JP5726778B2 - Failure detection device and failure detection method for generator excitation device - Google Patents

Description

  Embodiments described herein relate generally to a failure detection device and failure detection method for a generator excitation device.

  Generally, in a synchronous generator, a direct current is supplied to a generator field winding, and an induced electromotive force generated by a magnetic flux that changes as the rotor rotates is taken out on the stator side. In order to perform excitation by supplying a DC current to the generator field winding, a method of generating a DC current by rectifying an AC output generated using an AC exciter with a rectifier is often used. Typical excitation methods in this case include the brushless excitation method and the AC exciter method described below.

  The brushless excitation method rectifies the AC output from the armature winding of a rotary armature-type AC exciter with a rotary rectifier mounted on the same rotating shaft, and does not use a slip ring or brush. In this method, a direct current is supplied to the magnetic winding for excitation.

  The AC exciter system rectifies the AC output from the armature winding of the AC exciter installed on the same axis as that of the generator with a rectifier, and generates power by bringing the brush into contact with the slip ring on the rotating body. In this method, excitation is performed by supplying a direct current to the machine field winding.

JP-A-8-19231

  In recent years, the capacity of generators such as turbine generators has been increasing. Accordingly, the capacity of generator exciters including AC exciters and rectifiers used for excitation is also increasing. As the capacity increases, if a fault occurs in an AC exciter, a rectifier, etc., if the fault discovery is delayed, the effect will be great.

  For example, when the discovery of a failure is delayed, there may occur a situation where the generator must be stopped. If the generator operation line is stopped, it will affect the area that receives power from the generator, and if there is a large factory, it will cause the factory facilities to stop operating and have a significant impact on the industry. .

  The problem to be solved by the invention is to provide a failure detection device and a failure detection method capable of accurately detecting a failure occurring in a generator excitation device.

The failure detection device according to the embodiment is a failure detection device for a generator excitation device that rectifies an alternating current output of an alternating current exciter with a rectifier and supplies a direct current to a generator field winding, the rectifier and the generator A waveform observing means electrically connected to the field winding via a slip ring and a brush, and observing at least a field voltage waveform; and at least a field voltage waveform observed by the waveform observing means. Failure detecting means for detecting various failures occurring in the generator excitation device based on a change in wave number per cycle or a change in continuous wave interval, and the waveform observation means further includes a field current. Means for observing the waveform of the generator, and the failure detection means further includes various reasons that occur in the generator excitation device based on the presence or absence of pulsation of a field current waveform observed by the waveform observation means. And a means for detecting.

The figure which shows an example of schematic structure of the synchronous generator provided with the failure detection apparatus common to each embodiment. The figure which shows an example of the circuit structure of the synchronous generator provided with the generator excitation apparatus of the brushless excitation system which concerns on 1st Embodiment. The figure which shows the example of another circuit structure which changed a part of circuit structure shown by FIG. The figure which shows an example of arrangement | positioning of each slip ring. The figure which shows an example of a function structure of the failure detection apparatus applied in common to the circuit structural example shown by FIG. 2 and FIG. The figure which shows an example of a structure of the various functions contained in the accident detection part with which the failure detection apparatus shown by FIG. 5 is equipped. The graph which shows an example of the field voltage waveform at the time of "1 arm short circuit failure" generating in a rectifier. The graph which shows an example of a field voltage waveform at the time of "two phase short circuit failure" having occurred in an AC exciter. The graph which shows an example of a field voltage waveform when the "phase short circuit fault" occurs in an AC exciter. The graph which shows an example of a field current waveform at the time of "phase short circuit failure" having occurred in an AC exciter. The graph which shows an example of a field voltage waveform at the time of "three-phase short circuit failure" having occurred in an AC exciter. The graph which shows an example of a field voltage waveform at the time of "1 arm opening failure" generating in a rectifier. The figure which shows an example of the circuit structure of the synchronous generator provided with the generator excitation apparatus of the alternating current exciter system which concerns on 2nd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

(Matters common to each embodiment)
FIG. 1 is a diagram illustrating an example of a schematic configuration of a synchronous generator including a failure detection apparatus common to the embodiments.

