GB2474246A

GB2474246A - Apparatus for inspection of a gap

Info

Publication number: GB2474246A
Application number: GB0917531A
Authority: GB
Inventors: Josef Erni; Simon Honold; Niklaus Hugi; Philip Isler; Bernhard Mark; Roland Moser
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2009-10-07
Filing date: 2009-10-07
Publication date: 2011-04-13
Anticipated expiration: 2029-10-07
Also published as: GB0917531D0; GB2474246B

Abstract

An apparatus for inspection of a gap between two surfaces, at least one of which is ferromagnetic, for example in a generator, comprises a sensor platform 26 for one or more sensors 26a attached to an elongated flexible mount 23. The mount can be extended out over the length of the gap and can be rolled up outside the gap by means of a drive 24. In the extended state, the mount has a curvature in a cross section at right angles to its longitudinal extent. The mount also has a plurality of magnets 27, in order to bring the mount into contact with the ferromagnetic surface. The magnets are attached to the side of the mount facing away from the ferromagnetic surface, so that the mount 23 slides along this surface. The mount may have a low friction coating and moveable magnets and the sensor platform may include a camera and mirror.

Description

Apparatus for inspection of a gap

Technical field

The invention relates to an apparatus for inspection of a narrow air gap between surfaces by means of a probe, at least one of the surfaces being ferromagnetic.

Prior art

Machines, motors and industrial apparatuses with a long operating life are typically inspected for their serviceability at regular time intervals. For example, 1 0 turbines, boilers or generators are inspected for damage on the surfaces of the components, in order to prevent failure or damage during operation, in that any damage must be rectified or components must be replaced. In order to carry out an inspection with as little effort as possible and in a short time, the machine should if possible not be disassembled. However, only a limited amount of space and narrow accesses are frequently available for inspection. For example, the stator and rotor of the generator are inspected via a narrow air gap between the surfaces of the stator and rotor.

Various inspection apparatuses are known, as follows, for inspections of this type.

By way of example, US 6,672,413 discloses a remotely controlled apparatus for inspection of spaces which are not accessible by people. This comprises one or more carriages which are connected to one another by a hinge. The carriages have a motor as well as magnets which ensure contact with the surfaces, in particular with surfaces from which the apparatus would otherwise slide off because of the force of gravity. Because of its size and complexity, the apparatus is suitable only for spaces above a specific size.

EP 684483 discloses a system for inspection of a generator whose rotor need not be removed for inspection. It comprises one or more sensors on a carriage with wheels which roll at the same time along the surfaces of the rotor and in slots in the stator. The apparatus is moved by means of a motor outside the machine to be inspected and a cable which extends over the length of the machine to its two ends.

While the system allows inspection of a narrow gap with a size of more than 40 mm, access is required from both sides of the machine for its installation.

EP 1420260 discloses a detector for inspection of a generator stator with a built-in rotor having a rail which is mounted at one end of the stator and is magnetically attached in stator slots. After installation of the rail, the carriage can be moved along the rail by means of a remotely controlled drive, a cable which can be pulled on, preferably with a direction-changing roller, and a spring.

EP 1233278 discloses an apparatus for inspection of the air gap between the stator and the rotor of a generator with a built-in rotor, for whose attachment access is required from both sides of the air gap.

US 6,100,711 discloses an apparatus for inspection of an air gap in a generator.

1 0 The apparatus comprises a telescopic mast which is brought into contact with its side walls by means of side elements for positioning in the air gap. A motor for onward movement of the apparatus is mounted on this itself. The apparatus requires a minimum air gap height of half an inch.

