Use of fiber optic sensor techniques for monitoring and diagnostics of large AC generators

• US 20120026482A1
• Filed: 03/31/2011
• Published: 02/02/2012
• Est. Priority Date: 04/05/2010
• Status: Active Grant

• Current Assignee: Innovative Diagnostic Systems, Inc.
• Original Assignee: Innovative Diagnostic Systems, Inc.
• Inventors: Dailey, George Franklin
• Granted Patent: US 8,520,986 B2
• Time in Patent Office: Days
• US Class Current: 356/43
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01D 5/35358 using backscattering to detect the measured quantity
• CPC Class Codes: G01K 11/32 using changes in transmittance, scattering or luminescence in optical fibres
• CPC Class Codes: G01K 13/08 in rotary movement
• CPC Class Codes: G01K 13/10 for measuring temperature within piled or stacked materials by special arrangements for conducting heat from the object to the sensitive heat element G01K1/16
• CPC Class Codes: G01L 1/242 the material being an optical fibre

Abstract

A method for monitoring the operating conditions of an electric generator including the entire stator core and all winding components for conditions of mechanical strain and temperature throughout the machine by means of distributive fiber optic sensors based on both Rayleigh back scattering techniques and Brillouin frequency shift fiber optic sensor analysis both of which do not have the gaps and limitations associated with standard fiber Bragg grating fiber optic point sensors, by virtue of the fact that both Rayleigh and Brillouin scans and allow accurate strain and temperature determinations at all points along standard fiber optic cables of considerable length, approximately two kilometers in the case of the Brillouin, which effectively yields many tens of thousands of sensors throughout the entire standard fiber optic cable. Raman distributive temperature sensing also has a limited application. Single mode and polarizing maintaining fibers can both be analyzed and read with any Rayleigh or Brillouin distributive fiber optic sensor laser system allowing great flexibility in sensor spatial resolution, total sensed length, resolution and other factors not possible with conventional fiber Bragg gratings. A sealed fiber collection box located outside the electric generator permits enhanced reliability and reconfiguration into any number of desirable fiber layouts necessary for specific static and dynamic measurements in an optimal manner.

Claims

1. A system for monitoring the on-line (or off-line) key operational and maintenance parameters of an electric utility power plant electric generator, said system comprising:

Attaching at least one standard fiber optic cable to commonly-used non-conducting, non-magnetic shims which as filler means said shims are commonly used in the stator core portion of all said electric generators for the purpose of obtaining distributive fiber optic sensor measurements from said shim means;

Attaching at least one standard fiber optic cable to the electric generator stator core electrical steel lamination clamping means, including through bolts, building bolts, and associated hardware used for said stator core clamping means and then connecting said standard fiber optic cable to a Rayleigh back-scattering or Brillouin Frequency shift laser analyzer means;

Inserting at least one standard fiber optic cable contained within a small high-temperature, mechanically strong non-conducting, non-magnetic special tube and socket separable and slideably adjustable length fitting means and attaching said tubular fiber containment means to all desired and or necessary electrical winding components not within the slot portion of said electric generator, such as but not limited to series electrical connections, phase electrical connections, parallel ring, stator coil end-region sections, and main lead electrical connections when said standard fiber optic cable is placed within a small high strength, high temperature plastic tubular means so as said fiber is free to expand and contract within said tubular means and said tubular means is then rigidly bonded and or non-magnetically, non-conductively banded to said electrical component(s) and by such means all relevant hot spots monitored and trended as well as mechanical strains measured by slideably adjusting sections of said adjustable tubular fiber support means, thereby exposing the bare fiber, and attaching (bonding) portions of said standard fiber optic cable directly to the desired electrical component in order to obtain said strain measurement when said standard fiber optic cable is then connected to a Rayleigh back-scattering or a Brillouin Frequency shift laser analyzer means;

Routing at least one standard fiber optic cable through strategically place co-linear holes and or within grooves in the stator core electrical grade steel laminations and associated core supporting plates and brackets for the purpose of monitoring the temperature(s) of all said and or required stator core electrical steel laminations, which when said fibers are arrayed in sufficient quantity can by distributive fiber optic sensor analysis using Rayleigh back-scattering, Brillouin Frequency shift, or Ramam distributive laser analyzer give temperature results sufficient to eliminate the need for Electromotive core Imperfection Testing (EL-CID) so as to provide full stator core lamination temperature diagnostic means;

Routing all said standard fiber optic cables to a sealed, but openable distributive fiber optic cable collection box located outside the frame of said electric generator for distributive fiber optic sensor means;

Said distributive fiber optic cable collection box so arranged to receive all standard fiber optic cables each with suitable mechanical connectors, which allow various changeable configurations of fiber layouts and fiber optic cable run lengths to take advantage of the different spatial resolutions and cable lengths optimally scannable based on spatial resolution and total fiber length associated with and unique to various commercially available Rayleigh, Brillouin, and or Ramon fiber optic sensor laser analyzers for the purpose of measuring all distributive mechanical strains and temperatures along each said standard fiber optic cable by said Rayleigh back-scattering or Brillouin Frequency Shift laser analyzer means;

Connecting all said fiber optic cables to a fiber optic multiplexor or fiber optic switches by means of standard mechanical fiber optic connectors located within said fiber optic connection box so as each standard fiber optic cable is separately scannable with said fiber optic sensor Rayleigh, Brillouin and or Ramon distributive fiber optic sensor laser analyzer(s), the latter analyzer being capable of only temperature measurements.

