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As we know the three phase AC is used for transportation of electricity . during the transportation, both the active and reactive power balance must be maintained between the generation and utilization AC power. Good quality of electrical power system means both the voltage and frequency to be fixed at desired values irrespective of change in loads that occurs randomly.
Frequency is mostly dependent on the active power and voltage is mostly dependent on the reactive power. Demand for power increasing every day, because of the various activities of the consumers. The load of the system varies from instant to instant. In a power system both active and reactive power demand are not constant, so steam input to generator or water input to hydro-generator must be continuously regulated to match the active power demand, failing which the machine speed will vary with consequent change in frequency and it may be highly undesired.
Also, excitation of generator is continuously regulated to match the reactive power demand with reactive power generation; otherwise the voltaes at various system buses may go beyond the given limits.
Necessity of maintaining a constant frequency in a power system operation:
- All AC motors should required constant frequency supply so as to maintained speed constant.
- With continuous process industry, it affects the operation of the process itself.
- For synchronous operation of various units in a power system, it is necessary to maintain frequency constant.
- Frequency affects amount of power transmitted through interconnecting lines.
- The operation of a transformer below the rated frequency is not advantageous. When frequency goes below rated frequency at constant system voltage then the flux in the core increases and then the transformer core goes into the saturation region.
Therefore, it is necessary to maintain frequency constant so that the power stations runs satisfactory in parallel. Also, the various motors operating on thee system run at the desired speed and correct time is obtained from synchronous clocks in the system. Also all the devices function properly.
Voltage control in an electrical power system is important for proper operation for electrical power equipment to prevent damage such as overheating of generators and motors, to reduce transmission losses and to maintain the ability of the system to withstand and prevent voltage collapse.
