Partial-discharge measurement method and high-voltage device inspected using same

#The present invention relates to a partial discharge measurement method for a high-voltage device, particularly, high-voltage rotating machines (generator and motor).

#Due to recent improvement on an operation rate of a device, higher reliability on a high-voltage electric power device is earnestly demanded more than ever. Known typical factors of troubles which may jeopardize reliability of such high-voltage electric power devices are insulation deterioration and a breakdown phenomenon. As a detecting means for an insulation defect that may cause such insulation deterioration and breakdown, partial discharge measurement is widely used now. Further, there is also a proposed partial discharge measurement method whereby not only existence but also a position of a partial discharge defect is located. For example, there is a related art described below as such a detecting means for a partial discharge defect position. According to this related art, a partial discharge measurement sensor circumferentially swept along a surface of a stator winding of a rotating machine, and the partial discharge defect position is located by detecting a position where intensity of a measured signal becomes highest. Alternatively, a position of a partial discharge defect is located by detecting a position where a difference of arrival time between signals measured by a plurality of sensors becomes largest. This kind of method is effective in a low-voltage rotating machine where there is extremely few number of partial discharge defects and measurement can be easily performed in an environment with little ambient noise, such as a shield room, because a sample size is small. However, in a high-voltage device represented by a high-voltage generator and a motor that may have numerous partial discharge defects inside an insulation layer, partial discharge occurs at a plurality of positions. Therefore, a position where signal intensity is highest or a difference of signal arrival time is largest does not clearly appear, and the partial discharge defect position can be hardly detected. Further, in general, the high-voltage device has large capacity and a large size. Therefore, the high-voltage device can be hardly brought into a shield room for testing, and in many cases, partial discharge has to be measured in an environment with much ambient noise. Under such an environment, there may be problems in which noise intrudes inside measurement data while the sensor is swept around, and correct signal intensity distribution of partial discharge cannot be measured. Moreover, even though the partial discharge defect position can be located, there is a difference in a risk between a defect extending in an electric field direction and a defect extending in a direction orthogonal to the electric field. Therefore, a site having a large apparent charge of partial discharge is not always a defect position having a high risk, and there may be a problem in which risk assessment cannot be performed only with intensity distribution of partial discharge signals.

#To solve such a problem in risk assessment, attempted in recent years is a method in which a risk of a defect is diagnosed by measuring a following pattern: a voltage phase of partial discharge occurrence-an apparent charge of partial discharge-number of occurrence of partial discharge (hereinafter, abbreviated as pattern φ-q-n). However, even in this method, the patterns φ-q-n of a plurality of partial discharge signals are superimposed in a high-voltage rotating electrical machine having numerous partial discharge defects, and there may be problems in which defect detection in a product and risk assessment cannot be correctly performed.

#FIG. 1 is a configuration diagram illustrating a partial discharge measurement system according to the present invention.

#FIG. 2 is a cross-sectional view illustrating a rotating electrical machine.

#FIG. 3 is a cross-sectional view illustrating a stator winding of the rotating electrical machine.

#An embodiment of the present invention will be described below using the drawings. FIG. 1 is a configuration diagram of a partial discharge measurement system according to the present invention. Here, reference sign 1 indicates a high-voltage test power source, 2 is a sample, 3 a partial discharge defect inside the sample, 4 an electromagnetic sensor, 5 an electromagnetic signal measuring instrument, 6 a signal spatial intensity distribution comparator, and 7 is a device for partial discharge/noise detection, defect position location, and risk assessment. According to the present measurement system, high voltage such as AC, impulse, or direct current is applied to the sample 2 at the high-voltage test power source 1. At this point, a signal emitted from the sample 2 is detected by a partial discharge detection sensor formed of electromagnetic sensors #1, #2, #3 having mutually fixed relative positions, and signal intensity at each of the electromagnetic sensors is measured by the electromagnetic signal measuring instrument 5. At this point, there are at least two kinds of measured signals, more specifically, an electromagnetic signal generated at the partial discharge defect 3 and an electromagnetic signal intruding from the power source side, and patterns of the respective signals are measured. The signal patterns are illustrated at reference sign 8. In the signal spatial intensity distribution comparator 6, at least these two kinds of signals are compared with electromagnetic spatial signal intensity distribution 9 of partial discharge preliminarily obtained through simulation or measurement, and comparison is made whether any of plots of signal intensity of the electromagnetic sensors #1, #2, #3 match the electromagnetic spatial signal intensity distribution 9 of partial discharge. Alternatively, comparison is made whether any of the plots of signal intensity of the electromagnetic sensors #1, #2, #3 match a relative signal intensity ratio between these electromagnetic sensors #1, #2, #3 obtained from a function of the electromagnetic spatial signal intensity distribution 9 of partial discharge. Next, a signal is transmitted to the device for partial discharge/noise detection, defect position location, and risk assessment 7. In the case where the signal is obtained from matching with the electromagnetic spatial signal intensity distribution of partial discharge, an occurring position of partial discharge is located based on a peak intensity position in the preliminarily-obtained electromagnetic spatial signal intensity distribution 9 of partial discharge. Further, along with the above-described electromagnetic signal measurement, a signal and data measured by an apparent charge of partial discharge detector 10 are combined, and the pattern φ-q-n at the occurring position of partial discharge is created. Then, a risk of the detected partial-discharge defect is assessed.

#Meanwhile, in the partial discharge measurement system of FIG. 1, in the case where the electromagnetic sensors are charged at high voltage, a person who performs measurement can be prevented from electrical shock by using electric-optic conversion and photo-electric conversion in at least one of signal connecting portions of the electromagnetic signal measuring instrument, signal spatial intensity distribution comparator, and device for partial discharge/noise detection, defect position location, and risk assessment.

#A measurement method in the case of using a rotating electrical machine (generator or motor) as the sample 2 in FIG. 1 will be described by using FIGS. 2 to 4. FIG. 2 is a cross-sectional view illustrating the rotating electrical machine. Reference sign 23 indicates the rotating electrical machine, 24 is a stator, 25 a stator winding, 26 a rotor, 27 a frame, and 28 is a secondary winding, field winding, or a permanent magnet. In an induction motor or a synchronous motor, a rotational magnetic field is generated by applying AC to the stator winding 25 inserted into the stator 24, thereby rotating the rotor 26. In the case of the induction motor, a secondary winding is disposed in the rotor 26, and in the case of the synchronous motor, a field winding or a permanent magnet is disposed in 28, and rotation is made at a speed according to the rotational magnetic field.