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In Reply to: RE: please teach me... posted by jea48 on September 15, 2016 at 07:10:28
Jae quote " The transformer that feeds your home, and maybe 3 to 5 other houses, is an isolation transformer. You can pretty much discount any noise found on the primary feed side of the transformer" While I pretty much don't know about this subject I'm reading stuff like an iso transformer blocks DC but not much RF and or EMI. Since we don't live in a perfect AC world dreamed of by Cloudwalker it seems very unlikely to me that even if the iso transformer before the house was designed to limit RF and EMI that it would not eliminate it, some would likely still get in to harm sound quality. My theory at this point from preliminary readings on the subject. T456
Follow Ups:
Aren't power transformers in U.S. tuned to 60Hz?. Should not
pass much noise if not 60 Hz.
What motors make noise?. Any motor with brushes. Good examples
are blenders and mixers. Or an induction motor with digital speed
control.
I can't imagine that power transformers, or isolation transformers are "tuned" to 60cps. Now I could be wrong, but I doubt it. T456
Yes. they are designed to be efficient at 60. The design would
be different for 50 Hz. I can't picture much, if any, noise passing
to the secondary.
Coner, I read that rf will go through the isolation transformer just like the ac one wants to go through. They block DC and make things safer, so I read. I think this is the physics of the situation. Easy enough to test with a scope at least with a small iso transformer on a bench. T456
I suspect interwinding capacitance will allow RF to couple through. You always have to keep parasitics of real world components, as apposed to ideal, in mind. One of the benefits of using isolation transformers is the ability to rebalance the AC output. There is a reason power companies use balanced lines to transmit power to your house.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
There is a reason power companies use balanced lines to transmit power to your house.
I assume you are speaking of the 240/120V nominal secondary winding output of the utility power transformer.
The power company in my area sends out 3 phase 4 wire WYE power from the substation to an area intended for 3 phase as well as single phase power.
In residential areas one hot phase and the neutral, (the earth grounded Conductor), are used to feed step down utility power transformers to feed residential dwelling units. The secondary side of the transformer is single phase 240/120V. It is called a split phase winding. You could say balanced power, 120V - 0V - 120V.Only the imbalanced load of Line 1 to Neutral and Line 2 to neutral returns on the service entrance neutral to the transformer neutral. The balanced load is in series with Line 1 and Line 2.
Example, if at the main service electrical panel Line 1 to neutral load is 10 amps and line 2 to neutral load is 10 amps then zero amps will return on the service entrance neutral to the transformer neutral. The two 120V 10 amps loads are in series with one another.The Link below is a great example how a single phase split phase winding works.
Edits: 09/18/16
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