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DYAGNOSYS FOR THE MAGNETIC CORE OF POWER GENERATORS, USING INFRARED THERMOVISION
IFAC Workshop ICPS'07 2007, July 09-11 Cluj-Napoca, Romania
SAMPLE PAGES TO BE FOLLOWED EXACTLY IN PREPARING SCRIPTS
DYAGNOSYS FOR THE MAGNETIC CORE OF POWER GENERATORS, USING INFRARED THERMOVISION
Petre Ungureanu, Ciprian Veres
S.C. Hidroelectrica S.A. – Hidrocentrale Cluj Subsidiary
Abstract: The classical Thermal Loop Test up to national standards of prophylactic measurement for high voltage rotating machinery was improved by the intermediate of thermo-graphic inspection with a last generation of INFRARED THERMOVISION CAMERA. The method generates thermo-graphic maps by intermediate of a dedicated software of the internal cylindrical surface of the magnetic core of the rotating machinery. The thermo-graphic maps are generated in strictly identical condition at the start of the generator, as well as at the major planned outages after 5, 10, 15, 20 years of functioning. The proposed method of testing allowed the users to compare the thermo-graphic maps and to put in evidence the “thermal hot spots” (respectively the magnetically failures) and their evolution in time and gives the users the possibility to establish the moment of partial or complete replacement of the iron core. Copyright © 2007 IFAC
Keywords: power generators, magnetic core diagnosis, infrared thermo-vision, temperature mapping.
1. INTRODUCTION
and it is strongly recommended after any intervention at the iron core of the generator.
The traditional method of Thermal Loop Test (or High Flux Ring Test) consists in the removal of the rotor and by intermediate of three to five cable loop to induce in the iron core a magnetically flux at the level of 95% from the standard magnetization. Up to the national ”Standards of Prophylactic Measurements” the induction in the iron core has the level of: - 1,00 Tesla during 90 minutes or - 1.41 Tesla during 45 minutes
*** The tendency to extended the periods between major planned outages were generated by the modern method of “online monitoring & diagnosis” like: general surveying of bearing vibration, polar graph of generator air-gap, stator bar vibration & temperature constant monitoring, as well as the permanent surveillance of electrical parameters (to not point out only: the partial discharges monitoring system or magnetic flux track monitoring).
The temperature on the inner cylindrical surface of the iron core is measured by intermediate of alcohol thermometers, uniformly distributed in minimum 20 distinct points The difference of temperature must not exceed 15 degrees Celsius between two adjacent points of temperature measurement.
These tendencies toward extended periods between major planned outages have developed the new generation of test equipments under the generic name of “Electromagnetic Core Imperfection Detector” with the acronym “EL CID”.
The test is recommended at the start of the generator, and after any major planned or accidental outages;
From the late 1970’ up to this day, generations of producers of “EL CID” testing equipments, have -246-
tried to demonstrate to the power generation companies, the great advantages of their method with the following arguments: - the stator is energized only at the level of 4% of nominal magnetic flux, - the time for the EL CID test is evidently sorter that the standard test, - the possibility to detect magnetically failure even “behind stator.
The error of equalizing the the magnetic disturbances with the “Hot Spots”.
2.2. The method of weak induction:
In order to made compatible the Thermal Loop Test with the advantages of EL CID, an hybrid method was proposed: The stator is energized of the low level : 0.05-0.1 TESLA.
In spite of these strong arguments, the power companies, at the major moments of capital decisions like the partial or the entire replacement of the iron core, have as their final argument the recommendation of the classical “THERMAL LOOP TEST”. In order to avoid the polemical attitude we will try to present in the following paragraph only the technical data of our “Method of diagnoses for the magnetic core by intermediate of magnetically map comparison”.
