An electric power station that operates at 30 kV and uses a 20:1 step-up ideal transformer is producing 330 MW (Mega-Watt) of power that is to be sent to a big city which is located 260 km away with only 2.5% loss. Each of the two wires are made of copper (resistivity = 1.72×10^−8 Ω.m). What is the diameter of the wires?

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Answer:

The diameter of the wire is 1.45cm

Explanation:

We can obtain the new voltage value using the transformer relationship:

[tex]V=V_o*n_t\\V=30kV*20\\V=600kV[/tex]

Having the new voltage we can obtain the current value going through the wires:

[tex]I=\frac{P}{V}\\I=\frac{330*10^3kW}{600kV}\\I=550A[/tex]

We know that 2.5% of power is loss because the wire, so the power dissipated by the wires is:

[tex]P_w=330MW*(0.025)\\P_w=8.25MW[/tex]

The resistance value of the wire is given by:

[tex]P_w=i^2*R\\R=\frac{P_w}{I^2}\\\\R=\frac{8.25MW}{(550A)^2}\\\\R=27.3ohm[/tex]

We also know that:

[tex]R=\rho*\frac{L}{A}\\A=1.72*10^{-8}*\frac{(260*10^3)}{27.3}\\A=164\µm\\\\A=\pi*(\frac{d}{2})^2\\d=1.45cm[/tex]

Based on the data provided,  the diameter of the wire is 1.44 cm

What is electrical power?

Electrical power is the rate at which electrical energy is expended.

  • P = IV

where;

  • I is current
  • V is voltage

Using the transformer formula to obtain the new voltage V:

V = V₀ * N₁/N₂

V = 30 kV * 20/1

V = 600 kV

Current passing through the wires is calculated thus:

I = 330 *  1000 kW/600

I = 550 A

2.5% of power is dissipated in the wires

Power dissipated, Pw = 0.025 * 330 MW

Pw  = 8.25 MW

The resistance in the wires is determined using the formula;

R = Pw/I²

R =  8.25 * 1000 / (550)²

R = 27.3 ohms

The diameter of the wire is determined using the formula;

R = ρL/A

A = ρL/R

where

A = area of wire

ρ = resistivity of wire

L = length of wire

A = 1.72 × 10⁻⁸ Ω.m * 260 * 1000 m / 27.3 Ω

A = 1.64 * 10⁻⁴ m²

Also,

A = πd²/4

d = √4*A/π

d = √(4 * 1.64 * 10⁻⁴ m² * 7/22)

d = 0.0144 m

d = 1.44 cm

Therefore, the diameter of the wire is 1.44 cm

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