Patent Application
20060114002
This application claims of priority from a Japanese application Serial No. 2004-142327, filed on May 12, 2004, the content of which is hereby incorporated by reference into this application.
The present invention relates to a method of connecting electrical winding conductors for large capacity electric magnets, generators and motors, and more particularly to a method of improving connecting quality of brazing.
Electrical winding of large scaled electric apparatuses have been manufactured by assembling a number of shaped turns of winding conductors, in general. For example, internal cooling windings have a structure wherein each of the windings has a continuous hollow through which low temperature pure water flows to cool it. As shown in
Brazing work greatly depends on experience and skill of workers; internal defects in the brazed portion after brazing are detected by an X-ray transmittance inspection or ultrasonic wave inspection. Since the gap into which the brazing alloys permeate is only about 0.05 mm, the X-ray transmittance inspection is applied to such a thin conductor as 1 mm or less. Therefore, the X-ray inspection was not appropriate for such a thick conductor as having 2 to 10 mm.
A connected interface evaluation method by the ultrasonic wave inspection using an ultrasonic wave C scope is known as disclosed in non-patent publication No. 1. In this method, an aluminum plate and a copper plate are brazed by a method of superimposed brazing. Probing results on both faces are displayed on a C scope. A measured error is 0.1 to 0.3 mm with respect to a size of defects of 0.9 to 4.6 mm at a peeling destruction face.
In an inspection apparatus of connected portions of clips of water cooled stator bars of a turbine generator (Patent publication No. 1), an ultrasonic wave probe is moved in the axial direction of the bars, while the probe is rotating around the connected portion; the detected reflection wave signals and position information are processed by a computer. Since a scanner is set to a screw position of the object to be inspected, an automatic inspection can be realized.
(Patent publication No. 1) Japanese patent laid-open No. 2001-343367
(Non-patent publication No. 1) “Non-destructive Inspection”, vol. 39, No. 9, 2-17
Since the brazing alloy permeates into the brazing portion by the action of surface tension of a melted brazing alloy in the electrical machines, a gap between a conductor and sleeve of 0.05 to 0.25 mm is used in general. The diameter is the same as in the case of conductors to be brazed having a thickness of about 1 to 10 mm. The defects such as portions where the brazing alloy does not permeate, bubbles occurred in the brazing alloy, empty nests (subsided ball like nests), cracks in the brazing alloy, etc should be thinner than the thickness of the brazing gap. Since the defects have a large area and a large length, but have a very small thickness, a detection technology for the very thin defects is demanded.
Since the detection limit of the X-ray transmittance inspection method is demanded to be 2% or more of the total thickness of the conductor and the sleeve of 0.05 to 0.25 mm, the detection of a defect of 0.05 mm thick was impossible in the case of a conductor of a thickness smaller than 2.5 mm.
The ultrasonic wave probing of the brazed portion is theoretically possible, as mentioned above. However, in electrical windings of the electromagnets or generators, the brazing portions are formed at narrow portions where the turns of the windings are often located and there are different angles of the connecting portions in order to increase a space factor. Therefore, it has been desired that an ultrasonic probing method or system is applicable to the narrow portions.
There are various types of defects caused by brazing; the evaluation result of the electrical windings should satisfy electrical and mechanical requirements. Particularly, the inspection of defects in the brazed portion should be done from the viewpoints of an area and length of the defects so as to prevent leakage of a cooling liquid flowing through the hollow in the conductor.
Various causes are involved in formation of the defects; skill of workers, equipment used and conditions for the equipment, conditions of conductors and brazing alloys may be involved. In actual jobs, an evaluation method or system is necessary for evaluating by observing the interior state of the brazed portions to pick up characteristics and to find out the causes of the formation of the defects so that the evaluation results can be reflected on instructions to the repairing work and on achievement of skill of the workers.
