Total Losses in Power Distribution & Transmission Lines-(Part 1)

TOTAL LOSSES IN POWER DISTRIBUTION & TRANSMISSION LINES-PART 1

INTRODUCTION:

Power generated in power stations pass through large & complex networks like transformers, overhead lines, cables & other equipments and reaches at the end users. It is fact that the Unit of electric energy generated by Power Station does not match with the units distributed to the consumers. Some percentage of the units is lost in the Distribution network. This difference in the generated & distributed units is known as Transmission and Distribution loss. * Transmission and Distribution loss are the amounts that are not paid for by users. * T&D Losses= (Energy Input to feeder(Kwh)-Billed Energy to Consumer(Kwh)) / Energy Input kwh x100 * Distribution Sector considered as the weakest link in the entire power sector. Transmission Losses is approximate 17% while Distribution Losses is approximate 50%. * There are two types of Transmission and Distribution Losses

(1) TECHNICAL LOSSES:

The technical losses are due to energy dissipated in the conductors, equipment used for transmission Line, Transformer, sub- transmission Line and distribution Line and magnetic losses in transformers. * Technical losses are normally 22.5%, and directly depend on the network characteristics and the mode of operation. * The major amount of losses in a power system is in primary and secondary distribution lines. While transmission and sub-transmission lines account for only about 30% of the total losses. Therefore the primary and secondary distribution systems must be properly planned to ensure within limits. * The unexpected load increase was reflected in the increase of technical losses above the normal level * Losses are inherent to the distribution of electricity and cannot be eliminated. * There are two Type of Technical Losses.

(A) PERMANENT / FIXED TECHNICAL LOSSES:

Fixed losses do not vary according to current. These losses take the form of heat and noise and occur as long as a transformer is energized. * Between 1/4 and 1/3 of technical losses on distribution networks are fixed losses. Fixed losses on a network can be influenced in the ways set out below. * Corona Losses. * Leakage Current Losses. * Dielectric Losses. * Open-circuit Losses. * Losses caused by continuous load of measuring elements * Losses caused by continuous load of control elements.

(B) VARIABLE TECHNICAL LOSSES

Variable losses vary with the amount of electricity distributed and are, more precisely, proportional to the square of the current. Consequently, a 1% increase in current leads to an increase in losses of more than 1%. * Between 2/3 and 3/4 of technical (or physical) losses on distribution networks are variable Losses. * By increasing the cross sectional area of lines and cables for a given load, losses will fall. This leads to a direct trade-off between cost of losses and cost of capital expenditure. It has been suggested that optimal average utilization rate on a distribution network that considers the cost of losses in its design could be as low as 30 per cent. * joule losses in lines in each voltage level * impedance losses * Losses caused by contact resistance.

MAIN REASONS FOR TECHNICAL LOSSES:

(1) LENGTHY DISTRIBUTION LINES:

In practically 11 KV and 415 volts lines, in rural areas are extended over long distances to feed loads scattered over large areas. Thus the primary and secondary distributions lines in rural areas are largely radial laid usually extend over long distances. This results in high line resistance and therefore high I2R losses in the line. * Haphazard growths of sub-transmission and distribution system in to new areas. * Large scale rural electrification through long 11kV and LT lines.

(2) INADEQUATE SIZE OF CONDUCTORS OF DISTRIBUTION LINES:

The size of the conductors should be selected on the basis of KVA x KM capacity of standard conductor for a required voltage regulation but rural loads are usually scattered and generally fed by radial feeders. The conductor size of these feeders should be adequate.

(3) INSTALLATION OF DISTRIBUTION TRANSFORMERS AWAY FROM LOAD CENTERS:

Distribution Transformers are not located at Load center on the Secondary Distribution System. * In most of case Distribution Transformers are not located centrally with respect to consumers. Consequently, the farthest consumers obtain an extremity low voltage even though a good voltage levels maintained at the transformers secondary. This again leads to higher line losses. (The reason for the line losses increasing as a result of decreased voltage at the consumers end Therefore in order to reduce the voltage drop in the line to the farthest consumers, the distribution transformer should be located at the load center to keep voltage drop within permissible limits.

(4) LOW POWER…