0195136047.pdf

10.3 POWER TRANSMISSION AND DISTRIBUTION 463

G 1 G 2

To bus 6

To bus 7

Bus numbering 2

5

1

4

L 6

L 1

L 7

L 2

L 3

L 4 L 5

3

Load

Generator

Transformer

Bus

Circuit breaker

Transmission line

Line numbering

Tie-line connection

with neighboring

system

Figure 10.3.4One-line (single-line) diagram of part of a typical three-phase power system.

VS VR

Load

SS = PS + jQS SR = PR + jQR

Line impedance

Source bus

(sending end)

Load bus

(recieving end)

Figure 10.3.5Simple model of part of

an operating power system.

where subscriptRdenotes receiving end, NL indicates no-load, and FL stands for full-load. The
TLVR for our example can be seen to be 12.8% prior to power factor improvement, and 10.2%
after power factor improvement.
The two components of electric service aredemandandenergy. Demand is the maximum
level of real power which the electric utility must supply to satisfy the load requirements of its
customers. Energy is the cumulative use of electric power over a period of time. The demand
component of the electric-rate structure represents the capital investment needed by the utility
to provide the generation, transmission, and distribution facilities in order to meet the maximum
customer demand. The energy component represents the operating costs, which include fuel and
maintenance that must be provided to meet the demand requirements over a period of time.
Theload factoris the ratio of the actual energy usage to the rated maximum energy usage over
a given period. A low load factor is indicative of a substantial period during which the capacity