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ECE320_Chapter_3

# ECE320_Chapter_3 - ECE 320 Energy Conversion and Power...

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1- 1 ECE 320 Energy Conversion and Power Electronics Spring 2009 Instructor: Tim Hogan Chapter 3: Transformers (Textbook Chapter 2) Chapter Objectives In this chapter you will be able to: Choose the correct rating and characteristics of a transformer for a specific application Calculate the losses, efficiency, and voltage regulation of a transformer under specific operating conditions. Experimentally determine the transformer parameters given its ratings. Utilize the per unit system. 3.1 Introduction Transformers do not have moving parts, nor are they energy conversion devices, however their ability to modify the current-voltage characteristics of a given load or source, make them invaluable components in energy conversion systems. They are utilized for power applications and in low power signal processing systems. One application in power transmission is the use of transformers on a transmission line utility pole commonly seen as a cylinder with a few wires sticking out. These wires enter the transformer through bushings that provide isolation between the wires and the tank. Inside the tank there is an iron core commonly made of silicon-steel laminations that are 14 mils (0.014”) thick. The insulation often used is paper with the whole coil system immersed in insulating oil. The oil increases the dielectric strength of the paper and helps to transfer heat from the core/coil assembly. An drawing of one such distribution transformer is shown in Figure 2.2 in your textbook. Connection of the transformer to the transmission lines can take several electrical configurations. A relatively simple connection to a 2.4 kV three phase transmission line is shown in Figure 1. 2400 volt three-phase three-wire Δ primary system A B C 2400 2400 2400 H 1 H 2 X 1 X 2 X 3 120 volt one-phase two-wire service Figure 1. Example configuration of a distribution pole transformer connection to three phase power lines to provide 120 (V) service to your home.

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1- 2 2400 volt three-phase three-wire Δ primary system A B C 2400 2400 2400 H 1 H 2 X 1 X 2 X 3 120 (V) 120 (V) 240 (V) Figure 2. Example configuration of a distribution pole transformer connection to three phase power lines and provides 120 (V) and 240 (V) service. If a neutral line is also part of the three phase transmission line (perhaps between the substation and your home), then the connection could be made as shown in Figure 3. 4160Y/2400 volt three-phase four-wire Y with neutral B C 4160 4160 4160 H 1 H 2 X 1 X 3 120 (V) 120 (V) 240 (V) A N N 2400 2400 2400 X 2 Figure 3. Distribution transformer connection to provide 120 (V) and 240 (V) service from a 4160Y/2400 (V) four-wire transmission line.
1- 3 For a three phase line at the service end, a system could be connected to a four wire three phase transmission line source as shown in Figure 4 below. 4160Y/2400 volt three-phase four-wire Y with neutral primary service B C 4160 4160 4160 H 1 H 2 X 1 X 3 208 (V) 208 (V) 208 (V) A N N 2400 2400 2400 X 2 H 1 H 2 X 1 X 3 X 2 H 1 H 2 X 1 X 3 X 2 B C A N three-phase four-wire Y grounded neutral secondary service 120 (V) 120 (V) 120 (V) Figure 4. Three phase to three phase distribution transformer connection providing a

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ECE320_Chapter_3 - ECE 320 Energy Conversion and Power...

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