Arc extinguishing material

An arc quenching composition suitable for deionizing and extinguishing a high voltage electrical arc comprising an effective proportion of hexamethylenetetramine. Depending on the application in which the arc extinguishing composition is employed, the hexamethylenetetramine may be utilized alone, admixed with a suitable binder, or used to impregnate another material.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to arc quenching materials for high voltage 
electrical devices and equipment wherein under certain conditions of 
operation a high voltage electrical arc is produced that must be quenched 
to eliminate an undesirable current flow. More particularly, the present 
invention relates to the use of hexamethylenetetramine as an arc quenching 
material in devices such as high voltage fuses, circuit breakers, circuit 
interrupters, lightning arresters, and separable cable terminations. 
2. Description of the Prior Art 
It is well known in the art that to provide effective circuit interruption 
it is desirable to utilize an arc quenching material or substance in 
circuit interrupters and similar devices such as fuses to quench and 
suppress arcing during contact separation or fuse operation. Typically a 
trailer-liner configuration is used in circuit interrupters so that the 
arc is drawn into the annular space between the trailer and liner, each of 
which may be formed from an arc quenching material. The action of the 
gases produced by the trailer or liner on the confined arc tends to 
deionize the arc and force its extinction. In a high voltage fuse, 
typically a sleeve or liner surrounds the path of the arc during fuse 
operation. Many nonconductive materials are capable of being fabricated 
into the desired shapes, but the arc quenching current-interrupting 
effectiveness of such materials varies and many such materials are less 
effective in providing repeated arc quenching capabilities after initial 
use. Typically, circuit interrupters, excepting fuses, have utilized 
Plexiglas (methyl methacrylate polymer) as a trailer material and 
Plexiglas, horn fiber, or Delrin (polyoxymethylene) as a liner material. 
It is well known in the art that in order to perform properly, an arc 
quenching material should have three immportant qualities. First, the 
material should be highly effective in quenching arcs produced over a wide 
range of electrical operating conditions. The properties of the materials 
should be such that an arc extinguishing gas is evolved quickly and 
effectively with a minimum consumption of arc extinguishing material. By 
minimizing the consumption of the arc quenching material, its operating 
life is prolonged. 
Secondly, the arc quenching material and its solid fused residue should be 
relatively nonconductive to avoid reestablishing a current flow through 
the device after it has operated. 
Finally, the arc quenching material should be capable of being molded or 
compounded with other materials into a composition having sufficient 
structural properties for the particular device in which the arc quenching 
material is employed. 
Other properties of the arc quenching material may also be important, such 
as thermal stability. It is also desirable that the arc quenching gas 
evolved be neither obnoxious nor toxic. 
It has been discovered that hexamethylenetetramine is an effective and 
suitable arc quenching material. 
SUMMARY OF THE INVENTION 
The present invention concerns a new and improved arc quenching material 
comprising an effective proportion of hexamethylenetetramine. The 
hexamethylenetetramine may be utilized alone, admixed with a suitable 
binder, or used to impregnate other materials. 
Therefore, it is a primary object of the invention to provide effective arc 
quenching compositions meeting the three primary requirements noted above. 
Specifically, it is an object of the invention to provide an arc quenching 
material which is effective in quickly extinguishing high voltage 
electrical arcs over a wide range of electrical conditions and with a 
minimum consumption of the arc quenching material. 
Yet another object of the invention is to provide an arc quenching material 
capable of being formed and compounded into arc quenching compositions 
having structural properties sufficient for use in a wide variety of 
devices and applications. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention concerns arc quenching compositions comprising an 
effective proportion of hexamethylenetetramine. Hexamethylenetetramine has 
the following general chemical structure: 
##STR1## 
It has now been discovered that hexamethylenetetramine is an effective arc 
quenching material, i.e., the heat of a high voltage electrical arc causes 
hexamethylenetetramine to evolve a sufficient amount of deionizing and 
extinguishing gases that the electrical arc is extinguished rapidly and 
effectively. The gases evolved consist primarily of formaldehyde and 
ammonia but in such quantities as to be neither obnoxious nor toxic. 
