JPH0217465A - Method for advance detection of dielectric breakdown of winding of electric machine - Google Patents

Abstract

PURPOSE:To enable detection of an advance phenomenon of dielectric breakdown by fitting an acoustic emission (AE) sensor to the frame of a winding of an electric machine, by impressing a voltage on the winding and by measuring the amplitude of an AE signal generated at that time. CONSTITUTION:Four field windings 2 are disposed in combination with field cores 3 inside a frame 1 and they are wired so that a voltage can be impressed thereon from a power source device 8. An AE sensor 10 is fitted on the outer periphery of the frame 1 and an AE signal is inputted to an AE analyzer 6 through a preamplifier 5. While collecting AE data and an impression voltage signal 9, the analyzer 6 analyzes them immediately and displays the result in built-in CRT. When AE measurement is conducted for a voltage resistance check of the windings 2 by impressing thereon a prescribed voltage (5KV, a boosting speed 500V/sec), AE of an amplitude of 60dB or above does not occur in a sound insulation layer, while a number of large amplitudes of 60dB or above take place when dielectric breakdown comes near. By measuring and detecting these large amplitudes (the lower limit value is about 80dB) according ly, the dielectric breakdown can be detected in advance.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention solves the dielectric breakdown of electromechanical windings by acoustic
The present invention relates to a method of detecting in advance using an emission (hereinafter referred to as AE) method.

[Conventional technology]

In general, deterioration of the insulation of windings is a major factor that affects the reliability and lifespan of electrical machines. As insulation deterioration progresses, dielectric breakdown of the windings will eventually occur, but predicting dielectric breakdown is important when considering the effects when equipment is stopped due to dielectric breakdown during operation.

For this reason, various electrical and chemical methods for non-destructively diagnosing the degree of insulation deterioration are used to predict dielectric breakdown. The reality is that each of these various methods uses dedicated diagnostic equipment for diagnosis.

[Problem that the invention seeks to solve]

However, among the conventional methods for non-destructively diagnosing the degree of insulation deterioration in order to predict insulation breakdown, mechanical and chemical methods cannot be used to analyze the entire or part of the electromechanical winding or wire to be diagnosed. In many cases, the diagnosis is performed locally, and even the diagnostic methods that have been developed do not directly diagnose the precursor phenomenon of dielectric breakdown, but rather compare the mechanical and chemical properties with the residual breakdown voltage to diagnose insulation deterioration. This was an indirect determination of the degree of

In addition, many electrical methods have been proposed and implemented to diagnose the degree of insulation deterioration, but all of them indirectly determine the degree of insulation deterioration by comparing the obtained characteristic values and the residual breakdown voltage value. It was what I was looking for.

Therefore, although the above method can predict when dielectric breakdown will occur, it is insufficient as a preliminary detection method.

The present invention was devised in view of the above-mentioned points, and its purpose is to use AE to directly detect precursor phenomena of dielectric breakdown, rather than using the conventional diagnostic method of the degree of insulation deterioration as a method for detecting dielectric breakdown in advance. The purpose of this method is to detect dielectric breakdown easily and accurately in advance.

[Means for solving problems]

In other words, the means to achieve this purpose is to tightly fix an AE sensor to the core or frame near the electromechanical winding whose dielectric breakdown is to be detected in advance, and apply voltage to the winding. This is a detection method that measures and analyzes the generated human E signal, and determines the time when the amplitude (dB) of the AE parameters exceeds a certain value as a precursor to dielectric breakdown.

[For production]

The effect will be explained below.

When a partial discharge occurs inside the insulating layer, a shock wave containing an acoustic wave such as an ultrasonic wave is generated at the point where the discharge occurs, and the shock wave at this time can be detected by an acoustic detection means using an AE sensor.

When the insulation layer of an electromechanical winding is healthy, there are only minute voids inside the insulation layer, the starting voltage for partial discharges is relatively high, and the number of partial discharges that occur is small at the same applied voltage.
At the same time, the AE multiplied signal amplitude value detected by the AE sensor falls within a certain range.

When the insulating layer is subjected to various thermal and mechanical stresses and deterioration progresses, cracks appear in the insulating layer and the voids become larger than they were at the beginning, and even at the same voltage, the number of partial discharges that occur decreases. It will increase.

At the same time, the AE multiplied signal amplitude value detected by the AE sensor falls within a certain range.

When the insulating layer deteriorates significantly and approaches dielectric breakdown, the large voids in the insulator 1 become connected to each other and a large partial discharge occurs. At this time, the detected AE multiplied signal amplitude value exceeds a normal fixed range and becomes a large value. Eventually, the voids in the insulating layer are short-circuited and penetrated, leading to dielectric breakdown.

Hereinafter, one embodiment of the advance detection method of the present invention will be described in detail based on the drawings.

〔Example〕

1(a) and 1(b) show an assembly in which a DC machine field winding of a rotating electric machine is assembled into an iron core and a frame as an example of the advance detection of dielectric breakdown of the present invention. aJ is a plan view and an explanatory view showing the AE measurement method, and FIG. 1(b) is a side view.

In FIG. 1, four field windings 2, which are subject to preliminary detection of dielectric breakdown, are arranged in combination with field cores 3 at 90° intervals from the inner surface of the frame 1. ing. An applied voltage from a power supply 8 can be wired to each field winding 2 so that a withstand voltage check can be performed, and the frame 1 is grounded. A that occurs when checking withstand voltage
An AE sensor 10 is attached to the outer periphery of the frame 1 to detect the AE.
Enter analyzer 6. Note that 9 is an applied voltage signal, 7 is a printer, 8a is a voltage regulator, and A is a test transformer.

