-
7/31/2019 Ohl Reference Manual
1/8
Midlands Electricity plc
OVERHEAD LINES REFERENCEMANUAL
FIRST EDITION
PUBLISHED 1985
CONVERTED 03-01-04
-
7/31/2019 Ohl Reference Manual
2/8
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.
-
7/31/2019 Ohl Reference Manual
3/8
-
7/31/2019 Ohl Reference Manual
4/8
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.
-
7/31/2019 Ohl Reference Manual
5/8
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.
-
7/31/2019 Ohl Reference Manual
6/8
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
--
-
7/31/2019 Ohl Reference Manual
7/8
-
7/31/2019 Ohl Reference Manual
8/8
