Span Lengths of Electrical Transmission Line
- The distance between the two adjacent poles is known as span length. It is generally denoted by ‘l’ (L) and specified in meters.
- The location of the supports (towers) depends upon the profile of the land along which transmission line is to be run. This means the span length may not be equal.
- When successive spans are unequal, changes in load or temperature will bring unequal changes in tension in the different span.
- It is very difficult to calculate the sag and tension for each and every span and then to make adjustment while erecting the transmission line.
- Therefore it is necessary to have calculations assuming uniform tension in the conductor between the two tension towers.
- It can be shown mathematically that the variations in the tension with variation in load or temperature are within permissible limits.
- Hence for preparing a sag calculations , the equivalent span is used . The equivalent span length can be calculated as follows.
- Where L1, L2, L3 are the lengths of the individual spans between the two tension towers.
- It is to be noted that the method of sag template for locating towers should not be used for long spans as well as where the slope of the profile is very steep . In such cases it is desirable to make actual calculations for sag and tension.
