retained the Maguire Group in
Foxborough, MA to do the line
design. The new line was to
have a capacity of 360MW
but once again voltage limitations
have limited us to about
220MW until corrective measures
were taken. It was to be
built in two phases. Phase 1
was 7.5 miles long and went
north from the Jewfish substation
in Key Largo to the
Dade-Monroe county line
where it tied to FPL. Phase 2
was about 15 miles long and
extended south from Jewfish
sub to the new
switchyard at Tavernier.
A single pole line of steel
and spun concrete was chosen.
Since it was designed
for later upgrading to
230kV, the insulator selected
had to be such as
to provide adequate
leakage distance for operation
at the higher
voltage. This is important
because during
the long winter dry
spells, the insulators
accumulate a layer
of surface contamination
consisting
largely of salt from
the ocean spray.
The Ohio Brass
Hi*Lite XLHP
horizontal post
selected is equipped with 235
inches of leakage distance or 1.685 inches per kV to
ground at the maximum line to ground voltage for 230kV.
This compares to 1.19 inches for a porcelain post.
An additional advantage of the polymer post was its weight
of only 130 pounds compared to a weight of 374 pounds for
an equivalent porcelain insulator. The weight advantage becomes
even more pronounced when you employ a braced post
assembly on angle structures. In addition to the weight saving
in the post, polymer suspensions weigh only 5 to 10 percent as
much as porcelain suspensions.
Insulator failures have occurred on the original 138kV line
started in 1975. Investigation revealed that corrosion had taken
place in the cement joints of these insulators. This deterioration

esulted in wind resonance fractures. Wind
speeds in the Keys are consistently in the
7.4 mph range — about the resonant
wind speed for the porcelain posts on the
line. The resulting oscillations caused the
weakened insulators to fail in cantilever.
A consultant was retained to recommend
the line design tension and the type
of insulator to be used on the new line.
His study revealed that the line design
tension should not exceed 18 percent of
the conductor breaking strength. Since
we preferred not to use vibration dampers,
he recommended the use of polymer
posts which he indicated would perform
somewhat like dampers.
The ability of the Ohio Brass ESP
compound to withstand exposure to ultra
violet light was demonstrated by the
QUV test. This test which alternates
exposure to UV and condensation during
each cycle simulates the effect of
sunlight by means of fluorescent UV
lamps positioned within inches of the test
specimen. The relative humidity is maintained
at 100 percent. After the equivalent
of approximately 25 years of exposure
in the Arizona desert, the sample was
still hydrophobic and there was no cracking,
checking, crazing or erosion.
Samples of the ESP compound were
exposed to continuous corona. In addition,
an oxidative stability test was conducted
to determine its ability to withstand
exposure to ozone. All test results
revealed satisfactory characteristics.
Another consideration was the inherent
strength of the compound. The basic
EPDM used in this alloy is physically
much stronger than silicone rubber, as
such, it is less likely to be damaged during
handling and construction.
Certainly our objective was to bring
this project to fruition at minimum cost.
This had to be tempered with the need to
complete it without delay. The light
weight and one piece construction of the
polymer post simplified construction and
resulted in lower construction costs.
The removable base was attached to
the pole before the pole was set. The
insulator was then raised to the pole top
by a bucket truck and remounted on its
base. An equivalent porcelain post would
require that the insulator be assembled
on the ground. Due to the weight of the
porcelain insulator, a crane would be
required to raise it to the pole top. The
© Copyright 2001 Hubbell • 210 North Allen Street • Centralia, MO 65240
project contractor, Mr. Whitey Kohler of
Kohler Construction, estimated that the
installation time for the polymer post was
only one-half the time for porcelain posts.
In addition, the need for a crane on the job
site resulted in the polymer post having a
3 or 4 to 1 cost advantage over porcelain.
As alluded to earlier, time was of the
essence. We are convinced that the use of
Ohio Brass polymer insulators contributed
significantly to our ability to complete
the transmission project about one
year ahead of schedule. ■
&
TiPS NEWS
view from
Vol. 1, No. 5 November 1995
NOTE: Because Hubbell has a policy of continuous product improvement, we reserve the right to change design and specifications without notice.
EU1508-WB