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Class 2 (2nd Engineer) MET 📅 Nov 2024

Exam Question

(a) With the aid of delta and star connection diagrams, state the basic equation from which the delta-star and star-delta conversion equation can be derived. (6)

(b) Three batteries A, B, and C have their negative terminals connected together. Between the positive terminals of A and B there is a resistor of 0.5 ohm and between B and C there is a resistor of 0.3 ohm.

Specifications of the three batteries are given below:

Battery A 105 V, Internal resistance 0.25 ohm

Battery B 100 V, Internal resistance 0.2 ohm

Battery C 95 V, Internal resistance 0.25 ohm

Determine the current values in the two resistors and the power dissipated by them.

Reference Answer

(a) In a three-phase AC system, a star connection means that one end of each of the three phase windings is joined together to form a neutral point. The other ends of the windings are connected to the three line terminals.
For a star-connected system:
$$V_{line}=\sqrt3\:V_{phase}$$
$$\frac{V_{line}}{V_{phase}}=\sqrt3\:=\:1.732$$

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