Find Potential on a Transformer

[palreddyanurag]

What I fail to understand is how to find if SHIELD is shorted to Point A or Point B Without Access to Secondary Transformer Coil...
We Have Access to Primary Winding,Shield and are provided with Signal Generator

 

[FvM]

Can't be determined without knowledge about windings design and inter-windings capacitance, I think.

 

[chuckey]

As the circuit is completely symmetrical it would not make any difference.
Frank

 

[palreddyanurag]

Hi FvM The Transformer Winding Ratio Lp:Ls is 1:1 (Isolation Transformer) and is an ideal one so negligible inter-winding capacitance.We are here trying to find a Mathematical Solution to Problem instead of Practical Values...

Also Primary Side Winding is an unbalanced one i.e. one side is Grounded

 

[chuckey]

As the secondary has a load of 3 K this will be reflected back to the primary, add to this the extra 1K, gives a total impedance of 4 K. makes no difference where the secondary is earthed.
Frank

 

[palreddyanurag]

As the secondary has a load of 3 K this will be reflected back to the primary, add to this the extra 1K, gives a total impedance of 4 K. makes no difference where the secondary is earthed.
Frank

Hi Thanks for the Reply ,The Problem here is not to find Impedance Reflected on Primary Side but to Find whether Shield is Shorted at Point A or B of Secondary Coil,Thats the Tricky Part...

 

[FvM]

I wonder where the problem comes from.

As stated (no interwindings capacitance respectively no asymmetry in winding capacitances) it has no solution. Not "the tricky part", just no way.

 

[palreddyanurag]

I wonder where the problem comes from.

As stated (no interwindings capacitance respectively no asymmetry in winding capacitances) it has no solution. Not "the tricky part", just no way.

The Problem is a Practical One And one needs to Find Short of Shield on Secondary Side(Because then the bus becomes Suceptible to EMI with a Shield Shorted to a Conducting Wire) from Primary Side...:roll:

 

[The Electrician]

Connect the two primary terminals together and measure the capacitance from that point to the shield. That capacitance will most likely be substantially different if there is a short from shield to secondary.

 

[FvM]

The Problem is a Practical One And one needs to Find Short of Shield on Secondary Side(Because then the bus becomes Suceptible to EMI with a Shield Shorted to a Conducting Wire) from Primary Side...

There's no "bus" or other distributed load in the posted schematic. Seems like you are withholding essential information.

 

[palreddyanurag]

There's no "bus" or other distributed load in the posted schematic. Seems like you are withholding essential information.

Actually Bus Starts after Point A/B where a line is Marked(After which shield can get shorted) ,it is a Balanced Transmission Line with Load attached at other end and can be of any length(0 to 3λ)...

 

[chuckey]

As there is no phasing indications on the circuit, there is no difference where the short is. If however you seem to think that it is important, put secondary in series with the primary, earth one terminal of primary, measure impedance. Repeat with the primary connected the other way around. Now you can work out where the short is likely to be.
So what are you going to do, if you find its point A or B?.
Frank

 

[FvM]

Even the original question is ambiguous. Is the emphasis on "find if SHIELD is shorted " or on "Point A or Point B"?

The existence of any short will show in the input impedance if the transmission line has some length. For zero TL length we're back to windings capacitance respectively transformer common mode properties.

We are here trying to find a Mathematical Solution to Problem instead of Practical Values...

A mathematical solution starts with a complete equivalent circuit of the circuit with all parasitic elements. With your assumptions given up to now (ideal transformer), there's no solution at all.

 

[palreddyanurag]

The Goal is to Find SHIELD short and if Shorted to which Point oint A or Point B
Since it is a Practical Question You can Assume parasitic Capacitances,Resistances(of Practical Values) But the Circuit is Symmetrical One as chuckey Points out

 

[FvM]

The Transformer Winding Ratio Lp:Ls is 1:1 (Isolation Transformer) and is an ideal one so negligible inter-winding capacitance.We are here trying to find a Mathematical Solution to Problem instead of Practical Values...

Since it is a Practical Question You can Assume parasitic Capacitances,Resistances(of Practical Values) But the Circuit is Symmetrical One as chuckey Points out

I wonder how many different answers we'll still get to the same question.

No real transformer is truely symmetrical. The windings configuration matters, also if it has an inter-windings screen.

If it is actually a "practical question", the actual transformer parameters should be determined.

 

[palreddyanurag]

Okay..., the CMR(Common Mode Rejection) of Transformer is 45db(Min) and wire-to-wire distributed capacitance is 30 pf/feet(Max)...

 

[ahsan_i_h]

The Problem is a Practical One And one needs to Find Short of Shield on Secondary Side(Because then the bus becomes Suceptible to EMI with a Shield Shorted to a Conducting Wire) from Primary Side...

To avoid EMI problems, you should connect the shield to the ground (not any wire of primary side).

 

[D.A.(Tony)Stewart]

View attachment 111066

What I fail to understand is how to find if SHIELD is shorted to Point A or Point B Without Access to Secondary Transformer Coil...
We Have Access to Primary Winding,Shield and are provided with Signal Generator

An ideal shield with balanced flux inside conducts no current.

A shorted shield conducts current that is frequency dependant on many coupling capacitance variables.

Therefore detection done by done by primary swept frequency response.

One can use a CC swept frequency to measure impedance with voltage.

 

[palreddyanurag]

Equivalent Circuit of Transformer...

 

[palreddyanurag]

Connect the two primary terminals together and measure the capacitance from that point to the shield. That capacitance will most likely be substantially different if there is a short from shield to secondary.

Hi,
I measured the impedance(and so the capacitance) and it is varying,But
-It is varying for transformer to transformer and also the Base capacitance is Varying(i.e. Capacitance with no short).
-If the length of Bus on Secondary side is considerable no considerable difference was observed(As I Believe BusShield to Conductors capacitance exist and presents a short cirucit at measured Frequency..)