  The generator 10 is mainly composed of a stator 1 and a rotor 2, and a generator excitation device (not shown) for exciting the generator on the stator 1 side or the rotor 2 side is provided. This generator excitation device corresponds to either the brushless excitation method or the AC excitation device method, generates an AC output by the AC excitation device, performs rectification by the rectifier, and supplies a DC current to the generator field winding. .

  Further, the generator 10 is provided with a failure detection device 11 that detects a failure of an AC exciter, a rectifier, or the like that constitutes the generator excitation device.

  On the rotating shaft 3 that supports the rotor 2, annular slip rings (rotating electrodes) 4 and 5 that rotate together with the rotating shaft 3 are fixed, and contact with the outer peripheral surfaces of these slip rings 4 and 5, respectively. Thus, the brushes (fixed connectors) 6 and 7 are held by a brush holder (not shown).

  The slip rings 4 and 5 are electrically connected between the rectifier of the generator exciter and the generator field winding so that the field voltage of the generator can be detected. It functions as a side electrode.

  The brushes (fixed connectors) 6 and 7 are made of carbon or the like, and supply electric signals obtained through the slip rings 4 and 5 to the failure detection device 11.

  The failure detection device 11 detects a failure of the generator excitation device based on electrical signals obtained through the slip rings 4 and 5 and the brushes 6 and 7.

(First embodiment)
FIG. 2 is a diagram illustrating an example of a circuit configuration of a synchronous generator including the brushless excitation type generator excitation device according to the first embodiment. In addition, the same code | symbol is attached | subjected to the element which is common in FIG.

  The generator exciter 21 of the brushless excitation system provided in the generator 10 includes an armature winding of an AC exciter and a rotary rectifier coaxially with the generator. That is, the generator exciter 21 includes a stator-side field winding 22A and a rotor-side armature winding 22B, and a rotor-side rectifier (rotary rectifier) 23 that constitute the AC exciter 22. A direct current generated from the rectifier 23 is supplied to the generator field winding 8 without passing through an exciting slip ring or brush. However, in this embodiment, slip rings 4 and 5 and brushes 6 and 7 for failure detection are provided. In this configuration, when a field current flows through the field winding 22A and an AC current is output from the armature winding 22B, rectification is performed by the rectifier 23, and the generated DC current is used as the field current as a generator. The electric field is supplied to the field winding 8 and the generator is excited.

  A slip ring 4 is connected between the generator field winding 8 and the positive side of the rectifier 23, while a slip ring 5 is connected between the generator field winding 8 and the negative side of the rectifier 23. Is done. The slip ring 4 is connected to the terminal 12 of the failure detection device 11 through the brush 6, and the slip ring 5 is connected to the terminal 13 of the failure detection device 11 through the brush 7. Further, in the failure detection device 11, a voltmeter (not shown) that measures the voltage value between the terminal 12 and the terminal 13 is provided.

  With the configuration shown in FIG. 2, the failure detection device 11 can observe the field voltage through a voltmeter, and determines and detects various failures in the generator excitation device 21 from the field voltage waveform. Can do. The types of faults that can be detected from the waveform of the field voltage are: “1-arm short-circuit fault” of the rectifier, “2-phase short-circuit fault” of the AC exciter, “1-arm open fault” of the rectifier, and “field” on the rectifier output side. "Ground fault".

  “One-arm short-circuit failure” refers to a state in which one of the upper and lower arms of each phase constituting the rectifier 23 is short-circuited due to destruction of an element (diode) or the like.

  The “two-phase short-circuit failure” refers to a state in which two phases are short-circuited among the three phases of the AC output of the armature winding 22 </ b> B constituting the AC exciter 22.

  “One-arm open failure” refers to a state in which one of the upper and lower arms of each phase constituting the rectifier 23 is opened due to disconnection or the like.

  The “field ground fault” refers to a state in which a line supplying a field current to the generator field winding 8 is grounded.

  A specific method for detecting these failures will be described in detail later.

  FIG. 3 is a diagram showing an example of another circuit configuration in which a part of the circuit configuration shown in FIG. 2 is changed. Elements that are the same as those in FIG. 2 are given the same reference numerals, and redundant descriptions are omitted.

