AU610669B2 - A leak indicator - Google Patents

Description

P/00/011 -1 RUST 6 0669 PATENTS ACT 1952-1973 Form COMPLETE SPECIFICATION

'ORIGINAL)

FOR OFFICE USE Class: Int. CI:.

Application Number: Lodged: aedments made undr SSection 49 and is cgrrect for printing Complete Specification-Lodged: Accepted: Published:- Priority: at it Related Art: TO VE COMPLETED BY APPLICANT Name of Applicant:.

Address of Applicant: EB DISTRIBUSJON a Norweigan company of Peter Feilbergsgt. 4B, N-3700 Skien, Norway.

Actual lnvelitor: Address for Service:.

JAN MORTEN ERIKSEN, JAAP E. DAALDER PIETRO

CIBOLDII

Care of: COWIE, CARTER HVIV 71 QUEENS ROAD, MELBOURNE, 3,904, AUSTRALIA Complete Specification for th,9 invention entitled:* A. LEAK( INDICATOR The following statement is a full description of this invention, including the best method of performing it known to me a- 'Note: 'The description Is to be typed In double spacing, pica type faco, In an area not exceeding 250 mm In depth and 180 mm In width, on tough white paper of good quality slid it Is to be inserted Inside this form,

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11t76-L C.J.70%sos, Commonwealth Gaornmern Printer.Canberm 1 A A LEAK INDICATOR The present invention relates to a leak indicator for a gas filled plant, said leak indicator being of the Bourdon-tube kind, where the Bourdon-tube is filled with a gas which has the same properties as the gas surrounding the Bourdon-tube, and is in a sealed state, with the nominal gas pressure in the plant deviating from the ambient atmospheric pressure in the plant.

A leak indicator is previously known which is mounted inside one of the applicant's plants for compact, gas filled high voltage switches with the utilized gas being SF 6 The leak S e indicator may be red through a window in the incapsulation of cc the plant. The known indicator 1, shown in Figure 1, has a E: 15 graduation with three zones, a green zone 2 indicating correct pressure, a red zone 3 indicating a leak in the plant, and a ,white zone 4 bordering said green zone and indicating a fault .P of the indicator.

The leak indicator is compensated for temperature by the fact that the Bourdon-tube (not shown) of the indicator is filled with the same kind of gas as the gas used in the plant.

ao 0 oo o S Normally, a decrease of temperature would result in a lower 25 o o pressure inside the incapsulation of the plant, in the same manner as an increase of temperature would cause an increase of pressure. The leak indicator is, however, unaffected by such variations, and will only indicate decreasing pressure 30 inside the incapsulation due to SF 6 -gas leaking to the surroundings.

The position of the indicator marker in case of normal operation is on the left hand side of the green zone, close 3 to the white zone, as indicated by dot-dash-arrow In case of a defect, e.g. a gas leak from the incapsulation of the plant, marker 5 will move towards red zone 3. In case of a defect of the indicator per se, i.e. a leak of the Bourdoni 2

SF

6 gas at a nominal pressu'e of 1.4 bar abs. at 20 0

C.

The nominal pressure inside the encapsulation of the compact plant is 1.2 bar abs. at 20 OC. Thus, the indicator which is placed inside the encapsulation will under normal condit- "a 10 ions show an overpressure of 0.2 bar (green zone). In case of 10 re€ a leak the pressure inside the encapsulation will drop 0 towards atmospheric pressure. Indicator marker 5 will w a consequently move towards red zone 3 (in accordance with a S:,e differential pressure of 0.4 barbetween the pressure in the in- 15 dicator and the pressure in the encapsulation) A leak in the indicator (Bourdon tube) will equalize the pressure between indicator and encapsulation, and the indicator marker will oa move towards white zone 4.

0 0o Temperature compensation is, as mentioned, automatically achieved by this concept. A change of temperature will cause the same change of pressure inside and outside the Bourdon tube. This means that the differens of pressure inside the 00 0o Bourdon tube and the pressure inside the encapsulation will stay constant, and so the position of indicator marker 5 will 25 remain cOnstant, independently of operation temperature. This method provides an exceptionally simple and reliable control of the pressure inside the encapsulation. The advantage of this known leak indicator will be especially obvious when compared to other instrumentation used by producers of SF 6 6 compact plants.

The known concept shown in Figure 1 was used for some time for the applicant's S plant for compact gas filled high voltage switches with voltage levels of 12 and 24 kW.