An object of the present invention is to provide, in light of the above-mentioned problems, a method of conducting an accurate evaluation of defect portions of the connecting portions, which are electric conductive and the connecting portions can keep quality that withstand sufficiently a mechanical power, and also provide a method and apparatus for connecting electrical winding conductors that displays an appropriate repairing guidance.
In order to achieve the above-mentioned object, a method of connecting electrical winding conductors comprising connecting electrical windings each having a continuous hollow with a brazing alloy is characterized in that a connected portion is probed with ultrasonic wave; the sound portion and defect portion are displayed, and the portions are evaluated in accordance with predetermined criteria.
The electrical winding conductors to be connected are aligned to constitute pairs and each of the pairs is aligned in a longitudinal direction. At least one of the conductors of the pair may have a continuous hollow extending in a longitudinal direction.
According to the present invention, since the quality of the defect having a very thin thickness can be electrically and mechanically evaluated, the conductive state and possibility of water leakage in the connecting portion (brazing portion) can be presumed. So, the accuracy of evaluation of the connecting increases. Further, it is possible to pursue working conditions for acquiring high stable quality of connecting and to confirm the degree of achievement skill of workers.
Since the scanner for moving the probe of the measuring mechanism and the holder for fixing the scanner are separated into at least two, and then they are assembled after the installment, it is possible to conduct measurement in a narrow portion.
Since the measurement mechanism is provided with a bottom echo standard gate, it is possible to conduct an accurate and easy detection even in the case of relatively thin defects.
1; conductor having a continuous hollow of electrical winding conductor of a generator, 2; sleeve for connecting conductors, 3; hollow in the conductor, 4; gas burner, 5; groove for placing a brazing alloy, 6, 7; brazing alloy, 8; solidified brazing alloy, 9, 9′; defects formed in the brazing alloy, 10; measurement mechanism, 11; ultrasonic wave probe, 12; rotating ring, 13; rotating supporting plate, 14; driving section, 15; supporting rod, 16; rotating shaft, 17; motor, 18; motor, 19; holder, 20; display mechanism, 21; screw hole, 22; cramping bolt, 23; sound portion, 24, 25, 25′; defects, 26; phase connection of electrical winding of a generator, 27; lead of the electrical winding of the generator, 28; solid conductor, 101; scanner.
In the following, the embodiments of the present invention will be explained by reference to the drawings.
The first embodiment (hereinafter referred to as embodiment 1) according to the present invention is explained.
The connecting evaluation apparatus comprises an ultrasonic wave probe 11, a scanner 101, a measurement mechanism 10 including measurement device 102, etc, a display section 20 for displaying measurement results in the form of patterns, and an evaluation mechanism 30 for outputting the sound portion or defect portion of the measurement results as a length or an area. Further, the evaluation of the connecting portions are judged based on the predetermined judging standards or criteria; if the judging result can not meet the judging standards, similarity and relationship between the displayed patterns and the cause-and-defect patterns that are stored in advance are investigated, thereby to choose patterns with a high correlation. This investigation is carried out by a judging mechanism 40. The cause-and-defect patterns 51 and judging standards 52, which are capable of reference to the judging mechanism 40 are stored in the memory device 50.
At first, brazing starts; then the connecting portion is inspected by an ultrasonic wave inspection; the results are displayed on a screen in the form of patterns. A length and area of the sound portions and defect portions are measured on the screen. Then, the connecting portions are judged based on predetermined judging standards 52 to determine the connecting portions as “accepted” (sound) or “not accepted” (defect).
If the judging result is “not accepted”, repair brazing is carried out. Thus, measurement of the connecting portions is conducted by the measurement mechanism 1. The measurement results are displayed on the screen as patterns. Again, the evaluation and judging are carried out. The difference between the previous connecting and the repaired connecting is detected by the repaired portion judging mechanism 60 to find out whether the repair brazing was effective or a further re-brazing is necessary. The repaired portion judging mechanism 60 pursues conditions of works and equipment and optimization of brazing materials; when the quality is satisfactory, the brazing repairing is finished.
