POWER DISTRIBUTION
The electric energy obtained in the electric generation process must be transported to the end user by electric conductors without large resistive power losses in the distribution process. A key part of the strategy for doing so involves using transformers to increase the voltage to hundreds of thousands of volts to minimize loss to heat in the transmission wires. The three high voltage conductors shown on the utility pole at right indicate that the power distribution is "three-phase", with each conductor 120 degrees in phase away from each of the others. If each section of the large insulators can withstand a working voltage of 10,000 volts, these conductors may be operating at something like 150,000 volts. Distribution transformers are normally located at a service drop, where wires run from a utility pole or underground power lines to a customer's premises. They are often used for the power supply of facilities outside settlements, such as isolated houses, farmyards or pumping stations at voltages below 30 kV. Another application is the power supply of the overhead wire of railways electrified with AC. In this case single phase distribution transformers are used. The number of customers fed by a single distribution transformer varies depending on the number of customers in an area. Several homes may be fed off a single transformer in urban areas; rural distribution may require one transformer per customer. A large commercial or industrial complex will have multiple distribution transformers. Padmount transformers are used in urban areas and neighborhoods where the primary distribution lines run underground. Many large buildings have electric service provided at primary distribution voltage. These buildings have customer-owned transformers in the basement for step-down purposes. In a secondary network system as used in urban areas, many distribution transformers may be connected in parallel, each equipped with its own network protector circuit breaker to isolate it from the secondary network in case of a fault. Distribution transformers are also found in the power collector networks of wind farms, where they step up power from each wind turbine to connect to a substation that may be several miles (kilometres) distant.
