US 3596134 A
Description (OCR text may contain errors)
United States Patent Frederick D. Burke 1612 Morton St., Alameda, Calif. 94501 121 Appl. N0, 775,984
122 Filed 061. s, 1968 145] Patented July 27, 1971 172] Inventor  APPARATUS FOR DISCHARGING ELECTROSTATIC ENERGY 9Clailm,7l)nwingligs.
s21 u.s.c1. 317/211, 2/161 1511 1111.0 ..A6lm1/14, HOSf 3/00, A4ld 19/00 1501 FleldolSeareh 317/2,2.2;
 ReterencesCited UNITED STATES PATENTS 2,712,098 6/1955 Legge 317/2 3,379,932 4/1968 Legge 317/2 3,310,709 3/1967 Phillips... 317/2 3,089,915 5/1963 Plummer 174/36 1,940,491 12/1933 Freitag. ....,..........r. 174/5 318,172 5/1885 Delanym. 174/5 2,842,771 7/1958 Foti 2/159 FOREIGN PATENTS 16,111 7/1914 Great Britain .1 317/262 Primary Examiner-Lee T. Hix Assistant Examiner-C. L. Yates Attamey0wen, Wickersham & Erickson 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.
PATENTED .mLensn 3,596,134
SHEET 1 OF 2 34 FIG...3
INVENTOR. FREDERICK D. BURKE ATTORNEYS PATENTED m2? m 3596,1134
SHEET 2 [1F 2 INVENTOR. FREDERICK D. BURKE BY 1 ATTORNEYS APPARATUS FOR DISCHARGING ELECTROSTATIC ENERGY 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,=l:', 21rfc, where E is the line'voltage, f is its frequency, and c, 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 linemans body in contact with a grounded surface, this represents a steady state current of about I 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 0, in addition to a line to body capacitance, q. The body to ground capacitance c,, 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= 015, or about 8XlO Joules at 8 kv., a reasonable voltage for a man located 3 feet from the tower and I2 feet from the line.
During the time the man is drawing an are from the grounded surface the energy in the arc represents the discharge of the body to ground capacitor 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 I00 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 mans 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 Iiner'nans 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 0 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 wearers skin surface. The band may also be in the form of a belt that may fit around the linemans 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 linemans 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 5 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 takt 1 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. I; and
FIG. 7 is a view in section taken along the line 7-7 of FIG. 6.
Referring to the drawing, FIG. I 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 5 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 wearers skin. On the linemans 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 throughthe 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 or the waistband 100, 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 wearers 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 thefront to the back surface (a relatively short distance of approximately 6 V4 of an inch), a situation if allowed to occur would cause uncomfortable hot spots on the wearer's skin. 1
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 workmg.
As shown in detail in FIGS. 4 and 5, the sandals l6 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 I0 and I it is held in place by the sole I6 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.
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 wearers 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 saiddevice, 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 ofsaid device.
5. A protective device adaptedto 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 I 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 isa 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 persons 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 wearers 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 wearers skin and electrically connected to said band;
and footwear means having a conductive sole electrically connected to one of said garters.