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My
invention relates to insulators and while it is applicable generally, it
is particularly useful in connection with outdoor service. The
teaching of my invention is applicable to various, forms of insulating
bodies, such as post type insulators, pin type insulators, suspension
insulators, strain insulators, all manner of insulating bushings such as
bushings for terminals of transformers, circuit breakers, potheads, or
the like, floor, wall, and ceiling bushings, bus supports, and in fact
for all purposes where a conductor is to be supported in insulated
relation or guarded against leakage, and, therefore, I do not confine
the invention to any one form of insulator but intend the appended clams
to cover the invention broadly. The
problem of an outdoor insulator as heretofore known is difficult and has
grown increasingly so with increases in voltage The outdoor insulator
employed for supporting high tension conductors as heretofore
constructed when subjected to atmospheric conditions accumulates a
coating of dust, soot, and the like, which lowers its creepage
resistance value. It has been customary to provide petticoats which are
adapted to serve as rain sheds, keeping a portion of the surface dry
This is particularly true in connection with pin type insulators, such
as are disposed vertically for supporting high tension conductors.
The petticoat type of construction of the prior art has presented
a number of objections: 1.
The petticoat type of insulator necessarily presents a varying
cross-section in its own body. 2.
The surfaces which are protected from rain accumulate dirt and never
become washed. 3.
The electrical stresses on a wet insulator ale concentrated at the worst
possible place, namely, at the point of smallest cross-section, and they
result in the formation of spark discharges which tend to injure the
insulator and particularly are likely to induce complete flashovers. From time to time, the importance of an insulator having a uniform
cross-sectional area
from the live part to the grounded supporting structure, or between
parts of different phase or potential, has been impressed upon me by the
observation of insulators under operating conditions. I have observed
that a dry, clean insulator begins to show signs of flashover first in
the restricted areas. I
have observed also that an insulator when wet, and having dry spots,
shows small arcs over dry spots without indications of arcs over the wet
surfaces, and I have observed that these dry spots occur in the
restricted areas on the insulator. It appears that the arcs increase in
length as the insulator drys either by the heat of the arc or the action
of the elements and this occasionally causes arc-over of the entire
insulator. I have observed also that this arcing at the dry spots causes
heating and deterioration of the insulator. In running tests on
insulators for corona formation I have caused the insulator to be placed
in a dark room and observed from a small window in the side of the room.
As the voltage impressed on the insulator is raised corona forms around
the tie wire. Then it forms in the restricted area under the top shell.
It appeared to me to be logical that as the voltage was raised the
corona under the ton shell would spread until it met the corona formed
around the tie wire and then cause a flashover to take place. The
high voltage can be induced on these restricted areas either by raising
the voltage on the entire insulator or by raising the voltage on the
restricted areas only by wetting the rest of the insulator. This causes
a greater voltage drop across these restricted areas. The exposed
surfaces being wet and conductive would compel the dry, dirty surfaces
to have much higher voltage gradient over these surfaces than normally
this being equivalent to raising the voltage over the entire insulator.
It then occurred to me that an insulator with spiral flanges
would tend to eliminate the above trouble by providing a uniform
cross-sectional area and I conceived that by properly shaping the
flanges the insulator would be self cleaning. Certain
important advantages flow from this form of insulator, namely, 1.
The insulator is very strong mechanically. 2.
By turning the outer edge of the flanges upwardly and disposing them
spirally or helically, rain coming from any one direction will follow
around the insulator and wash the other surfaces. 3.
Due to the helical or spiral design and the upward turn of the flanges
it is easy to clean the insulator by hand. 4.
When arc-over occurs on this spiral insulator, the heat of the arc will
cause a current of air to pass upwardly over the surface of the
insulator and the spiral shape of the insulator will cause the current
there to rotate, carrying the arc around the insulator and preventing
concentration at any one point, saving the insulator from destruction
and exerting a quenching effect upon the arc. Now
in order to acquaint those skilled in the art with the manner of
constructing and operating a device embodying my invention I shall
describe in connection with the accompanying drawing a specific
embodiment of the same. In
the drawing: Figure
1 is a plan view of an insulator embodying my invention; Figure
2 is a side elevational view of the same with parts broken away; Figures
3, 4 and 5 are diagrams to explain the action of the insulator; Figure
6 is a vertical section through a conventional form of insulator; and Figure
7 is a side elevational view of a suspension type of insulator. Referring
to Figure 3, assume that the terminals 1 and 2 are metallic terminals
between which there is connected a straight insulating rod or body 3 and
that a potential is put upon these terminals as by means of the line
wires 4 and 5. An insulator is a highly resistant conductive body.
