U.S. patent number 3,596,134 [Application Number 04/775,984] was granted by the patent office on 1971-07-27 for apparatus for discharging electrostatic energy.
Invention is credited to Frederick D. Burke.
United States Patent |
3,596,134 |
Burke |
July 27, 1971 |
APPARATUS FOR DISCHARGING ELECTROSTATIC ENERGY
Abstract
An apparatus adapted to be worn by persons working in an
electrostatic field for eliminating the discomfort and ill effects
of discharges of electrical energy through the person. It comprises
one or more bands in the form of wearable garters or a belt, each
having a flexible conductive element that will conform to the body
shape and thus lie close to the skin so that electrical discharges
will occur a relatively large body area rather than at a small area
or point contact thereon. The garters and belt are each connected
by flexible leads to conductor devices for contacting grounded
structures, such as foot sandals, gloves or bonding devices at the
ends of the leads.
Inventors: |
Burke; Frederick D. (Alameda,
CA) |
Family
ID: |
25106128 |
Appl.
No.: |
04/775,984 |
Filed: |
October 8, 1968 |
Current U.S.
Class: |
361/220; 2/161.6;
361/223 |
Current CPC
Class: |
A43B
7/36 (20130101); A61N 1/14 (20130101); A43B
1/0054 (20130101) |
Current International
Class: |
A43B
7/36 (20060101); A43B 7/00 (20060101); A61N
1/14 (20060101); A61N 1/00 (20060101); A61m
001/14 (); H05f 003/00 (); A41d 019/00 () |
Field of
Search: |
;317/2,2.2 ;174/5.1
;128/362,329,381,384,385 ;307/92--94
;2/158,159,160,161,164,167 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Hix; Lee T.
Assistant Examiner: Yates; C. L.
Claims
I claim:
1. An apparatus for protecting a person from electrical discharges
in an electrostatic field comprising:
an elongated, flexible, bandlike device adapted to be worn around a
portion of a persons's body said device having a conductive surface
on a front side, a rear side of conductive material connected to
said front side around its edges, insulation material between said
front and rear sides, and means on said device for holding its
conductive surface close to the person's skin when being worn;
terminal connector means spaced apart on said rear side of said
device;
lead means attached to one of said terminal connector means;
and bonding means at the end of said lead means for making an
electrical ground connection with structure near the wearer;
whereby the electrical charge on the person's body is collected
from a relatively large area and is forced to travel from said
front side to said rear side of said device before reaching said
terminal connector means, thereby eliminating a concentration of
charge at any one point on the wearer's body that can cause
discomfort.
2. The apparatus as described in claim 1 wherein said bonding means
comprises a sandal attachable to the wearer's boot;
a conductive sole on said sandal;
and an electrically conductive member forming the termination of
said lead means and embedded in said sole of said sandal.
3. The apparatus as described in claim 1 wherein said bonding means
comprises a pair of gloves to provide additional protection for the
person wearing said device, each said glove comprising a flexible
outer cover, a lining of conductive material attached to the inner
surface of the outer cover and a terminal means electrically
connected to said conductive lining and by a lead means to said
rear side of said device, whereby any contact of a said glove with
structure of a different potential will cause a charge flow from
said bandlike device through the glove instead of through the
wearer's hand and body.
4. The apparatus as described in claim 1 wherein said bandlike
device comprises:
an outer cover having said front and rear sides formed of
rubberized cloth material that is electrically conductive;
a braided metal strip located directly adjacent the inside surface
of said cloth material along said rear side of said device and
connected to said terminal connector means;
a flexible strip of insulation material between said braided metal
strip and said front side of said device.
5. A protective device adapted to be worn by a person working in an
electrostatic field comprising:
an outer cover having outside and inside surface having two side
portions and formed of flexible, conductive material;
a flat flexible strip of metal between said cover side portions of
the inside surface and directly adjacent the inside surface of one
of them;
a flat strip of insulating material between the other side portion
of the inside surface of said cover and said metal strip;
means holding said cover side portions together at their edges with
said strips inside;
and spaced-apart lead connector means fixed to said metal strip and
extending through and outside said cover from its side portion, not
adjacent to said insulating material.
6. The device as described in claim 5 wherein said flexible outer
cover is a conductive, rubberized cloth providing a relatively high
impedance and said metal strip is braided copper providing a
relatively low impedance.
7. The device of claim 5 including means on one side portion of
said cover for securing it tightly around a portion of a person's
body.
8. The device as described in claim 5 wherein said insulating means
is a thin strip of varnished cambric.