2. The method of claim 1 in which the clamping force provided to stator core electrical grade steel laminations by means of through bolt and building bolt hardware is measured by Rayleigh distributive fiber optic sensor back scattering or fiber Bragg grating wave division multiplexing as measured by circumferential length change of said fiber (or fiber Bragg grating) when bonded to a non-metallic, non-conducting band which is in intimate contact with a non-metallic non-conducting compression member which carries the full load of said hardware and thereby expands in diameter causing said band to elongate in proportion and hence said fiber to elongate with said band shielding said Rayleigh fiber optic distributive sensor (or fiber Bragg grating) from transverse compressive loads as would be present if said distributive fiber optic sensor were attached directly to said compressive member and said Rayleigh back scattering fiber optic sensor (or fiber Bragg grating) is fully temperature compensated by means of a section of standard fiber optic cable (or fiber Bragg grating) that is totally isolated from said compressive loads and therefore expands (contracts) only due to temperature change and by so compensating for compressive load and temperature the tightness of the stator core electrical steel laminations may be periodically measured and trended without the need for partial disassembly of the electric generator providing that at least three so instrumented through bolts and at least three so instrumented building bolts are measured by these distributive fiber optic sensor means alone or is distributive fashion with other aspects of the invention.

3. The method of claim 1, wherein the tightness of all necessary stator coil segments and individual stator slot wedges within the slots of said stator core are ascertained for tightness at all necessary stator core slots by means of Rayleigh back scattering distributive fiber optic sensors or a Brillouin frequency shift laser analyzer means connected to singly or multiplexed with standard fiber optic sensor cable(s) bonded within specially shaped rounded bottom grooves milled into long shims said shims having additional pseudo-parabolically shaped shims, said shims being uniquely designed, in position, shape, and mechanical attributes such as spring rate, and by these unique shim means consistent with deflection rates of said stator coil portions within said stator coil slots so that when said standard fiber optic cable is suitably attached to said long shim and the bending of said long shim and the mechanical strain therein measured by means of said Rayleigh back scattering or Brilluoin frequency shift distributive fiber optic cable is by distributive fiber optic sensor means calibrated to the force of the top ripple springs which is necessary and sufficient to ascertain and trend stator coil tightness said long shim being located above the top coil, between top and bottom coils, beneath the bottom coil in any combination thereof,

And said mechanical strain measurement when fully temperature compensated by means of a section of said Rayleigh back scattering distributive means or Brillouin frequency shift fiber optic sensor means which is isolated from mechanical strain and responsive only to changes in backscattered laser light as caused by temperature only such as the standard fiber within the tubes located on one or both outer edges is said shim which places the fiber in very close proximity to the stator core electrical steel laminations thereby measuring the temperature of said laminations all inclusively or by ingressively looping the tube encased standard fiber within the central portion of said shim, either the top or bottom of said shim thereby ascertaining stator coil top or bottom coil ground-wall insulation temperature by means of said distributive fiber optic sensor laser analyzer means,

And by the Rayleigh back scattering or Brillouin frequency shift distributive fiber optic sensor means any desired number of top ripple springs may be measured for adequate tightness and so trended so as to preclude stator coil slot pounding at any and all positions within the stator core at any time whether the electric generator is on-line or off-line at any load level without the need for any disassembly of the electric generator.

4. By the method of claim 1, wherein stator coil ground-wall temperature within the stator slot portion of the stator core is desired, special grooves can be milled into the said long non conducting non magnetic standard shim and special covered grooves added to said shims, such that the Rayleigh back scattering or Brillouin frequency shift distributive fiber optic sensor means within said groove or non-conducting, non-magnetic tube within said groove is free to expand contract with temperature so as said standard fiber optic cable is not influenced by mechanical stain in said long shim and if said groove are in near contact with said stator coil portion ground-wall, then temperatures of said stator coil electrically insulating ground-wall any where within said stator slot portion may be monitored at any time during unit operation without the need to for unit disassembly.

5. By the method of claim 1, wherein electric generator winding components not Within the stator core portion, those areas commonly referred to as end windings, parallel rings, main leads, and all the electrical connections associated with these areas such as series connection, phase connections, parallel ring connectors, and main lead flexible connectors, all of these said components can be monitored for mechanical strain and temperature throughout their expanse and at all locations desired by means of Rayleigh back scattering or Brillouin frequency shift distributive fiber optic sensor means said standard fiber optic cables which are contained within small high temperature, mechanically strong adjustable-length non-magnetic, non-conducting tubular support means;

Said tubular support means being of length through which said fiber can be easily inserted at which point a tube coupling of the same plastic material and of any desired length couples and protects the fiber and overlaps to the next small tube section, thus making long sections possible in which the coupling tube and small tube can be moved slide-ably with respect to each other thereby enabling short sections of said Rayleigh distributive fiber to be exposed for bonding directly to said generator windings or winding connections, in any way desired without the need to use precut small tube lengths and exposed fiber;

Said small tubes and coupling tubes are initially assembled over Rayleigh back scattering single mode distributive fiber optic cable and temporarily held in position with adhesive tape, which upon assembly to the generator components is removed and the tubing then firmly held in the desired positions with standard banding materials and resins thereby enabling distributive fiber optic sensing means.