Therefore, a certain current will flow therethrough, depending
upon the impressed voltage. In commercial forms of insulators the ratio
of resistance to voltage impressed thereupon is so high that we speak of
an insulator as a non-conductor. In reality it is merely a very poor
conductor, so poor, when properly designed, that the flow of current is
negligible. However, there are conditions under which the conductivity
of an insulator is very important. Assume
that the rod 3 is made of glazed porcelain or the like, and that it is
then subjected to wetting on the surface. The wetting of the surface
provides a film of moisture which is conductive to a greater degree than
the body of the porcelain. I have represented this by dotted line
resistance 6 which will thereupon conduct a flow of current until If,
however, the rod shown in Figure 3 be provided with a petticoat, as
shown at 7 in Figure 4 and the insulator exposed to the rain a film of
moisture will form on the exposed parts leaving the parts under the
petticoat, as indicated at 8, relatively dry. The result will be that
the film of moisture which is represented by the dotted line 9 is not
continuous but extends to the lip of the flange petticoat 7 as indicated
at 10 from above, and to a point adjacent the overhang of the petticoat
as indicated at 11 from below. Now
the effect of this interrupted film of moisture is to bring the
potentials of the conductors 4 and 5 to the terminals of the films,
namely to the points 10 and 11 so that the full voltage is impressed
upon the short space between said points 10 and 11 and also is impressed
upon the porcelain between these two points. That
is to say, the stress upon the air between the points 10 and 11 is now
the full voltage, and likewise the stress through the porcelain from the
point 10 to the point 11 is full voltage. It can be seen at once that
the air gap is too small, if the proper air gap is represented by the
distance between the line wires 4 and 5. Also, it can be seen that the
stress through the porcelain is now too high since the resistance of the
parts of the porcelain shunted by the film of moisture is a very large
percent of the total length of the bar 9. The result is that there will
be a breakdown and a discharge just as if the terminals 10' and 11'
shown in Figure 5, were connected to the line terminals 1 and 2 through
the high resistances 12 and 13. It is to be observed that the films of
moisture when no current is flowing are like good conductors so far is
transmitting potential is concerned. They act also somewhat like
condenser plates in that they have a certain amount of capacity and the
result is a snapping discharge will begin at the margin of the petticoat
of the insulator at 10, as shown in Figure 4, through the advance edge
of the moisture as indicated at 11 in Figure 4. Obviously, the part of
the rod protected by the petticoat is subjected to excessive potential.
Now if the film of moisture were continuous as shown in Figure 3, a
discharge of current flow would occur but it would be quiet and would
not arc, being in that respect like a very high resistance wire or other
conductor. Now
with the foregoing explanation conventional types of insulators, such as
shown in Figures 6 and 7, at once show the difficulties under which they
are required to operate. Referring
to Figure 6, I have shown a conventional type of petticoat insulator 15
which it will be seen has a relatively narrow waist 16 which when the
insulator is wetted is subjected to excessive electrostatic stress. This
wetting of the surface of the insulator is equivalent to raising the
voltage upon certain parts of the insulator with the result that the
insulator is immediately overloaded in the most constricted parts. Such
an insulator as shown in Figure 6 when supported by a clamp or base
attached to the lower petticoat instead of being mounted on a pin is
subject to particularly severe stressing. In
Figure 7 I have shown a conventional form of suspension insulator which
is provided with a plurality of narrow waists under the margins of the
petticoats. This insulator 17, like the one shown in Figure 6, is
subjected to the deposit of dust, soot, and the like, at places where
moisture does not succeed in washing off the same with the result that
the tendency to form corona is increased. This is true whether the
insulator he held in vertical or horizontal position. Figure
1 shows in plan view an insulator of my invention which comprises, in
this instance, a porcelain body having the wire receiving groove or
saddle 18 across the head 19. As shown in Figure 2, a threaded socket or
pocket 20 is provided for the reception either by threading or by
cementing of a supporting pin. The insulator is preferably made of a
single solid piece and it will be observed that from the point where the
threads begin, as indicated at 21 at the constricted part of the pocket
20 to the end of the said pocket 20 the cross-section is substantially
uniform. The thickness of insulation between the bottom of the pocket 20
and the saddle 18 is sufficient to withstand the electrostatic stress of
the line voltage and this, obviously, may be varied without any
departure from the invention. It
is not essential that the insulator he made of the pin type; it may be
made of the post type or it may be made in the form of a bushing with an
axial opening therethrough. It is not usually the stresses on the solid insulation
between the permanent metallic parts which gives trouble; it is the
exposed surface. The body of the insulator has a series of spiral or helical flanges 22 in this case four which are formed like multiple screw threads. The flanges which take the place of petticoats are preferably dished |
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upwardly
so that any water trapped or caught on the upper surface will be
conducted downwardly in a helical path to the bottom of the insulator
and there discharged at the bottom. Water engaging the edges or bottom
surfaces of the flanges will run down into the channel below and
dripping between flanges is thereby positively prevented. The flanges
are course enough, that is thick and wide enough, to
be relatively strong against breakage and they are spaced far enough
apart that there is no danger of any solid body of water which may
strike the insulator bridging the space between flanges.
