CA1292279C - Arrangement for measuring the slip of electric induction motors - Google Patents
Arrangement for measuring the slip of electric induction motorsInfo
- Publication number
- CA1292279C CA1292279C CA000579443A CA579443A CA1292279C CA 1292279 C CA1292279 C CA 1292279C CA 000579443 A CA000579443 A CA 000579443A CA 579443 A CA579443 A CA 579443A CA 1292279 C CA1292279 C CA 1292279C
- Authority
- CA
- Canada
- Prior art keywords
- slip
- motor
- filter
- coupled
- proportional
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
- H02P23/08—Controlling based on slip frequency, e.g. adding slip frequency and speed proportional frequency
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/34—Testing dynamo-electric machines
- G01R31/343—Testing dynamo-electric machines in operation
Abstract
Abstract of the Disclosure An arrangement for measuring the slip of electric induction motors determines the relative measure of the difference between rotary field speed and rotor speed of induction motors by utilizing the nonlinearity effects of the magnetization characteristics of ferromagnetic materials.
Slip-proportional current and/or voltage signals are detected at the terminals of the induction motor. By suitable processing of these slip-proportional signals, such as frequency conversion and filtering, a frequency-proportional measure of the slip is provided which is then subjectable to measuring or further processing.
Slip-proportional current and/or voltage signals are detected at the terminals of the induction motor. By suitable processing of these slip-proportional signals, such as frequency conversion and filtering, a frequency-proportional measure of the slip is provided which is then subjectable to measuring or further processing.
Description
7~3 Arrangsme~t ~or ~e~uring th0 , 81i~ of Eleotri~ Induation Notors 3 l¦ Field of the Invention 4 ~ The present invention relates to an arrangement ~or j measuring the slip o~ single or multiple phase electric 6 ¦ induction motors, and more particularly, to a measuring and 7 ¦ processing arrangement which directly indicates the slip of 8 induction motors in their operating range or makes it 9 accessible for further processiny. .
1~
11 Background o~ the Invention 12 Slip is a relative measure of the difference between 13 rotary field speed and rotor speed and hPnce is an important 14 operational parameter for induction motors.
Arrangements are known which meaeure the rotational ~6 speed (Trenkler, G. I'Die elektrische Messung ~on ~rehzahl und 17 Winkelgeschwindigkeit", Yerlag E. Geyer, Bad Worishofen, 1974, 18 in particular pages 36 and 37) so that the slip can be 19 calculated. For an inverter supply o~ a motor, it is known to calculate the slip by means o~ a slip computer from -the motor 21 current, motor flux, and ignition angle (German Published 22 Unexamined Patent Application 35 23 619). Also ~nown are 23 computer-assist~d methods o~ estimating slip (Hillenbrand, F., 24 "Identification of linear time-invariant systems and their application to induction motors", Dissertation, TU Berlin 26 1982, pages 149-157). Another ~nown method for measuring slip 27 is the proYision o~ a eeparate measuring motor ~Swiss Patent 28 449,770) having an air gap in which Hall probes are disposed.
1~`12~7~
Further, to determine the rotational speed in unlversal motors utilizing effective harmonics, application of the Fast Fourier Transform is known ~U.S. Patent 4,527,101).
The above known arrangements and methods require speed sensors or are suitable only for certain motor types and circuit variants, or else they require precise prior knowledge concerning the measured object. The cost involved in the evaluation electronics and so~tware is usually considerable.
To pxovide rotational speed determination, a measuring arrangement was proposed (in Canadian Patent Application Ser. No.
563,457 filed April 7, 1988), which detexmines the time responses of the voltayes at the electrical connections and~or the currents through the electrical connections of the motor.
The problem presented by the prior art is to provide an arrangement which permits in a universal and simple manner ~he measurement of the slip of electric induction motors.
Summary o~ ~he Inven~ion The above and other problems are solved by the present invention which provides an arrangement for measuring the slip of an electric induction motor having at least one phase, the arrangement comprising a level-adapted preliminary filter stage coupled to the motor. This stage is supplied with ~he current signals and/or the voltage signals which are generated by the motor, these current signals and voltage signals having a freguency proportional to the slip. A means for signal convolution o~ a frequency range at either a power supply frequency or its harmonics 79 20365-28~9 is coupled to an output of the level-adapted preliminary filter stage. A filter is coupled to an output of the means for signal convolution, while a display and evaluating unit is coupled to an output of the filter.
