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Core testers

Core testers

Core testers

Does anyboby know where I can get hold of a second hand stator laminated core tester, I have priced up the Adwell units but the price is too high. Or has anybody any advice on how to test for hot spots and interlamination insulation breakdown without the need for this piece of equipment.

RE: Core testers

I believe most of the Adwell equipment is low-power core tests.

You can also do a "loop test" as described in Appendix A4 of IEEE 432-1992 and Appendix A of IEEE56-1977.

Basically a high-current test set (? circuit breaker ductor?) is hooked up to a set of loops to produce required number of amp-turns, which can be calculated from core dimensions and parameters.  Also a separate single-turn "search" coil with voltmeter can be used to monitor the actual volts/turn induced, and to plot the saturation behavior as excitation current is increased.

Shorted laminations will generate heat.  Monitor temperatures with infrared if available (although I understand that feeling the core or using wax may work also).  In general, I think with approx 85,000 lines per square inch you should see no hotspots more than 10C above the rest of the core.  Problems deep within stator take longer to cause a temperature difference on the surface.  

Higher levels of flux will help minor/deep imperfections to show up more pronounced and more quickly.  I've heard that it shouldn't cause any core damage if flux were increased  to 100,000 lines per inch..... but don't quote me on that.

There are a lot more details in those IEEE standards, including methods for calculating flux, cable sizes and insulation levels to use, etc.

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