113
—
7. Operation of the switchgear
7.3 Service trucks
Instead of earthing, short-circuiting and testing
with Testing and Earthing truck (Figure 187) it is
possible to use the service trucks. These trucks
(optional accessories) are divided into three
different types:
Earthing truck without making capacity
These trucks carry out the same function as the
earthing switches without making capacity.
Therefore they do not have any capacity to earth
the live circuits under fault conditions. They are
used to ensure fixed additional earthing, as
required by the plant service and maintenance
procedures, as a further safety measure for
personnel. The use of these trucks anticipates
removal of the switching device from the
switchgear (circuit-breaker or contactor) and its
replacement with the truck. The panels preset for
use of earthing trucks are fitted with a key lock
which, if activated, prevents their racking-in. This
truck is available in two versions:
• Main busbar system earthing
• Power cable earthing
During the racking-in phase, the main busbar
earthing truck only lifts the top shutter and
earths the contacts connected to the top
branches (and therefore to the main busbar
system) by the switchgear structure. During the
racking-in phase, the power cable earthing truck
only lifts the bottom shutter and earths the
contacts connected to the bottom branches (and
therefore to the power cables) by the switchgear
structure. These trucks can also be used in the
bus-tie panels. In this case, they earth the two
sides of the main busbar system.
Earthing truck with making capacity
These trucks carry out the same function as the
earthing switches with making capacity. They
consist of circuit-breakers only fitted with top
(main busbar earthing) or bottom (power cable
earthing) terminals. The contacts without
terminals are short-circuited by means of a
copper bar and connected to earth by the
apparatus truck. They keep all the characteristics
of the circuit-breakers, such as full making
capacity and opening of the live circuits under
fault conditions. They are used to ensure
extremely effective earthing on circuits stressed
by a fault. They allow opening and closing
operations to be carried out rapidly with remote
electric control.
The use of these trucks anticipates removal of the
switching device from the switchgear (circuit-
breaker or contactor) and its replacement with
the truck. The panels preset for use of earthing
trucks are fitted with a key lock which, if
activated, prevents their racking-in. This truck is
available in two versions:
• Main busbar system earthing
• Power cable earthing
During the racking-in phase, the main busbar
earthing truck only lifts the top shutter and
presets the contacts connected to the top
branches (and therefore the main busbar system)
for closing to earth by the control.
During the racking-in phase, the power cable
earthing truck only lifts the bottom shutter and
presets the contact connected to the bottom
branches (and therefore to the power cables) for
closing to earth by the control. These trucks can
also be used in bus-tie panels. In this case, they
earth the two sides of the main busbar system.
Figure 186:
1 Contact system
2 Contact arms
3 Actuating bars
4 Earthing contact
5 Earthing module without short circuit switching
capability
Earthing truck without making capacity
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