VISAX
MV Metal-clad Switchgear
T&D
Power Distribution
VISAX: A New Generation of Medium Voltage Switchgear
Simple architecture
The innovative design of VISAX is
based on new metal-clad
switchgear architecture (fig.1)
where all the functional elements
are mounted in a direct line
between the busbar and the cable
terminals.
VISAX combines the advantages of
the most advanced withdrawable
switchgear and the benefits
associated with simplified
architecture: reliability, functional
safety, security.
Original architecture
The circuit breaker engages directly
with the busbar, the number of
connections and isolating elements
is significantly reduced.
Low voltage compartment
Busbar compartment
Circuit breaker compartment
Cable compartment
Compartment for the extraction of hot gases
1
Fig. 2 - Lateral cross-section of
conventional switchgear.
2
Fig. 1 - Direct power line.
3
4
6
5
Fig. 3 - Lateral cross-section
of VISAX switchgear.
1
2
3
4
5
6
2
- Busbar secured to the connection spouts
- BLV self-isolating circuit breaker
- Multipurpose bushing
- Current transformers
- Cable terminals
- Earthing switch
Fig. 4 - Longitudinal circuit breaker.
The originality of VISAX :
an isolating circuit breaker
The circuit breaker is incorporated
in a rotary isolator, thus forming a
dual-purpose module : circuit
breaker and isolator.
This technical innovation has been
made possible by the use of a
vacuum circuit breaker, the poles of
which are arranged longitudinally
(the three poles of the operating
mechanism are aligned along a
single axis).
Description of the 3 positions
• In the "service" position (Fig. 6a),
the poles of the circuit breaker
are in the vertical position. Once
the circuit breaker has been
opened, the poles can rotate to
reach the "disconnected"
position. They therefore withdraw
from the connection spouts to
adopt a horizontal position
(isolated position).
During this rotation, a metal
shutter is automatically drawn
across and obstructs access to the
busbar.
VISAX switchgear concept
Innovation through rotation
The isolation function between the
busbar and the cables is provided
by 90° rotation of the
isolator/circuit breaker (Fig. 5).
• In the "disconnected" position
(Fig. 6b), the front face of the
cubicle may be opened in
complete safety. Tests and checks
may then be carried out.
Fig. 6b - “Disconnected” position or Test :
circuit breaker disengaged through rotation
(isolated position).
• The withdrawal of the circuit
breaker (Fig. 6c) is then possible
after insertion of an isolating
screen between the multipurpose
bushing and the circuit breaker.
Disconnection is thus performed by
rotation of the circuit breaker.
Fig. 6a - “Service” position: circuit breaker
engaged (opening/closure).
Fig. 6c - “Removed” position (the handling
trolley is not shown ) : testing and checking
operations may be performed on the circuit
breaker.
Fig. 5 - Disconnection by rotation.
3
VISAX: user safety
(1)
(2)
The circuit breaker compartment after
withdrawal : no access to live sections.
VISAX metal-clad switchgear
In order to guarantee the safety of
the operator during checking
operations, the circuit breaker
compartment on VISAX switchgear
is fitted with an earthed metal
shutter (1). When the circuit breaker
rotates, this shutter is automatically
drawn across to separate the
busbar and circuit breaker
compartments.
When the circuit breaker is in the
isolated position, access to the
connection spouts and the cable
terminals is therefore protected: the
door may be opened in complete
safety.
Enhanced interlocks
and safety devices
Apart from the conventional
interlocks, a particularly reliable
chain of interlocks has been
developed. These mechanical
interlocks are simple, robust and
are located, for the most part, on
the front of the unit.
For total reliability, the preassembled interlock plate has been
designed as an independent subassembly, requiring no adjustment
during integration into the unit. The
reliability of the interlocks is thus
enhanced for the greater safety of
the personnel.
Safety in use
The original architecture of VISAX,
combined with the presence of a
gas extraction duct, make it
possible to install the unit flush to
the wall.
In this way, all the steps involved in
switchgear operation are performed
from the front of the unit for
complete user safety.
The optional motorisation of
isolation and earthing operations is
fully integrated into the interlocking
devices. Therefore, in the event of
the loss of the auxiliary power
supply, the manual operations can
be performed without risk to the
operator, as the mechanical
interlocks then take priority.
A unit which allows true wall mounting.
Prior to withdrawal of the circuit
breaker, an isolating screen (2)
must be inserted so as to prohibit
access to the multipurpose bushings
and thus provide the user with full
protection.
... and space saving
The fact that the unit can be
mounted against a wall allows
space saving in substations,
making it possible to overcome
certain dimensional restrictions.
