ELECTRICAL POWER III (EEC 222)
With the aid of a simple diagram, explain what is meant by interconnected power system. (5 marks)
State three (3) advantages and two (2) disadvantages of interconnected power system. (5 marks)
1. Exchange of peak load: An important advantage of IPS is that the peak load of the power stations can be shared if the load curve of the system shows a peak demand that is greater than the relative capacity of the plant.
2. It ensure economical operation: This is done in such a way that sharing of loads among the stations is arrange in such a way that more efficient stations work continuously throughout the year at high load factor and the less efficient plant work on peak load hours only.
3. Higher system security: Operation of the power factor is to maintain system security.
4. Reduced plant reserved capacity: Every power system (P.S) is required to have a standby unit for emergencies. However when several power system are constructed in parallel the reserved capacity of the system is reduced, this increases the efficiency of a system.
5. Increased reliability of supply: Interconnected power station (I.P.S) increases the reliability of supply. If a major breakdown occur in one station continuity of supply can be maintain by the other healthy stations.
6. Use of older plant: Power system makes it possible to use older plants and less efficient plant to carry peak loads of short duration, although such plant may be drastically drained easily when used alone, yet they have sufficient capacity to carry short peaks of load when interconnected with other modern plant.
7. Increases diversity factors: The load curves of different I.P.S are generally different, the result is that the maximum demand in different system. In other words the diversity of the system is improved.
Thereby increasing the effective capacity of the system.
1. It requires more investment for load control centers and automatic controls.
2. With synchronous tie (tie lines) the frequency disturbance of one area are transferred to the adjacent area.
3._Cascade tripling and overall blackout may occur in large interconnected power system
4. Technical problems of large I.P.S regarding planning and control are more complex.
5. It requires more automation, high reliability and security of each system.
A 2-wire feeder ABC has a load of 120A at C and of 60A at B, both at power factor 0.8 lagging. The impedance AB is (0.04+j0.08)Ω and that of BC is (0.08+j0.12)Ω if the voltage at the far end C is to be maintained at 400v, determine the voltage at A and B (10 marks)