In some applications, hexamethylenetetramine may be utilized without the 
addition of other materials. In these instances hexamethylenetetramine may 
be molded or compressed directly into the form in which it is to be 
employed in the particular electrical equipment. 
In a number of other uses, it may be desirable to employ 
hexamethylenetetramine with a binder. Suitable binders include 
thermoplastic and thermosetting organic resins, elastomers, and inorganic 
binders. Suitable thermoplastic or thermosetting organic resin binders 
include acrylonitrile butadiene styrene terpolymers, acetal copolymers and 
homopolymers, and acrylic, alkyd, allyl, cellulosic, epoxy, ionomer, 
polyallomer, polyethylene, polymethylpentene, polypropylene, and 
polystyrene resins. 
Similarly, the following natural and synthetic elastomeric materials may be 
useful as binders in arc quenching compositions of this invention: natural 
rubber, styrene-butadiene rubbers, butyl rubber, ethylene-propylene 
rubbers, reclaimed rubber, polyacrylic rubber, Hypalon (chlorosulfonated 
polyethylene--a synthetic rubber), nitrile elastomers, silicone 
elastomers, fluorocarbon elastomers, polyurethane elastomers, synthetic 
polyisoprene, neoprenes, and polysulfide polymers. Suitable inorganic 
binders include portland cement, plaster of paris, clay, ceramics, and 
water glass (sodium silicate).

The foregoing examples are illustrative of suitable materials which may be 
utilized as binders to provide the requisite structural properties for the 
particular application in which the hexamethylenetetramine arc quenching 
composition of the present invention is to be employed. Other materials 
than those specifically listed may also be employed and the present 
invention is not limited to the examples listed above. 
To further strengthen the arc quenching compositions, it may be desirable 
to employ additional fillers or fibers. Fibrous materials which may prove 
useful in particular applications include, among others, asbestos, 
cellulose, glass, inorganic materials, including ceramics, and synthetic 
organic fibers, such as polyacrylonitrile, polyamide and polyester fibers. 
Typical fillers include calcium carbonate, metal oxides, including 
alumina, beryllium oxide, magnesia and zinc oxide, comminuted polymers, 
and natural and synthetic silica materials. These materials are primarily 
employed to lend desirable structural properties to the arc quenching 
composition and to reduce cost. However, in some instances fibrous 
materials such as those listed may be impregnated with 
hexamethylenetetramine and utilized in this form without a binder. In 
addition, the arc quenching compositions may also include small amounts of 
other materials which have arc extinguishing ability or which enhance the 
arc extinguishing ability of hexamethylenetetramine. Such materials 
include, for example, hydrated alumina and boric acid. 
The arc quenching compositions of the present invention typically include 
from 5.0 to 100.0 percent by weight of hexamethylenetetramine and 
preferably from 10 to 70 percent by weight hexamethylenetetramine. The 
minimum amount of hexamethylenetetramine which is effective in any 
composition and the most effective percentage of hexamethylenetetramine 
employed in any specific composition depends on the nature of the binder, 
fillers, and other effective arc quenching materials which are utilized. 
The minimum and most effective proportions of hexamethylenetetramine for 
particular circuit interrupting capabilities are primarily determined by 
empirical methods. 
Numerous methods known in the art may be employed to incorporate 
hexamethylenetetramine into arc quenching compositions in which a fibrous 
support material or a binder is employed. For example, an aqueous solution 
of hexamethylenetetramine can be prepared and the solution used to 
impregnate the fibrous material preformed in the appropriate part of the 
electrical apparatus. The absorption of hexamethylenetetramine from the 
solution can be facilitated by applying a vacuum. Alternatively, the 
solution can be used to impregnate fibrous material which is then 
incorporated into the binder. Another alternative is to mill the 
hexamethylenetetramine and binder on a plastics mill and then transfer 
mold or extrude the mixture into the appropriate shape. Other suitable 
methods known in the art can be utilized to prepare the 
hexamethylenetetramine arc quenching compositions of this invention. 