In another embodiment of the invention, a converter is coupled between the motor and the level adapted preliminary filter stage. This converter senses from at least one phase of the motor the slip-proportional current signals that are generated ~y the motor.
In still another embodiment of the invention~ the neu-tral points of the power supply and the motor are not connected, and the multi-phase motor is in star connection. The level-adapted preliminary filter stage is coupled to both neutral points so as to pick up~he slip-proportional voltage signals.
The ambodiments of the invention described above pro-vide an arrangement for a simple measurement of the slip of electric induction motors.
Brief Description of t e DraWings ~igure 1 is a block diagram o~ an embodiment of the present invention which uses a current signal.
Figure 2 is a block diagram of another embodiment of the present invention which uses a voltage signal.
De-tai-led Descri~'tion Before describing the embodiments of the invention, the following is an explanation of the principle on which the invention is based.
~ 2~7~ 20365-2849 In induction motors, ferromagnetic materials are used that have magnetization characteristics which are nonlinear in the normal operating range, that is, outside saturation. A multipli-cative linkage of flux components of slip and power supply fre-quency occurs, resulting in combination frequencies which are detectable by induction at the terminals of the motor as current and/or voltage signals. In the signal spectrum thes~ components appear as frequency groups at once or twice the distance of the slip frequency about the power supply ~requency as well as their odd-numbered and even-numbered harmonics. The amplitude of these components is dependent, among other things, on the magnet mater-ial and degree of saturation. The amplitude of the components is normally very small (about -60 to -90 dB), compared to the power supply parameters. Since the flux components are very close to the power supply frequency or its harmonics, especially when the slip is small, direct selection and evaluation of these com-ponents is not possible.
What is possible, however, is the selection of one or more suitable frequency groups. Undesirable signal components, 2Q such as rotor slots harmonics, are sufficiently suppressed by this selection. When the slip-proportional components are shifted by convolution in the frequency range into an undisturbed frequency band, e.g. the base band, they can be obtained ~y simple filter-ing due to the large relative frequency distance from interference components existing in this undisturbed band. The slip-propor-tional components can then be displayed directly and/or ~urther processed.
_ ~ _ ~ 20365-2849 Thus, for example, a frequency group ~ith components at the distance of twice the slip frequency 2xfs can be selected.
After convolution and filtering, a frequency counter can then be used for displayin~ the slipo For a 50 Hz power supply, the slip s is then indicated directly as a percentage, independently of the number of pole pairs of the motor, since 2xfs = 2xsx50= 100 s = s (%~.
In the embodiment of the invention illustrated in Figure 1, the raw signal, comprising the ~eometric sum o~ all com-ponents delivered by the power supply and generated by the motor, is obtained from a single or multi-phase induction motor l by at least one converter 2. This raw signal is supplied to a level-adapted preliminary filter 3, preferably with a band pass char-acteristic. ~ subsequent convolution 4 (see E. Oran Brigham, "FFT Fast Fourier-Transformation", pages 68 to 94, 2nd edition, R. Oldenbourg Verlag Munich Vienna 1985) is done, for example, by simple squaring or synchronous rectification with the power supply frequency. For this convolution, known aevices such as parabolic function networks, multipliers or ring modulators may be used.
Undesire~ frequency components of the convolved signal are sup-~0 pressed by a filter 5. As the amplitude o~ the useful signal in-creases with increasing slip because of the also increasing reaction of the rotor, an almost constant output signal is generat-ed by suitable selection of the properties of the filter 5. Such filters are known for example fro~ the publication by Stearns, "Adaptive Signal Processing" Prentice Hall, Inc., Englewood Cliffs, N~ 07632, pages 316 et seq. The selection of the proper-ties of the filter 5 is a simple matter ~or one of ordinar~ skill in the art.
1 If the filter 5 is, .Eor example, a low-pass filter, 2 in most cases level control and limitiny devices are dispensable if a proper selection of the cut-off frequency and 4 edge steepness is made. Thus, the output signal is able to be supplied to a display and/or evaluat.ing unit 6 directly.