A mobile magnetic sensor is moved along the vertical space between two adjacent magnetic poles (the sensor cower all the meridians of the inner surface of the stator). A dedicated software integrate the electrical signals of the sensor a passing the meridians of the stator a magnetic map by extrapolation The method limits are the following: - the error of magnetic sensor - the error of recording the signals from a sensor in motion along the spaces between the adjacent magnetic poles, - the error of extrapolation when a magnetic map is generated for the entire inner surface of stator , with signals recorded along a limited numbers of meridians. - the error of interpretation of those magnetic maps regarding the magnetic disturbances deep in the iron core.
The method improves the classical “Thermal Loop Test” with the performances of the new generation of INFRARED THERMO-GRAPHIC CAMERA combined with a personalized software that allows the user to compare the INFRARED THERMOGRAPHYC MAGNETIC CORE MAPS realized at the first start of the generator with those made after 5, 10, 15, 20 years of maintenance (the maps are realized in strictly identical conditions).
2. TEST METHODS
2.3 The method of “Diagnosis for the magnetic core of the high power generators by infrared termovision”:
2.1 The classical THERMAL LOOP TEST
The classical THERMAL LOOP TEST has been improved after the apparition of computers, which made it possible to integrate the signals of electronic temperature devices, uniformly positioned at the inner cylindrical surface of the stator. These temperatures measured in minimum 20 points or a multiple of 20 points were extrapolated and thermal maps were generated.
A standard magnetization at the level of: - 1.00 TESLA during 30 minutes - 1.41 TESLA during 15 minutes is obtained by intermediate of an A.C. source of 0.4 Kv, (8001500) A. The source is connected to an 0.4kV mono phase cooper cable with the section of 150-240 square millimeters. The cable encircles the magnetically core of the generator with 3 - 5 loops.
The interpretation of these maps has given the users approximate information about the localization of the ”hot spots”, in other words it gave them the possibility to approximate the magnetic perturbations in the iron core.
The method uses an infrared camera that has the following technical requirements: - the sensitivity 0.08 degree Celsius - the accuracy r 2 degree Celsius - the specter range 7.5 – 13 micrometers - the temperature range - 40 y +120 degree Celsius
The major inconveniences of the method are the following: The error of thermo couples or thermo resistances used for temperature measurement
A dedicated software gives the operator the possibility to edit a thermo graphic image in a multiple palette of colors as well as in black and white.
The error of extrapolation when a thermal map of the entire surface of stator is edited by the input of the limited point measurements.
The infrared camera is placed in the center area of inner cylindrical zone of the magnetically core.
The software error
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The camera performs a rotation motion recording four images of the surface in the first moment of the thermal process. The next images are recorded in the exact previous first position every two minutes during the entire process of thermal maps edition The method consist in the comparison of thermo graphic map of the power generator with the maps recorded at the previous dismantling. If there are not previous images in the infrared spectrum the method allows the user to put in evidence the ”hot spots” and to make a decision regarding: a. The “OK” for the following period of maintenance. b. The decision to remove the damaged part of magnetically pole iron lamination and to replace them. c. The decision to replace the entire iron core of the generator. The method has the following advantages: The perfect control of all input technical data of the test allows to record comparable thermal maps (the input data strictly controlled are the following: - magnetic flux level - duration of the test - mathematical recorded infrared maps - the infrared camera is placed at the same distance in the same direction versus the tested inner surface of magnetically core. - all these parameters allow the users to delimitate the area of the hot spots with the precision of a few millimeters; by comparison between the images recorded at the start of the test with those recorded after 2, 4, 6, … minutes gives to the dedicated soft for thermal image processing, the possibility to diagnose the deepness of magnetically disturbance in the iron core.