Some typical hexamethylenetetramine containing arc quenching compositions 
which may be employed include the following: 
______________________________________ 
Com- 
position 
Ingredients 
______________________________________ 
A hexamethylenetetramine 
(no additional materials) 
B hexamethylenetetramine 
100 parts by weight 
polyethylene 50 parts 
C hexamethylenetetramine 
20 parts 
nylon paper 80 parts 
D hexamethylenetetramine 
100 parts 
polypropylene 50 parts 
E hexamethylenetetramine 
100 parts 
bisphenol A liquid epoxy resin 
100 parts 
diethylenetriamine 10 parts 
dibutyl phthalate 20 parts 
F hexamethylenetetramine 
50 parts 
alumina trihydrate 100 parts 
bisphenol A liquid epoxy resin 
100 parts 
diethylenetriamine 10 parts 
dibutyl phthalate 100 parts 
G hexamethylenetetramine 
100 parts 
polyester resin 100 parts 
methyl ethyl ketone peroxide 
1 part 
H hexamethylenetetramine 
50 parts 
alumina trihydrate 100 parts 
polyester resin 100 parts 
methyl ethyl ketone peroxide 
1 part 
______________________________________ 
EXPERIMENTAL EVALUATIONS 
The following tests were conducted to illustrate the effectiveness of 
hexamethylenetetramine as an arc quenching composition. 
Evaluation 1 
In this evaluation, arc interrupting compositions of the present invention 
were prepared and tested in a loadbreak device as described and 
illustrated as element 55 in U.S. Pat. No. 2,351,826 to Lindell et al. 
which is assigned to the assignee of the present invention. The 
composition utilized consisted of two-thirds by weight 
hexamethylenetetramine to one-third polyethylene ("2:1 H/P") corresponding 
to composition B above. The hexamethylenetetramine and polyethlene were 
compounded on a two-roll plastics mill and then transfer molded into 
liners (bore 65 of the device shown in the referenced patent) and trailers 
(75). Rather than using a stack of rings as shown in the referenced 
patent, the liners were molded in a one piece cylindrical form. The liners 
were approximately 3.4 inches long with outside and inside diameters of 
0.87 inches and 0.63 inches, respectively. The trailers were molded on 
polyester glass fiber rods and were approximately 3.6 inches long and 0.60 
inches in diameter. The liners and trailers were then installed in the 
loadbreak device and tested at a number of operating conditions as shown 
in Table I. The average time needed to quench the arc was determined and 
is reported in Table I. These results are compared to the results of 
similar tests performed on a standard arc extinguishing material ("STD") 
comprising a trailer fabricated of Plexiglas and a liner fabricated of 
Delrin. Test 1 tested the arcing time under load circuit conditions. Tests 
2-6 evaluated the materials under fault switching conditions. The severity 
of tests 2-6 was increased by increasing the natural frequency of the 
transient recovery voltage. Testing of each material was continued until 
failure occurred or the limit of the test equipment was reached. 
For the purposes of this test evaluation and the following test 
evaluations, it should be understood that the following terms have the 
following commonly well known definitions. 
The "recovery voltage" refers to the 60 hertz voltage that appears across 
the switching device after interrupting the circuit. Recovery voltage is 
normally the open circuit voltage and the recovery voltage does not 
contain any transient components. 
The "transient recovery voltage" is the voltage that appears across a 
switch or loadbreak device during the time when the switch goes from a 
current conducting state, i.e. when the voltage across the switch is 
nominally zero, to the time when the voltage is the 60 hertz recovery 
voltage described above. During fault switching, this transient recovery 
voltage oscillates at a usually high frequency and this frequency is 
called the "transient recovery voltage frequency." This oscillatory 
transient voltage overshoots the crest of the recovery voltage and can 
have a maximum value of twice the nominal recovery voltage. 
The "power factor" is a measure of the reactive nature of the test circuit. 
