Pylon transformer
From Wikipedia, the free encyclopedia
A pylon transformer is a transformer mounted on a pylon. Because of weight restrictions transformers for pylon transformers are only built for voltages under 30kV.
Pylon transformers are often used for the power supply of facilities outside settlements, such as farmyards or pumping stations at voltages below 30kV. Another application is the power supply of switch heatings from the overhead wire of railways electrified with AC. In this case single phase pylon transformers are used.
In North American utility practice, these devices are called "pole mount" transformers, or nicknamed "pole pigs", and are very commonly used for distribution in areas with overhead primary lines. An alternative to a pole pig is used on underground distribution systems. These transformers are mounted in locked steel cases mounted on a concrete pad on the customer's premises. These are called pad mount transformers. These are used in many urban areas and neighborhoods where the primary lines run underground.
Outside a typical house one can see one of these devices mounted on the electricity pole. It's a step-down transformer used to convert the high voltage (7200 or 14400 volts) down to the standard 120/240 volts used in the home. The high voltage distribution lines (7200 or 14400 volts in the US) attach to the two bushings on top. The low voltage wires (two hot wires and one neutral) attach to the three terminals on the side. The secondary winding is center-tapped and grounded, making the two end conductors "hot" with respect to the center tap. These wires run down to the electric meter and breaker panel inside the building. Connecting a load between either hot wire and the neutral gives 120 volts. Connecting between both hot wires gives 240 volts. This is the setup for single-phase power in the United States. If the power customer needs three-phase power, three pole pigs of the appropriate KVA rating are wired in either a wye or delta transformer bank. High voltage experimenters often use these transfomers in reverse (step-up) by feeding 120 or 240 volts into the secondary and drawing the resulting high voltage off the primary bushings, using it to power things like Jacob's Ladders and Tesla coils.