Fig.1 The hydropower generator Sugag 10,5kV: infrared images. Time12:10:10 The material presents superficial faults of the inner surface of magnetic core. Time 12:20:05
The objectivity of the method (the input data for analyses are not disturbed by intermediate devices like magnetically field sensors, thermo couples or thermo resistances, the high accuracy and the great sensitivity of the last generation infrared camera ensures the perfect correspondence between the localization of the ”hot spots” with the real magnetically disturbances in the tested iron core. *** The method of magnetically core testing by infrared thermo vision was tested on two hydro power generators: the Hydro Power Plant of Sugag – Hydro Power Company Sebes Romania, and the Hydro Power Plant Vaduri – Hydro Power Company Piatra Neamt Romania. The starting time of the test: 12:10:10
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Fig.2 The hydropower generator Sugag 10,5kV: infrared images. Time12:20:05 The faults inside the iron core material near the surface (2-3 cm deepness) Time 12:30:10
Fig.4 The hydropower generator no. 1 Sugag 10,5kV: normal images The Hydro Power Plant Vaduri – HG1 22 MW The starting time of the test 10:05:00
Fig.3 The hydropower generator Sugag 10,5kV: infrared images. Time12:30:10 The faults deep inside the material. Fig. 5 The Hydro Power Plant Vaduri – HG1 22 MW. Time 10:05:00
The hydropower generator no. 1 Sugag 10,5kV: normal images
The faults on the surface of the iron core
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The time: 10:15:20
Fig. 6 The Hydro Power Plant Vaduri – HG1 22 MW. Time 10:15:20 The time 10:30:20
Fig. 7 The Hydro Power Plant Vaduri – HG1 22 MW. Time 10:30:20
REFERENCES Brad McNamara and Peter Demers, Correlation of results in assessing stator core in: The Electricity Forum 1999. D.B. Paley, FIEE, Current Low Power Core Testing Using EL CID in: IEEE Colloquium “Understanding your condition monitoring” April 1999. Dan Zlatanovici “PROFIM” The low induction magnetic core test in: CSCI-CI Bucuresti. Petre Ungureanu, Method of Iron Core Testing by Intermediate of IR Termographic Maps – Patent proposal. Romania 2005 Gheorghe Nainer, Turbogenerators – 100 years of production; History and general principles in: Ed. Electra Bucuresti 2002. J. Stein and A.J. Spisak, General core investigation and the importance of good lamination contact at the back of core in: Iris Rotating Machine Conference, June 2003, Santa Monica, CA. Romanian Standard of Electrical Prophylactic Measurement PE116/1994, ICEMENERG Bucureti.
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SAMPLE PAGES TO BE FOLLOWED EXACTLY IN PREPARING SCRIPTS
DYAGNOSYS FOR THE MAGNETIC CORE OF POWER GENERATORS, USING INFRARED THERMOVISION
Petre Ungureanu, Ciprian Veres
S.C. Hidroelectrica S.A. – Hidrocentrale Cluj Subsidiary
Abstract: The classical Thermal Loop Test up to national standards of prophylactic measurement for high voltage rotating machinery was improved by the intermediate of thermo-graphic inspection with a last generation of INFRARED THERMOVISION CAMERA. The method generates thermo-graphic maps by intermediate of a dedicated software of the internal cylindrical surface of the magnetic core of the rotating machinery. The thermo-graphic maps are generated in strictly identical condition at the start of the generator, as well as at the major planned outages after 5, 10, 15, 20 years of functioning. The proposed method of testing allowed the users to compare the thermo-graphic maps and to put in evidence the “thermal hot spots” (respectively the magnetically failures) and their evolution in time and gives the users the possibility to establish the moment of partial or complete replacement of the iron core. Copyright © 2007 IFAC
Keywords: power generators, magnetic core diagnosis, infrared thermo-vision, temperature mapping.
1. INTRODUCTION
and it is strongly recommended after any intervention at the iron core of the generator.
The traditional method of Thermal Loop Test (or High Flux Ring Test) consists in the removal of the rotor and by intermediate of three to five cable loop to induce in the iron core a magnetically flux at the level of 95% from the standard magnetization. Up to the national ”Standards of Prophylactic Measurements” the induction in the iron core has the level of: - 1,00 Tesla during 90 minutes or - 1.41 Tesla during 45 minutes
*** The tendency to extended the periods between major planned outages were generated by the modern method of “online monitoring & diagnosis” like: general surveying of bearing vibration, polar graph of generator air-gap, stator bar vibration & temperature constant monitoring, as well as the permanent surveillance of electrical parameters (to not point out only: the partial discharges monitoring system or magnetic flux track monitoring).
