0195136047.pdf

460 AC POWER SYSTEMS

XC=

2202

3. 04 × 103

= 15. 92 

Hence,

C=

1

2 π× 60 × 15. 92

= 166. 6 μF

Note thatZ = 3 ZY(see Figure 4.2.1), orC =(^1 
 3 )CY, as it should be for a balanced case.

10.3 Power Transmission and Distribution

The structure of a power system can be divided into generation (G), transmission, (T), and

distribution (D) facilities, as shown in Figure 10.3.1. An ac three-phase generating system provides

the electric energy; this energy is transported over a transmission network, designed to carry power

at high or extrahigh voltages over long distances from generators to bulk power substations and

major load points; the subtransmission network is a medium to high-voltage network whose

purpose is to transport power over shorter distances from bulk power substations to distribution

substations. The transmission and subtransmission systems are meshed networks with multiple-

path structure so that more than one path exists from one point to another to increase the reliability

of the transmission system.

The transmission system, in general, consists of overhead transmission lines (on transmission

towers), transformers to step up or step down voltage levels, substations, and various protective

devices such as circuit breakers, relays, and communication and control mechanisms.

Figure 10.3.2 shows a typical electric-power distribution system and its components. Be-

low the subtransmission level, starting with the distribution substation, the distribution system

usually consists of distribution transformers, primary distribution lines or main feeders, lateral

G 1

G 2

To other

pool members

End user

End user

Transformer

Bus

End user

End user

To other

pool members

Generating

system

(13.8–24 kV)

Transmission

system

(138–765 kV)

Subtransmission

system

(34–138 kV)

Primary

distribution

(4–34 kV)

Subtransmission

distribution

(120–600 v)

Figure 10.3.1Typical power-system structure.