The working principle of a distribution transformer is based on the principles of electromagnetic induction. A distribution transformer is used to step down high voltage levels from power grids to lower voltages suitable for distribution to residential, commercial, and industrial areas. Here is a simplified explanation of its working principle:
- Primary Coil (High Voltage Side): The primary coil, also known as the high voltage (HV) winding, is connected to the high voltage power source, such as a power transmission line. It consists of a large number of turns of insulated copper or aluminum wire.
- Core: The primary and secondary coils are wound around a laminated iron core. The core provides a low reluctance path for the magnetic flux generated by the transformer.
- Magnetic Flux: When an alternating current (AC) flows through the primary coil, it creates a changing magnetic field around the coil. This changing magnetic field induces a magnetic flux in the iron core.
- Secondary Coil (Low Voltage Side): The secondary coil, also known as the low voltage (LV) winding, is connected to the load or the distribution network. It has fewer turns of wire compared to the primary coil, which allows for a lower voltage output.
- Electromagnetic Induction: The changing magnetic flux in the core induces a voltage in the secondary coil according to Faraday’s law of electromagnetic induction. The induced voltage is proportional to the ratio of the number of turns in the secondary coil to the number of turns in the primary coil.
- Voltage Step-Down: The induced voltage in the secondary coil is lower than the input voltage in the primary coil due to the difference in the number of turns. The transformer acts as a voltage step-down device, reducing the high voltage from the primary side to a lower voltage suitable for distribution.
- Efficiency and Losses: Distribution transformers are designed to be highly efficient to minimize power losses during the transformation process. However, some losses, such as core losses (hysteresis and eddy current losses) and copper losses (I^2R losses), occur in the transformer.
By regulating the turns ratio between the primary and secondary coils, distribution transformers can step down the voltage to the desired level while efficiently delivering electrical power to distribution networks and end-users.
The main types of losses in a distribution transformer are:
Copper Losses (I²R Losses): These losses occur due to the resistance of the transformer windings. When current flows through the windings, there is a power loss proportional to the square of the current (I²) multiplied by the resistance (R) of the windings. Copper losses are also influenced by the temperature rise of the windings.
Iron Core Losses: Iron core losses consist of two components: hysteresis losses and eddy current losses.
a. Hysteresis Losses: Hysteresis losses occur due to the magnetization and demagnetization of the transformer’s iron core as the alternating current passes through it. This causes molecular friction within the core material, resulting in energy losses.
b. Eddy Current Losses: Eddy current losses are caused by the circulating currents induced in the iron core due to the changing magnetic field. These circulating currents generate heat in the core material, leading to energy losses.
Both hysteresis losses and eddy current losses contribute to iron core losses and are dependent on the magnetic properties of the core material and the frequency of the alternating current.
Stray Losses: Stray losses are additional losses that occur in a transformer due to various factors, including leakage flux, electromagnetic radiation, and losses in structural components such as clamps and tanks. These losses are typically smaller than copper losses and core losses but can still contribute to the overall efficiency reduction of the transformer.
Efficiency is a critical factor in transformer design, and minimizing these losses is essential to improve the overall efficiency of the transformer. Design techniques such as using high-quality magnetic core materials, optimizing winding design, and implementing efficient cooling systems are employed to reduce these losses and enhance the performance of distribution transformers.