JP2001013225A - Online insulation diagnosing method and device for a.c. rotary machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly diagnose insulation degradation in a coil which an A.C. rotary machine such as an A.C. motor comprises in an operating state. SOLUTION: An online insulation diagnosing device for an A.C. rotary machine to diagnose the insulation of a coil by detecting partial discharge which occurs in a three-phase A.C. generator in operation is provided with detecting parts 10A-10C to detect currents of phases (r), (s), and (t) passing through the A.C. rotary machine, HPFs 12A-12C to attenuate fundamental-wave components from each detected current signal, an A/D converting part 14 to digitize a current signal passed through each HPF, a processing part 18 to shift one of any two current signals by 120 deg. and perform subtraction between both signals after matching phases, a processing part 20 to determine the polarity that indicates in which phase the result of subtraction is a partial discharge which occurs, and a display device 22 to display the result of determination by a combination of two phases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for diagnosing insulation of an AC rotating machine, and more particularly to detecting an insulation deterioration of windings of an AC rotating machine such as an operating AC motor or an AC generator during operation. The present invention relates to an on-line insulation diagnosis method and apparatus for an AC rotating machine, which is suitably applied at the time.

[0002]

2. Description of the Related Art As a method of detecting insulation deterioration of a winding while an AC motor is stopped, a method of applying a test voltage to a motor and measuring the amount of partial discharge charge generated at that time, and a method of detecting winding deterioration are described. There is a method of determining the degree of deterioration from the capacitance and the amount of the loss angle (tan σ).

Conventionally, the most effective method for diagnosing insulation deterioration of windings of a motor is to measure the amount of partial discharge charge when a test voltage is applied while the motor is stopped, and calculate the amount of charge. This is a method of determining the degree of deterioration from the magnitude of.

However, in this method, diagnosis of insulation deterioration can be made only when the motor is stopped, so that a diagnosis cycle may not be properly set for a motor of a plant that is operated continuously for a long period of time.

In this method, it is possible to determine the insulation deterioration between the winding and the ground. However, since a test voltage is not applied between the windings, the insulation deterioration between the windings may occur. Even if it occurs, it has the disadvantage that it cannot be accurately determined. However, even when the motor is stopped, insulation diagnosis between windings can be performed by using a special test power supply in a place such as a motor factory, but it is not realistic from the viewpoint of cost as a test performed on site. I can not say.

[0006] Further, the diagnosis with the motor stopped is as follows.
For example, since electrical and mechanical stresses such as temperature rise and vibration are different from the actual operation state, accurate diagnosis cannot be performed.

Therefore, in order to accurately determine the degree of insulation deterioration of the winding, it is desirable to make a diagnosis when the motor is in an operating state.

[0008] In view of this, detection of insulation deterioration of a field winding of an AC motor during operation has been performed, and such an online detection technique couples a high-frequency current caused by corona discharge caused by insulation deterioration. High-frequency CT (Curr)
ent Transformer: A method of detecting with a current transformer has been devised. Further, as a device for detecting the corona discharge and monitoring the insulation, there is, for example, a device proposed in Japanese Utility Model Publication No. 59-4294.

[0009]

However, a method of detecting a high-frequency current with a coupling capacitor or a method of detecting a high-frequency current flowing into a ground line with a high-frequency CT using the online diagnosis (detection) technology that has been devised. In this case, there is a problem that accurate detection of partial discharge is difficult because harmonic noise present in the power supply is always superimposed on the partial discharge signal.

[0010] In particular, in an iron making plant, VVVF
(Variable Voltage Variable Frequency) and accurate speed control using a cycloconverter, etc., so many harmonics are superimposed on the power supply, and only a weak partial discharge signal is extracted from the detection signal. Is extremely difficult.

In addition, there is a method of capturing corona discharge sound (ultrasonic waves) caused by insulation deterioration with a microphone. However, since the microphone is subjected to electromagnetic induction under a strong magnetic field of a motor, a minute ultrasonic wave is captured. It is difficult to find out and it has not been put to practical use.

The present invention has been made in order to solve the above-mentioned conventional problems, and it is possible to accurately diagnose insulation deterioration of windings of an AC rotating machine such as an AC motor or an AC generator in an operating state. An object of the present invention is to provide a method and an apparatus for diagnosing insulation of an AC rotating machine.

[0013]

SUMMARY OF THE INVENTION The present invention relates to an on-line insulation diagnosis method for an AC rotating machine, which detects partial discharge generated in an n-phase AC rotating machine during operation and diagnoses insulation of a winding. The detected current signal nearest to the target current signal thus shifted is shifted by (360 / n) degrees to match the phases of the two current signals, and a subtraction is performed between the shifted detected current signal and the target current signal to perform subtraction. The problem has been solved by extracting a partial discharge signal from a later signal.

