Here is one question about isolation transformers in use for audio systems.
Here comes to the shop one machine which is one isolation transformer but its configured in a way that i am not familiar with
Transformer is torodial
The primary has a tap for 230 -240 use ...fine with that
Secondary though is made from two windings of 115 V center taped .
so secondary will provide side to side 220-230V depending in the input
The center tap though goes to ground connected also in the enclosure and to the mains ground
I am not familiar with this practice can any one comment on pros and cons ?
kindest regards
Sakis
Here comes to the shop one machine which is one isolation transformer but its configured in a way that i am not familiar with
Transformer is torodial
The primary has a tap for 230 -240 use ...fine with that
Secondary though is made from two windings of 115 V center taped .
so secondary will provide side to side 220-230V depending in the input
The center tap though goes to ground connected also in the enclosure and to the mains ground
I am not familiar with this practice can any one comment on pros and cons ?
kindest regards
Sakis
I've read this and hope it may be helpful:
"If you ground center tap, one-half of the output will be positive about the ground. The other half will be negative and 180° out of phase with the voltage in the secondary’s first part.
Therefore, you should ground the center tap to ensure you earth unsymmetrical currents that result from loads facing imbalance."
"If you ground center tap, one-half of the output will be positive about the ground. The other half will be negative and 180° out of phase with the voltage in the secondary’s first part.
Therefore, you should ground the center tap to ensure you earth unsymmetrical currents that result from loads facing imbalance."
First we need to know what do you expect to plud at the output ( nominal voltage of the equipment ) and also what is is voltage of the mains in your lcation.
If your concern is the fact that the center tap is connected to ground, then the following information may help:
The secondary winding is isolated from ground. As long as only one point (e.g. the center tap) is connected to ground there will be no current flow to ground.
The secondary winding is isolated from ground. As long as only one point (e.g. the center tap) is connected to ground there will be no current flow to ground.
Another "pro":
The centre tap splits the winding into 2 sides with each having only 120V with respect to earth. In case of an electric shock, this limits the magnitude of the shock potential to 120 V, half of 240V.
The centre tap splits the winding into 2 sides with each having only 120V with respect to earth. In case of an electric shock, this limits the magnitude of the shock potential to 120 V, half of 240V.
Mains here is 230-240 isolation trafo ratio is 1:1 im not going to talk about that ( any one thinks that this is a 240-110 trafo should read again )
Ok safety talk is understood no probs about that
The real question is that in this case mains ground often is not clean, carries with it a lot and the transmission line ( s) in general suffers from capacitance
indeed excesive capacitance of a line is calculated easilly and most of times suggest a filter way out of acoustic frequncies .
though the existance of capacitace is a huge problem when you transfer energy .
So if one doesnt use the trafo has to deal with EMI that might be carried from the line and the ground
Now from ground to live or neutral there is no actuall conection ( even tough in some places here neutral and ground are tied in the entance of the power supply as a more effective safety ) so if there is any issue in the ground its only inducted in the power lines
( i could add the total capacitance of the line but this doesn't matter much or that much )
so if you use the trafo as is , you actully hard wire the ground to the secondary winding
more or less you inject any problem of EMI that travels in the lines back in the secondary again
that cant be right
in total you might gain safety from the galavanic isolation but the perpus of such a trafo is to deliver cleaner power
Ok safety talk is understood no probs about that
The real question is that in this case mains ground often is not clean, carries with it a lot and the transmission line ( s) in general suffers from capacitance
indeed excesive capacitance of a line is calculated easilly and most of times suggest a filter way out of acoustic frequncies .
though the existance of capacitace is a huge problem when you transfer energy .
So if one doesnt use the trafo has to deal with EMI that might be carried from the line and the ground
Now from ground to live or neutral there is no actuall conection ( even tough in some places here neutral and ground are tied in the entance of the power supply as a more effective safety ) so if there is any issue in the ground its only inducted in the power lines
( i could add the total capacitance of the line but this doesn't matter much or that much )
so if you use the trafo as is , you actully hard wire the ground to the secondary winding
more or less you inject any problem of EMI that travels in the lines back in the secondary again
that cant be right
in total you might gain safety from the galavanic isolation but the perpus of such a trafo is to deliver cleaner power
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I don´t see the point of going through the trouble and expense of going through a big heavy isolation transformer and then grounding its secondary, don´t care if either end or a centertap to ground again. WTF?
Even if potential danger is lowered from 230V to 115V, it´s still dangerous, still ground referenced.
Does not make sense.
A NON round referenced secondary is excellent to work on, say, SMPS "mains side" and such ... but that advantage is wasted here.
jm2c
Even if potential danger is lowered from 230V to 115V, it´s still dangerous, still ground referenced.
Does not make sense.
A NON round referenced secondary is excellent to work on, say, SMPS "mains side" and such ... but that advantage is wasted here.
jm2c
The isolation transformer in question is referred to as a Balanced Power Transformer. I've found the following information, but do not have the expertise in this area to judge whether or not it will be helpful to you.
"Balanced Power Transformers are designed with a center-tapped secondary winding which consists of two identical, mirrored secondary windings in series and an electrostatic shield. When the center tap is grounded, these two identical windings short circuit the equal amplitude but opposite phased noise current and greatly attenuate (low to medium frequency) common mode noise. The ground noise amplitude goes to zero, allowing audio to be free of noise interference."
A basic schematic of such a device is attached for interested parties.
