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: (10)

(i) Battery A 105 V, Internal resistance 0.25 ohm

(ii) Battery B 100 V, Internal resistance 0.2 ohm

(iii) Battery C 95 V, Internal resistance 0.25 ohm

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

Answer 1

Part (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:

$$V_{line}=\sqrt3\:V_{phase}$$

$$\frac{V_{line}}{V_{phase}}=\sqrt3\:=\:1.732$$

In a star connection, the line current is equal to the phase current:

$$I_{line}=I_{phase}$$

✓ Verified Model Answer (Text Solution)

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.