A commonly known method for measuring the SFP pressure inside a plant encapsulation is utilization of a pressure gauge i U -u s-e b p o c s f F o U- Iopctpans -3 is provided externally on the encapsulation.

00 0 0 0 0 0 0 0000 00 00 0 00 0 00 0 000 00 0 00 0 00 0 00 0 0 0 0 00 0 0 0

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0 0 00 0 0 0 0 00 0a0 0 0 This known concept, however, shows some weak points, as it is influe-iced by differencies of temperature inside and outside the encapsulation and by atmospheric pressure differencies.

Changes of temperature and atmospheric pressure may cause pressure differencies in the encapsulation of several tenths of a bar. For this reason it is necessary to use graphs showing the SF 6 pressure inside the encapsulation as a function of temperature and atmospheric pressure, such graphs commonly being shown on a signboard which is placed close to the manometer. Correct indication of pressure, however, can only be achieved if the temperature of the SF, gas is known, but this is an information commonly not available. Dependent on the electrical load on the plant, and ambient conditions the temperature of the SF 6 gas will be highly variable, and may be much different from the external ambient temperature. Precise readings of the manometer are, thus, difficult, especially considering 20 the fact that the nominal difference of pressure inside the encapsulation and outside is only in the order of 0.2 bar.

Basically, a user of a SF 6 -plant is not interested in the pressure inside the encapsulation and how it varies 25 dependent on the load on the plant, temperature, and atmospheric conditions. The only information relevant to the user is whether the encapsulation is tight or not.

Utilization of a leak indication as mentioned above in connection with Figure 1 will provide the user with a quite 30 unambiguous answer to that question. It was, however, desirable to provide remote transmission of the measurements of a manometer or a leak indicator, and, thus, to provide a mechanically more simple leak indicator than those previously known.

-4ooa «o 6 00 S0 0 0000 0000 oo a o 0o 0 O0 0 00 0 0 a o According to the present invention, there is provided a leak indicator for a gas filled electrical plant, with said leak indicator being of the Bourdon tube kind, the Bourdon tube being filled with a gas having the same properties Ps the gas surrounding the Bourdon tube, and being in a sealed off state, both the. no'3:inal gas pressure in the Bourdon tube and the nominal gas pressure in the plant deviating from the surrounding atmospherical pressure, nominally a difference being present between the pressure inside the Bourdon tube and the pressure in the plant, wherein the free end of the closed Bourdon tube is arranged to influence, a switch means, for instance a multi-step switch with at least two terminals, and wherein the leak indicator may be supplied with voltage directly from the plant, irrespective of' direction of supply to the plant, a first terminal of the switch means being voltage connected capacitively to a high voltage bushing in the plant, and a second terminal of the switch means being connected with a first terminal of a voltage indicator, a second terminal of said voltage indicator being connected to earth, and with contact between said first and second switch means terminals in a normal plant condition, but with no contact between said switch means terminals in case of a deviation from the normal state.

Further characterizing features of the leak indictor mentioned above will appear from the following claims as well as from the following disclosure with reference to enclosed drawings.

Figure 1 shows a known leak indicator.

Figure 2 illustrates a completely mounted leak indicator according to the invention.

Figures 3 and 4 show a side elevation, and an end view, respectively of the leak indicator according to the invention.

Figure 5 illustrates the functional concept of the leak indicator according to the invention.

Figure 6 shows a wiring diagram for testing in connection with leak indicator of Figures 2<4 according to the invention.

Figure 7 is a diagrammatic illustration of the principle for capacitive voltage switch off.

The indicator function proper is based on a manometer 00 0 a 0 00 0 O 00o 0 0 L 71 4A principle with a Bourdon tube 6 actuating a switch 7, via a flexible coupling 8, as will appear from Figure 4, where the free end 6' of the Bourdon tube is connected with an end of flexible coupling 8, whereas the other end of the flexible coupling is connected with a shift arm 7' on switch 7.

Because the indicator must be temperature compensated, as mentioned above, it is placed inside the plant, as will.

appear from Figures 2 and 3. The Bourdon tube activates 10 switch 7, as shown in Figure 4. Switch 7 may be a multi- 0 00 eo step switch, 0 0 o oo o 00 0 00 0 0 0 0000 00 0 0 0 00 0 00 0 00 0 00 00 0' 0 00 0 00.000 0 00 0 0 o o 0 a aooaaI I but in the shown embodiment it is a three-step switch with a central position and two extreme positions, as indicated by designations I, 0, and II at the right hand side in Figure 4.

