GB2293923A - A thermocouple electrical wiring harness - Google Patents

Abstract

A thermocouple electrical wiring harness 22, for monitoring the burner exhaust operating temperature of a jet engine or gas turbine (10 Figure 1), uses a multiplethermocouple array 21, co-operatively linked in sensor groups (80 Figures 11 and 12), through thermocouple looms 28, connected to intermediate connector housings 23, mounted through insulation blocks 24 upon the engine housing, and interconnected through intermediate looms 26, located within reinforced sheaths (50 Figure 7), mechanically coupled to the housings by unions (42 Figures 4, 5A and 6A), in order to preserve overall mechanical and electrical integrity against the adverse operating environment and temperature conditions. <IMAGE>

Description

Electrical Thermocouple Harness for Industrial Jet Engine or Gas Turbine Exhaust Burner Can or Flame Tube Assembly This invention relates to electrical wiring harnesses and is particularly, but not exclusively, concerned with heavy duty, high temperature, thermocouple wiring harnesses such as are employed on the exhaust burner flame can or tube assembly of a jet engine or gas turbine.

Engine temperature, and in particular main combustion chamber burner and exhaust temperatures are extremely high and must be monitored not only to optimise engine performance, such as power output, but to avoid engine overheating and ultimate (catastrophic) failure.

Aeronautical jet engines or gas turbines originally designed for dynamic service in aircraft installation are commonly converted for stationary industrial use, such as for driving generators or pumps.

However thoroughly the conversion is designed, such engines remain vulnerable to their unintended new service role.

In stationary engine environments there is no ('forced') cooling air flow around the jet or turbine by virtue of the (high speed) movement of the structure through the atmosphere.

Accordingly, the engine is vulnerable to operational overheating - particularly in continuous cycle.

As a safety aid, and in order to counteract this tendency, a responsive, yet physically robust, thermocouple array is typically provided to monitor the highest temperature areas, such as the burner exhaust flame tube assembly.

There is a compromise between transducer sensitivity and speed of response and mechanical strength to withstand the arduous service conditions.

Yet the functionality of such a thermocouple assembly and attendant wiring harness is critical to the performance, life and serviceability of the engine being monitored.

In critical installations, such as oil or gas rig pumps, the continuing availability and reliable duty of an industrial pump is of paramount importance - not least since pump turbine failure can lose valuable production time.

Moreover, such engines are commonly run on the lower grade fuel, such as crude oil, being pumped, rather than high grade aviation kerosene.

The combustion process for such fuels is not conducive to thermocouple transducer life and thus undermining engine temperature monitoring.

Relatively high harness failure rates have been experience in practice with existing engine conversions.

Both the replacement harness cost and the cost of removal, testing and refurbishment are prohibitive if costly engine failures are to be obviated.

Some attempts have been made to improve individual thermocouple design, but still it is common practice for multiple thermocouples in different locations to be connected to a common terminal block - so that, even if only one thermocouple fails, the entire assembly has to be replaced.

Generally, a multiple thermocouple sensor transducer array is used to trigger an automatic engine monitoring and shut down controller, which averages the thermocouple readings, allowing for minor sporadic fluctuations but taking prompt action when out of range - it taking only a few seconds for engine damage to occur.

The present invention provides a replacement for existing thermocouple wiring harnesses.

Many hundreds of industrial engine conversions are in use and admit of conversion by the present invention.

According to one aspect of the invention an electrical wiring harness 22 for high temperature operation comprises a series of intermediate looms 26, with an outer sheath 50 shielding, a plurality of individually insulated cores 49, 59, 69, termination connectors 51, 61, 70 on said cores, a plurality of terminal blocks 23, 25, a plurality in terminals 53 in each terminal block, for receiving said core connector terminations; and a plurality of transducer looms 28, for connecting terminal blocks 23 to transducers 21.

Such a construction provides an electrically and mechanically secure harness construction.

Sheath connectors may be employed to connect the loom outer shield or sheath to the body of the terminal blocks.

The terminal blocks may incorporate an integrated connector housing and spacer to allow mounting of the block upon the engine body, but with the connector housing marginally spaced therefrom.

Conveniently, the terminal block body incorporates a mounting flange for engine mounting and a removable cover plate to allow access to the connectors.

Desirably, each transducer comprises a thermocouple probe incorporating three thermocouple sensing elements, one element reading being compared with the average of the other two - and a (say, 40 degree C) spread in readings allowed, before triggering action, such as an engine shutdown alert.

