17-05-2012, 05:23 PM
power transformer
power_transformers.ppt (Size: 1.63 MB / Downloads: 184)
INTRODUCTION
Electricity is a basic human need. It is to be gene-rated, transmitted, distributed and effectively used to meet energy needs. Government is committed to ensuring that every village in India is to be electrified throughGRAMIN VIDYUTIKARAN YOJNA Every village of this country will be provided with a connecting road, a telephone, safe drinking water and electricity. Power is a critical infra-structure for socio-economic development.
Three phase a.c. system at 50 Hz (60 Hz in USA) is used for generation, transmission, distribution and utilization of electri-cal power (for transmission, HVDC system is also used). Power transformers are necessary between consecutive voltage levels for raising or lowering a.c. voltage at the same frequency. As the transformation of voltages is carried out successively in generating stations, sub-stations, distribution systems and near load points, the total cumulative installed MVA capacity of the power transformers is approx. 6 times the cumulative installed MVA capacity of generators. With introdu-ction of Wind Mills and electricity generation using non-conve-ntional energy resources, this ratio has reduced to 5.5. Therefore, transformers are very important apparatus in the electrical network. Transformer is well known electrical equip-ment which deserves attention. It is costly and important equipment. Transformers should give reliable service of more than twenty years.
Reactors:
Reactors are equipment of transformer family. A reactor has a predominantly inductive coil.Reactors are used in the power system network for current limiting and for compensation of reactive power. There are two types of reactors: (1) Series reactors, connected in series for current limiting and(2) Shunt reactors, connected in shunt, for compen-sation of reactive power. Oil insulated Reactors are similar to transformers in external appearance and have some design features similar to those of power transformers. Air-core dry type reactor looks like a large coil.
PRINCIPLE OF OPERATION
transformer has two or more separate winding placed on a common magnetic core. It works on induction principle. The primary winding is supplied with alternating current of supply frequency. Thereby alternating magnetic flux of the same frequency is produced in the magnetic core. The flux linkage of the secondary winding also changes at the same frequency, resulting in induced e.m.f. of the same frequency in the secondary winding by electromagnetic induction.