The temperature on the inner cylindrical surface of the iron core is measured by intermediate of alcohol thermometers, uniformly distributed in minimum 20 distinct points The difference of temperature must not exceed 15 degrees Celsius between two adjacent points of temperature measurement.
These tendencies toward extended periods between major planned outages have developed the new generation of test equipments under the generic name of “Electromagnetic Core Imperfection Detector” with the acronym “EL CID”.
The test is recommended at the start of the generator, and after any major planned or accidental outages;
From the late 1970’ up to this day, generations of producers of “EL CID” testing equipments, have -246-
tried to demonstrate to the power generation companies, the great advantages of their method with the following arguments: - the stator is energized only at the level of 4% of nominal magnetic flux, - the time for the EL CID test is evidently sorter that the standard test, - the possibility to detect magnetically failure even “behind stator.
The error of equalizing the the magnetic disturbances with the “Hot Spots”.
2.2. The method of weak induction:
In order to made compatible the Thermal Loop Test with the advantages of EL CID, an hybrid method was proposed: The stator is energized of the low level : 0.05-0.1 TESLA.
In spite of these strong arguments, the power companies, at the major moments of capital decisions like the partial or the entire replacement of the iron core, have as their final argument the recommendation of the classical “THERMAL LOOP TEST”. In order to avoid the polemical attitude we will try to present in the following paragraph only the technical data of our “Method of diagnoses for the magnetic core by intermediate of magnetically map comparison”.
A mobile magnetic sensor is moved along the vertical space between two adjacent magnetic poles (the sensor cower all the meridians of the inner surface of the stator). A dedicated software integrate the electrical signals of the sensor a passing the meridians of the stator a magnetic map by extrapolation The method limits are the following: - the error of magnetic sensor - the error of recording the signals from a sensor in motion along the spaces between the adjacent magnetic poles, - the error of extrapolation when a magnetic map is generated for the entire inner surface of stator , with signals recorded along a limited numbers of meridians. - the error of interpretation of those magnetic maps regarding the magnetic disturbances deep in the iron core.
The method improves the classical “Thermal Loop Test” with the performances of the new generation of INFRARED THERMO-GRAPHIC CAMERA combined with a personalized software that allows the user to compare the INFRARED THERMOGRAPHYC MAGNETIC CORE MAPS realized at the first start of the generator with those made after 5, 10, 15, 20 years of maintenance (the maps are realized in strictly identical conditions).
2. TEST METHODS
2.3 The method of “Diagnosis for the magnetic core of the high power generators by infrared termovision”:
2.1 The classical THERMAL LOOP TEST
The classical THERMAL LOOP TEST has been improved after the apparition of computers, which made it possible to integrate the signals of electronic temperature devices, uniformly positioned at the inner cylindrical surface of the stator. These temperatures measured in minimum 20 points or a multiple of 20 points were extrapolated and thermal maps were generated.
A standard magnetization at the level of: - 1.00 TESLA during 30 minutes - 1.41 TESLA during 15 minutes is obtained by intermediate of an A.C. source of 0.4 Kv, (8001500) A. The source is connected to an 0.4kV mono phase cooper cable with the section of 150-240 square millimeters. The cable encircles the magnetically core of the generator with 3 - 5 loops.
The interpretation of these maps has given the users approximate information about the localization of the ”hot spots”, in other words it gave them the possibility to approximate the magnetic perturbations in the iron core.
The method uses an infrared camera that has the following technical requirements: - the sensitivity 0.08 degree Celsius - the accuracy r 2 degree Celsius - the specter range 7.5 – 13 micrometers - the temperature range - 40 y +120 degree Celsius
The major inconveniences of the method are the following: The error of thermo couples or thermo resistances used for temperature measurement
A dedicated software gives the operator the possibility to edit a thermo graphic image in a multiple palette of colors as well as in black and white.
