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Midlands Electricity plc
OVERHEAD LINES REFERENCEMANUAL
FIRST EDITION
PUBLISHED 1985
CONVERTED 03-01-04
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OVERHEAD LINES REFERENCE MANUALISSUE 1 1985
INDEX
1. Conductor Vertical and Inclined Clearances.
2. Conductor Horizontal Clearances.
3. Conductor Spacing.
4. Electrical Clearances.
5. Conductor Clearances Other Lines.
6. Arc Gaps.
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OVERHEAD LINES REFERENCE MANUALSECTION 1 PAGE 2ISSUE 1 1985
3. CONDUCTOR SPACING
The minimum conductor spacing at mid span determines the crossarm lengthfor horizontal formation or the vertical spacing. The conductor spacing at thesupport should be 0.65 x maximum sag at mid span. As the sag varies as thespan length squared, the maximum span for any crossarm length can bedetermined. A first approximation for crossarm spacing at 33 and 11kV is:-
= Span length100
NB When a change in conductor formation from horizontal to verticaloccurs the span should be restricted to a maximum of 60 metreswith standard crossarms and standard vertical spacing.
4. ELECTRICAL CLEARANCES
4.1 Fixed Conductor Clearances
The minimum clearances tabled are measured at positions where there isno mechanical movement of the live conductors such as at insulators andbushings.
METRES
LOCATION 66kV 33kV 11kV LV REMARKS
Phase/Phase 0.79 0.43 0.23 0.15 BS 162
Phase/Earth 0.69 0.38 0.178 0.025 BS 162
Jumper/Ground 4.3 4.3 4.3 4.3 O/H Regulations
Clearances at 400, 275 and 132kV are determined by design.
4.2 Moving Conductor Clearances
Where conductors and jumpers are subject to movement by wind, fallingice, fault current or birds and may swing and oscillate at differentfrequencies, the fixed conductor clearances should be increased andunsupported jumper lengths kept to a minimum (2.5m maximum). Themid span situation is covered by Clause 3.
The clearances for down leads requires detailed design considerations.
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OVERHEAD LINES REFERENCE MANUALSECTION 1 PAGE 3ISSUE 1 1985
5. CONDUCTOR CLEARANCES OTHER LINES
5.1 Parallel Lines
Where lines are routed to run parallel the separating distance should notbe less than 1.5 x tallest line plus any difference in ground levels.
5.2 Double Circuit Lines
The circuit spacing is determined at the supports and limits the maximumspan length to achieve the necessary referred spacing at mid span.
Typical spacing at the supports is given as follows:-
132kV 66kV 33kV 11kV
Horizontal 5.6 4.57 3.35 3.35
Vertical 3.75 1.52 1.1 1.1
5.3 Line Crossing
When lines of different voltages cross, the higher voltage shall always be
uppermost.
The vertical separation at the point of crossing as tabled below, arebased on the upper line being at its maximum operating temperature andmaximum sag and the lower line unloaded and at an ambienttemperature of 5.6oC. The figures tabled are read for the highestvoltage line and refer to lower lines at any voltage.
METRES
400kV 275kV 132kV 66kV 33kV 11kV LV
4.57 4.57 3 2.44 2.44 1.83 -
The point of crossing should be planned to be near a support of the upperline where the sag will be at a minimum distance between live conductorsof the lower line and the upper line support shall be 15 metres.
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OVERHEAD LINES REFERENCE MANUALSECTION 1 PAGE 4ISSUE 1 1985
6. ARC GAP SETTINGS
METRES mm
LOCATION400kV 275kV 132kV 66kV 33kV 11kV
PlantLines1.6km from S/SBeyond 1.6km
-
2.542.79
-
1.902.13
0.66
0.991.12
0.53
0.610.61
2 x 95
--
2 x 25
--
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