EP 1 863 153 discloses an inspection apparatus for an air gap which comprises a mast in the form of an expandable tube which can be folded up and on which a sensor head is mounted. For this purpose, the mast comprises two parts which are separated from one another along their length and thus widen the mast. The mast is composed of material which can be rolled up and can be rolled out and rolled up 2 0 by means of a drive outside the air gap. The mast is inserted, in a folded-up state, into the air gap from one end of the gap. Once it has been inserted, its width is widened, as a result of which it achieves the required stiffness to move the sensor onward. The sensor and mast are then guided by means of the drive along the length of the gap. When the sensor is not in use, the mast is stored, rolled up, in its folded-up state.

Summary of the invention

The present invention provides an apparatus for inspection of nanow air gaps between opposing surfaces using a probe, at least one of the surfaces being ferromagnetic, e.g., in machines such as generators. The apparatus has a motor for movement of the probe, wherein the motor is arranged outside the gap and the probe can be moved into the gap through a single access.

In more detail, an apparatus for inspection of an air gap between surfaces, at least one of the surfaces being ferromagnetic, comprises: one or more sensors located on a sensor platform, an elongate flexible member comprising a mount for the sensor platform, the mount being longitudinally moveable for advancing into the gap and retracting out of the gap, drive means external of the gap to enable the mount to be extended into and retracted out of the gap, and a plurality of magnets distributed over the length of the mount to bring the mount into contact with a ferromagnetic surface of the gap, the magnets being attached to a surface of the mount facing away from the ferromagnetic surface.

1 0 The magnets can be arranged directly on the mount surface, or they can be arranged in depressions in the mount, and secured in either case by a suitable adhesive. To further increase security, a fabric can be secured over the magnets by adhesive.

The apparatus allows inspection of narrow air gaps without having to enlarge the air gaps by removal of machine components. Tt is also possible to install the apparatus, and to move it within the air gap, easily and efficiently.

Advantageously, the sensor platform may also have one or more magnets and one 2 0 or more rolling or sliding elements, the physical height of the one or more rolling or sliding elements above the platform surface being greater than that of the magnets. E.g., the magnets may be embedded in the platform flush with the platform surface and the rolling or sliding elements may be arranged to project slightly above the platform surface.

The magnets are provided to bring the sensor platform and the extended mount into contact with the ferromagnetic surface, and hold them there, even against the force of gravity. The magnets result in continuous lengthwise contact of the mount with the surface to be inspected and allow the sensor platform to be advanced without the mount bending away from the surface. The arrangement of the magnets on the side of the mount facing away from the ferromagnetic surface ensures they are not in direct contact with the ferromagnetic surface but act through the mount from the opposite side. This not only allows correct sliding along the surface without any possibility of the magnets being impeded by irregularities on the surface, but also prevents the mount from being held excessively strongly on the surface by the magnetic forces, which would also impede sliding.

The or each rolling or sliding element on the sensor platform (for example, rolling element bearings or low-friction plastics) rolls or slides directly on the ferromagnetic surface because it project further above the platform surface than the magnets. This ensures that each sensor always remains in the correct relationship to the ferromagnetic surface, at all positions in a gap, while at the same time allowing the sensor platform to slide or roll along the surface with as little resistance as possible, because the magnet(s) do not contact the ferromagnetic surface.

1 0 In an alternative arrangement, the or each sensor platform magnet is arranged on or embedded in the platform surface and covered with a low-friction material to enable easy sliding of the sensor platform on the ferromagnetic surface.

In another variant, at least one magnet is additionally arranged such that it is moveable in a recess or recesses on the sensor platform. The magnet(s) in the recess(es) are moveable in a direction at right angles to the longitudinal direction of the mount to allow optimum positioning of the magnets with respect to the ferromagnetic surface, and therefore optimum guidance of the sensor platform along the surface which is intended to be inspected.

Preferably, the apparatus comprises storage means for storing the mount in a rolled-up state when the the mount is retracted, the mount being withdrawn from the storage means when the drive means advances the mount. The storage means may be a spool or roller, which allows storage in a small volume and therefore also versatile placing of the apparatus at points in machines where the spatial conditions are confined. Furthermore, the efficient use of space for storage simplifies transport and handling of the apparatus, e.g., transport for inspection of a further machine.