6 I t Figure ~ illustrates another embodiment for 7 1 obtaining the raw signal. If a three-phase motor 1 i5 8 ,l operated with a star connection, the converter 2 is not needed 9 li if the neutral point of the motor is not connected with the 1I neutral point of the power supply. Since the useful signal ~ components do not cancel each other out because of a lack of 12 ¦~ symmetry, they are available directly as voltage signals 13 1 against the neutral point of the power supply. The further lÇ - processing for ~he embodiment is the same as that shown in Figure 1.
~6 ~ ~Z~7 ~8 ~0 28 ~I
~ 1 2 g 30 ,1 ~ - 6 -
1~
11 Background o~ the Invention 12 Slip is a relative measure of the difference between 13 rotary field speed and rotor speed and hPnce is an important 14 operational parameter for induction motors.
Arrangements are known which meaeure the rotational ~6 speed (Trenkler, G. I'Die elektrische Messung ~on ~rehzahl und 17 Winkelgeschwindigkeit", Yerlag E. Geyer, Bad Worishofen, 1974, 18 in particular pages 36 and 37) so that the slip can be 19 calculated. For an inverter supply o~ a motor, it is known to calculate the slip by means o~ a slip computer from -the motor 21 current, motor flux, and ignition angle (German Published 22 Unexamined Patent Application 35 23 619). Also ~nown are 23 computer-assist~d methods o~ estimating slip (Hillenbrand, F., 24 "Identification of linear time-invariant systems and their application to induction motors", Dissertation, TU Berlin 26 1982, pages 149-157). Another ~nown method for measuring slip 27 is the proYision o~ a eeparate measuring motor ~Swiss Patent 28 449,770) having an air gap in which Hall probes are disposed.
1~`12~7~
Further, to determine the rotational speed in unlversal motors utilizing effective harmonics, application of the Fast Fourier Transform is known ~U.S. Patent 4,527,101).
The above known arrangements and methods require speed sensors or are suitable only for certain motor types and circuit variants, or else they require precise prior knowledge concerning the measured object. The cost involved in the evaluation electronics and so~tware is usually considerable.
To pxovide rotational speed determination, a measuring arrangement was proposed (in Canadian Patent Application Ser. No.
563,457 filed April 7, 1988), which detexmines the time responses of the voltayes at the electrical connections and~or the currents through the electrical connections of the motor.
The problem presented by the prior art is to provide an arrangement which permits in a universal and simple manner ~he measurement of the slip of electric induction motors.
Summary o~ ~he Inven~ion The above and other problems are solved by the present invention which provides an arrangement for measuring the slip of an electric induction motor having at least one phase, the arrangement comprising a level-adapted preliminary filter stage coupled to the motor. This stage is supplied with ~he current signals and/or the voltage signals which are generated by the motor, these current signals and voltage signals having a freguency proportional to the slip. A means for signal convolution o~ a frequency range at either a power supply frequency or its harmonics 79 20365-28~9 is coupled to an output of the level-adapted preliminary filter stage. A filter is coupled to an output of the means for signal convolution, while a display and evaluating unit is coupled to an output of the filter.
In another embodiment of the invention, a converter is coupled between the motor and the level adapted preliminary filter stage. This converter senses from at least one phase of the motor the slip-proportional current signals that are generated ~y the motor.
In still another embodiment of the invention~ the neu-tral points of the power supply and the motor are not connected, and the multi-phase motor is in star connection. The level-adapted preliminary filter stage is coupled to both neutral points so as to pick up~he slip-proportional voltage signals.
The ambodiments of the invention described above pro-vide an arrangement for a simple measurement of the slip of electric induction motors.
Brief Description of t e DraWings ~igure 1 is a block diagram o~ an embodiment of the present invention which uses a current signal.
Figure 2 is a block diagram of another embodiment of the present invention which uses a voltage signal.
De-tai-led Descri~'tion Before describing the embodiments of the invention, the following is an explanation of the principle on which the invention is based.
