Sub-station
Earthing Equipment
This range of equipment provides portable earthing
on outdoor high voltage substations during maintenance or erection. It has
been designed to provide safe and secure clamping where connections are
to be made to dirty or heavily oxidised copper/aluminium busbars or stubs
and to meet the requirements of modern 132, 275 and 400kV substations.
Design and Construction
The equipment is constructed from light materials for ease of handling
but is of a robust design to withstand a reasonable amount of rough handling.
The clamps, operating poles, sockets and cables have safely withstood
their respective mechanical type tests and/or short time current type
tests as specified in ESI 41-21 Section 5.
Equipment
EARTH END CLAMPS
The spring loaded feature of these clamps makes them suitable for application
by hand to copper or aluminium earth bars in any natural condition.
LINE END CLAMPS
All types whether spring loaded or not should be applied by means of an
operating socket attached to an insulated operating pole. The design of
all Line End Clamps is such that once hooked over a busbar they become
self-supporting whilst the operating screw is tightened or loosened.
OPERATING SOCKETS
Made from light alloy material and available as either an S9D (ESI-S1)
or an CEA/S (ESI-S2) type. These essentially support the Line End Clamp
when fitted to an operating pole and also actuate the operating screw
of the Line End Clamp when being secured in position or being removed.
Socket type S9D supports clamps being applied in an upward direction.
Socket type CEA/S is spring loaded to control the operating screw of the
Line End Clamp.
OPERATING POLES - INSULATED
These should be limited to a length of 16ft. (4.88m) as it is considered
that this is the maximum length of pole with clamp and lead attached which
can normally be handled with safety. Poles of these lengths are made up
in multiple sections usually of 4ft. lengths. The joints are machined
to provide a rigid assembly and include a double sided snap action spring
locking device. All details are in accordance with Specification ESI 41-21.
EARTH LEADS
Only cables from approved manufacturers and fitted with approved compression
end lugs and support springs in accordance with specification ESI 41-21
are supplied for earthing leads, for connecting between the Line End Clamps
and the Earth End Clamps. The conductor resistance per 1000m at 20 deg.
does not exceed 0.208 ohms.
Selection of clamps and cables
CURRENT RATING
Portable earthing equipment for use in open type H.V. substations consists
of Line End Clamps, Earth End Clamps, Earth Leads, Operating Poles and
Operating Sockets. These components are suitable for assembly into sets
of earthing equipment and the maximum current/time rating of one set is
17.5kA rms for 2 seconds, except when applied to a 10mm diameter line
conductor the maximum current rating of the conductor/equipment combination
is 13.1 kA for 2 seconds.
The Clamps are suitable for application to existing Line
and Earth End conductors. One set of earthing equipment is the maximum
that can be safely applied by a person of average strength. At locations
where the fault current level exceeds the specified current/time rating
of 17.5kA for 2 seconds it is intended that more than one set of equipment
be used. It should be noted that with solidly earthed neutrals the single
phase fault current can be up to 1.2 times the three phase fault current.
Guide to suitable Number of Leads
|
Prospective Single Phase
Symmetrical Fault Current
|
Number of Leads
|
|
17.5 kA
|
1
|
|
31.5 kA
|
2
|
|
47.25 kA
|
3
|
|
63 kA
|
4
|
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