A power plant produces energy at a voltage of Vi = 11723 V. Before being sent al

Question

A power plant produces energy at a voltage of Vi = 11723 V. Before being sent along long distance power lines this electricity is sent through a transformer with 139 turns in the primary coil and 5612 turns in the secondary coil.

Q1 What is the voltage of the electricity sent through the long distance wires?

Q2 If the wires have an efficiency of 99.10% and a resistance of 1408 , what current flows through these wires?

Q3 How much power do the wires carry?

Q4 Select the true statements from the following list below (More than one may be correct)

1)An iron core increases the efficiency of a transformer in comparison to an air core.

2)Less power is lost when electricity is transmitted at high voltage over a long distance than when transmitted at a low voltage.

3)A step down transformer has more turns of wire in the secondary coil than in the primary coil.

4)The electricity that travels along the wires is AC (alternating current)

5)A step-up transformer will be needed between the long distance wires and people's homes.

6)The electricity that travels along the wires is DC (direct current).

Explanation / Answer

(Q1) Voltage of the electricity sent through the long distance wires -

Vs = Vi x (Ns/Ni) = 11723 x (5612/139) = 473305.58 V = 473.30 kV

(Q2) Normal current of through the wire, I = 473305.58 / 1408 = 336.15 A

Now the efficiency = 99.10 %

So, the actual current through the wire = 336.15 x 0.991 = 332.12 A

(Q3) Power carried by the wire = V*I = 473305.58*332.12 = 157194249.23 W = 157.19 MW

(Q4) True statements are -

Only statements (1) and (2) are correct.

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