3.1 What is the purpose of a transformer? 3.2 Name the type of loss that is dissipated in a transformer due to the internal resistance in the windings - NSC Electrical Technology Electronics - Question 3 - 2017 - Paper 1

The type of loss dissipated due to internal resistance in the windings of a transformer is called copper loss or I²R loss, which occurs due to the resistance of the wires that carry the current.

1. Oil cooling: Uses transformer oil to dissipate heat from the windings and core.
2. Air cooling: Utilizes fans or natural convection to remove heat from the transformer.

If a cooling method fails, the transformer may overheat. This overheating can lead to insulation breakdown and short circuits, resulting in transformer failure or reduced operational life, and can also pose a fire hazard.

1. Industrial power distribution: They are used to convert high-voltage electricity from the grid into lower voltage for factory operations.
2. Power generation plants: They allow the distribution of electricity generated from wind or solar farms in a suitable voltage for consumer usage.

To determine the secondary line current, use the formula:

$I_L = \frac{S}{\sqrt{3} V_{L}}$

Substituting the values:

$I_L = \frac{120000}{\sqrt{3} \times 380} \approx 182.32 A$

The secondary phase current can be found using the line current:

$I_{ph} = I_L$

Thus,

$I_{ph} = 182.32 A$

The input power can be calculated using the formula:

$P = \sqrt{3} V_{L} I_{L} \cos \theta$

Substituting the known values:

$P = \sqrt{3} \times 380 \times 182.32 \times 0.9 \approx 107999.32 W$

The secondary winding of a step-down transformer has a thicker wire because it carries a higher current than the primary winding due to the step-down voltage transformation. Thicker wires can handle the increased current, helping to reduce resistive losses and prevent overheating.