  In the example of FIG. 3, one slip ring 4 shown in the example of FIG. 2 is divided into two slip rings 4A and 4B. Further, one brush 6 shown in the example of FIG. 2 is divided into two brushes 6A and 6B. The slip ring 4A is connected to the positive side of the rectifier 23 and is connected to the terminal 12A of the failure detection device 11 through the brush 6A. On the other hand, the slip ring 4B is connected to the positive side of the generator field winding 8 and is connected to the terminal 12B of the failure detection device 11 through the brush 6B. Note that the slip ring 4A and the slip ring 4B are not connected. Moreover, in the failure detection apparatus 11, the terminal 12 and the terminal 13 are connected, and the ammeter (not shown) which measures the current value of the field current which flows through this is provided.

  With the configuration as shown in FIG. 3, the failure detection apparatus 11 can observe the field current using an ammeter in addition to observing the field voltage through a voltmeter. Various faults of the generator excitation device 21 can be determined and detected from both waveforms of the current, and more types of faults can be detected compared to the example of FIG. As the types of failures that can be detected from the field voltage waveform and the field current waveform, in addition to the various failures described above, “interphase short-circuit failure”, “three-phase short-circuit failure”, and the like of the AC exciter 22 can be cited.

  The “phase short circuit failure” refers to a state in which a short circuit has occurred between two phases of the three phases of the AC output of the armature winding 22 </ b> B constituting the AC exciter 22.

  The “three-phase short-circuit failure” refers to a state where all three phases of the AC output of the armature winding 22 </ b> B constituting the AC exciter 22 are short-circuited.

  A specific method for detecting these failures will be described in detail later.

  FIG. 4 is a diagram illustrating an example of the arrangement of individual slip rings.

  For example, the slip rings 4A, 4B, and 5 shown in the example of FIG. 4 are arranged on the outer peripheral side of the rotary shaft 3 or a member attached to the shaft, while being separated from each other while maintaining an insulating state. . The brushes (not shown) are arranged so as to contact the outer peripheral surfaces of the slip rings 4A, 4B, and 5, respectively, and the internal circuits on the rotor side are arranged on the inner peripheral sides of the slip rings 4A, 4B, and 5, respectively. Wiring (not shown) connected to is provided. The slip rings 4 and 5 shown in the example of FIG.

  In addition, arrangement | positioning of each slip ring is not limited to the example shown in FIG. For example, the slip ring 5 is made larger than the slip rings 4A and 4B, or each slip ring is further composed of a plurality of slip rings and a plurality of brushes corresponding to them are arranged. You may make it prevent poor contact. Further, the individual slip rings may be joined close to each other with an insulator interposed therebetween so as to be compact as a whole, and the occupied space of the entire slip ring may be reduced.

  FIG. 5 is a diagram illustrating an example of a functional configuration of the failure detection apparatus 11 that is commonly applied to the circuit configuration examples illustrated in FIGS. 2 and 3. FIG. 6 is a diagram illustrating an example of a configuration of various functions included in the accident detection unit 42 provided in the failure detection apparatus 11 illustrated in FIG.

  However, when the functional configuration shown in FIG. 5 and FIG. 6 is applied to the failure detection apparatus 11 in FIG. 2, waveform observation of “field current”, determination using the same, and failure detection cannot be performed. .

  The failure detection apparatus 11 shown in FIG. 5 includes a waveform observation unit 41, an accident detection unit 42, an input unit 43, and a display unit 44.

  The waveform observation unit 41 has a function of observing the waveform of the field voltage and field current supplied to the generator field winding 8 through individual slip rings and brushes.

  The accident detection unit 42 has a function of detecting various failures occurring in the generator excitation device 21 based on changes in the field voltage and field current waveforms observed by the waveform observation unit 41. For example, the generator excitation device 21 is determined by determining the number of waves per period of the field voltage waveform observed by the waveform observing unit 41, the interval between successive waves, or the presence or absence of pulsation exceeding a certain value in the field current waveform. It is possible to detect various faults in the AC exciter 22 and the rectifier 23 that constitute.

  The input unit 43 is a function for inputting and setting threshold values used for various accident determinations.

  The display unit 44 has a function of displaying and outputting observed waveforms, accident detection results, and the like.