To ensure that the mount has adequate stiffness, it is preferred that the mount when extended has a curved profile when seen in a cross section at right angles to its longitudinal extent. Together with the magnets, this makes it possible for the sensor platform to be inserted in a controlled manner into the gap as far as necessary, and to be withdrawn again, without the mount bending, curving or moving away from the ferromagnetic surface, thereby ensuring that the same distance is maintained between the sensors and the ferromagnetic surface at every position along the gap.

The storage means may subject the mount to a rolling-in stress that flattens the mount when the mount is retracted into the storage means, the mount having a lateral bending stress that overcomes the rolling-in stress when the mount is advanced from the storage means, whereby the mount assumes its curved profile in cross-section.

The apparatus may have one or more pairs of guide elements between which the mount is passed as it moves out and which are used to fix the direction of the mount as it moves out. In a first variant, a pair of guide elements comprises a 1 0 stationary element and an element which can rotate about its own axis. The stationary element has surfaces which form a convex curve or parts of a convex curve. The element which can rotate comprises a roller with surfaces which form a concave curve or parts of a concave curve. The stationary element and the element which can rotate are arranged such that convex surfaces project into the concave surfaces. In a second variant, a pair of guide elements comprises a pair of guide rollers, with each pair of guide rollers comprising a roller with a convex cross section and a roller with a concave cross section of the same curvature. The convex roller is arranged with respect to the concave roller such that the convex-curved part projects into the concave-curved part of the other guide roller.

In both variants, the mount can be passed through between the two guide rollers, with its curvature corresponding to the curvatures of the rollers.

Advantangeously, the drive means includes a transport roller having a plurality of studs equi-distantly spaced around its circumference for engagement with holes correspondingly spaced longitudinally of the mount. The mount is propelled without slipping via this transport roller in that, when the mount is being advanced and retracted, the studs on the transport roller engage in the openings on the mount. The studs and openings also make it possible to determine the length of the mount that has been moved out and the position of the mount within the gap, on the basis of a pulse signal from the drive. At the same time, the transport roller can also be used as a guide element with correspondingly shaped surfaces as described above.

Advantageously, the apparatus further comprises transmission means for transmitting measurement signals from the one or more sensors to a signal processing apparatus. The transmission means may simply comprise electrical leads or cables for transmitting measurement signals from the sensor to the signal processing apparatus, the electrical leads or cables extending along the mount and being attached to it, such that they can be rolled up together with the mount.

Furthermore, electronic circuit means may be provided on or in the sensor platform for digitizing and transmitting the measurement signals in accordance with a transmission protocol. This ensures that the signals are transmitted accurately and reliably.

The apparatus is preferably provided with a slipring for correct transmission of the 1 0 measurement signals from the electrical leads or cables via the storage roller to the signal processing apparatus.

The mount may comprise a strip of a elastically flexible metal, for example steel, and an additional elongate element composed of a low-friction plastic which can slide on metal, for example polyethylene or polytetrafluorethylene (PTFE), also referred to as TeflonTM. The elongate plastic element is arranged in the form of a strip or a coating on the convex side of the mount, that is to say on the side of the mount which faces the ferromagnetic surface. This allows the mount to slide along the ferromagnetic surfaces and the magnetic force to be influenced by the material of the mount. The TeflonTM or polyethylene is also used for insulation, which is required during a measurement of the magnetic field, and protects both the ferromagnetic surface and the mount against wear. The material of the mount is distinguished on the one hand by its flexibility, which is required for the mount to roll up, and at the same time by its stiffness, which is required for outward movement and guidance in the gap. Furthermore, it has a fatigue resistance which allows it to be unrolled and rolled up again many times without any loss of stiffness.

The stiffness of the mount may be further increased, in that the mount may comprise a plurality of elastically flexible metal strips resting one on another, the plastic strip or coating being arranged on the convex surface of the outermost metal strip.