The present invention also provides an on-line insulation diagnosis apparatus for an AC rotating machine for detecting partial discharge generated in an operating n-phase AC rotating machine and diagnosing winding insulation. Detecting means for detecting the flowing current; and detecting the detected current signal closest to the detected target current signal by (360 /
n) shifting means for shifting the phase of both current signals by shifting by degrees, subtracting means for subtracting between the shifted detected current signal and the target current signal, and extracting a partial discharge signal from the subtracted signal. And the display means for displaying the information.

That is, in the present invention, the current of the n-phase AC rotating machine during operation is detected, and the detected current signal that is closest to the detected target current signal is shifted by (360 / n) degrees so that both currents are shifted. Since the subtraction is performed between the two current signals after the signal phases are matched, only the harmonic noise can be removed. Therefore, the current signal (partial discharge signal) caused by the partial discharge is obtained from the subtraction result. It can be extracted reliably.

In the case of n = 1 single-phase alternating current, the latest detected current signal is one cycle (3
60 °) or the same current signal before or after, and when n = 2 or more, it is a detected current signal of the adjacent phase (360 / n) degrees after or before the target current.

[0017]

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

FIG. 1 is a block diagram showing a schematic configuration of an insulation diagnosis apparatus according to one embodiment of the present invention.

The insulation diagnostic apparatus according to the present embodiment is applied to a three-phase AC motor (AC rotating machine), and detects current signals flowing through the windings of the r, s, and t phases of the motor M. Sections 10A, 10B, and 10C, high-pass filters (HPF) 12A, 12B, and 12C for attenuating fundamental components from the detected current signals of the respective phases, and signals that have passed through these HPFs 12A to 12C. An A / D converter 14 for converting the digital signals and storing each digital signal in a buffer memory (not shown); a shifter 16 for shifting one of the stored two-phase signals by 120 degrees; A subtraction processing unit for subtracting the one of the signals from the other signal to remove a harmonic component, and comparing the polarity of the signal after subtraction (the result of subtraction) with the polarity of the original signal to determine the result of the subtraction. Chi And a polarity determination processing unit 20 that determines the polarity of the partial discharge, and a discharge amount display device 22 that displays the partial discharge whose polarity has been determined by the determination processing unit 20 in association with the generated phase. I have.

In the present embodiment, the detecting units 10A, 10A
The current signals detected by B and 10C are branched from a secondary circuit of a not-shown CT (current transformer) or divided CT in order to increase the resolution of A / D conversion by the A / D converter 14. I'm taking it out.

Further, the shift processing by the shift section 16 performed before the subtraction processing by the subtraction processing section 18 is performed by accumulating the signal digitized by the A / D conversion section 14 in the buffer memory, and then converting one of the input signals. Memory address equivalent to a phase difference of 120 degrees (360 degrees / 3) (= Fs / 60 /
3, Fs: sampling frequency).

In this embodiment, the combination of the input signals to be subtracted may be any of the r phase and the t phase, the r phase and the s phase, and the s phase and the t phase. This will be described in detail focusing on the combination of s phases.

First, the shift subtraction method obtained as a result of the inventor's intensive study will be described.

As shown in FIG. 2A, when the current of each phase of r, s, and t flowing in the three-phase AC motor M similar to that of FIG. 1 is detected, these are detected as harmonics included in the power supply. Due to the influence, as shown in FIG. Therefore, even if an attempt is made to detect a partial discharge inside the motor with a zero-phase current corresponding to a three-phase combined current as shown in the image of FIG. Is superimposed greatly and does not become 0 A, so that partial discharge cannot be accurately detected.

In order to eliminate only the harmonic noise by utilizing the difference between the characteristics of the harmonic noise and the partial discharge,
The present applicant has devised a shift subtraction method.

The principle of the shift subtraction method is as follows.
It is caused by artificial operation such as VVF, and its generation cycle has a periodicity in a short time, and the generation pattern is almost the same between different phases, but the partial discharge shows an accidental generation form. It has no periodicity, and the occurrence pattern differs between different phases. The difference in nature is used to shift and subtract the sampling signal by 120 degrees (360 degrees for a single phase), which is a repetition cycle of harmonics in three-phase AC, and cancel the harmonic components. That is the shift subtraction method.

This shift subtraction method will be described in detail by taking the case of three-phase alternating current as an example. Figure 4 shows the r-phase current.
Assuming that the current is detected by the observation waveform shown in (A), this current is formed in a waveform formed by overlapping the fundamental wave, harmonics, and partial discharge shown in FIGS. (B), (C), and (D), respectively. ing. On the other hand, the s-phase current obtained by the observation waveform shown in FIG. 5A is also formed by overlapping the fundamental wave, harmonic wave, and partial discharge shown in FIGS. 5B, 5C, and 5D, respectively. It is formed in a waveform, and has a phase difference of 120 degrees from the r phase.

