GB2295294A

GB2295294A - Telemetry aerial

Info

Publication number: GB2295294A
Application number: GB9423283A
Authority: GB
Inventors: John Frederick Young
Original assignee: European Gas Turbines Ltd
Current assignee: Alstom Power UK Holdings Ltd
Priority date: 1994-11-18
Filing date: 1994-11-18
Publication date: 1996-05-22
Anticipated expiration: 2014-11-18
Also published as: GB2295294B; GB9423283D0

Abstract

A telemetry aerial for a machine rotor eg a turbine shaft is formed from a solid strip (3) of brass of dovetail cross-section mounted in a circumferential groove (1) of similar section. The aerial strip is locked in position by epoxy resin (7) fed into the gap between the two and cured. A wedge effect against radial movement is thus achieved so preventing escape of the aerial strip even at high rotational speeds. <IMAGE>

Description

TELEMETRY AERIAL This invention relates to telemetry aerials and particularly to telemetry aerials fitted to rotating shafts or rotors for transmitting electric data signals from transducers on the shaft to stationary receivers.

It is a common requirement in the field of large rotating machinery to obtain measurements of various rotor parameters, eg temperature at particular points on the rotor.

Transducers are fitted to the rotor at the relevant points and electrical signals are passed to an encoder and transmitter. An aerial on the shaft is then used to transmit the information to an adjacent receiver for decoding and recording.

It has been proposed to wind a length of insulated wire in a circumferential groove in the shaft to act as an aerial. However, in large machinery, particularly turbines, the rotational speed may be in the region of 12000 rpm and the centrifugal force on the wound aerial can be sufficient to damage it, even though it is apparently firmly fixed in position by adhesive or resin.

An object of the present invention is to provide a telemetry aerial for large rotating machinery which can withstand the centrifugal forces involved.

According to one aspect of the present invention, a telemetry aerial for transmitting test data from a rotating body to a stationary receiver comprises a circumferential strip of metal mounted in a circumferential groove in the body, the aerial strip being spaced from the groove wall by a solidified resin material and the groove and aerial strip cross-sections being of such shape and size that movement of the aerial strip under centrifugal force is resisted by wedge action of the aerial strip in the groove.

The aerial strip may be of trapezoidal cross-section, having a short parallel side in the mouth of the groove and a long parallel side in the bottom of the groove, the groove being of similar cross-section to the aerial strip the long parallel side of which is a clearance fit through the mouth of the groove.

The ends of the aerial strip preferably interlock in a dovetail joint.

According to another aspect of the invention, a telemetry arrangement comprises a rotatable shaft and a telemetry aerial as aforesaid, the groove being provided with periodic pads of insulating material to space the aerial strip from the bottom of the groove, and the remaining space between aerial strip and groove being filled with solidified epoxy resin.

According to a further aspect of the invention, a method of providing a rotatable shaft with a telemetry aerial, includes the steps of forming a circumferential groove in the shaft of dovetail section, forming a metal strip of similar dovetail section into an aerial ring to lie in the groove, the long side of the dovetail section of the metal strip being a clearance fit through the mouth of the groove, positioning the ring in the groove so that the ring is spaced from the walls of the groove, filling the space between ring and groove walls with an insulating resin, and curing the resin to lock the antenna ring in the groove.

Adhesive pads of insulating material may then be fixed to the bottom of the groove periodically prior to insertion of the aerial ring to space the aerial ring away from the groove surface while the resin cures.

A telemetry aerial arrangement for a turbine rotor will now be described by way of example, with reference to the accompanying drawings, of which: Figure 1 is a part section of the rotor and aerial in an axial plane; Figure 2 is a part section in a circumferential plane illustrating a feature of the assembly; and Figure 3 is a part elevation along a radius through the aerial.

Referring to the drawings, a groove is formed in an aluminium section of the rotor which is hollow and contains various electronic components of the telemetry system. The groove 1 extends around the rotor body 2 circumferentially and is of dovetail, ie trapezoidal, section having a short mouth dimension and a (relatively) long bottom dimension. The aerial is formed from a solid strip 3 of brass of similar dovetail/trapezium form but of such size that the bottom of the strip section will just pass through the mouth of the groove. In this particular example the aerial strip is 1.5 millimetres thick (between the parallel faces) and has short and long sides 3 and 4.5 millimetres respectively. Thus the mouth of the groove is marginally greater than 4.5 millimetres and the long edge of the groove section is about 7.0 millimetres.