The apparatus may be provided with an additional drive for moving it over the circumference of a generator rotor. Moreover, the sensor platform may have one or more sensors in the form of measurement instruments, such as a camera for visual inspection or sensors for low-induction iron measurements, or a measurement apparatus for checking the slot sealing in a generator.

The sensor platform may be provided with a pivotable mirror, for example in conjunction with the above camera, the mirror being moveable to a suitable position corresponding to the distance between the surface to be inspected and the sensor platform. Furthermore, the pivotable mirror ensures visual inspection of a surface from different viewing angles.

The sensor platform may further be provided with one or more instruments in order to grip and transport objects in the gap. This makes it possible to remove any 1 0 foreign bodies or undesirable material.

Due to the arrangement of the mount and the sensor platform, as well as the nature of the controlled movement of the sensor platform in the gap, the apparatus allows measurements to be taken in gaps as small as, for example, about 4mm in height.

Furthermore, the small and light weight construction, allows the apparatus to be transported and handled easily, and it can therefore be used in a versatile manner.

Brief description of the drawings

In the figures: 2 0 Figure 1 shows a perspective view of a generator in a power station, in which the apparatus according to the invention can be used, Figure 2 shows a more detailed perspective view of the stator and rotor of the generator shown in Figure 1, and of the air gap to be inspected, Figure 3 shows a view in a cross section along the rotor axis of a part of the stator and rotor annotated III in Figure 2, with an entrance geometry to the air gap, Figure 4 shows an overall view of the inspection apparatus according to the invention, Figure 5 shows a partial view of the inspection apparatus according to the invention, in particular a more detailed view of the apparatus for rolling up and unrolling an elongate flexible member or mount for the sensor platform, Figure 5a shows a first variant of elements for guidance of the mount, Figure 5b shows a second variant of elements for guidance of the mount, Figure 6 shows a cross-sectional view of the mount along VI -VI in Figure 4 at right angles to the longitudinal extent of the mount, Figure 7a shows a partial view corresponding to VITa in Figure 4 of a first variant of a sensor platform of the inspection apparatus, Figure 7b shows a partial view corresponding to VIIb in Figure 4 of a second variant of a sensor platform of the inspection apparatus, Figure 7c uses the same perspective as that in Figure 4 to show a view of the sensor platform with movable magnets and a pivotable mirror, Figure 7d shows the position of the sensor platform from Figure 7c on a ferromagnetic surface in the air gap of a generator, in a cross section at right angles to the generator axis, Figure 7e shows a further embodiment of the inspection apparatus with a guide rail for the mount in order to stabilize the mount outside the stator of a generator, Figure 8a shows an arrangement of the mount of the inspection apparatus in the air gap of a generator in a cross section at right angles to the generator axis, 1 0 Figure 8b shows a more detailed view of the inspection apparatus in the air gap of a generator as shown in Figure 8a.

Detailed description of embodiments of the invention Figure 1 shows a general view of a generator 1 in a power station, in particular of its stator 2 and rotor 3, each with ferromagnetic elements 4 (white) and non-ferromagnetic elements 5 (shaded grey).

Figure 2 shows a more detailed view of the stator 2 and rotor 3 between which a narrow, annular air gap 6 extends. The surfaces of the stator and rotor each have ferromagnetic elements 4 and non-ferromagnetic elements 5, which are arranged alternately over the circumference and extend parallel to the generator axis 7. The width of the individual elements on the stator is generally constant over its circumference. The width is likewise constant on the rotor, with the exception of the area of the magnetic poles. On the rotor, the ferromagnetic material is the rotor material itself A plurality of slots extend parallel to the rotor axis, in which slots the winding is arranged and is secured in the slots by means of wedges. These wedges and the winding form the non-ferromagnetic elements. The winding is composed of copper. The wedges may be composed of various non-ferromagnetic materials. In a similar manner to that in the case of the rotor, the ferromagnetic material on the stator is the stator material itself, with the non-ferromagnetic material being the material of the stator winding and securing wedges, which extend parallel to one another in slots and parallel to the axis of the generator.

