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Toroid w/3 ph pri and 1 ph sec.

Posted by Jerry Anderson on 7/8/2008, 9:30 am

 Bert, It's been awhile, and it's my sincere hope this message/question finds you well. I've changed jobs since our last communique and work installing fiber optic current and voltage sensors for power generating stations and the higher voltage class substations. Our sensors are competitive with conventional CT's and VT's down to about 138kV. My question is what does the output of the secondary of a toroid with 3 primary inputs (windings) that are square waves with 40khz, 20khz and 10khz respectively look like? I mean, I'm having a real difficult time wrapping my mind around why the use of the toroid to combine the 3 inputs. The coil would not have much of the way of either step up or step down. What purpose can you think of would constitute the need for this transformer? Best Wishes, Jerry

Re: Toroid w/3 ph pri and 1 ph sec.

Posted by Bert Hickman on 7/8/2008, 1:03 pm, in reply to "Toroid w/3 ph pri and 1 ph sec."

 --Previous Message-- : Bert, : It's been awhile, and it's my sincere hope this message/question : finds you well. I've changed jobs since our last communique and work : installing fiber optic current and voltage sensors for power generating : stations and the higher voltage class substations. Our sensors are : competitive with conventional CT's and VT's down to about 138kV. : My question is what does the output of the secondary of a toroid with 3 : primary inputs (windings) that are square waves with 40khz, 20khz and : 10khz respectively look like? I mean, I'm having a real difficult time : wrapping my mind around why the use of the toroid to combine the 3 inputs. : The coil would not have much of the way of either step up or step down. : What purpose can you think of would constitute the need for this : transformer? : : Best Wishes, : Jerry : Hi Jerry, That's a real poser! The output voltage will be a function of the incoming signal amplitudes and their relative phasing to one another. Assuming that the combined signals never saturate the toroidal core, and the input signals are driven by equal low impedance bidirectional AC signal sources, then the output will be proportional to the algebraic sum of the three incoming signals. An example of three +/-1 volt incoming signals that are synchronized with each another, with each having a 50% duty cycle, can be seen here for a single cycle (0 - 360 degrees) of the 10 kHz signal: http://www.capturedlightning.com/temp/MixedSignals1.jpg Shifting the 10 kHz signal by 180 degrees gives you this instead: http://www.capturedlightning.com/temp/MixedSignals2.jpg And, also shifting the 20 Khz signal by 90 degrees gives you this: http://www.capturedlightning.com/temp/MixedSignals3.jpg You can see that changing the phase relationship or individual amplitudes can give you virtually an infinite set of combinations and waveforms. It gets much more complex if the core is ever driven into saturation... Multi-input transformers are sometimes used in this fashion to combine signals from multiple sources in order to synthesize a waveform that is a closer approximation to a sine wave in power inverters. However, in this case all the signals are of the same frequency but each has different relative phasing and duty cycles. Multiple-input transformers can also be used in balanced configurations where the input from one signal source is cancelled by the input from another. If both signals are present and 180 degrees out of phase, the output sums to zero. However, if you lose one of the signals, or if their relative phase relationship changes, then an output voltage will appear. This can be used to trigger a loss of signal (or loss of phase lock) alarm. However, in this case you would have an even number of input windings and each signal would have the same frequency. I honestly don't have any idea what your toroid and circuitry is being used for. What is the circuit imbedded within or how is it being used within your application? Bert

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