9. An apparatus for protecting a person from electrical discharges
in an electrostatic field comprising:
an elongated, flexible band adapted to be worn around the waist,
and a pair of garters each adapted to be worn around the legs of a
person, both said band and said garter including an elongated,
flexible cover of conductive material formed from first and second
side portions connected together along their edges, means on said
cover adapted to hold a first side portion close to the wearer's
skin, an elongated strip of braided metal between said side
portions and connected to terminal means extending outside of said
second side portion and a slightly larger strip of insulating
material secured between said metal strip and said first cover side
portion;
glove means having a conductive inner liner adapted to be next to
the wearer's skin and electrically connected to said band;
and footwear means having a conductive sole electrically connected
to one of said garters.
Description
This invention relates to apparatus for protection against
discharges of electric energy for persons working in an
electrostatic field.
A lineman working near active high voltage lines such as on towers
supporting such lines, is in an electrostatic field and there is a
capacitance current flow from the lines to his body. The magnitude
of this current is a function of the area which his body presents
to the transmission line, the area which the line presents to his
body, and the line to ground voltage.
The magnitude of this current is represented by: i.sub.c =E.sub.L
2.pi.fc.sub.1 where E.sub.L is the line voltage, f is its
frequency, and c.sub.1 is the line to the body capacitance. This
capacitance is a function of the conductor configuration, e.g.
whether single or bundled, and the distance and orientation of the
body with respect to the line and its magnitude may be of the order
of 2 to 8 picofarads. With the lineman's body in contact with a
grounded surface, this represents a steady state current of about 1
milliampere, which is just about at the lowest level of perception.
If, however, the man breaks contact with the grounded surface the
circuit model assumes a new configuration with a body to ground
capacitance c.sub.2 in addition to a line to body capacitance,
c.sub.1. The body to ground capacitance c.sub.2, when 2 or 3 feet
from a tower leg, is of the order of 250 picofarads. The energy
stored is found by the formula P=1/2 cE.sup.2, or about
8.times.10.sup..sup.-3 Joules at 8 kv., a reasonable voltage for a
man located 3 feet from the tower and 12 feet from the line.
During the time the man is drawing an arc from the grounded surface
the energy in the arc represents the discharge of the body to
ground capacitor c.sub.2. This discharge occurs as the voltage on
the body builds up to the level that will cause a discharge across
the existing gap. Once the discharge is initiated the impedance of
the discharge circuit is very small. If, for example, the impedance
of the discharge circuit were 80,000 ohms, instantaneous currents
of about 100 milliamperes or greater may occur for microsecond
pulses. With smaller discharge impedances the current pulses could
be greater for correspondingly shorter durations.
A capacitance discharge may occur between any two conductive or
semiconductive forms in the electrostatic field. Around a high
voltage link a discharge may occur between a steel sling on a
handline and the tower, an isolated piece of staging and an
isolated sling, or from any of these objects to a man's body. If
such current pulses reach a single point on the skin they are very
uncomfortable, although there is presently no evidence that there
is a hazard to heart action. In addition to the discomfort, such
discharges can cause a dangerous reflex reaction on the part of a
lineman or greatly impair his efficiency while he is working high
above the ground. However, it has been found that no sensation of
discomfort occurs when the discharging current is properly
dispersed over a large area of the lineman's skin.
Prior to the present invention an attempt was made to solve the
problem of dispersing the aforesaid discharge pulses by providing
linemen with suits, operating on the principle of the Faraday cage
and using fiberglass material with conductive yarn. These suits
were electrically satisfactory in some instances but proved to be
much too heavy, uncomfortable and somewhat cumbersome. Other
protective suits were made of handwoven cotton cloth with a carbon
yarn interwoven at half-inch intervals, and crocheted from a
combination of cotton thread and cotton yarn. While these products
were also electrically satisfactory, they did not overcome the
problem of wearability. Moreover, they lacked durability, were
subject to snags and were extremely expensive.
A general object of the present invention is to provide a wearable
apparatus for protecting a person against electrostatic discharges
that overcomes the aforesaid problems.
Another object of my invention is to provide such a protective
apparatus that will substantially reduce the discomfort of
electrical discharges on the surface of a person's body. Thus,
while particularly useful as a protective device where discharges
of static electricity may occur, my invention may also be useful to
provide a comfortable electrode for medical instrumentation and
treatment that requires the passage of electricity through the
body.
Another object of my invention is to provide a protective apparatus
for reducing the effects of electrical discharges on a person which
is light, easy to put on and take off, does not encumber the wearer
in any manner when he is working, and that is durable even after
long periods of use and not subject to tearing or snagging.
Another object of my invention is to provide an apparatus for
protecting against electrical discharges that is particularly well
adapted for ease and economy of manufacture.
Still another object of my invention is to provide a protective
apparatus for use in electrostatic fields that is safe and
reliable.