Figure 3 shows a typical entrance element to an air gap 6 between the stator 2 and the rotor 3 of a generator 1. The apparatus for inspection can be placed in this entrance element and the flexible member or mount for the sensor platform can be inserted into the gap.

A rotor cap 9 is located on the rotor 3 at the entrance to the gap on the rotor 3 and extends parallel to the generator axis and radially toward the stator bar 8. The stator bar 8 and the rotor cap 9 define the width d of the gap 6 through which the mount 23 with the sensor platform 26 of the apparatus is intended to be passed.

This width d may, for example, be only 4 mm. The mount 23 of the sensor platform 26 can then pass through a gap of this width when designed according to the invention.

A fan 10 is arranged outside the rotor cap 9. This further restricts the spatial 1 0 conditions for an inspection apparatus. A housing 21 can be placed there, thanks to the sensor mount being stored rolled up. Furthermore, by virtue of its compact size, the apparatus can be matched to different entrance geometries of different generators. In one variant of the invention, a guide rail can additionally be arranged between the position of the housing 21 and the entrance opening to the gap 6, and can guide the mount to the start of the ferromagnetic surfaces.

Figure 4 illustrates the inspection apparatus according to the invention as an entity; Figure 5 shows a view of an apparatus for rolling up and unrolling as well as guidance of the mount. This comprises a housing 21 for a storage roller 22 for storing a mount 23 as well as various elements for rolling up and unrolling and for moving the mount out of the housing 21. A sensor platform 26 with sensors for the inspection of the surfaces, for a low-induction iron measurement, and for testing the slot sealing etc. is arranged at the end of the mount. The mount is unrolled from the storage roller 22 by means of a drive 24 which drives the storage roller 22 and the transport roller 29. By way of example, the drive 24 has a return spring.

Over its circumference, the transport roller 29 has two rows of transport studs 32 which are separated at regular distances and engage in transport openings 28 in the mount 23. For this purpose, the transport openings are likewise arranged in two parallel-running longitudinal rows on the mount, with the separation, shape and dimension being matched to those of the transport studs thus ensuring that the mount is transported correctly, without sliding. An opening 25 through which the mount is moved out of the housing 21 is located in the housing 21.

Furthermore a plurality of magnets 27 are attached to the mount 23 along its length, and are distributed over the length of the mount. These allow the mount and the sensor platform to be positioned along the ferromagnetic surfaces without the mount becoming detached therefrom as a result of the force of gravity. The -10 -magnets are attached to the concave surface of the mount, with this concave surface facing away from the ferromagnetic surface. This makes it possible to move the mount such that it slides along the ferromagnetic surface, but remains in contact with it, and maintains its position relative to the ferromagnetic surface, in this context see also Figures 8a and b.

The magnets 27 are designed to be as small as possible, in particular with a physical height which is as small as possible, in order to allow the mount to be stored in as small an area as possible when in the rolled-up state. On the one hand, 1 0 the magnets can be secured directly on the mount surface by means of a suitable adhesive. Alternatively, the magnets can be arranged in depressions in the mount and can be secured by means of adhesive. In order to increase the security further, a fabric whose shape can easily be adapted can be placed above the magnets and can be secured by adhesive.

The mount is preferably composed of a elastically flexible material, for example steel, which is suitable for rolling up and rolling out. Preferably and in particular in order to increase the stiffness in the rolled-out state, the mount is subject to a rolling-in stress and a lateral bending stress in the rolled-up state, with the lateral 2 0 bending stress being greater than the rolling-in stress. This contributes to the mount having a curved cross section in the rolled-out state, and therefore being stiff in this state.

