Electrical Power Systems

ig. 15.6: Case of negative x 1.
Analysis of Sag and Tension 387
15.5 RULING SPAN OR EQUIVALENT SPAN (SPANS O UNEQUAL
LENGTH)
When a transmission line consists of spans of unequal length, theoretical tension of each span
depends to its own length. In fact, this is not possible with suspension insulators since the
insulator strings would swing so as to eqnalize the tension in each span. However, it is possible
to assume a uniform tension between dead-end supports by defining ruling span or equivalent
span.
Equivalent span or ruling span is defined as:
where
L e =
or L e =
3
3
L1+ L2+ L3+ ... + L
L + L + L + ... + L
n
å
i= 1
n
å
i= 1
3
1 2 3
L
L
3
i
i
3
n
L e = ruling span or equivalent span
L i = each individual span in line.
An approximate equivalent span or ruling span can be calculated as
n
...(15.67)