6. The means of claim 1 inclusive also are achievable in both mechanical strain measurement and temperature measurement by means of Brillouin frequency shift and birefringence-induced frequency shift by means of a polarizing maintaining fiber utilized differential pulse width pair Brillouin optical time-domain analysis and a local Brillouin (moving) grating created by the counter- propagating laser lights with a frequency offset equal to the Brillouin frequency shift;

If both ends of said Brillouin frequency shift polarizing maintaining fiber are available to be exposed to the requisite pump light (one end) and the pulse light (other end);

Which enables mechanical strain and temperature to be ascertained from the same Brillouin frequency shift fiber to an acceptable spatial resolution for a maximum reach of many hundreds meters, both specifications being adequate to achieve claim 1;

And said operational length of said Brillouin frequency shift distributive fiber optic sensor cable(s) permits the multiplexing device and Brillouin distributive laser analyzer to be located remotely in the electric generator control room.

7. All the methods of claim 1 apply to vacuum impregnated generators providing the open ends of the said tubular fiber optic tubular support means are sealed by suitable sealing means.

8. The invention of claim 1 is also applicable to the special Brillouin distributive fiber optic sensor analysis in which one single mode fiber of a specified refractive index is joined to a second single mode fiber of different refractive index, both fibers being securely bonded to the same electric generator component, and known algorithm means then used to separate mechanical strain from temperature, the analysis being made possible by the difference in refractive indices of the two joined fibers as required for distributive fiber optic sensor means.

10. The fiber optic cable box of claim 1 allows reconfiguration of the installed standard fiber optic sensor cables at any time thereby allowing optimal utilization of new Rayleigh, Brillouin, or Ramon distributive fiber optic sensor systems or analysis systems associated with these systems to be utilized as required for distributive fiber optic sensor means.

11. By all the means of claim 1 sufficient space is allowed for placement of spare standard fiber optic cables within said special tubular support means and shim groove means all said standard fibers terminating is said fiber optic collection box thereby permitting all means of on-line repairs, reconnections and continuation of distributive fiber optic sensor means.

12. By the means of claim 1 should a standard fiber optic cable be under interrogation by means of Brillouin Frequency shift, or equivalent means, and a break in said standard fiber occurs, both ends of said broken fiber can still be interrogated by means of Rayleigh backscattering or equivalent means that does not require light pulses be introduced to both ends of said standard fiber thereby maintaining continuity of distributive fiber optic sensor means.

13. By the means of claim 1, use of standard fiber optic cables for the distributive strain and temperature sensing of the generator stator core and windings eliminates the gaps of fiber optic sensing means associated with point fiber optic sensors such as fiber Bragg gratings interrogation means.

14. For the invention of claim 1, individual ripple spring (wedge tightness) can most directly be measured by placing the shim containing appropriate standard fiber optic cables above (radially inward in reference to the centerline of the generator) the top coil and then using Rayleigh back-scattering or Brillouin Frequency Shift laser analyzer means.

15. For the invention of claim 1 either standard single mode fiber or standard polarizing maintaining fiber may be utilized for distributive strain and temperature fiber optic sensor measurement, multi-mode standard fiber optic cable would be used only for distributive fiber optic temperature only laser analyzer means.

16. For the invention of claim 1, the means to measure stator coil ground-wall temperatures by means of standard fiber optic cables is far more spatially discriminating than RTD'"'"'s (resistance temperature detectors) and the distributive fiber optic sensor means of stator coil ground-wall temperature measurement eliminates the grounding potential attributable to said copper-wire RTD'"'"'s.

9. The special Brillouin distributive fiber optic sensor analysis of which distinguishes temperature from strain by means of differing refractive indices for the fiber optic cables, one index for the strain cable and a different index for the temperature cable is also applicable to all components used in any electric generator in that mechanical strain and temperature can be separated and both measured by this special means in which both the strain fiber and the temperature fiber by virtue of their differing refractive indices can then be both securely bonded to grooves milled into said semi-conducting side ripple springs, stator slot shims, or the electrical winding temperature strain measurements by means of a dual tube system in which both the strain fiber of one index of refraction is coated and bonded to a high temperature plastic, such as PEEK, and the same for the temperature fiber with different index of refraction, both fibers being coated and bonded to said PEEK, or equivalent covering, and then the dual pair so bonded and attached to the generator component(s) thereby permitting mechanical strain to be separated from temperature throughout the electric generator for all desired components selected for measurement by distributive fiber optic sensor means.