There are various types of defects formed in brazing, such as voids or stripes caused by permeation shortage of a brazing alloy, narrow scratches, etc. The shapes and properties of the defects may change according to shapes of the parts to be connected, workability, equipment used, skills of the workers, etc. Accordingly, if the connecting portions do not satisfy the standards or criteria, it is necessary to predict plural cause-and-defects and to determine optimum conditions in advance. In the present invention, the countermeasures are selected based on database of the actual jobs.
If there is a shortage of brazing alloy as the melting goes on, the brazing alloy wire 7 is supplied from the end portion of the sleeve as shown in
Further, the measurement mechanism is provided with a driving section 14 including a gear 5, a supporting rod 15 connected to the rotating supporting plate 13 for determining the position of the mechanism, a scanner 101 having a rotating shaft 16 for transmitting driving force to the rotating supporting plate 13 and motors 17, 18, and a dividable holder 19 for supporting the scanner on an appropriate position of the outer periphery of the sleeve 2.
The probe 11 and the driving section 14 are connected by means of a connecting conductor to the measurement mechanism, so that the positioning of the measurement mechanism is performed and measured data is taken into the measurement mechanism 10. The data is processed by the display mechanism 20, evaluation mechanism 30, judging mechanism 40, etc.
If the holder 19 and the scanner 101 are united, workers do not put their hand into the narrow portion of the stator winding, and it is difficult to screw the bolts. Further, since an angle between the opening of the rotating supporting plate 13 and the opening of the holder is normally different by 90 degrees, screwing for fastening and assembling are difficult to do.
Thus, the holder 19 and the scanner 101 are separated in advance. The holder 19 is inserted from the side of the sleeve 2 or the conductor 1 and is fastened by a screw 22. The scanner 101 is assembled from the upper direction on the holder 19 and is fastened at a screw hole 21. Numeral 22 denotes a cramp bolt. By this structure, it is possible to conduct an assembling job with minimum obstacles. If the number of the objects of measurement, it is possible to improve efficiency of job, when a number of the holders is prepared in advance.
Then, the operation of the connecting evaluation apparatus for electrical windings according to the present invention will be explained in detail.
The measurement device 102 that receives reflecting wave signals from the probe 11 to produce data of a depth of the predetermined measuring object as d0 of a peak height (s102). The d0 is compared with dc, which is evaluated as an effective threshold (s103) so as to avoid influence of noise at the time of measurement. If the value is larger than dc, the portion is judged as a defect or “not accepted”; if the value is smaller than dc, the portion is judged as being sound or “accepted” (s104) in a binary digit processing.
A defect “N” is displayed as a black dot and a sound portion “Y” is displayed as a white dot. Take a point A as a measurement position, for example, the position data is X1, θ1; since the height d0 of the echo is in relation of d0<dc, the result is “Y”, which is white (s105).
Next, the scanner moves the probe 11 to the point B (X1, θ2), and the measurement at the point B is carried out (s106). As a result, “N”, which is black is obtained (s107). This processing is continuously executed within a designated area (s108).
The thus obtained data is displayed on a two-dimensional coordinate (X, θ) (s109). As a result, defect portions (black) and sound portions (white) are developed on a plane. By forming steps to the threshold values dc, it is possible to easily recognize the extent of the height dc of echo with respect to the defect portions.
If the brazing portions are sound, the ultrasonic wave signals transmit to the sleeve 2 and the hollow conductor 1; they reflect at the surface of the hollow and should be measured as the bottom echo. If the bottom echo is not detected, measurement must be conducted again. This is an inspection of measurement data; if an inspecting person has already done this inspection separately, this step can be omitted in the procedure shown in
Among the data thus inspected, the total numbers ΣN of N and ΣY of Y are counted, respectively (s202). As a result, connected rate CR at the connecting portion is expressed by ΣY/Z×100(%) (s203). That is, the connected rate CR decreases as the area of defect portion Z increases. Z is shown in
The shortest route from X1 through Xn on the two dimensional coordinate wherein the total number ΣY is minimum is scrutinized to find out the total number of Y, which is expressed as YMIN (s204). If the actual length of one division in the X direction is 1 mm, the shortest seal length LMIN is obtained by YMIN×1 mm (s205).
