ALUMINIUM CONDUCTOR SAG & TENSION CALCULATION

INCLINED SPAN

ALUMINIUM CONDUCTOR SAG & TENSION CALCULATION – INCLINED SPAN

INTRODUCTIONThe purpose of this document is to calculate the conductor sag and tension by using Parabolic Method. Calculation of conductor tension is to ensure that it shall not greater that the terminal load capacity of equipments where the conductor are to be terminated.

Among the factors that influencing the conductor tension are conductors span, type, weight and number of parallel conductor per phase. Weight of conductor spacer if any, also to be considered during the design stage.

LEGENDS Horizontal distance between support points [m].H Horizontal component of tension [kg]S1 Sraight-line distance between support points [m].D Sag measured vertically from a line through the points of conductor support to a line

tangent to the conductor [kg].DR Sag in right sub-span section [m].DL Sag in left sub-span section [m].TR Tension in right sub-span section [kg].TL Tension in left sub-span section [kg].h Vertical distance between support points [m].XL The horizontal distance from the left support point to the low point in the catenary [m].XR The horizontal distance from the right support point to the low point in the catenary [m].

DIAGRAM

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FORMULA

1) XL = S + Sh 2 8D

2) XR = S - Sh 2 8D

3) Sag at Mid SpanD = wS 2

8H

or

D = H cosh w√(s 2 + h 2 ) -1 2H

w

4) Actual Conductor Length (m)

L = S + (XL3 + XR3) w 2 6H2

5) DR = wX R 2 2H

or 2

DR = D 1 – h 4D

6) DL = wX L 2 2H

or 2

DL = D 1 + h 4D

7) TR = H + w DR

8) TL = H + w DL

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CALCULATIONSCalculation of Actual Conductor Length and Conductor Tension for AAC between CT and Line Disconnector. Type of conductor and conductor sagging shall be specified by the substation designer.

Figure 1. Section view shows inclined span between LISO and CT.

Figure 2. Measurement on inclined span between CT and LISO.

Design Data Type of conductor: All Aluminium Conductor Conductor size: 400mm2

No. of conductor/span: 2 Weight of conductor/length, w: 1145kg/km (refer to OEM) Span length (distance between support), S:

2.276m (measurement based on side view or plan view)

Condition of conductor span: Inclined span Conductor sagging, D: 0.15m Vertical distance between support points, h: 0.473m (measurement based on side view)

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1) Weight of conductor/length, wW = (1145kg/km ÷ 1000) x 2 (where no. of conductor/span = 2, or according

to design)= 2.29kg/m

2) XL = 2.28m + 2.28m x 0.473m 2 8 x 0.15m

= 2.0387m

3) XR = 2.28m - 2.28m x 0.473m 2 8 x 0.15m

= 0.2413m

4) H = 2.29kg/m x (2.28m) 2 8 x 0.15m

= 9.92kg

5) L = 2.28m + [(2.0387m)3 + (0.2413m)3] x [(2.29kg/m)2/{6 x (9.92kg)2}]= 2.36m

6) DR = 2.29kg/m x (0.2413m) 2 2 x 9.92kg

= 6.72 x 10-3m

7) DL = 2.29kg/m x (2.0387m) 2 2 x 9.92kg

= 0.48m

8) TR = 9.92kg + 2.29kg/m x 6.72 x 10-3m= 9.94kg= 97.37N

9) TL = 9.92kg + 2.29kg/m x 0.48m= 11.02kg= 107.99N

CONCLUSIONThe conductor tension must be less than the Terminal Load capacity of both CT and LISO, for any size of AAC selected.

Plan view of of typical substation arrangement need to be review to get the actual conductor span, where the span between equipment/support might be varies at different phases when view from the top.

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