The ends of this antenna strip are formed with interlocking dovetail sections 9, as shown in Figure 3, so that the strip can be formed into a 'continuous' aerial ring. The length of the strip 3 is arranged to be such that when closed to form the ring in position in the groove 1, the inner face of the ring stands off the bottom of the groove 1.

Before assembling the ring to the groove, a series of hard pads of electrically insulating material 5 (Figure 2) are attached by adhesive to the bottom of the groove periodically. The thickness of these pads is such as just to permit the aerial strip to be closed at its dovetail joint.

Uncured epoxy resin in the form of a paste may then be squeezed into the gap between aerial and groove wall to fill the remaining gap. The pads 5 maintain the aerial ring in its correct position (out of contact with the groove walls) until the epoxy resin cures - which may be speeded up by raising the temperature. The aerial ring 3 is then locked into position in the groove by wedge action, the solid resin 7 being compressed when the ring is subjected to centrifugal force.

The aerial strip 3 is of such a thickness initially as to be slightly proud of the rotor surface when assembled and the resin cured. It can then be machined flush with the rotor surface.

If it is found that the gap between aerial ring and groove is too small, or that the uncured resin is too viscous, to squeeze it into the gap after assembly of the aerial ring, then the groove may be partially filled with resin prior to insertion of the ring so that the resin oozes up to fill the gap as the ring is pressed into position.

Connection to the aerial ring is by way of an insulated wire soldered to the ring and running radially through a hole in the rotor.

The resulting aerial is found to be exceedingly robust and capable of withstanding forces produced by speeds in excess of 20000 rpm on a typical machine. The solid ring aerial is also found to have good coupling and sensitivity characteristics.

Claims

1. A telemetry aerial for transmitting test data from a rotating body to a stationary receiver, the aerial comprising a circumferential strip of metal mounted in a circumferential groove in the body, the aerial strip being spaced from the groove wall by a solidified resin material and the groove and aerial strip cross-sections being of such shape and size that movement of the aerial strip under centrifugal force is resisted by wedge action of the aerial strip in the groove.

2. A telemetry aerial according to Claim 1, wherein the aerial strip is of trapezoidal crosssection, having a short parallel side in the mouth of the groove and a long parallel side in the bottom of the groove, the groove being of similar cross-section to the aerial strip the long parallel side of which is a clearance fit through the mouth of the groove.

3. A telemetry aerial according to Claim 1 or Claim 2, wherein the ends of the aerial strip interlock in a dovetail joint.

4. A telemetry aerial according to any preceding claim wherein the aerial strip is coated with an insulating varnish to ensure no electrical contact between aerial strip and body.

5. A telemetry arrangement comprising a rotatable shaft and a telemetry aerial according to any preceding claim, wherein the groove is provided with periodic pads of insulating material to space the aerial strip from the bottom of the groove, the remaining space between aerial strip and groove being filled with solidified epoxy resin.

6. A method of providing a rotatable shaft with a telemetry aerial, including the steps of forming a circumferential groove in the shaft of dovetail section, forming a metal strip of similar dovetail section into an aerial ring to lie in the groove, the long side of the dovetail section of the metal strip being a clearance fit through the mouth of the groove, positioning the ring in the groove so that the ring is spaced from the walls of the groove, filling the space between ring and groove walls with an insulating resin, and curing the resin to lock the antenna ring in the groove.

7. A method according to Claim 6 wherein adhesive pads of insulating material are fixed to the bottom of the groove periodically prior to insertion of the aerial ring to space the aerial ring away from the groove surface while the resin cures.

8. A method according to Claim 6 or Claim 7, wherein the metal strip has a radial depth such as to protrude from the groove after curing of the resin, and including the step of machining the outer surface of the aerial ring so that it lies flush with the adjacent shaft surface.

9. A method according to any of Claims 6, 7 and 8 wherein the aerial ring is coated with insulating varnish prior to its positioning in the groove.

10. A telemetry arrangement substantially as hereinbefore described with reference to the accompanying drawing.

11. A method of providing a rotatable shaft with a telemetry aerial, substantially as hereinbefore described with reference to the accompanying drawing.