The defect portion is correctly displayed in the form of patterns. The connected rate CR and the minimum seal length LMIN are obtained from the measurement results; thus the processing of the evaluation mechanism 30 is finished.
According to the embodiment mentioned above, since the judgment of “accepted” or “not accepted” is made by reference to CR and LMIN, the connecting portions of the electrical windings are evaluated from the standpoints of electrical and mechanical points including leakage protection. Of course, the judgment can be made based on either Cr or LMIN.
On the other hand, the defect occurring status of the brazing portions are displayed as patterns of causes of defects. The displayed patterns are compared with “typical patterns” to find similarity (s303) to select typical patterns with high similarity (s304). The selected patterns may be plural. The comparison of similarity between the displayed patterns and the typical patterns is made by extracting the relative relation of the two kinds of patterns. Of course, the comparison can be made by eye-observation.
It is possible to choose a cause of the defect as a too much low temperature if the dimension records of the members are checked to find out whether the gap is proper or not. Further, a defect like a peninsula represents that a large defect is present at a particular position. This defect may possible be caused by an improper temperature distribution.
Basically, the guidelines or instruction for repair brazing may be acquired by try-and error methods. For example, if it is presumed that a defect is caused by brazing at a too much low temperature, a repair brazing is conducted at a relatively higher temperature. If a defect due to a too much high temperature, a second repair brazing at a relatively lower temperature is conducted thereby to achieve the targeted brazing connection. If the first repair brazing is not successive, the second repair brazing is conducted at a different condition such as a slightly lower temperature.
In addition to the try-and-error method, a repair brazing is conducted in accordance with guidelines previously stored in a memory device, an operator may select the most appropriate guideline. Of course, this method in accordance with the previously stored guidelines may be adopted besides the try-and-error method.
If the repair brazing needs a pretreatment such as degreasing or surface machining, the connected portion is disassembled so as to conduct the pretreatment.
As has been discussed, since causes are accumulated, based on the results of investigations, studies and arrangements of actual works, the causes of formation of brazing defects can easily be understood. If the actual works are compiled as data base, it is possible to obtain results with relatively stronger relative relation, and a higher probability of causes can be found out. Countermeasures to the causes are prepared, and they are displayed if necessary.
Since the judgment mechanism 40 judges the connecting result as “not accepted” and since the cause of the defect can be immediately found out, a policy of repair of the brazing is easily decided. If the repair of the brazing is done in accordance with the policy, measurement, evaluation and judgment are conducted again. The results are compared with the results previously obtained to calculate effects of the repair. Since the effects of the repair can be confirmed, it is possible to conduct improvement of the quality of the brazing.
In the case of the strip shape defect in No. A, for example, a repair brazing is conducted at a slightly lower set temperature. The results are measured and evaluated again. If the evaluation is “not accepted”, changes of CR and LMIN are evaluated by the repaired article re-judgment mechanism. If the results are in the direction of improvement, the brazing temperature is further lowered to produce a brazing portion with a higher quality. By repetition of the loop shown in
On the other hand, brazing workers can concretely know where the causes of defects are, and know how the conditions are changed so as to alter the results. If the causes come from the brazing procedures, they can quickly know the results of the trial after the conditions are altered. At the same time, they can improve their ability or skill. As a result, it is possible to obtain a connecting method for electrical windings with improved, more proper quality.
According to the present invention, it is unnecessary, in general, to cut or break the product after manufacturing of the product so as to investigate the connected state; if the connected portion is judged as “not accepted”, repair can be made to greatly reduce a cost of the product.