In addition, the AE sensor 4 used has a resonant frequency of 150 KHz, and the gain of the preamplifier 5 is 40 dB%A.
The main amplifier gain in the E analyzer 6 was set to 20 dB, and the threshold value was set to 0.1 V for measurement.

The AE analyzer 6 analyzes in real time while recording AE data obtained during AE measurement and applied voltage signals 9 sent from external equipment, and displays the results as a graphic on the built-in CRT. After the measurement, a graph or the like can be printed out using the printer 7.

Furthermore, in order to perform a life test due to thermal deterioration of the field winding 2 incorporated in the frame 1 and the field core 3, a constant current was applied.
A heat cycle test was conducted with a heating time of 5 hours and a cooling time of 1 hour. Withstand voltage checks were performed periodically during the heat cycle. In addition, the withstand voltage check was carried out to 5KV (step-up rate of 500V/sec) after cooling the field winding, but in order to be able to detect insulation breakdown in advance, A
E measurement was performed at the same time. AE at the time of dielectric breakdown of field winding
An insulating sheet with a thickness of 50 μm was inserted between the AE sensor 10 and the frame 1 to prevent high voltage from entering the measurement system from the sensor. AE sensor 10 to prevent AE measurement errors.
A flat surface is provided on the outer periphery of the frame 1 to ensure close contact between the frame 1 and the insulating sheet, and grease is also applied between the insulating sheet and the frame 1, and between the insulating sheet and the AE sensor 10, and then pressed firmly from above. It was fixed.

Figures 2 (a), (b), and (C) are characteristic diagrams when the same field winding was checked for withstand voltage while performing AE measurements using the measurement circuit diagram in Figure 1. After checking the withstand voltage, the printer 6 This drawing was published in . Here, the vertical axis of the characteristic diagram in FIG. 2 indicates amplitude, and since 100 dB corresponds to the preamplifier output peak value of 10 V after 40 dB amplification, the lower limit of the measured and displayed amplitude with the current settings is 40 dB. In addition, in Fig. 2 (a), (b), and (C),
Thermal deterioration progresses in the order of Figure (a), Figure (b), and Figure (C).

In the figure (C), the model coil has dielectric breakdown at a withstand voltage of 5KV. At this time, the applied voltage is 3.4KV to 5.
0KV (7) l'lJ'lte A E (7) al[f normal (7) 40dB ~ 60dB (7) outside the range 82.
Five AEs of 7 dB to 89.0 dB were measured. The last one is AE at the time of dielectric breakdown. The four AEs except for the last one are AEs generated by large partial discharges, which can be said to be a precursor to dielectric breakdown.

Figure (b) is a characteristic diagram when the withstand voltage check was repeated one time before the withstand voltage check in figure (C). Here, the applied voltage is 4.
A large partial discharge of 86.3 dB at 7 KV is 1 as an AE.
measured. This is also a precursor to dielectric breakdown during the next withstand voltage check.

(Figure 21 is a characteristic diagram when the insulating layer is healthy without any dielectric breakdown precursor phenomenon.The amplitude of the measured AE is 40 dB to 6
It is distributed in a range of 0 dB, and no abnormality is observed in the insulating layer.

As can be seen from Figures 2 (a), (b), and (C) above, in a healthy insulating layer with little deterioration, AE with a large amplitude of 60 dB or more does not occur, and the deterioration progresses and dielectric breakdown is near. Then, large amplitudes of 60 dB or more are observed, and many large amplitudes of 60 dB or more occur immediately before dielectric breakdown. By measuring and detecting these large amplitudes, dielectric breakdown can be detected in advance. As a result of various studies, it is considered that the lower limit of the amplitude to be a precursor to dielectric breakdown is approximately 80 dB.

In this embodiment, the method was used to detect dielectric breakdown in advance during a withstand voltage check, but it is also considered to be effective as a method for detecting dielectric breakdown in advance when a constant voltage is applied.

〔Effect of the invention〕

As explained above, according to the present invention, although conventionally it was not possible to directly detect the precursor phenomenon of dielectric breakdown and detect it in advance, by performing AE measurement, advance detection becomes possible easily and with high accuracy. .

[Brief explanation of the drawing]

Figures 1(a) and 1(b) show an embodiment of the method for detecting dielectric breakdown in advance according to the present invention, and Figure 1(a) is a plan view of the sample and an explanatory diagram showing the AE measurement method. Figure 1 (b) is a side view, Figure 2 (a), (b), and (c) are characteristic diagrams output from the AE analyzer in Figure 1, and Figure 2 (a) is when the insulation layer is healthy. The characteristic diagram, FIG. 2(b) is a characteristic diagram when dielectric breakdown is near, and FIG. 2(C) is a characteristic diagram at dielectric breakdown. 1... Frame, 2... Field winding, 3...
...Field iron core, 4...AE analyzer, 5.
...Printer, 8...Power supply device, 8a.
...Voltage vI4 rectifier 1sb...Test transformer, 10...AE sensor.

Claims (1)

[Claims] In a method for detecting dielectric breakdown in electromechanical windings in advance, acoustic emissions caused by partial discharge when voltage is applied to the windings are detected by an acoustic emission sensor attached closely to the electric machine. A method for detecting dielectric breakdown in electromechanical windings in advance by distinguishing between a normal partial discharge before breakdown and a large partial discharge immediately before breakdown based on the amplitude, which is one of the parameters of acoustic emission.