Therefore, when the s-phase current signal is shifted by 120 degrees, its waveform becomes a waveform similar to the r-phase.
As shown in (A) and (B), the subtraction side is a negative signal, and the fundamental wave and the harmonic wave are shown as negative signals. These are canceled out, and the remaining difference signal waveform is shown in FIG. It becomes the component of the partial discharge of the phase and the s phase.

As described above, by using the shift subtraction method, harmonic noise can be canceled and only partial discharge can be extracted. Therefore, according to the insulation diagnostic apparatus of the present embodiment shown in FIG. 1, the normal state is shown in FIG. 7, and the abnormal state is shown in FIG. 8 together with the observed s-phase current signal in FIG. In addition, the signal of the partial discharge can be accurately detected, and these signals are displayed on the discharge amount display device 2.
2 can be displayed. In the drawing, CH1 is an s-phase current signal, and CH2 is a partial discharge current signal.

As described in detail above, according to the present embodiment, the partial discharge generated when the insulation of the winding of the AC motor is deteriorated is continuously reduced by separating the harmonic noise while the motor is operating. Because it can be detected, online diagnosis that has been difficult until now has become possible.

Further, it has become possible to diagnose on-line the insulation deterioration between the windings, which has not been possible even in the test in the stopped state.

Although the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and can be variously modified without departing from the gist thereof.

For example, in the above embodiment, the case of three-phase alternating current has been described. However, the present invention is not limited to this, and may be single-phase alternating current or other than three-phase alternating current. For single-phase AC,
The same effect can be obtained by shifting the current of the own phase by 360 degrees and subtracting it instead of the phase. 3
In the case of phase alternating current, the current of a particular phase is shifted by 360 degrees and subtracted, so that the discharge related to that phase can be detected. In the case of a zero-phase circuit, the internal parts can be shifted by 360 degrees and subtracted. Discharge can be detected.

In the above embodiment, an AC motor has been described. However, it is needless to say that the present invention can be similarly applied to an AC generator.

[0035]

As described above, according to the present invention,
Insulation deterioration of windings of an AC rotating machine such as an AC motor or an AC generator can be accurately diagnosed in an operating state.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an insulation diagnosis device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a current waveform of a three-phase AC motor.

FIG. 3 is a diagram showing a zero-phase current waveform of a three-phase AC motor.

FIG. 4 is a diagram showing an observed waveform of r-phase current and its component waveform.

FIG. 5 is a diagram showing an observed waveform of an s-phase current and its component waveforms.

FIG. 6 is a diagram showing shift subtraction results of r-phase and s-phase current components;

FIG. 7 is a diagram showing a partial discharge signal measured according to the embodiment;

FIG. 8 is another diagram showing a partial discharge signal measured according to the embodiment;

[Explanation of symbols]

 M: AC motor 10: Detection unit 12: High-pass filter 14: A / D conversion unit 16: Shift unit 18: Subtraction processing unit 20: Polarity determination processing unit 22: Discharge amount display device

Claims (5)

[Claims] An on-line insulation diagnosis method for an AC rotating machine for detecting partial discharge generated in an n-phase AC rotating machine during operation and diagnosing insulation of a winding, comprising the steps of: The detected current signal is expressed as (3
60 / n) degrees to adjust the phases of both current signals, subtracting between the shifted detected current signal and the target current signal, and extracting a partial discharge signal from the subtracted signal. Online insulation diagnosis method for AC rotating machines. 2. The online insulation diagnosis method and apparatus for an AC rotating machine according to claim 1, wherein n is a positive integer including at least 1 and 3. 3. An on-line insulation diagnosis device for an AC rotating machine for detecting partial discharge generated in an n-phase AC rotating machine during operation and diagnosing insulation of a winding, wherein a current flowing through the AC rotating machine is detected. Detecting means for detecting the detected current signal,
Shift means for shifting the phase of both current signals by 60 / n) degrees, subtraction means for subtracting between the shifted detected current signal and the target current signal, and converting the partial discharge signal from the subtracted signal. And a display means for extracting and displaying the on-line insulation diagnostic device for an AC rotating machine. 4. A high-pass filter according to claim 3, wherein the high-pass filter attenuates a fundamental wave component of the current signal detected by said detection means, and an A / D conversion means for converting a signal passed through said filter into a digital signal. Storage means for storing the converted current signal, and the shift means stores the memory address of the latest detected current signal digitized and stored in the storage means as (3
An on-line insulation diagnostic device for an AC rotating machine, having a function of shifting by 60 / n) degrees. 5. The online insulation diagnostic device for an AC rotating machine according to claim 3, wherein n is a positive integer including at least 1 and 3.