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变电所毕业论文中英文资料外文翻译文献

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2021-01-26 09:24
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2021年1月26日发(作者:gotta)
毕业设计(论文)






变电所毕业论文







外文资料翻译


Reliability of Lightning Resistant
Overhead Distribution Lines










Lighting continues to be the major cause of outages on overhead power
distribution lines. Through laboratory testing and field observations and
measurements, the properties of a lightning stroke and its effects on electrical


distribution system components are well-understood phenomena. This paper
presents a compilation of 32 years of historical records for outage causes,
duration, and locations for eight distribution feeders at the Oak Ridge National
Laboratory (ORNL) .
Distribution
type
lightning
arresters
are
placed
at
dead-end
and
angle
structures
at
pole
mounted
wormer
locations
and
at
high
points
on
the
overhead line. Station class lightning arresters are used to protect underground
cable
runs,
pad
mounted
switchgear
and
unit
substation


transformers.
Resistance
to
earth
of
each
pole
ground
is
typically
15
ohms


or
less.
At
higher
elevations
in
the
system,
resistance
to
earth

is
substantially
greater

than 15 ohms, especially during the dry summer months. At these high points,
ground
rods
were
riven
and
bonded
to
the
pole
grounding
systems

in
the
1960's in an attempt to decrease lightning outages. These attempts were only
partially
successful
in
lowering
the
outage
rate.
From
a
surge
protection

standpoint the variety of pole structures used (in-line, corner, angle, dead end,
etc.)
and
the
variety
of
insulators
and
hardware
used
does
not
allow
each


13.8
kV
overhead
line
to
be
categorized
with
a
uniform
impulse
flashover
rating
(170
kV,
etc.)
or
a
numerical
BIL
voltage

class
(95
kV
BIL;
etc.).

For simplicity purposes in

the analysis, each overhead line was categorized
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毕业设计(论文)

with a nominal voltage construction class (15 kV, 34 kV, or 69 KV). Six of the
eight
overhead
lines
(feeders
1
through
6)
were
built
with
typical
REA
Standard horizontal wood cross arm

construction utilizing single ANSI Class
55-5 porcelain pin

insulators (nominal 15 kV insulation). The shield angle of


the
overhead
ground
wire
to
the
phase
conductors
is
typically

45
degrees.


One
overhead
line
(feeder
7)
was
built
with
transmission
type
wood
pole
construction because the line extended to a research facility which was to have
generated electrical power to feed back into the grid. Pole structure of this line
are
of
durable
wood
cross
a
construction
which
utilize
double

ANSI
52-3

porcelain
suspension
insulators
to
support

the
conductors
(nominal
34
kV
insulation).
The
shield
angle
of
the
overhead
ground
wire
to
the
phase
conductors
for
feeder
7
is
typically
30
degrees.
In
1969,
an
overhead
line
(feeder 8) was intentionally built with
attempt
to
reduce
lightning
caused
outages.
Pole
structures
of
the
line
have


phase
over
phase
24-inch
long
fiberglass
suspension
brackets
with
double


ANSI 52-3 porcelain suspension insulators to support the conductors (nominal


69 kV insulation). The shield angle of the overhead ground wire to the

phase
conductors
for
feeder
8
is
typically
30
degrees.

The
failure
data
was


compiled
for
each
of
the
eight
13.8
kV
feeders
and
is
presented
in
Table,

along
with
pertinent
information
regarding
feeder
construction,
elevation,
length, and age.
A
key
finding
of
the
failure
analysis
is
that
weather-related
events

account for over half (56%) of the feeder outages recorded. Fifty-seven of the
76 weather- related outages were attributed to lightning. Insulation breakdown
damage
due
to
lightning
is
also
suspected
in
at
least
a
dozen
of
the


equipment
failures
observed.
The
data
indicates
overhead

lines
which
pass
over high terrain are less reliable because of the greater exposure to lightning.

For example, feeder 3 had the most recorded outages (48), of which two- thirds
were due to weather-related events; this feeder is also the highest line

on the
plant site, rising to an elevation of 450

above the reference valley elevation.