For the purposes of these test evaluations, the smaller the power factor, 
the more severe is the peak of the transient recovery voltage, and 
consequently the test circuit is more severe. 
TABLE I 
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ELECTRICAL CONDITIONS 
Transient 
Recovery 
RESULTS 
Recovery Voltage 
No. of Time 
Voltage 
Amperes 
Power 
Frequency 
Operations 
(milliseconds) 
(kV) (rms) 
Factor 
(kHz) 2:1 H/P 
STD 
2:1 H/P 
STD 
__________________________________________________________________________ 
TEST 1 
15.2 600 1 -- 5 5 10.8 13.5 
25 600 1 -- 5 5 14.8 29.1 
24 900 1 -- 8 6 21.8* 
31.3 
TEST 2 
9 93 .3 5 5 5 11.9 16.1 
9 600 .3 5 5 5 13.6 15.4 
15.5 87 .3 3.6 5 5 17.2 22.4 
15.5 87 .3 8.7 5 2 18.1 F 
15.5 87 .3 13.3 5 0*** 
22.6 --*** 
TEST 3 
15.5 590 .34 4.3 3 3 10.5 17.3 
15.5 590 .34 8.6 3 3 11.8 16.5 
15.5 590 .34 11.3 3 2 12.5 F 
15.5 590 .34 14.6 3 0 16.3 -- 
15.5 590 .34 18.2 3 0 21.3 -- 
15.5 590 .34 20.8 1 0 F** -- 
TEST 4 
27 100 .3 4.5 3 1 F F 
TEST 5 
15 1200 .3 5 3 3 14.0 14.2 
15 1200 .3 9.3 3 1 14.8 F 
15 1200 .3 14.3 3 0 17.5 -- 
TEST 6 
14 2000 .3 8.3 3 1 F F 
__________________________________________________________________________ 
*One sample exhibited an external flashover caused by extraneous gas flow 
along the insulator surrounding the sleeve but this factor is not a 
measure of the effectiveness as an arc extinguishing material. 
**F the arc was not extinguished at the indicated conditions. 
***Test was discontinued following a failure. The data in Table I 
illustrates the ability of hexamethylenetetramine to rapidly extinguish 
electrical arcs produced over a variety of electrical conditions. 
It should be noted that the two to one composition of 
hexamethylenetetramine and polyethylene ("2:1 H/P") material demonstrated 
substantially shorter arcing times under load conditions (Test 1) than the 
standard ("STD") material. Further under fault switching conditions, the 
2:1 H/P material not only demonstrated shorter arcing times, but also 
demonstrated effectiveness in extinguishing arcs at more extreme 
conditions than the standard ("STD") material. 
Evaluation 2 
In this evaluation, arc quenching compositions were prepared employing 75 
percent by weight hexamethylenetetramine and 25 percent polyethylene ("3:1 
H/P"). Liners and trailers were prepared as in Evaluation 1 and 
incorporated into a loadbreak device as previously described. However, in 
place of the toggle linkage incorporated in the loadbreak device of the 
referenced patent, an air cylinder was used to provide the force to snap 
the electrical contacts apart and thereby form an arc. 
The liners and trailers were then tested under the following two different 
sets of electrical conditions, and the results are reported in Table II. 
Similarly, the same tests were conducted on a standard ("STD") material 
comprising a liner fabricated of Delrin and a trailer fabricated of 
Plexiglas, and the results of these tests are also reported in Table II. 
______________________________________ 
Test #1 
Test #2 
______________________________________ 
Recovery Voltage (kV) 
15.5 15.5 
Amperes (rms) 40 46 
Power Factor .27 .60 
Transient Recovery 5.0 2.8 
Voltage Frequency (kHz) 
______________________________________ 
TABLE II 
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Clearance Average 
Between Arcing 
No. of Sleeve Time Weight Loss 
Ma- Oper- & Trailer (milli- 
(grams/cycle*) 
Test terial ations (ins.) seconds) 
(Sleeve) 
(Trailer) 
______________________________________ 
1 3:1 25 .034 35.08 0033 .0033 
H/P 
STD 25 .038 44.33 .0427 .0430 
2 3:1 25 .034 20.42 .0012 .0009 
H/P 
STD 25 .034 17.78 .0013 .0014 
______________________________________ 
*As in Evaluation 1 alternating current at 60 hertz was utilized. 
