Page 23 - Handbook of Electrical Engineering

2 HANDBOOK OF ELECTRICAL ENGINEERING

Table 1.1. Voltages used in different countries for generation,
distribution and transmission
Low voltage High voltage High voltage
generation and generation and transmission
three-phase distribution less than 75 kV
consumers (volts) (kilovolts) (kilovolts)
910 18 7.2 ∗ 70 24.5
660 16 6.9 69 ∗ 24
600 ∗ 14.4 6.6 ∗ 66 ∗ 23
525 13.8 ∗ 6.5 65 22
500 13.2 ∗ 6.3 60 20
480 12.6 6.24 50 19
460 12.5 6 ∗ 46 15
440 ∗ 12.47 5.5 45
420 12.4 5 44
415 ∗ 12 4.8 38
400 ∗ 11.5 4.16 ∗ 36
380 ∗ 11.4 4 35
346 11 ∗ 3.3 ∗ 34.5 ∗
277 10.4 3 ∗ 33 ∗
260 10 2.4 31.5
254 ∗∗ 9 2.3 30
240 ∗∗ 8.9 27.6
230 ∗∗ 8.4 27.5
220 ∗∗ 8.3 27
208 8 25
200 7.3 24.9
190
Notes ∗ Commonly used voltages in the oil industry.
Notes ∗∗ Commonly used as single-phase voltages.

in their final form at the completion of the project. They act as a diary and record the development
of the work. Single-line diagrams are also called ‘one-line diagrams’.
At this stage the engineer can begin to prepare a load schedule for each subsidiary switchboard
and motor control centre, and a master schedule for the main switchboard. The development of the
single-line diagrams during the project is discussed in sub-section 1.7.

The master load schedule will give an early estimate of the total power consumption. From
this can be decided the number of generators and utility intakes to install. The kW and kVA ratings
of each generator or intake will be used to determine the highest voltage to use in the power
system. Table 1.1 shows typical voltages used throughout the world for generation, distribution and
transmission of power at oil industry plants, see also sub-section 3.7.

1.2 LOAD SCHEDULES

Each switchboard will supply power to each load connected to it and in many cases it will also supply
power to switchboards or distribution boards immediately downstream. Hence the input power to a