Fluid handling – With indicator – register – recorder – alarm or inspection means – Plural
Reexamination Certificate
1999-04-09
2001-07-24
Chambers, A. Michael (Department: 3753)
Fluid handling
With indicator, register, recorder, alarm or inspection means
Plural
C137S377000, C137S382000, C137S557000, C073S030020, C073S438000
Reexamination Certificate
active
06263914
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to gas monitors for containers of electrical switching gear. More particularly, the present invention relates to an assembly for attaching a gas density monitor to a tank containing an electrical switching component.
BACKGROUND OF THE INVENTION
A preferred application for the present invention is in tanks or vessels containing high voltage circuit breakers. Therefore, the background of the invention is described below in connection with such devices. However, it should be noted that, except where they are expressly so limited, the claims at the end of this specification are not intended to be limited to applications of the invention in a high voltage circuit breaker. For example, the invention disclosed herein may be employed in association with a circuit switcher, circuit breaker, load break switch, recloser, or the like.
A high voltage circuit breaker is a device used in the transmission and distribution of three phase electrical energy. When a sensor or protective relay detects a fault or other system disturbance on the protected circuit, the circuit breaker operates to physically separate current-carrying contacts in each of the three phases by opening the circuit to prevent the continued flow of current. In addition to its primary function of fault current interruption, a circuit breaker is capable of load current switching. A circuit switcher and a load break switch are other types of switching device. As used herein, the expression “switching device” encompasses circuit breakers, circuit switches, load break switches, reclosers, and any other type of electrical switch.
The major components of a circuit breaker or recloser include the interrupters, which function to open and close one or more sets of current carrying contacts housed therein; the operating mechanism, which provides the energy necessary to open or close the contacts; the arcing control mechanism and interrupting media, which interrupt current and create an open condition in the protected circuit; one or more tanks for housing the interrupters; and the bushings, which carry the high voltage electrical energy from the protected circuit into and out of the tank(s) (in a dead tank breaker). In addition, a mechanical linkage connects the interrupters and the operating mechanism.
Circuit breakers can differ in the overall configuration. However, the operation of most circuit breakers is substantially the same. For example, a circuit breaker may include a single tank assembly which houses all of the interrupters. U.S. Pat. No. 4,442,329, Apr. 10, 1984, “Dead Tank Housing for High Voltage Circuit Breaker Employing Puffer Interrupters,” discloses an example of the single tank configuration. Alternatively, a separate tank for each interrupter may be provided in a multiple tank configuration. An example of a multiple tank circuit breaker is depicted in
FIGS. 1A and 1B
.
As shown in
FIGS. 1A and 1B
, the circuit breaker assembly
1
includes three cylindrical tanks
3
. The three cylindrical tanks
3
form a common tank assembly
4
which is preferably filled with an inert, electrically insulating gas such as SF
6
. The tank assembly
4
is referred to as a “dead tank” because it is at ground potential. Each tank
3
houses an interrupter (not shown). The interrupters are provided with terminals which are connected to respective spaced bushing insulators. The bushing insulators are shown as bushing insulators
5
a
and
6
a
for the first phase;
5
b
and
6
b
for the second phase; and
5
c
and
6
c
for the third phase. Associated with each pole or phase is a current transformer
7
. In high voltage circuit breakers, the pairs of bushings for each phase are often mounted so that their ends have a greater spacing than their bases to avoid breakdown between the exposed conductive ends of the bushings. Such spacing may not be required in lower voltage applications. The operating mechanism that provides the necessary operating forces for opening and closing the interrupter contacts is contained within an operating mechanism housing
9
. The operating mechanism is mechanically coupled to each of the interrupters via a linkage
8
.
During circuit breaker opening or closure, a high voltage potential develops across the contacts. As a result, an electrical arc can develop across the switch contacts, particularly the closer the contacts are to closure. It is desirable to minimize this arc. For this and other reasons, such circuit breakers are housed in tanks
3
which are then be filled with an inert gas such as SF
6
, which acts as an insulator to prevent arcing.
In order to ensure that the gas will perform its insulating task as design, it is important that the gas within the tank is maintained at about a preselected density. However, tanks may have leaks that over time allow the inert gas to escape from the tank. Hence, the density of the gas must be constantly monitored.
FIGS. 1A and 1B
illustrate a prior art gas monitoring system. As illustrated in those Figures, a network of pipes
2
feeds the gas from each of the three tanks back to a single density monitoring device. As one might expect, if the density falls to an insufficient level, this design makes it difficult to determine the location, i.e., which tank is actually experiencing the leak and exposes all of the circuit breakers to failure from a leak in a single tank. Moreover, the intricate piping network also creates more places for leaks to occur.
The system of
FIGS. 1A and 1B
also includes a separate tank temperature monitor
15
. The gas pressure and tank temperature are then fed into a control panel that calculates gas density.
Thus, there is a need for an improved gas density monitoring apparatus.
SUMMARY OF THE INVENTION
The invention meets the above need by providing an assembly for monitoring the fluidic contents of a tank containing an electrical circuit. Particularly, the system monitors a gas density of a tank containing a electrical circuit breaker in a inert gas filled tank. The assembly comprises a monitoring device in fluidic communication with the contents of the tank. The monitoring device is fixedly coupled at one end to an outside wall of the tank. A monitor device cover is disposed over the monitor device and against an outside wall of the tank to maintain the monitoring device at approximately the temperature of the tank.
The assembly is preferably fixed to the tank by way of the monitoring device. An insulator may be attached to an inside surface of the monitor device cover to maintain a temperature within said cover in relation to a temperature of the tank. Preferably, the assembly comprises a valve disposed between the monitoring device and the vessel.
Additionally, the invention contemplates the use of two different valve types. Preferably, at least one of the valves is a shut-off valve such as a ball valve. The other valve type is preferably a gas flow access valve, such as a shraeder valve. The shut-off valve is useful to shut-off the gas flow to the monitoring device during testing of the monitoring device.
Preferably, the shut-off valve handle is configured to prevent the cover from being placed back on the monitoring device when the valve is closed (i.e., shut-off). In this way, the invention insures that a valve that was shut-off during testing is not inadvertently left shut-off when testing is complete.
In addition, the invention contemplates the use of a shraeder valve between the shut-off valve and the monitoring device. A shraeder valve is similar to a tire valve, except of higher quality and having a metal body. An 0-ring sealed cap is also employed to prevent leakage. The use of a shraeder valve provides a test point to apply a predetermined pressure to the monitoring device. Preferably, the monitoring device monitors density. More preferably, the monitoring device monitor pressure and temperature as a proxy for gas density.
The assembly further comprises a gasket disposed between the cover and the tank. The gasket preferably comprises a low temperature vin
Freeman Willie B.
Meyer Jeffry R.
ABB Power T&D Company Inc.
Chambers A. Michael
Woodcock Washburn Kurtz Mackiewicz & Norris LLP
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