From step switch 7 wiring 9 is extended through a seal e.g. silicone matter, to the outside, providing a possibility for external testing and control.

Bourdon-tube 6 has a defined volume which is filled with SF 6 gas at 20 0 C to an overpressure of 0.4 bar. The Bourdon tube o 10 is provided inside the plant, generally designated 11, which 0090 defines a SF 6 gas chamber with chamber 11 filled with SF 6 gas S o 6 6 0 00 6 0 at 20°C to an overpressure of 0.2 bar. The indicator will, 0 D 0 oe thus, indicate a differential pressure of 0.4 minus 0.2 bar, o0 o i. e. 0.2 bar, independently of temperature and pressure var- 0000 Bo 5 iations in the plant. In Figure 2 reference number 12 design- °a 15 ates an enclosure, preferably made of ste;l, for plant 11.

Reference number 13 indicates air at atmospheric pressure and, O 09 00 thus, the space outside the enclosure of the plant. In order o°°o to ensure good sealing between plant chamber 11 and the out- 0 p0 2 side 13 of the enclosure seal means, e.g. an 0-ring 14 is 200 0 °o S suitably provided on plant side 11, with said seal means 14 o 00 00eo a forming a gas tight seal against the surroundings 13 when a 0 o nut 15 is tightened on a mantle screw 16 and in contact with 0 oo the outside of enclosure 12.

o00 o .0 0 25 With reference to Figure 4, it will be understood that switch 7 will have its shift arm 7' in position in case of normal operation. In case of a defect, i. e. a leak, in plant 11 the overpressure in the plant will disappear, and the differ- 3 ential pressure between pressure in the Bourdon tube and in 3O the plant will increase towards 0.4 bar. The Bourdon tube will then seek to "straighten' and will, thus, cause shift arm 7' to move to position In case of a defect, i.e. a leak in the indicator proper (Bourdon tube), the differential pressure between pressure in the Bourdon tube and in the plant will disappear, and end 6' of Bourdon tubj 6 will move downwards in Figure 4. This Will cause shift arm 7' to move into position "II The functional principle of switch 7 will be briefly disclosed with reference to Figure 5. During normal operation switch 7' is in position 0, as shown in Figure 5. In case of said defect of the plant the differential pressure between pressure Sin the Bourdon tube 6 and in the plant will increase towards 0.4 bar in the shown embodiment, so that arm 7' moves to position I. If switch 7 is incorporated in a circuit which is driven by an external feed source 17, e. g. an alternating voltage, and an indicator, e.g. a lamp 18 or, e.g. a voltmeter, a 10 lamp 18 will turn off when shift arm 7' reaches terminal I to 0 9 0 *00 indicate that normal conditions no longer prevail. If desired, 0 Qos,0 an alarm might, thus, be given if lamp 18 is, e.g. replaced 0 00 by an alarm device which is activated when voltage disappears.

0 00 0 0 0 0000 00oo 0 In a corresponding manner shift arm 7' will move to position 0 0O II in case of a leak in the Bourdon tube, the differential pressure between the pressure in Bourdon tube 6 and plant 11, 0a o0 thus, disappearing. Lamp 18 will turn off or an alarm will be 0 00 o0,°o given, indicating a deviation from the normal condition.

o 0a 0 o If a leak control does not lead to de'ection of voltage or 0 d0 O if an infinitely large resistance is measured at clamping points 19, 20 in Figure 5, there is probably a leak in the o0 0 plant, and a representative of the manufacturer's must be fetched.

00o o S The user of the plant should normally do nothing with the o0o° 25 plant, apart from seeing to it that the plant is in a normal condition, and summoning assistance if there is a deviation from the normal conditions.

Before the plant is possibly turned off, the leak indicator proper is tested, so that the user may ascertain whether it is a defect of the Boudon tube 6 that caused the fault indication. If such a defect exists shift arm 7' will be in Dosition II, and the representative from the factory will make a 3 check by arranging a short circuit 23 between terminals 21 and 22 representing switch terminals 0 and II, respectively.

Xf lamp 18 lights, this indicates that there is a defect in the leak indicator proper. If lamp 18 still does not light

I

it means that shift arm 7' is in position I, ascertaining that there is a leak in the plant proper or a so called tank leak.