  The accident detection unit 42 shown in FIG. 6 includes a voltage value determination unit 51, a wave number determination unit 52, and a wave interval determination unit 53 as various determination functions using the observed field voltage, and the observed field current. As various determination functions using, a current value determination unit 61 and a pulsation determination unit 62 are provided. The various functions shown in FIG. 6 may be provided in the waveform observation unit 41.

  The voltage value determination unit 51 has a function of determining the field voltage value. For example, it is also determined whether or not the state in which the field voltage is 0 [V] has continued for a certain period of time.

  The wave number determination unit 52 has a function of determining the wave number per cycle of the field voltage waveform. For example, it is determined whether the wave number per cycle has changed from 6 to 2, or whether the wave number has changed from 6 to 4. Determine whether or not.

  The wave interval determination unit 53 has a function of determining the interval between successive waves of the field voltage waveform. For example, it is determined whether the interval between consecutive waves is equal, or the interval between consecutive waves is unequal. Judgment is made as to whether or not it has changed.

  The current value determination unit 61 has a function of determining the value of the field current.

  The pulsation determination unit 62 is a function for determining whether or not the field current waveform exhibits a pulsation of a certain magnitude or more. For example, there is a current change exceeding a certain value first, and thereafter, the current change gradually increases. It is determined whether or not there is a tendency to decrease and converge to a constant current value.

  Next, with reference to the graphs shown in FIGS. 7 to 12, the field voltage waveform or the field current waveform observed when various failures occur will be described. In each graph, the horizontal axis represents time [s], and the vertical axis represents field voltage [V] or field current [kA]. In each graph, the left half shows the waveform before the occurrence of the failure, and the right half shows the waveform after the occurrence of the failure.

  FIG. 7 is a graph showing an example of a field voltage waveform when a “one-arm short-circuit failure” occurs in the rectifier 23.

  In the example of FIG. 7, from a certain point in time, the wave number of the field voltage waveform changes from 6 to 2 per cycle, and the interval between continuous waves becomes unequal. When such a condition is satisfied, the accident detection unit 42 determines that a “one-arm short-circuit failure” has occurred in the rectifier 23 and issues information indicating the failure by display, voice, or light.

  FIG. 8 is a graph showing an example of a field voltage waveform when a “two-phase short-circuit failure” occurs in the AC exciter 22.

  In the example of FIG. 8, from a certain point in time, the wave number of the field voltage waveform changes from 6 to 2 per cycle, and the interval between continuous waves becomes equal. When such a condition is satisfied, the accident detection unit 42 determines that a “two-phase short-circuit failure” has occurred in the AC exciter 22, and displays information indicating the failure by display, voice, or light. .

  FIG. 9 and FIG. 10 are graphs showing examples of the field voltage waveform and the field current waveform when the “phase short-circuit failure” occurs in the AC exciter 22, respectively.

  In the example of FIGS. 9 and 10, the field voltage becomes 0 [V] from a certain point of time and continues for a certain time or more, and the field current waveform shows a pulsation with a certain magnitude or more. For example, first, there is a current change exceeding a certain value, and thereafter, the current change gradually decreases. When such a condition is satisfied, the accident detection unit 42 determines that an “interphase short-circuit failure” has occurred in the AC exciter 22 and issues information indicating the failure by display, voice, or light.

  FIG. 11 is a graph showing an example of a field voltage waveform when a “three-phase short-circuit failure” occurs in the AC exciter 22.

  In the example of FIG. 11, the field voltage becomes 0 V from a certain point in time, and the state in which the field current waveform (not shown) shows no pulsation continues for a certain time or more. When such a condition is satisfied, the accident detection unit 42 determines that a “three-phase short-circuit fault” has occurred in the AC exciter 22 and issues information indicating the fault by display, voice, or light. .

  FIG. 12 is a graph showing an example of the field voltage waveform when the “one-arm open failure” occurs in the rectifier 23.

  In the example of FIG. 12, the wave number of the field voltage waveform changes from 6 to 4 per cycle from a certain point in time. When such a condition is satisfied, the accident detection unit 42 determines that a “one-arm short-circuit failure” has occurred in the rectifier 23 and issues information indicating the failure by display, voice, or light.

  In addition, in the brushless excitation method, as shown in the example of FIG. 9, when the field voltage becomes 0 [V] and continues for a certain time or more from a certain point in time, the accident detection unit 42 sets the AC exciter 22. It may be determined that a “field ground fault” has occurred on the output side of the rectifier 23, and information indicating that fact may be issued by display, voice, or light.