Next, the second example of the present invention (hereinafter referred to as Example 2) is explained. In a connecting conductor having a thickness of 1-10 mm, defects in the brazing portions occur in narrow gaps of 0.05 to 0.25 mm. Accordingly, by knowing the position of the defects and forming a narrow gate to the position, it is possible to precisely detect the defects.
In general, a surface echo in the detected portion is detected and the gate is disposed based on the surface echo; it is necessary to make the range of the gate wider if the distance between the surface and the defects changes. If not, a reflection echo from the object other than the defects may be detected.
In Example 2, there is shown a disposition of the gate based on the bottom echo.
An ultrasonic wave beam impinged from the probe 11 to the connecting portion partly reflects at the outer surface Y2 of the sleeve 2 at first, and received by the probe 11. The remaining ultrasonic wave propagates in the sleeve 2 to arrive at the brazing portion; if there are brazing defects, the ultrasonic wave beam reflects at the interface Y2 (surface of the defects) and returns the probe 11 and is received. If there is not a brazing defect, the ultrasonic beam propagates into the interior of the hollow conductor 1 to arrive at the inner surface Y3 of the continuous hollow where the beam reflects and returns to the probe 11.
In order to accurately measure the defects at the brazing portions, the probe 11 should have a function for focusing the ultrasonic wave beam as a spot in the vicinity of the brazing portion. A spread of the ultrasonic wave is suppressed; a range of depth at which the reflection wave arrives is set as a gate in advance; the reflection wave signal detected in the gate is utilized as data for evaluation of the brazing portion.
In Example 2, the standard position for setting the gate is positioned at the surface (Y3) of the continuous hollow of the hollow conductor.
In Example 2, the gate time width t2 is fixedly set based on the time difference t3 between the reflection wave signal S3 from the hollow surface (Y3) as the standard and the reflection wave signal S2 from the brazing defect. According to this method, it is not necessary to change or widen the gate time width t2, even if the thickness of the sleeve 2 changes. Thus, it is possible to detect and measure the defects precisely. If a large defect is present whereby the reflection wave signal S3 is not detected effectively, the surface echo standard gate can be employed.
As shown in
The third example (hereinafter referred to as Example 3) will be explained.
When the defect area of the brazing portion is wide, S2 becomes large and, on the other hand, the bottom echo S3 becomes small since part of the ultrasonic wave that propagates in the hollow conductor 1 reduces. When the brazing defect is small, there may be a case where the reflection wave signal S2 is small or S3 is not detected because S2 is smaller than the detection limit; in the above case, the reflection wave signal S3 is large and detected. These examples are all normal.
However, in case where the reflection wave signal S2 is not detected, this is not always meant that there are no defects. For example, there may be a possibility that the probe 11 separates from the sleeve 2 so that the ultrasonic wave does not propagate. Accordingly, if the reflection wave signal is not detected, it is necessary to confirm whether the ultrasonic wave has surely propagated by confirming the existence and measurement of the reflection wave signal S3.
In Example 3, it is proved that the measurement results are judged as being correct when the reflection wave signal S3 is measured, but the reflection wave signal S2 is not measured at the position where S3 exists.
The fourth example (hereinafter referred to as Example 4) in which the hollow conductor and the solid conductor are brazing-connected will be explained.
In Example 4, if the reflection wave signal S2 is selected as the measurement object, and if the gate is set to that position, it is possible to measure and evaluate, the same as in Example 2. If the reflection wave signal S5 is selected as the bottom echo, and if the propagation of the ultrasonic wave is confirmed, it is possible to obtain the same effect as in Example 3.
As having been explained, according to Examples 1 to 4, since bonding portions of electrical windings with high reliability are produced, the life of the windings is extended and the long term operation of electric machines is expected, and a cost of operation will be reduced.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-142327 | May 2004 | JP | national |