The error of extrapolation when a thermal map of the entire surface of stator is edited by the input of the limited point measurements.
The infrared camera is placed in the center area of inner cylindrical zone of the magnetically core.
The software error
-247-
The camera performs a rotation motion recording four images of the surface in the first moment of the thermal process. The next images are recorded in the exact previous first position every two minutes during the entire process of thermal maps edition The method consist in the comparison of thermo graphic map of the power generator with the maps recorded at the previous dismantling. If there are not previous images in the infrared spectrum the method allows the user to put in evidence the ”hot spots” and to make a decision regarding: a. The “OK” for the following period of maintenance. b. The decision to remove the damaged part of magnetically pole iron lamination and to replace them. c. The decision to replace the entire iron core of the generator. The method has the following advantages: The perfect control of all input technical data of the test allows to record comparable thermal maps (the input data strictly controlled are the following: - magnetic flux level - duration of the test - mathematical recorded infrared maps - the infrared camera is placed at the same distance in the same direction versus the tested inner surface of magnetically core. - all these parameters allow the users to delimitate the area of the hot spots with the precision of a few millimeters; by comparison between the images recorded at the start of the test with those recorded after 2, 4, 6, … minutes gives to the dedicated soft for thermal image processing, the possibility to diagnose the deepness of magnetically disturbance in the iron core.
Fig.1 The hydropower generator Sugag 10,5kV: infrared images. Time12:10:10 The material presents superficial faults of the inner surface of magnetic core. Time 12:20:05
The objectivity of the method (the input data for analyses are not disturbed by intermediate devices like magnetically field sensors, thermo couples or thermo resistances, the high accuracy and the great sensitivity of the last generation infrared camera ensures the perfect correspondence between the localization of the ”hot spots” with the real magnetically disturbances in the tested iron core. *** The method of magnetically core testing by infrared thermo vision was tested on two hydro power generators: the Hydro Power Plant of Sugag – Hydro Power Company Sebes Romania, and the Hydro Power Plant Vaduri – Hydro Power Company Piatra Neamt Romania. The starting time of the test: 12:10:10
-248-
Fig.2 The hydropower generator Sugag 10,5kV: infrared images. Time12:20:05 The faults inside the iron core material near the surface (2-3 cm deepness) Time 12:30:10
Fig.4 The hydropower generator no. 1 Sugag 10,5kV: normal images The Hydro Power Plant Vaduri – HG1 22 MW The starting time of the test 10:05:00
Fig.3 The hydropower generator Sugag 10,5kV: infrared images. Time12:30:10 The faults deep inside the material. Fig. 5 The Hydro Power Plant Vaduri – HG1 22 MW. Time 10:05:00
The hydropower generator no. 1 Sugag 10,5kV: normal images
The faults on the surface of the iron core
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The time: 10:15:20
Fig. 6 The Hydro Power Plant Vaduri – HG1 22 MW. Time 10:15:20 The time 10:30:20
Fig. 7 The Hydro Power Plant Vaduri – HG1 22 MW. Time 10:30:20
REFERENCES Brad McNamara and Peter Demers, Correlation of results in assessing stator core in: The Electricity Forum 1999. D.B. Paley, FIEE, Current Low Power Core Testing Using EL CID in: IEEE Colloquium “Understanding your condition monitoring” April 1999. Dan Zlatanovici “PROFIM” The low induction magnetic core test in: CSCI-CI Bucuresti. Petre Ungureanu, Method of Iron Core Testing by Intermediate of IR Termographic Maps – Patent proposal. Romania 2005 Gheorghe Nainer, Turbogenerators – 100 years of production; History and general principles in: Ed. Electra Bucuresti 2002. J. Stein and A.J. Spisak, General core investigation and the importance of good lamination contact at the back of core in: Iris Rotating Machine Conference, June 2003, Santa Monica, CA. Romanian Standard of Electrical Prophylactic Measurement PE116/1994, ICEMENERG Bucureti.
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