  As described above, according to the first embodiment, it is possible to accurately detect various failures that may occur in the brushless excitation type generator excitation device. In particular, the AC exciter armature and rotary rectifier are on the same axis as the generator and are directly connected to the generator rotor and rotate at high speed. According to the embodiment, it can be easily found. Since failure detection at an early stage becomes possible, it is possible to avoid the stop of the generator and the stop of the operation line, and the influence on the area that receives power from the generator can be reduced.

(Second Embodiment)
FIG. 13 is a diagram illustrating an example of a circuit configuration of a synchronous generator including an AC exciter generator exciter according to the second embodiment. In addition, the same code | symbol is attached | subjected to the element which is common in FIG.

  The brushless excitation type generator exciter 21 ′ provided in the generator 10 is provided separately from the generator and includes an armature winding and a rectifier of an AC exciter. In addition, the armature winding and the rectifier of these AC exciters can be provided coaxially with the generator. In the example of FIG. 13, the generator exciter 21 ′ includes a rotor-side field winding 22 </ b> A ′ and a stator-side armature winding 22 </ b> B ′, and a stator-side rectifier constituting the AC exciter 22 ′. 23 ′, and the direct current generated from the rectifier 23 ′ is passed through the fault detection device 11 ′, and further through the slip ring 4 ′ and the brush 6 ′, and through the slip ring 5 ′ and the brush 7 ′ to the generator field. Supply to magnetic winding 8. In this configuration, when a field current flows through the field winding 22A ′ and an AC current is output from the armature winding 22B ′, rectification is performed by the rectifier 23 ′, and the generated DC current is converted into the field current. Is supplied to the generator field winding 8 to excite the generator.

  The positive side of the rectifier 23 is connected to the terminal 12A 'of the failure detection device 11', and the slip ring 4 'is connected to the terminal 12B' of the failure detection device 11 'through the brush 6'. On the other hand, the negative side of the rectifier 23 is connected to the terminal 13 'of the failure detection device 11', and the slip ring 5 'is connected to the terminal 13' of the failure detection device 11 'through the brush 7'. Further, a voltmeter (not shown) for measuring a voltage value between the terminal 12A '(or 12B') and the terminal 13 'is provided in the failure detection apparatus 11'. Further, in the failure detection apparatus 11 ′, the terminal 12 </ b> A ′ and the terminal 12 </ b> B ′ are connected, and an ammeter (not shown) for measuring the current value of the field current flowing therethrough is provided.

  In the example of FIG. 13, a configuration in which the existing slip ring 4 ′ and brush 6 ′ for excitation and the slip ring 5 ′ and brush 7 ′ are also used for field voltage detection is shown. Separately, a new slip ring and brush for field voltage detection may be added, or only a brush may be added.

  With the configuration as shown in FIG. 13, the failure detection device 11 ′ observes the field current using the ammeter in addition to observing the field voltage through the voltmeter, as in the circuit configuration example of FIG. 3. It is possible to determine and detect various failures of the generator excitation device 21 ′ from the waveforms of the field voltage and the field current. The types of faults that can be detected from each waveform of field voltage and field current are the same as in the circuit configuration example of FIG.

  The example of the arrangement of the slip ring shown in FIG. 4, the example of the functional configuration of the failure detection apparatus 11 shown in FIG. 5, and the example of the configuration of various functions shown in the example of FIG. 6 are described in this second embodiment. Also applies.

  Further, when various types of faults occur, field voltage waveforms or field current waveforms similar to those shown in the graphs shown in FIGS. 7 to 12 are observed. Therefore, the fault detection device 11 ′ uses various methods described above. Fault detection can be performed.

  As described above, according to the second embodiment, it is possible to accurately detect various failures that may occur in the AC exciter generator exciter. Moreover, since it can implement | achieve, without adding the slip ring for failure detection etc. which were shown in 1st Embodiment, a significant change is not added to an apparatus, but cost can be held down. In addition, as in the first embodiment, since early failure detection is possible, it is possible to avoid the stoppage of the generator and the operation line, and to reduce the influence on the area that receives power from the generator. Can do.

