EEE 360 Chapter 7: Transformers
Transformers Invention of transformers revolutionized electrical energy transmission A transformer can increase or decrease the voltage, which correspondingly results in the decrease or increase of the current The development of the transformer permitted the increase of the transmission voltage to a few hundred kV while simultaneously reducing the current, consequently allowing the transport of large amounts of energy over a few hundred miles
Construction The transformer has a laminated iron core, and primary and secondary windings. The primary winding is supplied by alternating current (ac) voltage, which generates an ac magnetic flux in the iron core. Figure 7.1 Basic components of a single-phase transformer.
Construction This magnetic flux generates ac voltage in the secondary winding. The loading of the secondary winding produces current in both the secondary and primary windings . Figure 7.1 Basic components of a single-phase transformer.
Construction The magnetic field transports the electric energy from the primary to the secondary. The ratios of voltages and currents in the primary and secondary sides depend on the turns ratio ( T ), which is the ratio of the turns in the primary ( N P ) and secondary ( N S ) coils. Figure 7.1 Basic components of a single-phase transformer.
Construction The turns ratio is the ratio of the number of turns in the primary ( N P ) and secondary ( N S ) coils Figure 7.1 Basic components of a single-phase transformer. S P N N T
Construction Figure 7.2 Single phase transformer arrangement In a real transformer, the primary and secondary windings are placed on the same leg of the core. This arrangement improves magnetic coupling and reduces the leakage flux of the windings.
Construction Figure 7.3 Polarity for transformer Primary winding terminals are marked H 1 and H 2 Secondary terminals are denoted as X 1 and X 2 Each transformer coil can be wound either clockwise or counterclockwise The winding directions determine the voltage polarity
Construction Figure 7.3 Polarity for transformer In Figure 7.3(a) both windings are wound in the same direction Consequently, the secondary (V S ) and primary (V P ) voltages are in phase as shown in the graph.
Construction Figure 7.3 Polarity for transformer In Fig. 7.3(b) the secondary winding is wound in the opposite direction of the primary This results in the primary and secondary voltages being reversed (180° out of phase)
Construction The small transformer is built with the E and I shaped lamination and the winding. The E and I sheets are stacked and insulated screws press the laminated iron core together. a) Lamination b) Iron core with winding Figure 7.4 Small transformer construction
Construction Figure 7.5 Winding Construction Thin paper or plastic insulation is placed between the layers.
You've reached the end of your free preview.
Want to read all 151 pages?
- Winter '16
- Volt, SPX Transformer Solutions