Optimizing Distribution Voltage To Reduce Technical Losses
- The drop of voltage is design consideration for the distributors the feeder size is based on the current carrying capacity of the conductor.
- In transmission systems, a voltage regulation of as much as 40%, in some cases be considered satisfactory. We are interested in the most economical method of working.
- The effect of increase in voltage is known to us Raising the voltage n times means reducing the conductor size to 1/n2 that of the original (assuming a constant efficiency of transmission). On the other hand a higher voltage involves higher cost of the system by way of increased insulation, switch gear and terminal apparatus.
- Thus, there is an optimum voltage of transmission for a particular system.
We will proceed as follows :
Power to be transmitted voltage of generation and length of transmission line are assumed to be known. We choose a standard voltage of transmission and work out the following costs :
- Transformers at generating and receiving end.
- Switch gear and lightning arrestors.
- Insulators.
- Supports and
- Conductor costs.
- All these items when added give the cost of transmission for the voltage assumed . Similar calculations should be made for various other voltages. Finally, a curve can be plotted for cost against the transmission voltage.
- A typical curve of this type is shown in Figure A the lowest point on the curve representing optimum voltage to be chosen.
- When in doubt about two voltages for which the costs do not differ appreciably it is always desirable to choose higher voltage as larger voltages are easier to control than large currents.
- Another advantage with higher voltages is the ease with which an increased demand of the load can be met when necessary.
- As a rough guide the working voltage may be taken as 0.6 kV per km (in practice it varies from 0.4 kV to 0.9 kV).
- According to modern American practice economical line to line voltage (in kV) = 5.5√ 62L+3P/100 where, L is the distance of transmission lines in km and is the estimated maximum kW per phase to be delivered over a single circuit.
- Another empirical formula used is Voltage in kV (line to line) = 5.5√ 0.62L=kVA/150 where, kVA is the total power, L in km.