# Thread: Student, have a few questions about breakers/ power in general

1. gar
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190614-1334 EDT

sengineer101:

The problem I saw in your first post was that you spoke like an electrician rather than like an engineering student. If I don't really know what your background is, then I am not in a good position to communicate with you.

Also, the sqrt(3) is derived from the relationship between VL-L and VL-N in a 3 phase system.
That really tells me nothing, and it does not tell me if you can derive that relationship, nor what assumptions are necessary for it to be true. It does not tell me if you understand the relationship. If the system is unbalanced is it true?

.

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understandable, the square root of 3 comes from the phase relationships when you sum up phasors. For example in a wye configuration the line to neutral voltages could have the form 1<0 and 1<-120. For VAN and VBN. Now if we wanna find VAB we subtract, and doing simple phasor addition, we realize that this is equal to 1- (-.5-.87j) which equals to 1.5+ .87j. Magnitude of this is 1.73 which is square root 3.

3. gar
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190615-2007 EDT

sengineer101:

Consider the following question, and if you desire to analyze it, then provide all details on your analysis.

A Simpson 260 or 270 meter is a Weston D'Arsonval type movement with Simpson meters after about 1960 being taut-band.

1. Use a DC regulated power supply to supply voltage to the Simpson.

2. Use the 50 V range.

3. Select AC and adjust for an exact reading of 50 V.

4. Switch to DC and record the reading.

5. Do a theoretical analysis of what the ratio should be.

6. How does an actual measurement compare, and why might it be different?

.

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