The data in Table II illustrate the ability of hexamethylenetetramine arc 
quenching compositions to effectively extinguish an electrical arc with a 
minimum consumption of arc quenching material. Further, in comparison, the 
3:1 hexamethylenetetramine polyethylene material demonstrated 
significantly less weight loss than the standard material under the 
conditions of Test 1, and measurably less weight loss under the conditions 
of Test 2. Thus, as shown by this data, the hexamethylenetetramine arc 
quenching material may be repetitively and successfully employed without 
requiring replacement. 
Evaluation 3 
In this evaluation, arc quenching compositions were utilized in a high 
voltage fuse. Typically such devices contain an inner sleeve surrounding 
the path of the arc which is produced when the fuse operates. In the 
present example sleeves of several different materials were impregnated 
with an aqueous solution of hexamethylenetetramine under vacuum. The 
sleeves were then dried. Comparative weighing revealed that the sleeves 
had absorbed between 5 and 35 percent by weight hexamethylenetetramine. 
The sleeves were then tested under various electrical conditions selected 
to simulate as closely as possible actual fault conditions on transformers 
and the results are reported in Table III. The specifications for the 
various samples listed in Table III are given in Table IV. Samples B-1 
through B-4 utilized nylon paper and samples B-5 through B-8 utilized 
cellulose paper. The tests were also conducted on standard ("STD") 
commercially available fuse link sleeves for comparison purposes, and the 
results of these tests are also reported in Table III. 
TABLE III 
__________________________________________________________________________ 
Test Conditions*** 
27kV 
50 amp 
27kV 
100 amp 
27kV 
200 amp 
27kV 
400 amp 
9 kHz 
.80 PF 
14 kHz 
.55 PF 
20 kHz 
.45 PF 
18 kHz 
.20 PF 
Sample 
Clear* 
Fail** 
Clear 
Fail Clear 
Fail Clear 
Fail 
__________________________________________________________________________ 
STD 10 0 0 10 0 10 5 5 
B-1 3 0 5 0 3 0 3 0 
B-2 3 0 2 1 0 3 2 1 
B-3 3 0 3 2 3 0 3 0 
B-4 3 0 3 0 2 1 1 2 
B-5 -- -- 3 0 2 1 2 1 
B-6 -- -- 3 0 3 0 0 3 
B-7 3 0 2 1 3 0 3 0 
B-8 -- -- 3 0 2 1 3 0 
__________________________________________________________________________ 
*Number of tests in which arc was successfully extinguished. 
**Number of tests in which arc was not extinguished. 
***Recovery voltage (kV), current (amp), transient recovery voltage 
frequency (kHz), and power factor (PF). 
TABLE IV 
______________________________________ 
I.D. Thickness Length 
Sample (in.) (in.) (in.) 
______________________________________ 
B-1 .210 .03-.04 55/8 
B-2 .210 .03-.04 81/2 
B-3 .260 .03-.04 55/8 
B-4 .260 .03-.04 81/2 
B-5 .210 .03-.04 55/8 
B-6 .210 .03-.04 81/2 
B-7 .260 .03-.04 55/8 
B-8 .260 .03-.04 81/2 
______________________________________ 
The data in Tables III and IV again illustrate the effectiveness of 
hexamethylenetetramine as an arc quenching material, in this instance in 
the form of impregnated paper rather than in conjunction with a binder. It 
should be noted that at the 100 and 200 amp range, the various test 
samples demonstrated marked superiority over the standard commercially 
available sleeves. At the 400 amp range, most of the test samples 
demonstrated superiority over the standard commercially available sleeves.