Electrical Engineering interview question and answers:
Job interview Topics for Electrical and Electronics Engineers (Part-1)
1.Per Unit (pu) Quantities:
The numerical per unit value of any quantity is defined as the ratio of its actual value to another arbitrarily chosen value of quantity of the same dimensions, assumed as the base or reference. It is basically used in one line diagram.
Per unit value ≈ (Actual value/ Base value of the same direction)
2. Advantage of Per Unit Representation:
- The Per Unit impedance value for apparatus of like rating lies within a very small range.
- The impedance of machines is specified by the manufactures of the machine in terms of per unit values.
- Per Unit value provides more meaningful information .The chance of confusion between line and phase voltage values on a 3-phase system is reduced.
- The computational disturbance or effect in power system is highly reduced with the use of Per Unit quantities.
- The Per Unit impedance which is referred on any side of a single phase transformer is the same.
- The Per Unit impedance which is referring to the either side of a three-phase transformer is the same regardless of the three-phase connection .Whether the connections are delta-delta, Y-Y, or delta-Y.
3. One –line Diagram:
In the Electrical Circuits there are various components in a circuit diagram. Sometimes, it is needed to simplified electrical circuit diagram by omitting the completed circuit through the neutral and by indicating the component parts by standard symbols, in place of their equivalent circuits. Circuit parameters are not shown and a transmission line is represented by a single line between its two ends.
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