There now follows a description of some particular embodiments of the invention, by way of example only, with reference to the accompanying diagrammatic and schematic drawings, in which: Figure 1 shows a general arrangement of a thermocouple harness on an engine burner exhaust duct; Figure 2 shows an improved substitute thermocouple and analyser harness according to the invention; Figure 3 shows another view of the harness of Figure 2; Figure 4 shows a part cut-away view of part of the harness of Figures 2 and 3.

Figures 5A and 5B show side part-sectional and part cut-away views of a main terminal connector housing for the harness of Figures 2 and 3; Figures 6A and 6B show side part-sectional and part cut-away views of an intermediated terminal connector housing for the harness of Figures 2 and 3; Figure 7 shows an integrated loom assembly for the harness of Figures 2 and 3; Figure 8 shows a double-ended loom for the harness of Figures 2 and 3; Figure 9 shows a thermocouple loom assembly for the harness of Figures 2 and 3; Figure 10 shows a part-sectional view of a thermocouple for the harness of Figures 2 and 3; Figure 11 shows a part-sectional view of the sensor or transducer head and attendant wiring of the thermocouple of Figure 10 for the harness of Figures 2 and 3; and Figure 12 shows a wiring scheme for the harness of Figures 2 and 3.

Referring to Figure 1, a thermocouple electrical wiring harness 12 is mounted on the burner exhaust assembly of a jet or gas turbine engine 10 (not shown in full) - for example a Rolls Royce Avon (Trade Mark) aero engine, converted to stationary industrial use.

Generally, the harness comprises a series of junction boxes 13 mounted upon the engine casing 10, which incorporates a series of mounting apertures 17 for receiving circumferentially-spaced thermocouple temperature sensing probes 11, wired together in a co-operative circuit, through the connector or junction boxes 13.

The thermocouples 11 are connected to a monitoring device (not shown), capable of shutting down the engine 10 in the event of excess operating temperature registration.

The location of the harness 12 in such close proximity to one of the hottest regions of the engine 10 creates a climate hostile to the long term mechanical and electrical performance of the probes 11 and attendant wiring.

Thus probe and wiring insulation degradation and connection overheating and failure are not uncommon - leading to failures to monitor engine operating temperature and consequent possible engine damage upon over-heating.

The present invention seeks to address this problem, by providing an altogether more robust harness, which can fit the existing engine location constraints.

Referring to Figures 2 and 3, a thermocouple and analyser harness 22 according to the invention has a particular construction of carefully contrived individually enhanced componentry in a co-operative combination.

Thus, generally, a series of four robustly shielded intermediate wiring looms 26 interconnect four intermediate (junction) housings 23 with a main (junction) housing 25 - to which is also connected a supplementary analyser wiring loom 27, fitted with a shielded multi-way connector 29.

The housings 23, 25 themselves are of robust thick-walled, high (purity) grade, (diecast) aluminium alloy construction, mounted upon substantial (separately-formed) insulated spacer blocks 24 - to promote heat dissipation.

The housings 23, 25 are provided with a close-fitting (sealable) covers 31, 33, and internal stainless steel fixed joint unions or couplings 42 in all thermocouple and loom entries.

The insulation blocks 24 themselves are moulded from high temperature plastics, with anti-rotating, or captive threaded fastener mounting inserts A circumferentially-spaced array of some eight double-insulated thermocouples 21, of enhanced construction described in more detail in relation to Figures 11 and 12, are connected in successive pairs to opposite ends of the intermediate housings 23 through individual shielded looms 28.

As is more evident from Figure 4, the overall loom outer sheathing integrity is preserved by integration with coupling unions 42 fitted into the threaded ports 41, 47 in the ends of each housing 23, 25.

Internally of the housings 23, 25 are a series of heavy duty paired connector terminals 53, accessible by removing housing cover plates 31, as depicted in Figures 5A and 6A.

Figures 5A and 5B show a main connector housing assembly 25 with individual side ports 41 for connection to the looms through union connectors 42 and locking spacer washers 43.

Figures 6A and 6B show an equivalent intermediate connector housing assembly 23 to the main housing 23, and with pairs of opposed side ports 47, for connection to the looms through union connectors 42.

Figure 7 shows the construction of a thermocouple and analyser integral loom assembly 27 fitted with a screw connector 29 at one end and splayed internal cores 49 with individual spade connectors 51 at the opposite end.

