Explanation:
The heating of the transformer is due to a combination of factors, including the heating effect of current and hysteresis loss. Here is a detailed explanation of why these factors contribute to the heating of the transformer:
1. Heating effect of current:
- When current flows through the transformer's windings, it encounters resistance, which results in the generation of heat.
- This is known as the heating effect of current, according to Joule's law, which states that the heat produced is directly proportional to the square of the current and the resistance.
- The resistance of the transformer windings, combined with the high currents flowing through them, leads to significant heat generation.
2. Hysteresis loss:
- Hysteresis loss is caused by the repeated magnetization and demagnetization of the transformer's core as the alternating current passes through it.
- During each cycle, the core experiences a reversal of magnetization, leading to energy losses in the form of heat.
- These losses are due to the inherent characteristics of the magnetic material used in the transformer's core, which has a limited ability to magnetize and demagnetize efficiently.
- Hysteresis loss contributes to the overall heating of the transformer.
3. Cooling with oil:
- Transformers are equipped with oil-filled tanks that circulate the oil to cool the transformer.
- The oil absorbs the heat generated by the transformer and carries it away through convection.
- The hot oil rises to the top of the tank, where it is cooled by contact with the tank walls or cooling fins.
- It then flows back down to the bottom of the tank, completing the cooling cycle.
4. Intense sunlight:
- The option D, intense sunlight at noon, is not a significant factor in the heating of the transformer.
- While sunlight can contribute to the overall ambient temperature, it is not the primary cause of the heating of the transformer.
In conclusion, the heating of large transformers is primarily due to the combination of the heating effect of current and hysteresis loss. The circulating oil helps to dissipate the heat and maintain the transformer's temperature within acceptable limits. The option C, both the heating effect of current and hysteresis loss, is the correct answer.

Heating of Large Transformers

The heating of large transformers is a result of various factors, and the cooling mechanism involves circulating oil. Let us discuss the reasons for heating and the role of circulating oil in cooling the transformers.

1. Heating Effect of Current
When a current flows through a conductor, it generates heat due to the resistance offered by the conductor. This phenomenon is known as the heating effect of current. In large transformers, significant amounts of current flow through the various windings, particularly in the primary winding. This current produces heat, contributing to the overall heating of the transformer.

2. Hysteresis Loss
Hysteresis loss is a phenomenon that occurs in transformers due to the continuous magnetization and demagnetization of the transformer's core. This process results in the generation of heat. Hysteresis loss is caused by the energy required to realign the magnetic domains within the core material. In large transformers, this loss can be substantial, leading to increased heating.

3. Both Current Heating and Hysteresis Loss
The heating of large transformers is not solely due to the heating effect of current or hysteresis loss alone. It is a combination of both factors. The current flowing through the windings and the hysteresis loss in the core material together contribute to the overall heating of the transformer.

4. Circulating Oil for Cooling
To mitigate the heating of large transformers, a cooling system is employed, which usually involves the circulation of oil. The oil acts as a coolant and absorbs the heat generated within the transformer. It flows through the transformer, carrying away the excess heat and releasing it to the surrounding environment through cooling equipment such as radiators or heat exchangers.

Conclusion
In conclusion, the heating of large transformers is a result of both the heating effect of current and hysteresis loss. The circulating oil serves as a cooling mechanism, absorbing the generated heat and dissipating it to maintain the transformer's temperature within safe operating limits.