~ 2~7~ 20365-2849 In induction motors, ferromagnetic materials are used that have magnetization characteristics which are nonlinear in the normal operating range, that is, outside saturation. A multipli-cative linkage of flux components of slip and power supply fre-quency occurs, resulting in combination frequencies which are detectable by induction at the terminals of the motor as current and/or voltage signals. In the signal spectrum thes~ components appear as frequency groups at once or twice the distance of the slip frequency about the power supply ~requency as well as their odd-numbered and even-numbered harmonics. The amplitude of these components is dependent, among other things, on the magnet mater-ial and degree of saturation. The amplitude of the components is normally very small (about -60 to -90 dB), compared to the power supply parameters. Since the flux components are very close to the power supply frequency or its harmonics, especially when the slip is small, direct selection and evaluation of these com-ponents is not possible.
What is possible, however, is the selection of one or more suitable frequency groups. Undesirable signal components, 2Q such as rotor slots harmonics, are sufficiently suppressed by this selection. When the slip-proportional components are shifted by convolution in the frequency range into an undisturbed frequency band, e.g. the base band, they can be obtained ~y simple filter-ing due to the large relative frequency distance from interference components existing in this undisturbed band. The slip-propor-tional components can then be displayed directly and/or ~urther processed.
_ ~ _ ~ 20365-2849 Thus, for example, a frequency group ~ith components at the distance of twice the slip frequency 2xfs can be selected.
After convolution and filtering, a frequency counter can then be used for displayin~ the slipo For a 50 Hz power supply, the slip s is then indicated directly as a percentage, independently of the number of pole pairs of the motor, since 2xfs = 2xsx50= 100 s = s (%~.
In the embodiment of the invention illustrated in Figure 1, the raw signal, comprising the ~eometric sum o~ all com-ponents delivered by the power supply and generated by the motor, is obtained from a single or multi-phase induction motor l by at least one converter 2. This raw signal is supplied to a level-adapted preliminary filter 3, preferably with a band pass char-acteristic. ~ subsequent convolution 4 (see E. Oran Brigham, "FFT Fast Fourier-Transformation", pages 68 to 94, 2nd edition, R. Oldenbourg Verlag Munich Vienna 1985) is done, for example, by simple squaring or synchronous rectification with the power supply frequency. For this convolution, known aevices such as parabolic function networks, multipliers or ring modulators may be used.
Undesire~ frequency components of the convolved signal are sup-~0 pressed by a filter 5. As the amplitude o~ the useful signal in-creases with increasing slip because of the also increasing reaction of the rotor, an almost constant output signal is generat-ed by suitable selection of the properties of the filter 5. Such filters are known for example fro~ the publication by Stearns, "Adaptive Signal Processing" Prentice Hall, Inc., Englewood Cliffs, N~ 07632, pages 316 et seq. The selection of the proper-ties of the filter 5 is a simple matter ~or one of ordinar~ skill in the art.
1 If the filter 5 is, .Eor example, a low-pass filter, 2 in most cases level control and limitiny devices are dispensable if a proper selection of the cut-off frequency and 4 edge steepness is made. Thus, the output signal is able to be supplied to a display and/or evaluat.ing unit 6 directly.
6 I t Figure ~ illustrates another embodiment for 7 1 obtaining the raw signal. If a three-phase motor 1 i5 8 ,l operated with a star connection, the converter 2 is not needed 9 li if the neutral point of the motor is not connected with the 1I neutral point of the power supply. Since the useful signal ~ components do not cancel each other out because of a lack of 12 ¦~ symmetry, they are available directly as voltage signals 13 1 against the neutral point of the power supply. The further lÇ - processing for ~he embodiment is the same as that shown in Figure 1.
~6 ~ ~Z~7 ~8 ~0 28 ~I
~ 1 2 g 30 ,1 ~ - 6 -
Claims (6)
1. An arrangement for measuring the slip of an electric induction motor having at least one phase, comprising: a level-adapted preliminary filter stage coupled to said motor so as to be supplied at least one of current signals and/or voltage signals generated by said motor, said current and/or voltage signals having a frequency proportional to the slip; means for signal convolution in a frequency range at at least one of a power supply frequency and/or its harmonics, said means for signal convolution being coupled to an output of said level-adapted preliminary filter stage;
a filter coupled to an output of said means for signal convolution, and at least one of a display unit and/or an evaluating unit coupled to an output of said filter.
a filter coupled to an output of said means for signal convolution, and at least one of a display unit and/or an evaluating unit coupled to an output of said filter.
