Apparatus and method for evaluation a condition of a magnetic circuit of an electric machine

• US 5,990,688 A
• Filed: 01/09/1998
• Issued: 11/23/1999
• Est. Priority Date: 01/09/1998
• Status: Expired due to Fees

• Current Assignee: Hydro-Quebec (Province of Québec)
• Original Assignee: Hydro-Quebec (Province of Québec)
• Inventors: Bourgeois, Jean-Marc, Lalonde, Fran.cedilla.ois
• Primary Examiner(s): Do, Diep N.
• Application Number:
  US09/005,036
• Time in Patent Office: 683 Days
• Field of Search: 324/521, 324/527, 324/528, 324/529, 324/545, 324/546, 324/547, 324/551, 324/557, 324/559, 324/239, 324/240, 324/241, 324/242, 324/772, 340/648
• US Class Current: 324/545
• CPC Class Codes: G01R 31/34 Testing dynamo-electric machines
• CPC Class Codes: G01R 33/12 Measuring magnetic properties of articles or specimens of solids or fluids involving magnetic resonance G01R33/20

Abstract

The method consists in positioning a probe in front of a pair of teeth provided on the face of the magnetic circuit of an electric machine. The probe has spaced apart magnetic prong portions having respective end faces adapted to match the teeth of the pair with the end faces in registry with the teeth. The prong portions are respectively provided with an excitation winding and a measurement winding. The excitation winding is excited to induce a magnetic flux in a test zone formed of the teeth in front of the probe and a portion of the magnetic circuit extending therebetween. The current flowing in the excitation winding and the voltage across the measurement winding are measured for calculating a resulting power which is indicative of the condition of the test zone. The apparatus is formed of the probe and electronics carrying out the above functions.

Claims

1. An apparatus for evaluating a condition of a magnetic circuit of an electric machine, the magnetic circuit having a face provided with a series of spaced apart projecting teeth, the apparatus comprising:

a probe having a magnetic transverse portion, first and second spaced apart magnetic prong portions projecting from the transverse portion on one side thereof, an excitation winding wound around the first prong portion, and a measurement winding wound around the second prong portion, the prong portions having respective end faces adapted to match a pair of said teeth with the end faces in registry with the teeth of said pair;

an excitation source electrically connected to the excitation winding;

current measuring means for measuring a current flowing in the excitation winding;

voltage measuring means for measuring a voltage across the measurement winding; and

calculating means for calculating a resulting power from the current and the voltage measured by the measuring means, the resulting power being indicative of the condition of a test zone formed of the teeth of said pair and a portion of the magnetic circuit extending therebetween.

2. The apparatus of claim 1, wherein the excitation source has an output to produce an AC signal having a voltage, the apparatus further comprising a control means for controlling the voltage of the AC signal as a function of the voltage across the measurement winding.

3. The apparatus of claim 2, wherein the control means comprise:

comparing means for comparing an induction B in the probe with an induction setting, the induction B being expressed as B=V/mSf where V is the voltage across the measurement winding, m is a number of turns of the measurement winding around the second prong portion, S is a section of the second prong portion, and f is a frequency of the AC signal; and

adjusting means responsive to the comparing means, for adjusting the voltage of the AC signal so that the induction B corresponds to the induction setting.

4. The apparatus of claim 1, wherein the calculating means comprise means for subtracting a reference power loss value from the resulting power.

5. The apparatus of claim 1, further comprising a meter connected to the calculating means to display a reading representative of the resulting power.

6. The apparatus of claim 1, wherein the portions of the probe comprise a number of superimposed laminations electrically insulated from each other.

7. The apparatus of claim 1, wherein the end faces of the prong portions have a center-to-center distance corresponding substantially to a center-to-center distance between the teeth of said pair.

8. The apparatus of claim 1, wherein the teeth have a predetermined width, and the end faces of the prong portions have a width smaller than the width of the teeth.

9. The apparatus of claim 1, wherein the end faces of the prong portions are provided with electrically insulating spacers adapted to abut against the teeth of said pair to fix a gap thickness between the probe and the teeth of said pair when the probe is in operating position.

10. The apparatus of claim 1, wherein the portions of the probe generally have together a C-shaped configuration.

11. The apparatus of claim 1, wherein the end faces of the prong portions are beveled with respect to main axes of the prong portions.

12. The apparatus of claim 1, wherein the measuring and calculating means are provided by a circuit comprising:

a first analog to digital converter having an input connected to the excitation winding, and an output;

a second analog to digital converter having an input connected to the measurement winding, and an output; and

a microcontroller having first and second inputs connected respectively to the outputs of the analog to digital converters, and an output to produce a signal representative of the resulting power.

13. The apparatus of claim 2, wherein the measuring and calculating means, the excitation source and the control means are provided by a circuit comprising:

a first analog to digital converter having an input connected to the excitation winding, and an output;

a second analog to digital converter having an input connected to the measurement winding, and an output;

a microcontroller having first and second inputs connected respectively to the outputs of the analog to digital converters, a third input to receive setting signals, a first output to produce a signal representative of the resulting power, and a second output to produce a digital signal representative of the AC signal; and

a digital to analog converter and amplifier circuit arrangement, having an input connected to the second output of the microcontroller, and an output to produce the AC signal.

14. The apparatus of claim 13, further comprising:

a meter connected to the first output of the microcontroller to display a reading representative of the resulting power; and

a keypad connected to the third input of the microcontroller, to generate the setting signals.

15. A method for evaluating a condition of a magnetic circuit of an electric machine, the magnetic circuit having a face provided with a series of spaced apart projecting teeth, the method comprising the steps of:

positioning a probe in front of a pair of said teeth, the probe having a magnetic transverse portion, first and second spaced apart magnetic prong portions projecting from the transverse portion on one side thereof, an excitation winding wound around the first prong portion, and a measurement winding wound around the second prong portion, the prong portions having respective end faces adapted to match the teeth of said pair with the end faces in registry with the teeth of said pair;

exciting the excitation winding to induce a magnetic flux in a test zone formed of the teeth of said pair and a portion of the magnetic circuit extending therebetween;

measuring a current flowing in the excitation winding;

measuring a voltage across the measurement winding; and

calculating a resulting power from the current and the voltage, the resulting power being indicative of the condition of the test zone.

16. The method of claim 15, further comprising the step of:

comparing the resulting power with a reference power value to determine a defect condition in the test zone.

17. The method of claim 16, wherein the reference power value is determined by calculating a typical power to be expected as a function of physical characteristics of the magnetic circuit and the probe.

18. The method of claim 16, wherein the reference power value is determined by performing the method before a first use of the magnetic circuit.

19. The method of claim 15, wherein the steps are repeated for all the teeth of the magnetic circuit to locate possible defective portions thereof.

20. The method of claim 19, wherein the excitation source is adjusted to induce a magnetic flux having a constant amplitude in each test zone.