Download hi*lite insulators save energy and dollars avoid generating non

HI*LITE INSULATORS
SAVE ENERGY AND DOLLARS
AVOID GENERATING
NON-REVENUE POWER
®
®
POWER SYSTEMS, INC.
Hi-Tension News
Reprinted from
9001-H
Fall/Wint. 1990
ISO 9001-94
Cert. No. 002196
The Ohio Brass Co.
Wadsworth, OH USA
®
POWER
SYSTEMS, INC.
573-682-5521
ANDERSON
Fax 573-682-8714
®
http://www.hubbellpowersystems.com
®
®
®
UNITED STATES • 210 N. Allen • Centralia, MO 65240 • Phone: 573-682-5521 • Fax: 573-682-8714 • e-mail: [email protected]
CANADA • 870 Brock Road South • Pickering, Ontario L1W 1Z8 • Phone: 905-839-1138 • Fax: 905-831-6353 • e-mail: [email protected]
MEXICO • Av. Coyoacan No. 1051 • Col. Del Valle • 03100 Mexico, D.F. • Phone: 525-575-2022 • Fax: 525-559-8626 • e-mail: [email protected]
NOTE: Because Ohio Brass has a policy of continuous product improvement, we reserve the right to change design and specifications without notice.
©
Copyright 2001 • Hubbell/ Ohio Brass
Bulletin EU1424-H
Printed in U.S.A.
Hi*Lite Insulators Save Energy
And Dollars – Avoid Generating
Non-Revenue Power
Your porcelain suspension
insulators may be costing you more
than you think! Recent test data
indicates that Hi*Lite polymer
insulators exhibit as much as a 90
percent reduction in energy loss in
comparison with equivalent
porcelain suspension insulator
strings. Similar energy loss ratios
have been reported in other industry papers.
A series of tests were conducted
at the Frank B. Black Research
Center to investigate and measure
the Power Loss on insulators.
Various system voltages were
examined as the losses are a function of both voltage and humidity.
The results of these tests are shown
in Figures 1-5. Curve “A” represents the energy losses associated
with porcelain insulator strings and
Curve “B” represents the losses
associated with Hi*Lite insulators.
The shaded area between curves
“A” and “B” reflects the difference
between real power lost through
leakage currents occurring across
the insulators.
The lower losses associated with
Hi*Lite insulators can best be
explained as a result of their design.
Five factors contribute to the lower
energy losses. These factors are:
(1) Leakage Distance
(2) EP/Silicone Alloy
Weathershed Material
(3) Core Diameter
(4) Electrical Stress Distribution
(5) Dielectric and Corona Losses
Within the Insulator String
Leakage Distance: Hi*Lite
insulators contain more inches of
leakage distance than an equivalent
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Figure 1
Figure 2
porcelain insulator string. Based
upon an equal insulator wet
switching surge strength, Hi*Lite
insulators have 14 percent greater
leakage distance at 138 kV and a 19
percent greater leakage distance at
500 kV. A longer leakage distance is
typically associated with lower
leakage currents and, therefore,
lower losses.
The typical design criteria used
for line insulator selection based
upon contamination performance
calls for no less than 1.0 inch of
leakage distance per kV-RMS to
ground in clean environments. In
areas with moderate contamination
conditions, this value is 1.1 to 1.25,
and for areas with heavy contamination, a value of 1.5 to 1.75 may be
used. Hi*Lite insulators exhibit a
level of 1.1 to 1.25 inches of leakage
distance which falls into the “Moderate Contamination” level. For
heavy contamination areas, additional porcelain units or a longer
Hi*Lite unit may be used to obtain
the desired leakage distance.
EP/Silicone Alloy Weathershed:
Hi*Lite insulator weathersheds are
molded from a proprietary Ethylene Propylene (EP) material alloyed
with Silicone. The EP material has
superb tracking resistance, excellent
mechanical strength, UV stability
exceeding 50 years, and is very
resistant to ablation from arcing
and ozone conditions. A small
amount of Silicone is alloyed with
the EP rubber to obtain a long
lasting hydrophobic property of the
insulator weathershed material.
This desirable hydrophobic property is the tendency to repel water,
thus preventing moisture from
forming a conductive sheet or
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continuous film across the
weathershed. This results in lower
leakage currents under wet conditions which correspond to lower
energy losses.
