Page 329 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Fig 2

The electric supply is transmitted at different voltages through over head lines and the types of power lines are
furnished below:
a Low voltage line ( should not exceed 250V)
b Medium voltage line ( should not exceed 650V)
c High voltage line (should not exceed 33000V (33 KV)

d Extra high voltage line (above 33KV)
Sag in Overhead Lines: The difference in level between points of supports and the lowers point on the conductor
is called ‘Sag’.

Fig 4 (a) shows a conductor suspended between two equal level supports A and B. The conductor is not fully
stretched but is allowed to have a dip. The lowest point of the conductor is O and the sag is S. Fig 4(b) shows
unequal level supports.
Conductor sag and tension: This is an important consideration in the mechanical design of overhead lines. The
conductor sag should be kept to a minimum in order to reduce the conductor material required and to avoid extra
pole height for sufficient clearance above ground level.
Method of erection of poles: The poles to be erected may be brought to the pit location by manual labour or by
improvised carts. Then the pole may be erected in the pit. Wooden support poles may be utilized to facilitate lifting
of the pole at the pit locations as in Fig 5.

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CITS : Power - Electrician & Wireman - Lesson 106-116