METHOD FOR DETECTION OF INTERLAMINAR SHEET SHORT CIRCUITS IN THE STATOR SHEET CORE OF ELECTROMACHINES

• US 20110012637A1
• Filed: 06/04/2010
• Published: 01/20/2011
• Est. Priority Date: 12/07/2007
• Status: Active Grant

• Current Assignee: General Electric Technology GmbH (GE Aerospace)
• Original Assignee: Alstom Technology Ltd. (Alstom SA)
• Inventors: Hobelsberger, Max
• Granted Patent: US 9,146,279 B2
• Time in Patent Office: Days
• US Class Current: 324/765.01
• CPC Class Codes: G01R 31/34 Testing dynamo-electric machines

Abstract

A method and an apparatus are described for detection of interlaminar laminate shorts in the laminated stator core of electrical machines, in which the laminated stator core (4) is subjected to an externally applied field current (2) or field voltage (V), and the short-circuit magnetic field (B_short) induced by short-circuit currents (5) is measured with the assistance of a sensor coil (S1) which is arranged in the gap in the machine and probes this gap. Improved identification of laminate shorts, in particular even of small laminate shorts with small short-circuit currents, is possible in that a field current (2) and a field voltage (V) are applied which have a waveform which differs significantly from a sinusoidal shape, in particular with a periodic character, and have significant harmonic components in the high frequency range. By way of example, a waveform in the form of a square-wave curve is proposed.

Claims

1. A method for detection of interlaminar laminate shorts in the laminated stator core (4) of electrical machines, in which the laminated stator core (4) is subjected to an externally applied field current (2) or field voltage (V), and the short-circuit magnetic field (B_short) induced by short-circuit currents (5) is measured with the assistance of a sensor coil (S1) which is arranged in the gap in the machine and probes this gap, wherein the field current (2) and field voltage (V) have a waveform which differs significantly from a sinusoidal shape.

2. The method as claimed in claim 1, wherein the waveform of the field current (2) or field voltage (V) is a periodic waveform with significant higher harmonics.

3. The method as claimed in claim 1, wherein the waveform of the field current (2) or field voltage (V) is a non-periodic waveform with significant higher harmonics.

4. The method as claimed in claim 1, wherein the waveform of the field current (2) or field voltage (V) is a non-periodic pulse function.

5. The method as claimed in claim 1, wherein the field current is chosen such that the operating direct-axis voltage is reached at least briefly.

6. The method as claimed in claim 1, wherein the waveform of the field current (2) or field voltage (V) is a sawtooth function, a square-wave function or a modified square-wave function.

7. The method as claimed in claim 1, wherein the waveform of the field current (2) or field voltage (V) is a symmetrical square-wave function with positive (a) and negative (b) sections of the same length.

8. The method as claimed in claim 1, wherein the waveform of the field current (2) or field voltage (V) has a fundamental frequency in the range 10-500 Hz, in particular preferably in the range 40-100 Hz.

9. The method as claimed in claim 7, wherein the fundamental frequency is synchronized to the mains voltage used for the field.

10. The method as claimed in claim 1, wherein measurement and evaluation are carried out on the basis of the phase angle (φ

), defined as the difference between the output phase angle and the input phase angle of the individual harmonics of the field current (2) or field voltage (V).

11. The method as claimed in claim 10, wherein the substantially linear relationship between the phase angle and frequency is used for identification of laminate shorts.

12. The method as claimed in claim 1, wherein the signal recorded in the sensor coil is subjected to spectral analysis with the assistance of a Fourier transformation for identification of laminate shorts, wherein, in particular and preferably, the phase spectrum of the various harmonics is used for identification of laminate shorts.

13. The method as claimed in claim 1, wherein the measurement apparatus is calibrated by means of a conductor loop, which is arranged on the bore surface, and a calibration current, which flows through this loop of a known magnitude and contains substantially the same harmonics as the waveform of the field current (2) or field voltage (V) during the actual measurement, wherein, in particular and preferably, the same waveform is used for calibration as for measurement.

14. The method as claimed in claim 1, wherein a combined current/voltage analysis is carried out for identification of laminate shorts, preferably taking account of the, in particular, falling, phase angle as a function of rising frequency.

15. The method as claimed in claim 1, wherein substantially a single pulse, in particular and preferably a square-wave pulse, is applied as the waveform of the field current (2) or field voltage (V) or a sequence of pulses which are evaluated independently of one another and are averaged overall, is in each case used for a measurement at a specific point.

16. The method as claimed in claim 1, wherein measurement and evaluation of laminate shorts is used on the basis of the phase angles and amplitudes in the individual harmonics.

18. The method as claimed in claim 1, wherein the phase angles and amplitudes of the harmonics are analyzed by means of Fourier analysis.

19. The method as claimed in claim 1, wherein a spatially simultaneous change in the phase angles of a plurality of harmonics is assessed as an indication of a laminate short circuit.

20. The method as claimed in claim 1, wherein a substantially linear relationship between changes in the phase angle and frequency of the harmonics is assessed as an indication of a laminate short.

21. An apparatus for carrying out a method for detection of interlaminar laminate shorts in the laminated stator core (4) of electrical machines, in which the laminated stator core (4) is subjected to an externally applied field current (2) or field voltage (V), and the short-circuit magnetic field (B_short) induced by short-circuit currents (5) is measured with the assistance of a sensor coil (S1) which is arranged in the gap in the machine and probes this gap, wherein the field current (2) and field voltage (V) have a waveform which differs significantly from a sinusoidal shape, wherein a sensor coil is arranged, as well as a field apparatus for production of a field voltage or a field current in the laminated core (4), wherein a frequency generator is additionally provided in order to operate the field apparatus, and is designed to operate the field apparatus with a field current (2) or a field voltage (V) with a waveform which differs substantially from a sinusoidal shape.

22. The apparatus as claimed in claim 21, wherein the frequency generator is an electronic full bridge.

23. The apparatus as claimed in claim 21, wherein a field coil (6) is used, in combination with a field yoke (14), if required, for energizing.