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毕业设计(论文)

Overhead
lines that
are longer
and
to
which
more
substations
and
equipment
are
attached
were
also
observed
to
be
less
reliable
(more
exposure
to

lightning and more equipment to fail). The age of the line does not appear to

significantly
lessen
its
reliability
as
long
as
adequate
maintenance
is
performed;

none of the lines have had a notable increase in the frequency of
outages
as
the
lines
have
aged.
As
would
be
expected,
the
empirical
data
presented
in
Table


I
confirms
the
two
overhead
lines
which
have
been
insulated
to
a
higher

level

(34
or
69
KV)
have

significantly
better
reliability
records
than

those

utilizing
15
kV
class
construction.
Feeder
7
(insulated
to
34
KV)
and
feeder
8


(insulated
to
69
kV)
have
bad
only
3
outages
each
over
their
32
and
23

year
life
spans,
respectively.
These lines
follow similar terrain and are comparable in length and age to the 15 kV class
lines,
yet
they
have
a
combined
failure
rate
of
0.22
failures
per
year
versus
4.32 failures per year for the remaining feeders.
On
typical
15
kV
insulated
line
construction,
lightning
flashovers
often
cause
60
cycle
power
follow
and
feeder
trip.
With
the
higher
insulation

construction,
outage
rates
are
reduced
by
limiting
the
number
of
flashovers

and
the
resultant
power
follow
which
causes
an
over
current
device
to
trip.

This
allows
lightning
arresters
to
perform
their
duty
of
dissipating
lightning
energy
to
earth.
The
number
of
re
closer
actions
and
their
resultant

momentary
outages
are
also
reduced.
This
is
beneficial
for
critical
facilities
and
processes
which
cannot
tolerate
even
momentary
outages.
An


additional
benefit

is
that
outages
due
to
animal
contact
are
also
reduced

because
of
the
greater
distance
from
phase
conductor
to
ground
on
pole
structures.

Distribution line equipment to increase line insulation values are

the
shelf
items
and
proven
technology.
New
lightning
resistant

construction
typical
by
utilizes
horizontal
line
posts,
fiberglass
standoff
brackets
or
any
other
method

which
world
increase
the
insulation
value.

The replacement of standard pin insulators with line post insulators of greater


flashover
value
is
an
effective
means
to
retrofit
existing
wood
cross
arm
3

毕业设计(论文)

construction.
The
doubling
and
tripling
of
dead
end
and
suspension

insulators

is
also
a
means
of
increasing
flashover
values
on
existing
angle
and
dead-end

structures.
Current
fiberglass,
polymer,
and
epoxy
technologies provide an affordable means to increase line insulation.
While the use of increased insulation levels to reduce lightning flashovers

and the resultant outages on overhead distribution lines has been

thoroughly
tested
and
demonstrated
in
laboratory
and
experimental
tests
[5],
long
term
history
field
data
has
positively
demonstrated
that
the
use
of

resistant
construction
can
greatly
reduce
outages.
Field
use
at
ORNL
has
shown
that
in
areas
which
are
vulnerable
to
lightning,
the
use
of
increased
insulation
and
a
smaller
shielding
angle
is
an
impressive
and
cost
effective

means
to
appreciably
increase
the
reliability
of
overhead
distribution
lines.


This
reliability
study
clearly
illustrates
that
the
insulation
requirements
for

high-reliability
distribution
feeders
should
be
determined
not
by
the
60
Hz
operating
voltage
but
rather
by
withstand
requirements
for
the
lightning
transients
or
other
high
voltage
transients
that
are
impressed
upon
the
line.


Electrical equipment (switchgear, insulators, transformers, cables, etc.) have a
reserve (BE level or flashover value) to handle momentary over voltages, and


by
increasing
that
reserve,
the
service
reliability
is
appreciably
increased.


As the electrical industry gradually moves away from standard wood cross arm
construction
and
moves
toward
more
fiberglass,
polymer
and
epoxy

construction,
increased
insulation
methods
can
be
applied
as
part
of
new
construction
or
as
part
of
an
upgrade
or
replacement
effort.
In
considering


new or upgraded overhead line construction, the incremental increased cost of
the
higher
insulation
equipment
is
d
in
proportion
to
the
total
costs
of
construction
(labor,
capital
equipment,
cables,
electric
poles,
right-of-way

acquisition),
Its
cost
effectiveness
varies
with
the
application
and
the


conditions
to
which
it
is
be
applied.
Economic
benefits
include
increased
electrical
service
reliability
and
its
inherent
ability
to
keep
manufacturing
processes and critical loads in service. Other more direct benefits include less

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