Method and apparatus for detecting winding errors in an electric motor stator

• US 5,907,244 A
• Filed: 07/24/1997
• Issued: 05/25/1999
• Est. Priority Date: 08/02/1996
• Status: Expired due to Term

• Current Assignee: Automation Technology, Inc. (California) (Intertek Group PLC)
• Original Assignee: Automation Technology, Inc. (California) (Intertek Group PLC)
• Inventors: Crabill, Monty L., Storar, Robert C.
• Primary Examiner(s): Do, Diep N.
• Application Number:
  US08/899,430
• Time in Patent Office: 670 Days
• Field of Search: 324/545, 324/546, 324/547, 324/772, 324/219, 324/220, 324/263, 73/116, 73/514.39, 340/648, 318/490, 322/99
• US Class Current: 324/546
• CPC Class Codes: G01R 31/34 Testing dynamo-electric machines
• CPC Class Codes: G01R 31/346 Testing of armature or field windings

Abstract

A method and apparatus for detecting winding errors in electric motor stators having a plurality of field windings is disclosed. The method involves the steps of applying a current source to at least one of the field windings to generate a magnetic field within the stator, measuring the polarity and strength of the field for each winding at preselected radial and angular positions about a circumference of the stator bore, and comparing the measured values to recorded values of radially and angularly corresponding measurements for a reference motor stator. Preferably, the current source is applied to each of the windings in succession. The apparatus includes a terminal block, switch, and power supply to connect a source of current to each field winding in succession to generate a magnetic field within the stator. In one embodiment, the apparatus includes a magnetic sensor mounted at a predetermined radial position for rotation on a shaft, and an encoder proximate the shaft to determine the angular position of the shaft. In a second embodiment, the apparatus includes a plurality of magnetic sensors mounted at preselected radial and angular positions about an arbor or drum sized to fit within the stator. Both embodiments include means for comparing the measured magnetic field values to recorded values of radially and angularly corresponding measurements for a reference motor stator.

Claims

1. A method of detecting a winding error in an electric motor stator including a field winding, said method comprising the steps of:

(1) applying a predetermined current to said field winding to generate a magnetic field within said stator;

(2) during application of said current to said field winding, generating a sensing signal representing a component of a magnetic field vector of said magnetic field at a predetermined circumferentially angularly disposed position within said stator; and

(3) comparing said sensing signal to an angularly corresponding sensing signal for a reference motor stator to detect said winding error when said generated sensing signal differs from said angularly corresponding sensing signal by more than a predetermined amount.

2. A method of detecting according to claim 1 wherein:

in said step of generating, a plurality of sensing signals are generated by positioning a magnetic field sensor at a plurality of different angular positions relative to said field winding during application of said current thereto; and

in said step of comparing, said plurality of generated sensing signals are compared to a plurality of angularly corresponding sensing signals for a reference motor stator.

3. A method of detecting according to claim 1 wherein:

in said step of generating, a plurality of sensing signals are generated by placing a plurality of magnetic field sensors at a plurality of different angular positions relative to said field winding during application of said current thereto; and

in said step of comparing, said plurality of generated sensing signals are compared to a plurality of angularly corresponding sensing signals for a reference motor stator.

4. A method according to claim 1 wherein said electric motor stator includes a plurality of field windings and said current is successively applied to each of said plurality of field windings of said stator.

5. A method of detecting winding errors in an electric motor stator including a plurality of field windings each having a pair of external leads comprising the steps of:

(A) connecting at least one of said pair of external leads to a source of current thereby to generate a magnetic field within said stator;

(B) rotating at least one magnetic field sensor to a plurality of predetermined different angular positions within said stator;

(C) operating said at least one magnetic field sensor to sense the polarity and strength of said magnetic field at said plurality of predetermined different angular positions within said stator; and

(D) comparing said polarity and said strength of said magnetic field at said angular positions within said stator with reference values for polarity and strength of a magnetic field at corresponding angular positions within a reference electric motor stator to detect a winding error whenever said polarity differs from said reference value for polarity, and whenever said strength differs from said reference value for strength by more than a predetermined amount.

6. A method according to claim 5 wherein said step of connecting comprises connecting each said pair of leads successively to a source of current thereby to generate a magnetic field within said stator and said step of rotating is performed for each said pair of leads connected.

7. A method of detecting winding errors in an electric motor stator including a plurality of field windings each having a pair of external leads comprising the steps of:

(A) connecting at least one of said pair of external leads to a source of current thereby to generate a magnetic field within said stator;

(B) positioning a plurality of magnetic field sensors at predetermined different angular positions within said stator;

(C) operating said magnetic field sensors to sense the polarity and strength of said magnetic field at said angular positions within said stator; and

(D) comparing said polarity and strength of said magnetic field at said angular positions within said stator with reference values for polarity and strength of a magnetic field at corresponding angular positions within a reference electric motor stator to detect a winding error whenever said polarity differs from said reference value for polarity, and whenever said strength differs from said reference value for strength by more than a predetermined amount.

8. A method according to claim 7 wherein said step of connecting comprises connecting each said pair of leads successively to a source of current thereby to generate a magnetic field within said stator and said step of positioning is performed for each said pair of leads connected.

9. An apparatus for detecting a winding error in an electric motor stator including a field winding, said apparatus comprising:

current source means for applying a current to said field winding to generate a magnetic field within said stator;

means for generating a sensing signal representing a component of a magnetic field vector of said magnetic field at a predetermined angularly displaced position within said electric motor stator; and

means for comparing said sensing signal to an angularly corresponding sensing signal for a reference motor stator to detect said winding error when said sensing signal differs from said angularly corresponding sensing signal by more than a predetermined amount.

10. An apparatus for detecting according to claim 9 wherein said means for generating a sensing signal comprises:

at least one magnetic field sensor; and

means for positioning said at least one magnetic field sensor at a plurality of different angular positions relative to said field winding during application of said current thereto.

11. An apparatus for detecting according to claim 9 wherein said means for generating a sensing signal comprises:

a plurality of magnetic field sensors; and

means for supporting said magnetic field sensors at a plurality of different angular positions relative to said field winding during application of said current thereto.

12. An apparatus for detecting according to claim 9 wherein said electric motor stator includes a plurality of field windings and said current source means comprises current source means for successively applying a current to each of said field windings.

13. An apparatus for detecting winding errors in an electric motor stator having a plurality of field windings comprising:

a fixture adapted to hold said stator to be tested;

a terminal block adapted to make temporary electrical connection to said plurality of field windings;

means for applying current to at least one of said plurality of field windings via said terminal block to generate a magnetic field within said stator;

means for sensing each said magnetic field as a function of angular position within said stator, said means for sensing providing sensing signals representative of said magnetic field; and

means for comparing said sensing signals with corresponding reference signals representative of a reference magnetic field of a reference motor stator to detect winding errors when said sensing signals differ from said corresponding reference signals by more than a predetermined amount.

14. An apparatus for detecting according to claim 13 wherein said means for sensing comprises:

a magnetic field sensor;

means for positioning said magnetic field sensor at a plurality of different angular positions relative to each of said field windings during application of said means for applying current thereto; and

means for sensing said angular position of said magnetic field sensor.

15. An apparatus for detecting according to claim 13 wherein said means for sensing comprises:

a plurality of magnetic field sensors positioned at a plurality of preselected angular positions within said electric motor stator.

16. An apparatus for detecting according to claim 13 wherein said means for applying current comprises means for successively applying current to each of said plurality of field windings via said terminal block to generate a magnetic field within said stator.