INTRODUCTION
An electric power system has the following basic functions:
1.Generation of electric energy economically with minimum ecological disturbance.
2.Transfer of this energy to consumers with maximum efficiency and high reliability at practically constant frequency.
Large amount of power is generated at the generating stations.The present trend is to install bigger size of alternators to generate large amount of power to cater the required increasing demand.The site of the power station depends upon the type of power station. The new thermal station are being constructed at pit heads(near the coal mines) because of the higher cost of transportation of coal.Hydro-power station sites are governed by the availability of water resources.The nuclear plants are also situated remote from the centers of consumption due to safety reasons.Thus,the difficulty of getting power station sites near the consuming centers make it inevitable to transfer bulk of electrical energy through longer distances.Long-distance,bulk power transfer is only possible by high voltage transmission system.Extra high voltage (EHV) and ultra high voltage ( UHV) transmission systems have been developed in most of the countries for transporting energy from remote power stations.By EVH is meant the voltage above 220 kV. The voltages above 760 kV are called ultra high voltages(UHV).
BASIC STRUCTURE OF AN AC POWER SYSTEM
Electrical energy generated at generating stations is transported to remote load centers. Between a generating station and a consumer we have transmission,sub transmission and distribution levels of voltage.since the long distance transmission at high voltage is cheap and,low voltage are required for utility purposes,the voltage level goes on decreasing from the transmission system to the distribution system.An electrical power system may be divide into three main components,namely,the generating system,the transmission system,and the distribution system.
DISTRIBUTION VOLTAGE LEVEL
The component of an electrical power system connecting all the consumers in an area to the bulk power sources is called a distribution system.Bulk power substations are connected to generating stations by transmission lines.They feed a number of substation which are usually situated at convenient point near the load centres. A substation distributes the power to domestic,commercial and relatively small consumers.The consumers requiring larger blocks of power are usually supplied at sub transmission or even transmission levels.A bulk power station or a generating station usually supplies power to a subtransmission system.
SUBTRANSMISSION LEVEL
The operation of a subtransmission system is similar to that of a distribution system.It differs from a distribution system in the following manner:
1.A subtransmission system has a higher voltage level than a distribution system.
2.It supplies only bigger loads.
3.It supplies only few substations as compared to a distribution system which supplies a number of loads.
TRANSMISSION LEVEL
A transmission system is quite different from either a subtransmission or a distribution system.It has a higher voltage level than a subtransmission system.It supplies only large blocks of power to bulk power stations or very big consumers.The third and the main consideration in which a transmission system differs from either a subtransmission or a distribution system is that it interconnects the neighbouring generating stations into a power pool.Thus, a transmission line performs two functions: First,the transport of energy from generating stations to bulk receiving stations,and second,the interconnected of two or more generating stations.The interconnection of two neighbouring subtransmission system is also done by transmission lines.
An electric power system has the following basic functions:
1.Generation of electric energy economically with minimum ecological disturbance.
2.Transfer of this energy to consumers with maximum efficiency and high reliability at practically constant frequency.
Large amount of power is generated at the generating stations.The present trend is to install bigger size of alternators to generate large amount of power to cater the required increasing demand.The site of the power station depends upon the type of power station. The new thermal station are being constructed at pit heads(near the coal mines) because of the higher cost of transportation of coal.Hydro-power station sites are governed by the availability of water resources.The nuclear plants are also situated remote from the centers of consumption due to safety reasons.Thus,the difficulty of getting power station sites near the consuming centers make it inevitable to transfer bulk of electrical energy through longer distances.Long-distance,bulk power transfer is only possible by high voltage transmission system.Extra high voltage (EHV) and ultra high voltage ( UHV) transmission systems have been developed in most of the countries for transporting energy from remote power stations.By EVH is meant the voltage above 220 kV. The voltages above 760 kV are called ultra high voltages(UHV).
BASIC STRUCTURE OF AN AC POWER SYSTEM
Electrical energy generated at generating stations is transported to remote load centers. Between a generating station and a consumer we have transmission,sub transmission and distribution levels of voltage.since the long distance transmission at high voltage is cheap and,low voltage are required for utility purposes,the voltage level goes on decreasing from the transmission system to the distribution system.An electrical power system may be divide into three main components,namely,the generating system,the transmission system,and the distribution system.
DISTRIBUTION VOLTAGE LEVEL
The component of an electrical power system connecting all the consumers in an area to the bulk power sources is called a distribution system.Bulk power substations are connected to generating stations by transmission lines.They feed a number of substation which are usually situated at convenient point near the load centres. A substation distributes the power to domestic,commercial and relatively small consumers.The consumers requiring larger blocks of power are usually supplied at sub transmission or even transmission levels.A bulk power station or a generating station usually supplies power to a subtransmission system.
SUBTRANSMISSION LEVEL
The operation of a subtransmission system is similar to that of a distribution system.It differs from a distribution system in the following manner:
1.A subtransmission system has a higher voltage level than a distribution system.
2.It supplies only bigger loads.
3.It supplies only few substations as compared to a distribution system which supplies a number of loads.
TRANSMISSION LEVEL
A transmission system is quite different from either a subtransmission or a distribution system.It has a higher voltage level than a subtransmission system.It supplies only large blocks of power to bulk power stations or very big consumers.The third and the main consideration in which a transmission system differs from either a subtransmission or a distribution system is that it interconnects the neighbouring generating stations into a power pool.Thus, a transmission line performs two functions: First,the transport of energy from generating stations to bulk receiving stations,and second,the interconnected of two or more generating stations.The interconnection of two neighbouring subtransmission system is also done by transmission lines.
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