In broad terms, my apparatus utilizes a unique garter or band
having as one of its components a flexible, conductive material
which will conform to the surface contour of the body portion to
which it is attached, and will disperse the discharge of
electricity thereto over a considerable area rather than at a point
contact. Moreover, a lead from the garter to grounded structure is
connected to the garter at a point remote from the portion of
conductive material which actually contacts the wearer's skin
thereby creating an impedance path which dissipates the charge at
the wearer's skin surface. The band may also be in the form of a
belt that may fit around the lineman's waist, and a lineman may
wear one or two such garters and a waistband or belt at the same
time. In conjunction with these bands or garters my apparatus also
preferably includes footwear such as sandals that fit over the
lineman's boots, and gloves worn on the lineman's hands. Both of
the latter components are connected each to a garter or belt by
flexible leads, and other lead members with magnetic ends or clamp
ends may be connected from a belt, band or garter to a conductive
structure adjacent the lineman's working area.
Other objects, advantages and features of my invention will become
apparent from the following detailed description which is presented
in conjunction with the accompanying drawings, in which;
FIG. 1 is a view in perspective of a protective apparatus embodying
the principles of the present invention as it appears when worn by
a person working in an electrostatic field;
FIG. 2 is an enlarged view in perspective of a detached garter
device as shown in FIG. 1, with portions broken away; 6
FIG. 3 is a plan view of the garter device of FIG. 2 with the
unfolded back side of the cover shown in phantom;
FIG. 4 is an enlarged plan view of one form of protective footwear
according to my invention with portions broken away;
FIG. 5 is a view in side elevation and in section taken along line
5-5 of FIG. 4;
FIG. 6 is a plan view showing a glove forming another component of
the protective apparatus of FIG. 1; and
FIG. 7 is a view in section taken along the line 7-7 of FIG. 6.
Referring to the drawing, FIG. 1 shows a protective apparatus
according to the principles of my invention as it appears when worn
by a lineman or some other person required to work in an
electrostatic field. Generally the apparatus includes a pair of
garters 10, each of which may be conveniently worn on the lineman's
leg, preferably below his knee. The garters are attached by means
of suitable hook members 12 at their ends so that they fit snug and
lie flat against the wearer's skin. On the lineman's boots 14 are a
pair of removable sandals 16 having soles 18 of some suitable
conductive material within which is embedded a suitable terminal
member 20. The latter forms a connection point for a conductive
lead which extends from the sandal soles to a garter 10.
The unique construction of my leg bonding garter 10 may be best
explained by reference to FIGS. 2--3. As shown, it comprises a
series of elongated layers of flexible material that are held
together by a pair of snap fasteners 24. In making the garter or
the waistband a strip 26 of conductive material such as copper
shielding braid is laid on a piece of cloth 28 which has been cut
to a predetermined size. This cloth piece is made of a rubberized
material that is also electrically conductive. It is longer than
and also wider than twice the width of the copper braid. With the
braid strip located along one side of the cloth the fasteners are
installed through the strip and the cloth piece so that their
female ends are on the opposite side of the cloth piece from the
braid strip. Now, a flexible strip 30 of insulation material, such
as varnished cambric is laid on top of the shielding braid and the
cloth piece is folded over on top of the insulation material. The
cloth piece is now closed as by stitching 32 around its other three
sides. On the side of the cloth cover from which the female ends of
the fasteners extend, the hook members 12 are attached, one of
which may be connected by an elastic strap 34. Thus, in its
finished form the garter 10 or the waistband 10a, having the same
construction on a larger scale, provides a means for dispersing the
flow of current applied to a fastener over a relatively wide skin
contacting area, that is, discharging pulse of current flowing
through a bonding lead 36 to the garter passes through one of its
fasteners 24 to the copper braid strip 26, and thence through the
rubberized but conductive cloth on the uninsulated side of the
garter to the wearer's skin.
The action of the garter in causing the current to flow around the
insulation strip and dispersing the current over a relatively wide
area, eliminates any uncomfortable sensation or shock to the wearer
so that his work can proceed without interruption.
In essence, the garter 10 is constructed so that the metallic or
low impedance conductive member, the conductive strip 26, is
separated by a relatively long path from the high impedance member,
the cover side which engages the wearer's skin. This forms an
impedance match transformer between the skin (having an impedance
similar to the rubberized cloth of the cover) and the metallic
elements of impedance similar to the grounded tower. The aforesaid
relatively long path is obtained in my garter construction by
causing the current to travel from the front skin engaging surface
and around the edge to the back of the garter where the lead
connectors project therefrom. The insulating strip 30 prevents the
current from going directly from the front to the back surface (a
relatively short distance of approximately 6 1/4 of an inch), a
situation if allowed to occur would cause uncomfortable hot spots
on the wearer's skin.