In the concept indicated in Figure 5 power source 17 may, if desired by replaced by supply from the network. Figure 6 illustrates the principle of the possibility of checking whether the enclosure is tight, which may be done by the aid of a voltmeter when the plant is in operation, or by the aid of an ohmmeter when the plant is without voltage. The indicato 10 or also permits Ohm testing when there is a voltage on the plant.

0 80 0 0 008 0 Q The compact plant is commonly provided with test points for aoo capacitive voltage testing at the high voltage ducts incorpo- 9008 0o° 15 rated in the plant. Capacitive voltage is taken from a metal screen which is embedded in epoxy bushings 37 to which the cables are connected (see Figure For a simple illustrato o ion only one phase is shown in Figures 6 and 7 but, as o0o° indicated in Figure 7, capacitive voltage take out is possible O90 for all three phases L L2, L 3 or L L2*, L3*. Such o"o capacitive voltage take out is commonly known to those skilled 0o s0 in the Art and will not be further disclosed. The capacitive 0 0 voltage point from bushings to phase L 1 and phase L respo 0o ectively, is generally indicated by reference number 24.

25 In normal operation of the plant said capacitive voltage points are earthed, as indicated of switches 25. Switches are in an open position 25' when measuring takes place.

Voltage testing may be carried out with suit ble testing equipment which is commercially available. Such testing equipment is, e.g. a so called Pfisterer/Horstmann voltage indicator 200 V.

The concept of permitting gastightness of the plant to be checked by use of said capacitive voltage, thus, provides the possibility of using the control equipment used for voltage testing. A voltmeter may also be used. Voltage testing of the high voltage cables is either made at A or at B. When

I

8 tightness of the plant is to be checked a spring loaded press switch 26 is activated so that voltage is supplied to leak indicator, to terminal 27 of switch 7 (see also Figure If shift arm 7' is in a normal state, i.e. in connection with terminal 21, the voltage wil also be applied to terminal 29, and voltage may, thus, be measured between terminal 29 and earth by the aid of voltmeter 30. In case of deviation from the normal state there will be no connection between terminal 27 and terminal 29, and a separate test must be carried out by the representative of the manufacturer, as mentioned above.

If the Bourdon tube is defect shift arm 7' will provide a connection between terminals 27 and 22, and following a short circuit between terminals 22 and 21 there will again be a 0 voltage between terminal 29 and earth, clearly indicating a defect of the indicator proper. If there is still no such ~voltage present, this means that shift arm 7' forms a connect- I t Sion between terminals 27 and 28. Terminal 28 must not necessarily be accessible, but if it is, a possible short circuit between terminals 28 and 21 will unambiguously indicate 20 whether shift arm 7' forms a connection between terminals 27 and 28, and it will, thus, be ascertained that there is a leak fault in the plant. During said voltage test contacts 0o 31, 32, 33, and 34 of spring loaded switch 26 will have the o o OOao positions shown by reference numbers 31', 32', 33', and 34', 25 respectively, 0 After completed voltage test between terminal 29 and earth switch 26 is released back to its normal position, represented by contacts 31, 32, 33, and 34. Terminal 27 will, thus, be S 30 without voltage, irrespective of terminal 29.

In this position of switch 26 resistance may be measured by the aid of an ohmmeter 35, if desired. Ohmmeter 35 is connected with terminals 29 and 36. If shift arm 7' is in a normal position the ohmmeter will deflect. If, however, the shift arm is either placed between terminals 27 and 28 or 27 and 22, the ohmmeter will not deflect, and checks as discussed in connection with Figure 5 must be carried out. It will be understood that said measuring of resistance by the aid of the ohmmeter may be carried out whether or not there is a voltage on the plant, as press switch 26 is in a normal position, and there is, thus, no voltage on the circuit between terminals 36 and 29.

During measuring operations with voltmeter 30 or ohmmeter and during any further test operations to ascertain whether a leak is due to a defect of the indicator or of the plant, switchi 25 is kept in an open position, as indicated by reference number If it is desired to measure the voltage of phase (Ll) or SO phase switch 25 will also be in the position indicated by reference number 25'. Voltage is then measured between the terminals indicated by A or B, respectively. Switch 26 will then be in its normal position.

E e During normal operations, when no measurements or testing of the leak indicator are to be carried out, switch 25 is placed in the position shown by a full line.