Figure 8 shows an integral intermediate loom assembly 26 with splayed internal cores 59 with individual spade terminal connectors 61 at each end.

Figure 9 shows a thermocouple assembly 21 with attendant wiring 28.

Referring to Figure 10, each thermocouple 21 comprises a generally cylindrical, hollow transducer probe body 62 tapering into a rounded nose 76.

As shown in Figure 11, the body 61 houses three discrete pairs of conductors 81, 82 and 83 of disparate material swaged together at their ends to form a composite tip assembly 76.

In particular, the conductor pairs are alumel-chromel junctions, encased in a sheath 72 of Inconel, further protected by an outer sheath 62, to afford supplementary mechanical rigidity and strength.

A waisted mounting shank 63 at one end of the outer sheath 62 fits within a locking collar 65, which is used to locate the thermocouple assembly 21 in a complementary profiled mounting aperture in the body of the engine 10.

Referring to Figures 7, 8 and 9, the wiring looms 26, 27, 28 are constructed from an outer stainless steel braided sheath 51, with a convoluted inner lining 50.

This construction houses internal mutually insulated wire conductors 49, 59, 69 individually insulated with Kapton/PTFE sleeving and then encapsulated with high temperature PTFE tubing, to produce a flexible one-piece loom 26, 27, 28.

Electrical connections between the thermocouples 21 and wiring looms 26, 27, 28 are made via (locking screw spade) terminals 53 situated in the housings 23, 25.

The terminals 53 are completely enclosed within the housings 23, 25, access to which is achieved by removing covers 31, 33.

The thermocouple connections 69, 70 enter the housings 23 by means of an integral unions 42, which are individually free to swivel, and then locked into position using a swagelock type nut 66.

The wiring looms 26, 27, 28 are swaged assemblies with a mounting nut 66 at each end for connection to the housings 23, 25 via double-ended unions 42.

The analyser loom 27 electrical connections enter the main housing 25 through a double-ended union assembly 42.

Operationally, the eight thermocouples 21 are mounted in locations within the engine exhaust cone 10 in the hot exhaust gas path.

Upon engine start-up, the exhaust gases pass across the thermocouples 21 - exciting the thermocouple elements 81, 82, 83 to generate voltage outputs - which will stabilize as the engine 10 reaches sustained speed and running temperature.

Within each thermocouple 21 there are three sensing junctions 81, 82, 83, two of which are dedicated to mean temperature readout - the other being for individual or 'spread' readout.

The mean temperature is afforded by connecting the thermocouples 21 in parallel circuits up to the main housing 25 and then via the analyser loom 27 to the installation fitment.

The individual readouts are connected via a common negative circuit via the main housing 25 then on to the installation fitment.

Figure 12 shows a general wiring diagram for the groups 80 of three sensor elements 81, 82, 83 in each thermocouple 21.

The entire harness assembly may be used as original equipment, or to replace and existing harness.

In contemplating harness repair or refurbishment for re-instatement, typical in service problems, which lead to degradation of thermocouple and wiring harness performance, are corrosion, cracking, nicks, splitting or fraying of insulation, heat distortion, indentations and burning.

Certain service repairs may be carried out, for example by welding and brazing and reprofiling to prescribed standards and selective replacement of parts.

The wiring circuitry incorporates ballast loading - that is the linking of localised variable (internal) thermocouple resistances - so that the presence of all thermocouple transducers can be detected - for example by a Wheatstone Bridge resistance tester.

An operational service life in engine service hours is prescribed between removal for inspection, overhaul or replacement.

Claims (5)

Claims

1. An electrical wiring harness (22) for a thermocouple array (21), for monitoring the engine operating temperature of a jet engine or turbine (10), and comprising a plurality of connector housings (23, 25) mounted on individual insulation blocks 24, with ports (41, 47) for receiving coupling unions (42) to which are fitted cable sheaths (50) housing wiring looms (26, 27).

2. A harness as claimed in Claim 1, wherein multiple sensing elements are incorporated into individual thermocouple sensing probes and comparative output readings taken therefrom.

3. A harness as claimed in Claim 1, wherein the housings are of aluminium and the unions of stainless steel.

4. A harness, substantially as hereinbefore described, with reference to, and as shown in, the accompanying drawings.

5. An engine incorporating a harness as claimed in any of the preceding claims.