A drop of water striking the surface of the insulator will
naturally tend to gravitate straight downwardly, but it will be
intercepted by the first channel under it and instead of being led
straight down the surface of the insulator will be conducted off
circumferentially and downward, that is, in a generally helical pass. The
grooves 23 between flanges are open at both top and bottom and
preferably the helical flanges are so arranged that the running out of
the groove at the bottom is out of register with the overrunning of the
groove at the top, although this is optional. In reverse manner it may
be said that the beginning of a flange such as 22 at the top overlaps
the trailing off of the same flange or another flange at the bottom. The
groove 24 under the head 18 may be employed for a tie wire or clamp as
is the present practice. Likewise, at the base of the insulator a groove
25 may be provided for gripping the base of the insulator with a clamp
or the like. The number of flanges may be anything desired within
limits. It is to be observed, however, that the flanges are to be of
such a coarse pitch helically that the incline will be swift enough to
cause water which is precipitated on to the flanges to run downwardly
with sufficient velocity to have a cleaning effect upon the surface.
That is to say, if water is precipitated upon the surface of the
insulator, the pitch of the helical flanges is preferably so steep as to
cause relatively rapid flow of the water to occur in the channels which
are thus formed and thereby tend to carry dust, soot, and the like,
which may be precipitated on the insulator downwardly and discharge the
same at the ends of the flanges at the bottom. Another
feature of the construction of the insulator of my invention is the
steepness of the under surface of the flanges, which is great enough
that any water gravitating down these surfaces will flow with sufficient
velocity to wash these surfaces clear of deposited dust, etc. The
steepness of the under surfaces is greater than that of the top surfaces
and hence the bottom surfaces can clean themselves with less water than
the top surfaces. While
I have shown this insulator as made of porcelain, it is to be understood
that it might be made of glass with equal facility or of any preferred
insulating material which is suitable for the service. This form of construction gives substantially a uniform section
throughout the major part of the insulator and this may be strictly true
in the case of a bushing having a uniform outside and uniform inside diameter
which is contemplated within my invention.
It is also to be observed that while the body which I have shown
is substantially cylindrical, the same may be frusto-conical or of
larger diameter at one end than the other, or the body of the porcelain
may be in general any surface of revolution with flanges of uniform or
of varying section formed upon the surface thereof. The
insulator of my invention may readily be formed by cutting as in forming
a screw thread. It, therefore, lends itself to a novel process of
manufacture. It is
preferably made of a single unitary piece although this is not
essential. In
use the insulator may be mounted in any position, that is, either
vertical or horizontal or at an angle between them and the advantages of
my invention may be secured to a great degree in any position. Rain from
one side of the insulator will be caught by the dished or upturned
flanges and conducted around to the other side. It is not strictly
necessary that the flanges be dished upwardly to secure certain of the
benefits of my invention but when they are so dished upwardly moisture
precipitated on one side will be conducted around the insulator and
thereby wash the opposite side which would otherwise be left dry. By
this scheme the electrostatic stresses are distributed over the surface
of the insulator rather than concentrated upon one side. A continuous
leakage path is thereby provided and since there is a tendency to
provide spiral paths moisture will tend to remain in the spiral paths
and the edges of the flanges will dry off first, leaving the spiral
paths to form conducting films providing continuous leakage paths until
they are dried off. If
a discharge over the surface should occur, it will be seen that the
heating of the air thereby reacting against the spiral flanges will tend
to move the arc and rotate it about the surface of the insulator.
