4.1 Name THREE losses that occur in transformers - NSC Electrical Technology Power Systems - Question 4 - 2018 - Paper 1

Delta-star transformers are used for:

1. Power distribution in commercial and industrial applications.
2. Power distribution for stepping down voltage from 380 V to 220 V.

The oil in transformers performs two main functions:

1. It improves the insulation of the transformer, allowing it to safely operate at higher voltages.
2. It conducts heat away from the windings, thus maintaining operational efficiency.

The operation of a transformer is based on electromagnetic induction. It consists of two windings: the primary and the secondary, wound around a magnetic core. When alternating current passes through the primary winding, it creates a varying magnetic field. This magnetic field induces a voltage in the secondary winding proportional to the turns ratio of the two windings. The transformer transfers electrical energy between these circuits without any mechanical motion.

Transformers have better efficiency compared to other machines primarily because they have no moving parts. This results in fewer mechanical losses and ensures that energy conversion from electrical to magnetic back to electrical is highly efficient. Moreover, transformers are designed to minimize losses, making them capable of delivering better power output.

The Buchholz relay is used to detect abnormal gas formation in the transformer. It isolates the transformer from the supply to prevent damage, thereby functioning as a crucial safety device.

The secondary phase voltage can be calculated using the formula: $V_{PS} = \frac{V_{LS}}{\sqrt{3}} = \frac{380}{\sqrt{3}} \approx 219.39 \, \text{V}$

The transformation ratio can be calculated using: $T_R = \frac{V_{P}}{V_{PS}} = \frac{2200}{219.39} \approx 10.1$

The number of secondary turns can be calculated using: $\frac{V_{P}}{V_{S}} = \frac{N_P}{N_S}$ Thus, $N_S = N_P \cdot \frac{V_{S}}{V_{P}} = 1500 \cdot \frac{219.39}{2200} \approx 149.58 \approx 150$

The transformer is a step-down transformer because the primary turns ($N_P$) is greater than the secondary turns ($N_S$).

The secondary windings of the transformer are connected in star or delta configuration, providing a neutral point. This allows the transformer to supply single phase and three-phase electrical systems efficiently, making it suitable for power distribution.