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 Power Systems - Question 3 - 2017 - Paper 1

The type of loss that occurs due to internal resistance in the windings is known as copper losses, often represented mathematically as $I^2R$ losses.

1. Air cooling
2. Oil filled self-cooling or oil filled water cooling.

If a cooling method fails, the transformer may overheat. This overheating could damage the insulation between the windings, depending on the heat degree. In severe cases, this could lead to an internal short circuit, and gas may form, which is highly combustible.

1. Used to distribute power to consumers at substations.
2. To step down the voltage to a 380 V three-phase and 220 V single-phase supply.

Given: $S = 120 \, kVA$ and $V_{L}= 380 \, V$

To find the secondary line current $I_L$:

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

Calculating: $I_L = \frac{120000}{\sqrt{3} \cdot 380} \approx 182.32 \text{ A}$

To find the secondary phase current $I_{ph}$:

Since $I_{ph} = I_L$, we have: $I_{ph} = 182.32 \text{ A}$

To determine the input power $P$ to the clinic:

$P = \sqrt{3} \cdot V_{L} \cdot I_L \cdot p.f.$

Calculating: $P = \sqrt{3} \cdot 380 \cdot 182.32 \cdot 0.9 \approx 108.47 \, kW$

The secondary winding of a step-down transformer has a thicker wire because it carries a higher current compared to the primary winding, which helps to prevent overheating and ensures efficient operation.