2. The arrangement according to claim 1, wherein said filter having filter parameters selected such that it supplies at least one of said display unit and said evaluating unit with a substantially constant, slip-independent amplitude.
3. The arrangement according to claim 1, wherein said filter stage is supplied with a current signal having a frequency proportional to slip and further comprising a converter, coupled between said motor and said level-adapted preliminary filter stage, which senses from at least one phase of said motor said slip-proportional current signals generated by said motor.
4. The arrangement according to claim 3, wherein said filter having filter parameters selected such that it supplies at least one of said display unit and said evaluating unit with a substantially constant, slip-independent amplitude.
5. The arrangement according to claim 1, wherein said motor is a multi-phase induction motor that is star connected to a power supply with no connection between a neutral point of said motor and a neutral point of said power supply, and said filter stage is supplied with a voltage signal having a frequency proportional to slip, and said level-adapted preliminary filter stage is coupled to said neutral points so as to pick up said slip-proportional voltage signals.
6. The arrangement according to claim 5, wherein said filter having filter parameters selected such that it supplies at least one of said display unit and said evaluating unit with a substantially constant, slip-independent amplitude.
, . ..
, . ..
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3734071.9 | 1987-10-08 | ||
| DE19873734071 DE3734071A1 (en) | 1987-10-08 | 1987-10-08 | ARRANGEMENT FOR MEASURING THE SLIP OF ELECTRIC INDUCTION MACHINES |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1292279C true CA1292279C (en) | 1991-11-19 |
Family
ID=6337909
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000579443A Expired - Fee Related CA1292279C (en) | 1987-10-08 | 1988-10-06 | Arrangement for measuring the slip of electric induction motors |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0310892A1 (en) |
| JP (1) | JPH01123177A (en) |
| CA (1) | CA1292279C (en) |
| DE (1) | DE3734071A1 (en) |
| IN (1) | IN171001B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2560559A (en) * | 2017-03-15 | 2018-09-19 | Zenith Oilfield Tech Limited | Methods and systems for monitoring the performance of electric motors |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19653913A1 (en) * | 1996-12-21 | 1998-06-25 | Schenck Process Gmbh | Method for determining damage to rotors of asynchronous machines and device for carrying out the method |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH449770A (en) * | 1967-01-06 | 1968-01-15 | Bbc Brown Boveri & Cie | Device for measuring the slip of asynchronous machines |
| DE3234683A1 (en) * | 1982-09-18 | 1984-03-22 | Robert Bosch Gmbh, 7000 Stuttgart | Method for measuring the speed of rotation of a direct-current motor |
| US4527101A (en) * | 1983-11-23 | 1985-07-02 | Black & Decker Inc. | Universal electric motor speed sensing by using Fourier transform method |
| US4562396A (en) * | 1984-07-02 | 1985-12-31 | General Electric Company | Phase-locked loop control of an induction motor drive |
| GB8428199D0 (en) * | 1984-11-08 | 1984-12-19 | Adwel Ltd | Motor monitor signal analysis system |
-
1987
- 1987-10-08 DE DE19873734071 patent/DE3734071A1/en not_active Withdrawn
-
1988
- 1988-09-23 EP EP88115715A patent/EP0310892A1/en not_active Withdrawn
- 1988-10-03 IN IN814/CAL/88A patent/IN171001B/en unknown
- 1988-10-05 JP JP63252865A patent/JPH01123177A/en active Pending
- 1988-10-06 CA CA000579443A patent/CA1292279C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2560559A (en) * | 2017-03-15 | 2018-09-19 | Zenith Oilfield Tech Limited | Methods and systems for monitoring the performance of electric motors |
Also Published As
| Publication number | Publication date |
|---|---|
| IN171001B (en) | 1992-06-27 |
| JPH01123177A (en) | 1989-05-16 |
| EP0310892A1 (en) | 1989-04-12 |
| DE3734071A1 (en) | 1989-04-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |