Requirement for distribution and transmission system
Requirements are;
(1) voltage regulation
(2) Dependability
(3) Balance voltage
(4) Efficiency
(5) Frequency
Some requirements we are going to be discussing below are;
(1) Voltage regulation: A voltage variation has a large effect upon the operation of power, machinery and lights.
A motor is designed to have its best characteristics at the rated voltage and consequently a voltage that is too high or too high will result in a decrease in efficiency
If the fluctuation in the voltage are sudden. These may cause the tripling of circuit breakers and consequent interruptions to service. Usually the voltage at the generator terminal where this is done, in some cases, the voltage variation at the load may be made sufficiently small by keeping the resistance and reactance of the line and feeders low.
(2) Dependability: are important requirement of electric supply is to furnish uninterrupted service. The loses which an industrial consumer sustains due to the failure of electric power supply are usually vastly greater than the actual value of the power that it would use during this period.
It is on account of expenses of idle workmen and machines and other overhead charges.
Interruption to service cause irritation and are sometimes positively dangerous to life and property.
For example, failure of power in hospitals, in crowded theatres and store may lead to a very grave consequence. Therefore, it is the duty of electric supply companies to keep the power system going and to furnish uninterrupted service.
(3) Balance voltage: it is very important that the poly phase voltage should be balanced.
If an unbalanced polyphase voltage is supplied to a consumer, synchronous or induction motors, it will result in a decrease in the efficiency of his machinery and also decrease in maximum power.
(4) Efficiency: the efficiency of a transmission system is not of much importance in itself.
The important economic feature of the design being the layout of the system as a whole so as to perform the requisite function of generating and delivering power with a minimum overall annual cost. The annual cost can be minimized to a considerable extent by taking care of power factor of the system. It is because loses, in the line and machinery are largely determined by power factor.
Therefore, it is important that consumers having loads of low power factor should be penalized by being charged at a higher rate per KWh than those who take power at high.
Power factor loads of low power also require greater generator capacity than those of high power factor (for the same amount of power) and produce large voltage drops in the lines and transformers.
(5) Frequency: the frequency of the supply system must be maintained constant. It is because a change in frequency would change the motor speed, thus interfering with the manufacturing operations.
(6) Sinusoidal wave form: the alternation voltage supplied to the consumer should have a sine wave form.
It is because by-harmonics which might be present would have detrimental effect upon the efficiency and maximum power output of the connected machinery.
Harmonics may be avoided by using generator of good design and by avoidance of high flux densities in transformers.
(7) Freedom from inductive interference: power lines running parallel to a telephone lines produce electrostatic and electromagnetic field disturbances. This field tends to cause objectionable noises and hums in the apparatus connected to communication circuits.
Inductive interference with telephone lines may be avoided by limiting as much as possible the amount of zero-sequence and harmonic current and by the proper transposition of beta power lines and telephone lines.
