# Homework Help: Detect a Shield Short on Transformer

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1. Nov 7, 2014

### Palreddy Anurag

1. The problem statement, all variables and given/known data

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...Also Primary Side Winding is an unbalanced one i.e. one side is Grounded
We Have Access to Primary Winding,Shield and are provided with Signal Generator
The Transformer Winding Ratio Lp: Ls is 1:1 (Isolation Transformer) and is an ideal one.We are here trying to find a Mathematical Feasibility to Problem instead of Practical Values...

2. Relevant equations
Transformer Equations:

i.e. Ratio of Voltages on Primary/Secondary is equal to Number of Turns of Primary/Secondary...

i.e. Change in Magnetic Flux induces Potential Difference in a Body...

3. The attempt at a solution

I Have Made Following Attempts on Solution:-

I tried to Measure Voltage on Shield w.r.t Ground of Primary Side But Failed to Obtain Voltage of Point A/B ,Then i Realized that the Both sides of Transformer don't have same Reference Point

2. Nov 7, 2014

### rude man

If either A or B is shorted to the shield then the output is no longer 'balanced'. You can therefore input a signal at the primary and look at A and B (one at a time) with a voltmeter or 'scope referred to the shield. What would you expect with/without the short?

3. Nov 8, 2014

### Palreddy Anurag

"You can therefore input a signal at the primary and look at A and B" with respect to What Reference Point is I Fail to Understand.

4. Nov 8, 2014

5. Nov 8, 2014

### Palreddy Anurag

No What I was saying is Measure Potential at A or B w.r.t to Which Reference Point (We don't have access to Secondary Coil,But only Shield which gets shorted to point A or B on Secondary Coil)Because we need Potential Difference to Measure the Voltage...

6. Nov 8, 2014

### Staff: Mentor

I'm puzzled why you emphasise how you don't have access to the secondary, yet A and B are the access terminals to the secondary!

If you energize the primary, then measure the potential difference between A and the shield, and also between B and the shield, will this be likely to tell you anything?

You are definite that the short, if it exists, will be between one of the terminals and the shield? That's what the problem statement says?

7. Nov 8, 2014

### Palreddy Anurag

In the Problem Statement I Mentioned that "if SHIELD is shorted to Point A or Point B Without Access to Secondary Transformer Coil",Here we don't have access to Secondary Coil and Point A and B are of Secondary Coil,What we do Have is that the Shield Gets Shorted to Point A or Point B hence an Access to ONLY that Point via SHIELD(A and B are not Terminal Accessible Directly to us)

8. Nov 9, 2014

### rude man

OK, so the only access points are the input windings, yes? And one of those windings is shorted to the shield.
In this case the answer is that there woud be no input impedance or other discernible change if the internal short is to point A or B, but if the short is to both A and B that would be an entirely different matter.