Question

Which of the following has to be considered for overhead/underground electrical power transmission / distribution system?

a) The voltage at the consumer’s premises must be maintained within ± 4 or ± 6% of the declared voltage.

b) The transmission cost should be unduly excessive.

c) The insulation resistance of the whole system should be very high

d) The loss of power in the system itself should be a small percentage (about 10%) of the power transmitted.

1. (a), (b) and (d)
2. (a), (c) and (d)
3. (b), (c) and (d)
4. (a), (b) and (c)

Answer 1

Correct Answer - Option 2 : (a), (c) and (d)

• One important requirement of a distribution system is that voltage variations at consumer’s terminals should be as low as possible. The changes in voltage are generally caused due to the variation of load on the system.
• Low voltage causes loss of revenue, inefficient lighting, burning out of motors.
• High voltage causes lamps to burn out permanently and may cause the failure of other appliances.
• Therefore, a good distribution system should ensure that the voltage variations at consumer's terminals are within permissible limits. The statutory limit of voltage variations is ± 6% of the rated value at the consumer’s terminals.
• Insulation resistance should be approximately one mega-ohm for every 1,000 volts of operating voltage, with a minimum value of one mega-ohm.
• High voltage drops, below the permissible level, can have many negative consequences. These result in an increase in the system maintenance cost and a decrease in the safety and performance of the network. Operating electrical equipment below its rated voltage can be dangerous as well as reducing the expected lifetime of the equipment.
• Reducing the voltage by 10% will reduce the power output by 19%, since power output correlates to the voltage squared.
• The cost for over head transmission should be very economical i.e as low as possible.