In order to define the direction in which the mount 23 moves out, the apparatus has a pair of guide rollers 30, 31 via which the mount 23 is guided. The pair of guide rollers each comprises a roller 30 with a convex cross-sectional shape and a roller 31 with a concave cross-sectional shape and with the same curvature, with these being arranged with respect to one another, as shown in figure 5a) such that the curvature of the convex roller projects into that of the concave roller, and guides the mount 23 through between the two. The guide rollers 30 and 31 are in this case used to define the direction of the mount 23, with the mount 23 retaining the curvature as shown in figure 6. The convex and concave surfaces of the rollers 30 and 31 are in this case positioned with respect to one another such that the mount 23 retains its longitudinal direction, in which it is moved out, and is not bent or kinked. The convex rollers 30 have a slot 33 approximately in their center and over their circumference, through which the magnets 27 can pass. Two further slots 34 are arranged on the convex roller 30, over its circumference and in each case at the -11 -same height as the transport studs 32 and transport openings 25. These allow the transport studs 32 to pass correctly.

In one variant, the mount can also be guided by elements as shown in Figure Sb).

There, a pair of guide elements comprises an element 30', which is attached in a fixed manner, and a roller 29' which can rotate about an axis. The mount 23 is passed through between the two elements, with the rollers defining the direction in which the mount moves out. Both elements have surfaces which are either curved in a corresponding manner to the curvature of the mount or form a tangent to the 1 0 curved surface of the mount. Once again, the element 30' has a slot 35' in each of its surfaces 33', which slots allow the studs 32' to pass.

A sensor platform 26 is attached to the end of the mount 23, on which sensor platform 26 one or more sensors and measurement apparatuses can be arranged, such as a camera, eddy-current sensor, sensor for low-induction iron measurement etc. Furthermore, electronics can also be arranged there, for example for amplification, digitizing and compression of measurement signals and image signals.

2 0 Measurement signals from the sensors are first of all amplified, digitized, if necessary compressed, and finally transmitted in accordance with the transmission protocol, by means of electronics on the sensor platform. This ensures the necessary accuracy of the transmission of the typically small signals.

For this purpose, cables (not illustrated) are mounted along the mount 23. These cables are rolled up with the mount on the storage roller 22 when the mount is stored. In order to allow the transmission of the signals from the end of the mount on the rotating storage roller 22 to a signal processing apparatus, the apparatus has a slipring on the storage roller. The position of the sensor platform in the gap can be determined by using pulsed signals from the drive 24 for the storage roller 22 and transport roller 29, with their position accuracy being dependent on the mount not sliding while being moved in and out, that is to say being dependent on the accuracy of the transport studs and transport openings.

Figure 7a shows the sensor platform 26 from the view indicated by the arrow VITa in Figure 4, and in particular the side of the sensor platform which comes into contact with a ferromagnetic surface. In this first variant, the sensor platform 26 is fitted with a number of magnets 26c which are embedded in the material of the -12 -sensor platform 26, and are covered by the platform material. In this case, the magnet strength and distance between the magnets and the platform surface are chosen so as once again to ensure that the platform always remains in contact with the ferromagnetic surface. Since the magnets do not project from the surface of the platform, this allows sliding along the ferromagnetic surfaces. Alternatively, the magnets 26c can also be embedded just so far in the platform material that their surface lies on the same plane as the sensor platform.

Figure 7c shows a sensor platform in the same perspective as in Figure 4, with magnets 26c and 26d being embedded in the sensor platform 26 such that they do not come into direct contact with the ferromagnetic surface. In the illustrated example, first magnets 26c are arranged in a fixed position. In contrast, second magnets 26d are arranged in a recess 26e, with the recess allowing manual movement of the magnets 26d in a direction at right angles to the longitudinal direction of the sensor platform 26 and of the mount 23, and in the plane of the sensor platform. When the inspection apparatus is used in the air gap of generators, the recess 26e allows the positioning of the magnets corresponding to the width of the ferromagnetic surfaces 4, as is shown in Figure 7d. There, the outer edges of the magnets 26d and the magnets 26c are positioned such that they are aligned 2 0 with the outer edges of the ferromagnetic surface 4.