As an additional part of my protective apparatus a larger band or
belt 10a which is similar in all respects except size to the
garters 10 is worn around the waist of the lineman. Connected to
this waistband are one or more flexible leads 36 which are provided
at their ends with a suitable bonding member 38. This bonding
member may be a magnet or any desired form of clip that will enable
the lead to be electrically connected to a grounding structure
while the lineman is working.
As shown in detail in FIGS. 4 and 5, the sandals 16 according to my
invention, are constructed so that the discharge of electrical
energy will be well dissipated regardless of which portion of the
footwear comes within close proximity to or touches grounded
structure.
In the embodiment shown, the sandal sole 16 has a uniform thickness
and is made of a flexible, conductive material with good wearing
qualities. A rubberlike composition material containing embedded
particles of graphite or some other conductive material is one
example of such sole material. Attached to the top of the sole is
an open cover 40 of leather or some other nonconductive material
such as a flexible plastic having a central portion which is
attached to the upper side of the sole as by stitching around its
edges. Integral strap portions extend from the central cover
portion for holding the sandal on a boot or shoe. The lead 22 from
the garter 10 extends through the cover 40 and into the conductive
sole 18 where its end is preferably attached to and anchored by the
rivetlike terminal 20. The latter terminal is also connected to a
striplike conductor 42 that extends longitudinally substantially
along the length of the sole between its upper surface and the
cover. This latter conductor may be a flexible strip of braided
metal similar to the conductive strip material 26 of the garter 10
and it is held in place by the sole 16 and the cover member 40.
What the conductor strip does is to provide a low resistance
current path to the lead terminal 20 from any point of external
discharge along the edge of the sandal thereby reducing the voltage
gradient along the length of the sandal or on whatever footwear it
is installed. Although the sole material 16 is conductive, it has a
relatively high resistance, so that a substantial voltage gradient
normally would occur (without the conductor strip 42 present)
between the lead terminal 20 at the heel end of the sandal and the
toe of the sandal. Heretofore, this gradient caused uncomfortable
secondary discharges to occur between the wearer's foot and the
conductive footwear. However, with the sandal 16, this problem is
now eliminated since a contact of the sandal sole at any point
provides a short path to the conductive strip.
Another component of my apparatus is a pair of unique gloves 44
which are worn by the lineman and are connected by a flexible lead
46 to either a garter 10 or his waistband 10a. As shown in FIGS. 6
and 7 my gloves 44 may have the conventional shape and external
construction, preferably comprising both palm and gauntlet outer
portions 48 and 50 of some flexible nonconductive material such as
leather or the like. However, on the inside of these outer portions
a conductive lining 52 is provided. This inner lining may be a
silver coated fabric material such as nylon which I have found to
be particularly effective in dispersing electrostatic currents.
The usual method for fabricating gloves is to cut the parts with a
die and sew them together. To install the fabric lining, I trace an
outline of the die which includes a slight margin, bond the piece
of leather to a sheet of the silver coated nylon cloth and, after
it has dried, I then die cut the lamination to give an integral
unit. However, in some instances I may prefer the conductive lining
to be a thin layer of silver which is applied directly to the
inside surface of the outer glove portions. This layer may be
extremely thin (i.e. less than one-thousandth of an inch) and it
may be applied while suspended in a thermal setting binder that can
be rolled onto the nonconductive glove material.
In order to provide bonding so that all parts of the conductive
liner are electrically connected to all other parts, an extra
half-inch tab 54 may be left at the lower side of the cuff or
gauntlet pieces and when the finished gloves are assembled, this
tab overlaps the lining which covers the thumb, palm and back of
the hand, thereby making good contact between all the conductive
lining surfaces of the gloves.
Near the edge of the glove cuff 50 or at some other convenient
location, a terminal fastener 56 is provided that makes a contact
with the inner conductive lining 52 and is connected to the lead 46
which preferably extends up the wearer's arm and is attached to his
belt band 10a. Although a high potential discharge may pass through
the outer glove material, the inner liner serves as a large contact
area and when connected to the waistband 10a it further dissipates
the charge.
With all of the aforesaid apparatus properly in place the wearer is
completely protected, and whenever his body contacts a piece of
structure that is electrically charged due to being in the
electrostatic field, the current will flow through any of his
external contacts on his sandals 16 or his gloves 44 or on the
various bonding leads to the garters 10 or waistband 10a which
disperse the electrical charge over a relatively wide body area,
thereby eliminating any discomfort or danger to the wearer.
To those skilled in the art to which this invention relates, many
changes in construction and widely differing embodiments and
applications of the invention will suggest themselves without
departing from the spirit and scope of the invention. The
disclosures and the description herein are purely illustrative and
are not intended to be in any sense limiting.
* * * * *