Another benefit of a hydrophobic surface is a reduction in the
capture of airborne contamination.
This translates to a cleaner surface
which will exhibit lower leakage
currents and, therefore, lower
energy losses. In contrast, the glaze
used on porcelain insulators is
hydrophillic, the opposite of
hydrophobic. Some utilities apply
special coatings to their porcelain
insulators to repel water, contamination, and to reduce flashovers
caused from excessive leakage
currents. Hi*Lite insulators do not
need these coatings to obtain these
desirable characteristics.
In summary, Hi*Lite insulator
weathersheds are specially compounded to obtain the hydrophobic
properties of a Silicone rubber with
the excellent mechanical and
electrical properties of an EP
rubber. This alloyed rubber limits
the energy losses associated with
the surface leakage currents.
Core Diameter: The small core
diameter of Hi*Lite is also a contributing factor to the lower energy
losses associated with these polymer insulators. Under wet or
contamination conditions, surface
leakage currents on Hi*Lite have a
greater current density in comparison to the large core diameters
associated with porcelain insulators. The higher current density
exists while the overall leakage
current on the insulator is less than
that for porcelain under identical
environmental conditions. This
4
higher current density leads to a
more rapid drying of the insulator
and a more rapid extinction of these
surface leakage currents. The
overall effect is that the small core
diameter of Hi*Lite insulators
results in faster drying of the
insulator while maintaining a
smaller overall leakage current in
comparison to the porcelain insulator.
Electrical Stress Distribution: In
conventional porcelain suspension
insulators, pinhole and cap lip
corona in the line end units of
higher voltage strings will also
contribute to the measured energy
losses. Changes occur in the voltage
distribution of the insulator string
as the string becomes wet. This
increases corona discharge. There is
no corresponding line end corona
source on the equivalent Hi*Lite
insulator as no intermediate metal
fittings exist. The lack of intermediate metal components in Hi*Lite
insulators contribute to their overall
lower energy losses.
Dielectric Losses Within the
Insulator: The dielectric material
inside Hi*Lite insulators is a solid
resin fiberglass core. This material
has a dielectric strength of 100 kV/
inch. The fiberglass core runs the
entire length of the insulator
providing a continuous insulating
medium between end fittings. The
total insulating material in a 5-3/4
inch section in the middle of the
Hi*Lite insulator is 5-3/4 inches. In
comparison, porcelain insulators
only have approximately 5/8 inch
of pure dielectric between the metal
cap and pin in a 5-3/4 inch section
length.
The power factor or dissipation
factor of a typical porcelain 5-3/4
inch x 10 inch suspension insulator
Polymer and porcelain suspension insulator equivalents.
5
TABLE 6
6
is in the range of 2.0-3.0 percent.
The power factor of an equivalent
Hi*Lite suspension insulator is
approximately 10 percent that of
porcelain or 0.2-0.3 percent. While
these losses are small, they contribute to the overall insulator energy
loss.
Converting the Energy Savings
to Dollars: The energy losses
associated with porcelain and
Hi*Lite insulators are a function of
humidity and voltage. Since the loss
relationship is nonlinear, it is
important to evaluate these losses
as a function of the time spent at the
varying humidity conditions. This
will result in a weighted loss
evaluation which will most accurately estimate the total losses on an
annual basis. (See Table 6.) These
losses can then be prorated over the
life of the line to obtain a present
worth value or savings of these
insulators. This present worth may
then be used for cost analysis
during purchasing, similar to the
evaluations conducted on most
utility transformer purchases. See
Table 7 for an example calculation.
A computer program is available
from Ohio Brass to assist in this
present worth analysis for energy
losses. Please contact your local
Ohio Brass District Manager or
Agent for your free computer
diskette. Be sure to specify size, 5.25
inch or 3.5 inch.
Polymer insulator application.
7
Present Worth of Savings Calculation
Present Worth Savings = [ (Avg Watts) (24 hrs/day) x (365 days/year)
(1 kW/1000 watts) (EC $/kW-hr) (P/A) ]
EC = Energy Cost in Dollars per kW-hr
n
n
P/A = [ (1 + i) – 1] / [i (1 + i) ]
i = Interest Rate (Rate of return for the utility)
n = Design Life of the Transmission Line
Present Worth Savings = $/Hi*Lite insulator*
* This value should be discounted from the purchase price of Hi*Lites at
time of bid review.
TABLE 7
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