Figure 7c additionally shows the arrangement of a camera 40 and of light sources 43 for visual inspection of the surfaces. The mirror 41 can be pivoted by means of a drive 42, for example by remote control during the inspection, and can thus be moved to an optimum position. This allows inspection of a surface corresponding to the focal length of the camera, and at different angles, as well as the inspection of different surfaces in an air gap, for example the surfaces of the stator and those of the rotor as well.

In the same view as in Figure 7a, Figure 7b shows a second variant of the sensor platform 26. In this case, the sensor platform 26 has one or more magnets 26d and a plurality of rolling elements 26b which ensure movement along the ferromagnetic surface. The magnets 26d are in this case not in direct contact with the ferromagnetic surface, but, because of their thickness and distance from the ferromagnetic surface, ensure that the sensor platform 26 remains in contact with the ferromagnetic surface in all their usage positions, for example in a generator.

-13 -A further embodiment of the inspection apparatus as shown in Figure 7e has a guide rail 45 which stabilizes the mount 23 over a first distance as of the opening in the housing 21. This embodiment has advantages for example when using the apparatus for inspection of the air gap of a generator. Since the apparatus can be moved only as far as a specific distance from the entrance to the air gap and thus from the ferromagnetic surfaces, the mount must be extended over this distance without the aid of the magnets. In order to prevent bending of the mount in this area in front of the air gap of the generator, the guide rail stabilizes the mount over this area.

Figures 8a and b show the position of the mount 23 with the sensor platform 26 in a gap 6 between a stator 2 and a rotor 3 of a generator. The curved mount 23 is shown in the form of a cross section with a magnet 27 in contact with a ferromagnetic surface 4 of the stator.

For the particular application of an apparatus for inspection of an air gap in a generator, the type of mounting of such an apparatus is generally known. A belt which can be tightened is typically used for this purpose, in order to mount the apparatus on the rotor, with the apparatus being arranged, for example, on rollers 2 0 or sliding elements which are moved over the circumference of the rotor.

In a further embodiment of the apparatus according to the invention, the apparatus has a drive in order to move it in the circumferential direction on the rotor. In particular, the radial position (relative to the rotor surface) of the housing 21 for the roller 22 to support the mount together with the mount and its guide rail is adjustable relative to the position of said drive for movement of the apparatus. This allows, for every generator to be inspected, an optimum radial positioning, corresponding to the generator type.

List of reference symbols 1 Generator 2 Stator 3 Rotor 4 Ferromagnetic elements Non-ferromagnetic elements 6 Air gap 7 Generator/rotor axis 8 Stator bar -14 - 9 Rotor cap Fan Tnspection apparatus 21 Housing 22 Roller for storing the mount 23 Mount 24 Drive Opening 26 Sensor platform 26a Sensors 26b Rolling element 26c Magnet 26d Movable magnet 26e Recess for movable magnet 27 Magnet 28 Transport openings 29 Guide and transport roller Guide roller (convex) 31 Guide roller (concave) 32 Transport stud 33 Slot in the convex roller 34 Slots in the convex roller 33' Obliquely running surfaces in the element 30' 34' Obliquely running surfaces in the element 30' 35' Slots in the element 30' d Gap width between the rotor cap 9 and the stator bar 8 Camera

