TYPES & CONSTRUCTION OF TRANSFORMERS POWER IN AN IDEAL TRANSFORMER Lecture No.3 By: Sajid Hussain Qazi

TYPES & CONSTRUCTION OF TRANSFORMERS The principal purpose of transformer is to convert ac power of one voltage level to ac power of same frequency at another voltage level. Transformers are also used for variety of purposes (e.g., voltage sampling, current sampling, and impedance transformation). Transformers are constructed on one of two types of cores. - Core Type, - Shell Type

Core Type: Its construction consists of a simple rectangular laminated piece of steel with the transformer windings wrapped around two sides of rectangle.

Shell Type: This type of construction consists of a three- legged laminated core with windings wrapped around the center leg.

In both types, the core is constructed of thin laminations, electrically isolated from each other to minimize the eddy currents. Generally primary & secondary windings in a physical transformer are wrapped one on top of the other, with low winding innermost. Such a arrangement serves two purposes. It simplifies the problem of insulating the high winding from the core. It result in much less leakage flux than would be in case if the two windings were separated by a distance on the core. Transformers are given different names depending on their use in power system.

UNIT Transformer: It is connected with the output of generator to step its voltage up for transmission levels. SUBSTATION Transformer: It is placed at the end of transmission lines to step the voltage down from transmission to distribution levels. DISTRIBUTION Transformer: It takes distribution voltage & step it down to the final voltage at which the power is actually used. All the devices are essentially same; the only difference is their intended use.

In addition to these transformers, two special type transformers are used in electric machinery & power system. Potential Transformer Current Transformer Potential Transformer Current Transformer

POWER IN AN IDEAL TRANSFORMER The power supplied to the primary circuit is given by the equation…. Here θp is the angle between primary voltage and current. The power supplied by secondary circuit to load will be… Here θs is the angle between secondary voltage and current.

The power out of ideal transformer is… Since voltage and current angles are unaffected by an ideal transformer, θp-θs=θ The primary and secondary windings of an ideal transformer have same power factor. The power out of ideal transformer is… Applying turns ratio equation gives... Thus the output power of an ideal transformer is equal to input power. and