Spring clip for a gas tube surge arrestor

Details Spring clip for a gas tube surge arrestor Spring clip for a gas tube surge arrestor

1999-09-20

2001-09-25

Reichard, Dean A. (Department: 2831)

Electricity: conductors and insulators

Insulators

Through wall or plate

C174S068300, C174S068300, C361S119000

Reexamination Certificate

active

06294740

ABSTRACT:

FILED OF THE INVENTION
The present invention relates to surge suppression devices. More specifically, this invention relates to a one-piece spring clip for a surge arrestor.
BACKGROUND OF THE INVENTION
Gas tube surge arrestors are broadband radio frequency (RF) devices that are capable of allowing a DC-bias to pass along the center conductor of a transmission line while harmlessly shunting the lower frequencies associated with faults or transients to ground. Faults or transients may be induced, for example, by lightning. Many gas tube surge arrestors contain a replaceable gas tube element. Under normal operating conditions, the gas tube element functions as a simple capacitor with a shunt capacitance of typically less than 1 picofarad. However, in the presence of a transient, the gas within the gas tube element ionizes and switches the gas tube element to a low impedance state. The gas tube element may be filled with any suitable inert gas. In this low impedance state, the gas tube element harmlessly passes any surge current present on the center conductor of a transmission line to ground.
Gas tube surge arrestors are known in the art. An example of one type of known gas tube surge arrestor is shown in FIG.
1
. There, a surge arrestor
110
includes a surge is arrestor cap
112
, an annular seal
114
, a bent disk spring
102
, a retention clip
100
, a gas tube element
118
, a center disk
120
, and a center conductor
122
. The retention clip
100
is best shown in
FIGS. 2
a
and
2
b
. The retention clip
100
fits into the surge arrestor cap
112
. The retention clip
100
was used to retain the gas tube element
118
in the surge arrestor cap
112
. The gas tube element
118
includes opposing first and second electrodes
140
,
142
. The electrodes
140
,
142
include radial rims which project radially beyond the outer diameter of the body of the gas tube element
118
. Other known gas tube elements have electrodes that include radial rims which may not project radially beyond the outer diameter of the body of the gas tube element. In any case, the retention clip
100
snaps over and/or beyond the electrodes and applies inward pressure on the gas tube element
118
to secure the gas tube element
118
in the retention clip
100
.
The surge arrestor cap
112
unscrews from the surge arrestor
110
to access the gas tube element
118
housed in the surge arrestor cap
112
, as shown in
FIGS. 1 and 3
. To remove the gas tube element
118
from the retention clip
100
, axial pressure was applied in a direction away from the cap
112
. However, the retention clip
100
had the dual functions of retaining the gas tube element
118
and securing itself in the cap
112
. These two different functions forced designers to produce the prior retention clip
100
and cap
112
within very tight tolerances. Consequently, the cost and time required to produce the retention clip
100
was increased. Likewise, the tight tolerances made installation of the retention clip
100
in the cap
112
and installation of the gas tube element
118
in the retention clip
100
more difficult. In addition, a separate piece, the bent disk spring
102
, was provided to apply downward pressure between the gas tube element
118
and the center disk
120
to ensure a good electrical connection between the first electrode
140
and the center disk
120
which was connected to the center conductor
122
of a coaxial geometry. The bent disk spring
102
also provided pressure between the gas tube element
118
and the cap
112
to ensure a good electrical connection between the second electrode
142
and the inner surface of the surge arrestor cap
112
. However, inclusion of an additional piece, the bent disk spring
102
, made installing the retention clip
100
into the cap
112
more expensive.
The opposing inner surfaces of the electrodes
140
,
142
within the gas tube element
118
define an arc gap, as shown in FIG.
5
. The path that a transient surge follows is also shown in FIG.
5
. For example, if an antenna were struck by lightning, that current surge would be conducted through the antenna, through the center conductor
122
of the connected transmission line, through the gas tube element
118
by sparking between the two end electrodes
140
,
142
(as shown in
FIG. 5
a
), through the retention clip
100
, through the bent disk spring
102
, through the metal surge arrestor cap
112
, through the body of the surge arrestor
110
to a metal bulkhead
104
and finally to ground.
FIG. 4
shows how the surge arrestor
110
is connected to the grounded metal bulkhead
104
.
The drawback of the prior surge arrestor clip design is that it consisted of two individual parts, a retention clip
100
and a bent disk spring
102
. This two-piece design increased the difficulty of installing a new gas tube element and increased orientation errors during assembly. In addition, the two pieces would often get caught together during shipping and handling, making them difficult to separate. Moreover, the prior two-piece design was difficult and expensive to manufacture. For example, it takes approximately 400 hours to manufacture 25,000 bent disk springs and 25,000 retention clips. The cost to manufacture 25,000 bent disk springs is approximately $2.00 each and the cost to manufacture 25,000 retention clips is approximately $3.30 each; thus, the two-piece design costs approximately $5.30 each to produce.
Therefore, there is a need for a simpler surge arrestor clip design that reduces the number of parts required, greatly reduces production costs, and reduces the complexity of assembling the surge arrestor and installing and replacing gas tube elements.
SUMMARY OF THE INVENTION
A one-piece spring clip is provided for retaining a gas tube element used in a surge arrestor having a cap with an interior portion. The spring clip includes a generally flat disk having a periphery, a first side and a second side. A plurality of first tabs extend from the first side of the disk at the periphery thereof to retain the gas tube element. A plurality of second tabs extend from the second side of the disk at the periphery thereof to provide a spring force between the interior portion of the cap and the gas tube element.


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patent: 6162995 (2000-12-01), Bachle et al.
patent: 6187088 (2001-01-01), Copeland
patent: 660 261 A5 (1987-03-01), None

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