00 Even though the present leak indicator was disclosed, espec- 0 ially with reference to utilization in connection with o o o 25 compact gas filled high voltage switch plants the leak indicator may obviously be used for any desired plant or chamber 0 0 which is under gas pressure. The disclosure is, thus, only meant as an example of a utilization of the present invention.

0 a 0000 a O 30 Even though switch 7 in Figure 4 is generally described as a Sswitch the shift arm 7' of which has an essentially linear movement, other equivalent concepts for forming a connection between the shift arm of a swith and end 6' of Bourdon tube 6 will obviously be covered by the concept of a technical 35 equivalent. The main issue is that the free end of the Bourdon tube acts on switch 7.

Although it was stated in the above disclosure that the mean asa xml faui aio ftepeetivnin 0, 00 Bourdon tube is provided with a nominal pressure above atmospheric pressure, it will obviously be possible to achieve equivalent results if the Bourdon tube were provided with a nominal pressure below atmospheric pressure. It is, however, important that the nominal pressure within the Bourdon tube should not be equal to the atmospheric pressure, since it will always be necessary to create a differential pressure between the pressures inthe Bourdon tube and the plant, resp.

This differential pressure may have a rather optional value, St, 10 whether it is positive or negative. The differential pressure o, of 0.2 bar, as described above, should, thus, only be regard- S, ed as an example without limiting the present invention in any way.

00 0 0 0 o 00 o a0 0 00 0 000

Claims (1)

1. 41-. The claims defining the invention are as follows: 00oo o e 0 00 a a« a o 000 OQ 0 006 0 Q0 00 0 0 9 0 1 t 0 0 0 00. 90 0 0o 0 00 0 0 0 0 0 0 0 00 0 i 0 *0 0 0*0*0 0 0 1. A leak indicator for a gas filled electrical plant, with said leak indicator being of the Bourdon tube kind, the Bourdon tube being filled with a gas having the same properties as the gas surrounding the Bourdon tube, and. being in a sealed off state, both the nominal gas pressure in the Bourdon tube and the nominal gas pressure in the plant deviating from the surrounding atmospherical pressure, nominally a difference being present between the pressure inside the Bourdon tube and the pressure in the plant, wherein the free end of the closed Bourdon tube is arranged to influence, a switch means, for instance multi-step switch with at least two terminals, and wherein the leak indicator ma be supplied with voltage directly from the plant, irrespective of direction of supply to the plant, a first terminal of the switch means being voltage connected capacitively to a high voltage bushing in the plant, and a second terminal of the switch means being connected with a first terminal of a voltage indicator, a second terminal of said voltage indicator being connected to earth, and with contact between said first and second switch means terminals in a normal plant condition, but with no contact between said switch means terminals in case of a deviation from the normal state. 2. A leak indicator as defined in claim 1, wherein any leak in the Bourdon tube is tested by having a third terminal of the switch means connected with said first terminal of the voltage indicator, so that when there is contact between the first and the third terminals of the switch means a defect of the Bourdon tube is measured by v'he voltage indicato;r 3. A leak indicator as defined in claim 1 or claim 2, wherein any leak in the plant is checked by establishing a connection between the first terminal of the voltage indicator and a fourth terminal of the switch means, whereby a leak condition in the plant is detected by the presence of any voltage indication on said indicator. 4, A leak indicator as defined in claim 1, wherein when said fist terminal of the switch means is voltage-free, an ohmmeter is selectively connected between said first terminal and said second terminal of the switch meaw 5. A leak indicator as defined in any one of the p: ,.ding claims, wherein contact between said first terminal ard a second terminal of the switch means indicates a normal state, whereas a break of contact between them indicates an abnormal state, A 0 wherein contact between 34z"! first terminal and a third terminal of the switch means indicates a fault of the Bourdon tube, and wherein contact between gaid first terminal and a fourth terminal of the switch means indicates a fault in the plant. 6. A leak indicator as defined in claim 5, wherein one or several further terminals is/are provided between said second and fourth terminals of said switch means to indicate interstages. 7. A leak indicator substantially as hereinbefore described with reference to the accompanying drawings. DATED this 12th day of F~ebruary, 1991. EB DISTRIBUSJON A.S. 0 0 0 0 S0 06 00 0 0 00 0 0 00 9 a, 0 0 0 0 0 0 0 PATEN4T Vk MELB~f~;~ ~Xy, ASTRALIA Vot~ N U