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Unclesyd, Personally, I don't think your question is dumb. The rolls we are applying induction to are cast iron rolls, not designed to be heated above 60 °C by the normal calendering process. Because we are applying almost 0.5 MW of heating energy to the rolls we apply induction to, bearing...

Gunnar, The ultrasound energy is a very, very minor portion of the energy generated by the induction heating system. The energy applied to the roll is in the form of heat from eddy currents. My old dog, which was probably deaf, would sleep beneath the wiring going from an induction power supply...

Gunnar, You have hit it right on with our induction heating application. We have installed two induction heaters per supercalender on 6 supercalenders, for a total of 12 induction beams on 12 rolls (24 bearings). Roll #3 at the bottom of the stack uses 120 sixty mm wide zones at 4 kW each...

Gunnar, We believe that our bearing current measurements are reliable. We have calibrated our Rogowski coils with a stationary wire inside the loop at 25 kHz. I agree with you that 80 Amps sounds awfully high. The RMS value is closer to 15 amps because our induction power supplies use PDM...

Since bearing problems first occurred about 1 1/2 year ago, we have been using Rogowski coils with oscilloscope to measure shaft currents. The Rogowski coil wraps around the roll shaft and accurately measures the current circulating inside its loop. We have found it not to be affected by...

Mike, Gees! Thanks a million for the clear explanations. You are telling me what I have been desperately waiting to hear from bearing experts. We have been swimming upstream during the last 6 months, unsuccessfully trying to get the attention of the end user, the system integrator and the...

Our company manufactures roll heating systems using 25 kHz induction heaters. Because we have measured that our induction roll heating equipment generates ultrasonic vibrations in the roll where induction is applied, we are asking ourselves whether the presence of ultrasonic vibrations on the...

You experts have lost me on electrical grounding and neutral a while back. However, one thing that I realized last night was that I created my own confusion by calling my High Frequency Inverters "power supplies". It took me all this time to realize that when you were talking about power supply...

Bill, I apologize, but I have a mental block concerning the discussion around neutral and ground. To help me understand how and where we should hook up connections, let me ask the following question. If our 3 phase Wye auto transformer was connected to a 3 phase electric motor, where should we...

Thanks again for all comments. Some answers to posts: -The problematic auto transformer powered systems are situated in Germany. They run from 400 VAC primary to 220 Volts. Our power supplies accept 200 to 250 VAC 3 phase input. Here in Canada, the transformer primary voltage will be 550-600...

Thanks for all your pertinent responses. Here are some comments: 1-The power for the control board comes from the same auto transformer. The 2 micro controllers on the board manage the power up and down functions. Power drawn is under 700 ma. Also, remember we have a whole lots of identical...

Itsmoked, Thanks for the useful info. Your point 3 is quite valid about IGBT shoot thru failures. However, because some of our induction systems simultaneously turn ON more than three hundred 6 k Watts power supplies every 20 to 30 minutes and OFF for about 10 minutes ( the time for a paper...

In all occasions, the dual IGBT used as a high frequency switch blows. It is a 200 Amps, 600 Volts device. This happened 3 times now on a group of 6 heaters. The transformer primary disconnect is manual; I presume one leg could disconnect before another, but for every short time. Also, each...

Our company sells and installs low power (max (12 kW induction heating systems to heat various elements in the industrial environment. For instance, there are more than 50000 of our power supplies reliably heating paper machines rolls. Our systems run on 3 phase power. Normal voltage is 208...