41 Pivotable mirror

42 Drive for pivotable mirror 43 Light sources Guide rail

Claims

-15 -Claims 1. An apparatus for inspection of a gap between surfaces, at least one of the surfaces being ferromagnetic, the apparatus comprising: one or more sensors located on a sensor platform, an elongate flexible member comprising a mount for the sensor platform, the mount being longitudinally moveable for advancing into the gap and retracting out of the gap, drive means external of the gap to enable the mount to be advanced and retracted into and out of the gap, and a plurality of magnets distributed over the length of the mount to bring the mount into contact with a ferromagnetic surface of the gap, the magnets being attached to a surface of the mount facing away from the ferromagnetic surface.
2. An apparatus according to claim 1, wherein the sensor platform has one or more magnets and one or more rolling or sliding elements, the physical height of the one or more rolling or sliding elements being greater than that of the magnets.
3. An apparatus according to claim 1 or claim 2, comprising storage means 2 0 for storing the mount in a rolled-up state when the the mount is retracted, the mount being withdrawn from the storage means when the drive means advances the mount.
4. An apparatus according to any preceding claim, wherein the mount when extended has a curved profile when seen in a cross section at right angles to its longitudinal extent.
5. An apparatus according to claim 4 as dependent on claim 3, wherein the storage means is operative to subject the mount to a rolling-in stress that flattens the mount when the mount is retracted into the storage means, the mount having a lateral bending stress that overcomes the rolling-in stress when the mount is advanced from the storage means, whereby the mount assumes its curved profile in cross-section.
6. An apparatus according to any preceding claim, further comprising one or more pairs of guide elements, each pair of guide elements comprising an element with convex surfaces and an element with concave surfaces complementary to the convex surfaces, the convex element being arranged with respect to the concave -16 -element such that the convex-curved part of the convex element projects into the concave-curved part of the concave element, the mount being advanced and retracted through and between the guide elements.
7. An apparatus according to any preceding claim, in which the drive means includes a transport roller having a plurality of studs equi-distantly spaced around its circumference for engagement with holes correspondingly spaced longitudinally of the mount.

1 0
8. An apparatus according to any any preceding claim, further comprising transmission means for transmitting measurement signals from the one or more sensors to a signal processing apparatus.
9. An apparatus according to claim 8, wherein the transmission means comprises electrical leads or cables extending along and attached to the mount.
10. An apparatus according to claim 8 or claim 9, further comprising electronic means for digitizing and transmitting the measurement signals in accordance with a transmission protocol.
11. An apparatus according to claim 10 as dependent from claim 3, wherein the storage means comprises a storage roller, and a slipring is arranged on the storage roller to enable transmission of the measurement signals from the electrical leads or cables to the signal processing apparatus.
12. An apparatus according to any preceding claim, wherein the side of the mount intended to contact the ferromagnetic surface is provided with a strip or a coating composed of a low-friction plastic.
13. An apparatus according to claim 12, wherein the plastic is polytetrafluorethylene or polyethylene.
14. An apparatus according to any preceding claim, comprising an additional drive operative to move the apparatus over the circumference of a generator rotor, the radial position of the apparatus being adjustable relative to the position of the drive.

-17 -
15. An apparatus according to any preceding claim, wherein the sensors are operative for visual inspection or low-induction iron measurements.
16. An apparatus according to claim 3, wherein the drive means includes a return spring operative to retract the mount into the storage means.
17. An apparatus according to any preceding claim, wherein each magnet on the mount is located within a depression in the mount.

1 0
18. An apparatus according to any preceding claim, wherein the sensor platform has means for gripping and transporting objects in the gap.
19. An apparatus according to any preceding claim, wherein the sensor platform is equipped with one or more magnets that are either embedded flush with the sensor platform or covered by a low-friction material.
20. An apparatus according to claim 18, wherein the sensor platform has at least one magnet arranged in a recess such that it is moveable in a direction transverse to the longitudinal direction of the mount.
21. An apparatus according to any preceding claim, wherein the sensor platform is equipped with a pivotable mirror.
22. An apparatus according to any preceding claim, further comprising a guide rail for stabilizing the mount externally of the gap.22. An apparatus for inspection of a gap between two surfaces, substantially as described herein with reference to the accompanying drawings.