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Technical
Information
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The Lexseco Core Loss Tester is a patented device for analyzing stator, rotor and armature cores. A one-turn test loop operating at high current and low voltage energizes the back iron. In conformity with core steel manufacturers' published data, the back iron is energized to 85,000 lines of flux per square inch density (13,175 Gauss) (MP4.0TM and MP6.0TM Software users may easily change this value). The core is metered as a toroidal magnetic transformer. The test may be performed with the windings in place or removed. Grounded, burned out or aged windings have no effect on the core loss test. In developing the Core Loss Tester, Lexseco performed thousands of tests on a wide range of motor and core types, creating an extensive empirical test database. Moreover, Lexseco studied and incorporated the electrical steel manufacturers' data used by the designers of electrical apparatus in arriving at output and performance characteristics. |
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Core Condition
Lexseco determined that the most important indication of core steel
condition is the watts of electrical energy lost per pound (kilogram)
of core steel when the core is excited to operating conditions. Common
electrical grades of core steel have inherent Epstein test rated watts
per pound (kilogram) losses ranging from 1 to 2 watts per pound (kilogram)
depending upon application. This value is increased by as much as a
factor of 1.5 to 2 once this steel is punched and assembled into motor
cores. This increase may be attributed to a combination of the following:
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Lamination punching or stamping burrs
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Lamination thickness
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Lamination clamping pressure
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Type of insulation coating used on the steel
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Heat treatment process used on punched laminations
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Lamination assembly method
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Silicon content and hardness of the steel
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Heavy welds across the back of the core stacking
Watts per pound (kilogram) core losses may be divided into hysteresis and eddy current losses. Hysteresis loss results from the alternating frequency reversals shifting molecules to adjust polarity and is dissipated in the form of heat. Hysteresis loss does not change with varying steel thicknesses. Eddy current loss is the cross current flow found in the lamination assembly. Unlike hysteresis loss, eddy current loss increases proportionally with steel thickness. Like hysteresis loss, eddy current loss is dissipated in the form of heat.
The Lexseco Core Loss Tester relies principally upon the watts per pound (kilogram) criterion to determine core loss. In addition, the software records the ampere turns per inch (centimeter) (AT/in or AT/cm), which is a measurement of the magnetizing power required to produce a certain flux density in the iron laminations. Similar to the watts per pound (kilogram) calculation, the lower the ampere turns per inch, the more efficient the core.
The Lexseco software interprets the meter readings, makes a judgement regarding overall core condition (OK, MARGINAL, or BAD), and produces a report reflecting the core condition judgement along with recommendations for further action including "hot spot testing."
Hot Spot Testing
Hot spot testing verifies the watts per pound (kilogram) reading. Upon
completion of the metering portion of the core loss test, the computer
software instructs the operator to apply a higher excitation current .
After approximately 1 minute, imperfections and problems with the core
should become apparent through a simple temperature check of core surface.