The present invention can be better understood on reading the following description and on examining the accompanying drawings, in which:
The casing defines an internal space 5 that is filled with a dielectric gas under pressure, e.g. sulfur hexafluoride (SF6) under gas pressure of 7 bars gauge at 20° C.
The checking apparatus includes a housing 6 secured to or integral with the casing 4. In the example, the housing is formed integrally in one piece with the casing 4, thereby making it possible to avoid problems of sealing between the housing and the casing 4.
The housing 6 defines an internal chamber 8 suitable for being put into communication with the internal space 5 of the casing 4 via a channel 9.
Thus, when the chamber 8 is in communication with the space 5, the pressure prevailing in the chamber 8 is equal to the pressure prevailing in the space 5.
In the example, shown, a densimeter 2 is mounted in gastight manner on the housing 6 and serves to measure the SF6 pressure in the chamber 8.
The densimeter is suitable for detecting at least one pressure threshold, and advantageously two pressure thresholds; a first threshold P1 corresponding to an alarm threshold corresponding to the need to take action on the densimeter, and a second threshold P2 corresponding to operation of the electrical equipment no longer being guaranteed, in particular the current not being interrupted when a short-circuit fault occurs. In which case, the equipment is either open and locked in the open position, or locked in the closed position.
The densimeter 2 is connected to a processing unit (not shown) suitable for indicating to users the state of the electrical equipment.
In accordance with the present invention, the chamber 8 has a volume that is suitable for varying.
In the example shown, the housing 6 has a top portion 12 that forms a lid, and a body 14 on which the lid 12 is mounted in gastight manner. The lid 12 is suitable for being moved in gastight manner relative to the body so as to modify the volume of the chamber 8.
In the example shown, the lid 12 has a smaller-diameter portion 12.1 and a larger-diameter portion 12.2 forming a base, the smaller-diameter portion 12.1 being mounted to slide in the body 14.
Dynamic sealing means 16 are provided between the lid 12 and the body 14 in order to provide sealing by friction while the lid is moving in the body 14. For example, said dynamic sealing means are mounted in a groove provided in an outside periphery of the smaller-diameter portion 12.1. For example, the sealing means are constituted by an O-ring seal or by a lip seal.
The base 12.2 is designed to come into abutment against a free end 14.1 of the body 14.
The checking apparatus also includes means 10 for isolating the chamber 8 from the volume 5 in gastight manner.
In the example shown, the means 10 are formed by a valve comprising a valve closure member 18 and a seat 20 surrounding the channel 9.
Advantageously, the valve closure member 18 is urged resiliently back into contact with the seat 20 so as to close off the channel 9, e.g. by means of a helical spring 25.
Advantageously, the valve is opened and closed directly by moving the lid 12. The valve has a valve closure member stem 22 that is integral with the valve closure member, that is mounted in the channel 9, and that projects into the chamber 8.
A free end 22.1 of the valve closure member stem 22 is suitable for coming into contact with the lid 12, and for being moved in the valve-opening direction indicated by the arrow F by the lid 12.
The spring 25 is mounted in reaction between an end 9.1 of the channel 9 that is opposite from the end carrying the valve seat 20 and the free end 22.1 of the valve closure member stem 22.
This embodiment offers the advantage of being simple and robust; it is then not necessary to provide external control means that are voluminous and exposed to bad weather. In addition, the valve is controlled without requiring additional external elements.
However, a solenoid valve controlled from the outside of the housing 6, for mutually isolating the chamber 8 and the space 5, lies within the ambit of the present invention.
In the example shown, a second channel 26 is provided in the lid 12 in order to bring the pressurized gas to the densimeter. However, it is possible to make provision for the densimeter to open out directly into the chamber 8.
The lid 12 is fastened directly to the body 14, e.g. by means of screws (not shown), e.g. four screws. When said screws are tightened, the checking apparatus is in the configuration shown in
Retaining means 24 for retaining the lid 12 on the body 14 are also provided. Said means also form guide means making it possible to move the lid relative to the body over a given stroke in order to avoid loss of gastightness between the lid 12 and the body 14.
The retaining means 14 are, for example, formed by screws held captive on the body 4 so that they cannot be lost.
Any other system, e.g. a threaded lid with a tapped body, can be considered for moving the lid in the body over a given stroke. Regardless of the system provided, the system is drivable even though the internal pressure generates an opposing force.
Operation of the checking apparatus of the present invention is described below.
In the normal monitoring state shown in
If the gas pressure becomes less than the determined pressure threshold P2, alarm contacts switch over, and the circuit-breaker opens.
When it is desired to check operation of the densimeter:
The screws are gradually loosened. In a first stage, the lid 12 moves away from the body, thereby causing the valve closure member 18 to move towards the seat 20, until said valve closure member comes into gastight contact with the seat 20 and isolates the chamber 8 from the space 5. Then, in a second stage, the loosening of the screws is continued to cause an additional increase in the volume of the chamber 8. The lid operates as a piston.
Boyle's Law states that the volume of a mass of gas is inversely proportional to pressure, at constant temperature.
If the densimeter is operating correctly, the alarm contacts switch over and the circuit-breaker opens. Otherwise, the densimeter requires action to be taken.
The initial volume of the chamber 8 and its volume variation are determined so that the pressure prevailing in the chamber 8, when its volume is at its maximum, is less than the second pressure threshold P2 of the circuit-breaker. It is also possible that the pressure the chamber corresponds to the first threshold P1. In which case, only operation of the alarm is verified, and not switching over of the contacts.
It is also possible to verify operation of the densimeter at the different thresholds.
When the checking shows that the densimeter is operating correctly, the screws are re-tightened, thereby, in a first stage, causing the volume of the chamber 8 as isolated from the space 5 to be reduced, and then, in a second stage, at the end of the stroke of the lid 12, causing the valve to open. The densimeter is, once again, in the configuration in which it monitors the volume 5.
The densimeter has thus been checked without releasing any greenhouse gas into the outside environment. In addition, by means of the present invention, no mass of gas is taken from the casing. Thus any pressure reduction is due only to inevitable leaks and not to the checking.
It is also possible to make provision to verify operation of the densimeter when the pressure in the chamber 8 increases.
By way of example, the filling pressure is at 7 bars gauge, the alarm threshold P1 is at 6 bars, and the threshold P2 is at 5.7 bars.
If a switch-over of the thresholds is desired for a threshold P2 of 5 bars, the variation in the volume V1 once the valve 18 is closed must be increased by more than 30%.
In the example shown, the increase in the volume of the chamber 8 is achieved manually. However, mechanisms can be provided that are controlled by an electric motor and/or by hydraulic actuators.
The checking method described above with reference to the checking apparatus shown in
The densimeter of the present invention offers the advantage of being very simple to construct and to operate.
Number | Date | Country | Kind |
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06 53999 | Sep 2006 | FR | national |