This gives a tendency to prevent concentration of the heat and to
chill and quench the arc. The
depth of the flanges may be widely varied and their thickness may,
likewise, be varied, but the design I have shown gives a form easily
shaped and fired. It is desirable to have the flanges sufficiently thick
to be rugged for the practical requirements of handling, end if the
flanges are made relatively short and thick the present great strength
against fracture even as against the discharge of missiles or bullets
against the same. The well
known and snapping discharge over high tension insulators subjected to
the precipitation of moisture which is particularly objectionable to
circuits and radio channels of communications systems is avoided by my
invention. It is known that the skirts on insulators of
the conventional type decrease wind velocity and allow dirt to be
deposited particularly under the petticoats on the more restricted
sections. In the insulator of my invention the subsequent precipitation
of moisture cleans the entire surface of the insulator and assists in
maintaining its optimum condition. The
insulator may be made in a great variety of forms or shapes without
departing from my invention. Where relatively great lengths are
required, as in transformer bushings and the like, it may be made up in
a series of sections. There is nothing to prevent its being made unitary
for long bushings since the cross-section throughout is substantially
uniform consisting then of a tubular body having helical flanges. I
claim: 1.
As an article of manufacture, an insulator having coiled flanges upon
its surface, said flanges being dished upwardly to provide water
conducting channels and being spaced apart to prevent bridging by
atmospheric moisture. 2.
As an article of manufacture, an insulator comprising a body of
porcelain having a helical flange, said flange being tilted upwardly
throughout its length to form a water collecting and conveying channel. 3.
As an article of manufacture, an insulator comprising a body of
porcelain having a helical flange, said flange being tilted upwardly
throughout its length to form a water collecting and conveying channel,
said channel being steep enough to wash deposited solids downwardly by
the flow of liquid in the channel. 4.
As an article of manufacture, an insulator having coiled flanges each
extending uninterruptedly from top to bottom of the insulator, said
flanges projecting from the surface of the insulator, said flanges being
dished upwardly to define water trapping and conducting channels for
both washing the exposed surface of the insulator and for preventing
dripping. 5.
As an article of manufacture, an insulator comprising a substantially
circular elongated body with a longitudinal axis, helically disposed
flanges each extending substantially from end to end of the body, said
flanges being inclined upwardly throughout their length to provide on
the upper surfaces water conducting channels and to provide on their
lower surfaces water collecting surfaces. 6.
In an outdoor insulator, an integral helically disposed rib having its
base thicker than its edge and being inclined upwardly, the upper
surface forming a helical channel for intercepting the flow of moisture
vertically and diverting it helically. 7.
In an outdoor insulator an integral helically disposed rib having its
base thicker 8.
As an article of manufacture, an insulator consisting of a body of
insulation comprising a circular head member with a peripheral tie wire
receiving groove and a transverse saddle groove, there being a pin
receiving recess which is formed in the lower end of the body and there
being coiled flanges extending out from the sides of the body, said
flanges having a pitch steep enough to cause water to travel by gravity
along the surfaces of said flanges fast enough to wash away impurities
deposited thereupon from the atmosphere, said flanges having their outer
margins tilted upwardly, to define between the outer margins and the
body of the insulator water-conducting channels preventing drip from one
flange to the flange below. 9.
An outdoor insulator having upwardly flared petticoats, said petticoats
being disposed helically. 10.
An outdoor insulator having upwardly flared petticoats, both top and
bottom sides of which are exposed to wetting by rain, said petticoats
being dished for collecting water toward the center of the insulator and
being open to discharge the water so collected, said openings being
angularly displaced with respect to one another. 11.
An outdoor insulator having a vertical axis and having a plurality of
upwardly and outwardly flared flanges both top and bottom surfaces of
which flanges are exposed to wetting by rain, the inclined top and
bottom surfaces being washed by rain water running downwardly and
inwardly towards the axis of the insulator, the water running down the
bottom inclined surface of one flange being collected upon the top
surface of the flange below, said flanges having discharge outlets for
the water collected upon their top surfaces, the outlets of said flanges
being angularly disposed relative to each other about the vertical axis. 12.
An outdoor insulator having a petticoat, all parts of which are directed
upwardly and outwardly so that top and bottom surfaces are exposed to
rain, said petticoat having an outlet for discharging the water which is
collected upon the top surface of the same, and there being a second
petticoat like the first named petticoat but having its outlet angularly
displaced from the first petticoat outlet. 13. An outdoor insulator having a petticoat,
all parts of which are directed upwardly and outwardly so that the top
and bottom surfaces are exposed to rain, said petticoat having an outlet
for discharging the water which is collected upon the top surface of the
same, and there being a second petticoat like the first named petticoat
but having its outlet angularly displaced from the first petticoat
outlet, said second petticoat being located below the first named
petticoat for receiving the rain water that strikes the bottom surface
of the first named petticoat. In
witness whereof I hereunto subscribe my name this 14th day of March, A.
D. 1929. CHARLES L. STROUP. |