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

Delta-star transformers are commonly used for:

1. Power distribution in Commercial and power distribution in Industries.
2. Power distribution for domestic use, particularly in converting 380 V to 220 V.

The oil in transformers serves two main functions:

1. Insulation: It improves the insulation of the transformer, preventing electrical breakdown.
2. Cooling: It conducts heat away from the windings, helping maintain optimal operational temperatures.

A transformer operates on the principle of electromagnetic induction. When an alternating current passes through the primary winding, it creates a magnetic field that induces an alternating voltage in the secondary winding. The ratio of turns between the primary and secondary windings determines the voltage increase or decrease.

Transformers have better efficiency due to:

1. No Moving Parts: They have no moving parts which minimizes mechanical wear and losses.
2. Higher Output: They are designed to deliver power output efficiently with fewer losses, thus ensuring that a larger portion of input energy is converted to output energy.

The Buchholz relay functions as a safety device in transformers. It detects abnormal gas formation, which can indicate internal faults, and isolates the transformer from the supply to prevent further damage.

To calculate the secondary phase voltage, we use: $V_{(S)} = \frac{V_{(L(S))}}{\sqrt{3}}$ Substituting in the values: $V_{(S)} = \frac{380 V}{\sqrt{3}} \approx 219.39 V$

The transformation ratio (TR) can be calculated using: $TR = \frac{V_{(P)}}{V_{(S)}}$ Substituting the known values: $TR = \frac{2200 V}{219.39 V} \approx 10:1$

Using the turns ratio, we can deduce the number of secondary turns ($N_2$) as follows: $\frac{V_{(P)}}{V_{(S)}} = \frac{N_P}{N_S}$ Thus, $N_{(S)} = N_P \times \frac{V_{(S)}}{V_{(P)}}$ Substituting in: $N_{(S)} = 1500 \times \frac{219.39}{2200} \approx 149.58 \approx 150$

The transformer is a step-down transformer as the number of primary turns (N_P) is greater than the number of secondary turns (N_S).

Transformers can distribute electrical power effectively due to their ability to adjust voltage levels for different applications. When connected in star, they create a neutral point to supply single-phase and three-phase systems, making them versatile for both domestic and industrial use.