Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-01-11
2001-02-06
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S547000
Reexamination Certificate
active
06184690
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to testing of multi-coil electric components, often referred to herein as multi-coil windings, which have a plurality of series connected wound coils with the individual coils being inaccessible, and, more particularly, to testing individual coils of such multi-coil windings to improve testing sensitivity. While the invention is generally applicable to multi-coil windings, it will be described herein with reference to testing motor stators for insulation defects, winding defects, reversed polarity of poles and the like for which it is being used initially.
A common procedure for determining various defects in multi-coil windings is known as a “surge test.” An apparatus for performing a surge test is illustrated in
FIG. 1
, wherein a high voltage pulse is applied to a multi-coil winding
10
, for example a stator, by charging a capacitor
12
via a capacitor charging circuit
22
and then activating a firing circuit
24
to connect the charged capacitor
12
across the multi-coil winding
10
through a high voltage silicon controlled rectifier (SCR)
14
. The high voltage
26
on the capacitor
12
, shown in
FIG. 2
, creates an oscillation within the circuit including a resistance
8
, the winding
10
and the capacitor
12
. The resistance
8
represents resistance of the winding
10
, wiring within the circuit and any additional resistance which may be provided to prevent excessive current flow within the circuit. The damped oscillating waveform created by the excited resistor-inductor-capacitor (RLC) circuit is measured across the winding
10
and shown in FIG.
2
.
The damped oscillating waveform created by the excited RLC circuit is measured across the series combination of the individual coils, or poles of a stator, of the multi-coil winding by a measurement circuit
20
shown in
FIG. 1
since the individual coils or poles are inaccessible. Analysis of the resulting waveform is used to detect any faults that may be present in one or more of the coils. In the case of a stator comprising a plurality of series connector coils, the analysis is best performed by comparison to stators which are known to be good since tolerances in the wire used to form the coils and the coil winding process itself makes comparison to an ideal standard stator effectively impossible.
Unfortunately, even when comparisons are made to a known good stator, if a stator has a large number of coils, contributions to the waveform from one or a small number of defective coils which indicate a stator fault may be “washed out” by contributions to the waveform from the remaining non-defective coils. In addition, relatively wide test acceptance ranges must be set to accommodate the normal process tolerances and resulting variations in waveforms or data from good multi-coil windings so that marginally defective windings are passed without detection. Several factors must be considered when specifying acceptable limits for production testing, such as wire variation, lamination quality, tolerance of process equipment and tolerance of test equipment. The combination of these factors make it difficult for manufacturers to specify surge test limits that will identify defective coils within multi-coil windings having large numbers of coils much less marginally defective coils.
Accordingly, there is a need for improved testing of multi-coil electrical components having a plurality of series connected coils, such as stators. Preferably, such improved testing would provide greater sensitivity to defects within such multi-coil windings without sacrificing yield and provide simplified and more uniform specification of acceptable test limits.
SUMMARY OF THE INVENTION
The present invention meets this need by providing a method and an apparatus for surge testing all of the individual coils within a coil assembly or multi-coil winding simultaneously. A pickup device is positioned adjacent each of the coils being tested. A voltage pulse is applied across the multi-coil winding. Each of the pickup devices generates a signal having a waveform representative of the magnetic field generated by the coil adjacent thereto in response to the voltage pulse. These signals are compared to each other to identify insulation defects, winding defects and polarity problems within the coils.
According to a first aspect of the present invention, an apparatus for testing a coil assembly comprising a plurality of series connected coils is provided. The plurality of coils extend between first and second ends of the coil assembly. The testing apparatus comprises a capacitor, a charging circuit, a switching circuit, at least one pickup device and a processor. The capacitor includes first and second terminals with the first terminal being connectable to the first end of the coil assembly. The charging circuit is coupled to the capacitor for charging the capacitor. The switching circuit includes a first terminal coupled to the second terminal of the capacitor and a second terminal coupled to the second end of the coil assembly. A voltage pulse from the capacitor is therefore applied across the coil assembly upon activation of the switching circuit. The pickup device is positioned generally adjacent to one of the plurality of coils generating a signal having a waveform representative of a magnetic field generated by the selected coil in response to the voltage pulse. The processor is configured to receive the signal from the pickup device and programmed to control the charging circuit and the switching circuit. The processor is further programmed to analyze the signal to evaluate the coil.
According to another aspect of the present invention, an apparatus for testing a coil assembly comprising a plurality of series connected coils is provided. The plurality of coils extend between first and second ends of the coil assembly. The testing apparatus comprises a capacitor, a charging circuit, a switching circuit, a plurality of pickup devices and a processor. The capacitor includes first and second terminals with the first terminal being connectable to the first end of the coil assembly. The charging circuit is coupled to the capacitor for charging the capacitor. The switching circuit includes a first terminal coupled to the second terminal of the capacitor and a second terminal coupled to the second end of the coil assembly. A voltage pulse from the capacitor is applied across the coil assembly upon activation of the switching circuit. Each of the pickup devices is positioned generally adjacent to a respective one of the plurality of coils generating a signal having a waveform representative of a magnetic field generated by the respective coil in response to the voltage pulse. The processor is configured to receive the signals from each of the plurality of pickup devices and programmed to control the charging circuit and the switching circuit. The processor is further programmed to analyze the signals to evaluate each of the respective coils.
The plurality of pickup devices are preferably housed within a test fixture that may be positioned around or within the coil assembly. The pickup devices are preferably coils or Hall effect sensors. Preferably, the processor is programmed to identify insulation defects or winding defects in the plurality of coils by comparing the signals relative to one another. The processor may also be programmed to compare phase relationships between coils to verify the coils have correct polarities.
According to yet another aspect of the present invention, a method of testing a coil assembly having a plurality of series connected coils comprises applying a voltage pulse across the coil assembly. At least one pickup device positioned generally adjacent to one of the plurality of coils is monitored as the pickup device generates a signal having a waveform representative of a magnetic field generated by the selected coil in response to the voltage pulse.
The step of monitoring the pickup device may comprise monitoring a first pickup device positioned generally a
Fisher Data Products, Inc.
Kerveros James C
King & Schickli PLLC
Metjahic Safet
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