  As described above in detail, according to each embodiment, it is possible to accurately detect a failure occurring in the generator excitation device.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Stator, 2 ... Rotor, 3 ... Rotating shaft, 4, 4A, 4B, 5 ... Slip ring, 6, 6A, 6B, 7 ... Brush, 8 ... Generator field winding, 10 ... Generator, 11, 11 '... failure detection device, 12, 12A, 12B, 13, 12A', 12B ', 13' ... terminal, 21, 21 '... generator excitation device, 22A, 22A' ... field winding, 22B, 22B '... armature winding, 23, 23' ... rectifier, 41 ... waveform observation part, 42 ... accident detection part, 43 ... input part, 44 ... display part, 51 ... voltage value judgment part, 52 ... wave number judgment part, 53: Wave interval determination unit, 61: Current value determination unit, 62 ... Pulsation determination unit.

Claims (10)

A fault detection device for a generator exciter that rectifies the AC output of an AC exciter with a rectifier and supplies a DC current to the generator field winding,
Waveform observing means electrically connected via a slip ring and a brush between the rectifier and the generator field winding, and observing at least a field voltage waveform;
Fault detection means for detecting various faults occurring in the generator excitation device based on a change in wave number per cycle of the waveform of the field voltage observed by the waveform observation means or a change in the interval of successive waves; equipped with,
The waveform observation means further comprises means for observing a field current waveform,
The failure detection means further comprises means for detecting various failures occurring in the generator excitation device based on the presence or absence of pulsation of a certain level or more of the field current waveform observed by the waveform observation means. Characteristic failure detection device.   2. The generator excitation device according to claim 1, wherein the generator excitation device is a brushless excitation generator excitation device in which an armature winding of the AC excitation device and the rectifier are mounted on a shaft of the generator. 3. Fault detection device.   In the generator exciter, the armature winding of the AC exciter and the rectifier are arranged on the generator shaft or separately from each other, and a direct current is supplied to the generator field winding via a brush and a slip ring. The fault detection device according to claim 1, wherein the failure detection device is an AC exciter type generator excitation device to be supplied. The failure detection means includes
When the wave number of the field voltage waveform observed by the waveform observing means changes from 6 to 2 per cycle and the interval between successive waves becomes unequal, one arm short-circuit failure occurs in the rectifier. The failure detection device according to claim 1, wherein the failure detection device is determined to have occurred. The failure detection means includes
Two-phase short-circuit fault in the AC exciter when the wave number of the field voltage waveform observed by the waveform observing means changes from 6 to 2 per cycle and the interval between successive waves becomes equal. 5. The failure detection apparatus according to claim 1, wherein the failure detection apparatus determines that an error has occurred. The failure detection means includes
2. It is determined that a one-arm open failure has occurred in the rectifier when the wave number of the field voltage waveform observed by the waveform observation means changes from 6 to 4 per cycle. The failure detection device according to any one of 1 to 5. The failure detection means includes
The fault detection according to any one of claims 1 to 6, wherein when the field voltage observed by the waveform observing means is 0V, it is determined that a field ground fault has occurred. apparatus. The failure detection means includes
When the field voltage observed by the waveform observing means is 0 V and the field current waveform shows a pulsation of a certain magnitude or more, it is determined that a short-circuit fault has occurred in the AC exciter. The failure detection apparatus according to claim 1, wherein: The failure detection means includes
When the field voltage observed by the waveform observing means is 0 V and the field current waveform does not show pulsation, it is determined that a three-phase short-circuit fault has occurred in the AC exciter. The failure detection apparatus according to any one of claims 1 to 8 . A fault detection method for a generator exciter that rectifies the AC output of an AC exciter with a rectifier and supplies a DC current to the generator field winding,
Observe at least the waveform of the field voltage through a slip ring and a brush electrically connected between the rectifier and the generator field winding,
Based on at least a change in the wave number per period of the observed waveform of the field voltage or a change in the interval between successive waves, various faults occurring in the generator excitation device are detected ,
In the waveform observation, further observe the waveform of the field current,
In the fault detection, the fault detection method further comprises detecting various faults occurring in the generator excitation device based on the presence or absence of a pulsation of a certain level or more of the field current waveform observed by the waveform observation. .

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