Introduction,Merits,Demerits of Interconnected System.

Introduction:

The power system in which a number of generators of the different area are operated in parallel to meet a total load of this area is known as an interconnected power system.The transmission lines which links one generator of one area to the another generator of another area is called tie lines. Almost all generating companies have tie-line interconnections to neighboring utilities. Tie lines allow the sharing of generation resources in emergencies and economics of power production under normal conditions of operation.

fig: an alternator interconnected system

For the two or more generating stations(alternators) may be connected in parallel; the following conditions must be fulfilled:

»Their phase sequence must be the same (phase A to phase A,phase B to phase B & phase C to phase C)

»Terminal voltage alternator must be equal.

»The waveform of emf generated by both alternator should be in phase.

»The frequency of the both alternator must be equal.

»The percent impedance of both alternators should be same.

Merits of interconnected system:

1)The peak load can be exchanged between the generation stations. From load curve if there is peak load demand which is more than related capacity of the plant then the excess load can be shared by other interconnected stations.

2) It is possible to use the older and inefficient plants with grid system for short duration to supply peak demands. Thus older plants can be effectively used with this system.

3)With interconnected grid system the economical operation of the plant is possible factor. The less efficient plants can be made to operate as peak load plants. The total load is arranged in such a way that more efficient plants can be used as base load stations which can work continuously throughout the year at high load.

4)Various interconnected plants have their load curves different due to which maximum demand on the system is reduced as compared to sum of individual maximum demands on various stations.Thus the effective capacity of the system increased as their is improvement in diversity factor.

5)The reliability and continuity of the supply is improved with interconnected grid system. With fault condition occurring in any one station, the supply can be maintained with the help of other stations.

6)larger generator units can be employed to reduce capital cost per kW.

7)Reliability of supply system increases.i.e.if one generator fails to operate or is under maintainance,remaining generators can feed to the load.

Demerits of interconnected system:

1)Fault current and fault level increases.This results higher rating of protective devices.

2)Long length transmission lines and tie lines are required which results increased cost of transmission.

3)Capacity increases with requirement of frequent synchronization of generators.Stability of system is more concerned for interconnected system.