4
Internal arc withstand
The rigid construction of the VISAX
unit, incorporating exhaust flaps on
each compartment, ensures perfect
internal arc withstand.
Designed and tested according to
the latest standard, CEI 298
Appendix AA, each compartment
has an internal arc withstand which
conforms to criteria 1 to 6.
Enhanced personnel safety is
offered as manual operations are
affected with the doors closed.
The gases are channelled in
a special compartment
An advantage specific to VISAX
architecture is to allow, thanks to a
single duct located at the rear of the
unit, the collection and the
evacuation of the hot gases in the
event of internal arcing.
This duct, a standard component in
VISAX units, is designed to collect
the gases from independent flaps,
specific to each of the
3 compartments: cables, circuit
breaker and busbar.
Should a problem arise in one of
the compartments, it does not affect
the others in any way.
A single duct for the extraction of hot
gases.
Operator safety
In this way, the hot gases are
extracted at the back of the unit,
towards the top, as far as possible
from the operator, for improved
safety.
The safety conditions within
substations are thus enhanced. The
hot gases coming from these ducts
can easily be collected from each
unit by a conduit (optional) and
expelled outside the substation.
5
Reliability of information and ease of operation
Operation from the front
panel
The original architecture of VISAX
provides the user with a new
dimension in reliability and safety,
both in terms of operation and
readings.
VISAX architecture allows all
actions associated with the circuit
breaker/isolator and the earthing
switch to be carried out in complete
safety from the front face of the unit
by direct action on the operating
mechanism.
Actions on the circuit breaker
(opening/closing) while it is at the
service position are performed
directly via the push buttons located
on the front door of the unit,
whereas isolation of the circuit
breaker is performed by inserting
the isolating crank handle through
the door.
Certainty of positional
information
The front-to-back layout of all the
elements in the main circuit enables
the operator to see directly the axes
of both the circuit breaker and the
earthing switch.
Status and positions clearly visible, without
intermediate or interface systems.
The operator is left in no doubt, of
the "service" or "disconnected"
positions therefore benefiting from
inherent reliability.
The position of the earthing switch is clearly
visible to the operator.
Operation from the front panel.
6
Fig. 1 - Status of the circuit breaker.
Self evident operation and
indication
The information essential to
operation of the switchgear is laid
out ergonomically and grouped on
the front face, in areas clearly
identified by specific blue
colouring. The operator thus has
access to the main information by
simply reading:
the slightest ambiguity, the status of
the circuit breaker: open, closed,
isolated, in operation.
• from the legend plate located on
the door of the circuit
breaker compartment (fig. 1),
The earthing switch mimic
diagram
The information on its status
correspond to reality without the
slightest risk of error, as the
position indicator forms an integral
part of the axis of the earthing
switch.
• from the band located on the
right hand side of the cable
compartment (fig. 2).
The circuit breaker mimic
diagram
The single line drawing of the unit
and the positions of the circuit
breaker are indicated by the mimic
diagram. The mimic diagram
allows the operator to view, without
Furthermore, the circuit breaker
rating plate, the operation counter
and the status of the spring of the
operating mechanism are clearly
visible from outside the unit, with
the door closed.
Mimic diagrams reflecting
reality in all circumstances
The mimic diagram (fig. 3) of the
single line drawing on the front
face of the unit incorporates the
position indicators directly. This
Fig. 2 - Status of the earthing switch.
mimic diagram is entirely made up
of mechanical elements which
remain operational even in the
event of loss of power supply to the
switchboard.
The isolation distances and the
position indicators are totally
reliable and are clearly visible from
the front face of the unit.
Fig. 3 - Circuit breaker status: clear, distinct information.
“Service” position
circuit breaker closed
“Disconnected” and Test position
circuit breaker open
circuit breaker closed
circuit breaker open
7
A solution suited to your applications
VISAX : created for a modern
world of communication
The environment is changing and is
leading to an evolution in needs,
particularly in the fields of
communication and remote control.
The basic design of VISAX units
incorporates the features of remote
control and remote signalling.
the very start of the development
process.
Motorisation : an easy
solution
The motorisation of the circuit
breaker/isolator and earthing
switch was taken into account from
On the motorised version,
operations can be performed
manually if required, and the
mechanical interlocks take priority
in all circumstances.
Main characteristics
Rated voltage (kV)
7.2/12
17.5
24
28
75
38
95
50
125
≤ 2500
≤ 2500
≤ 2500
≤ 2500
≤ 2500
≤ 2500
Short time current
Rms. value (kA 3s)
Peak value (kAp)
16/25/31.5/40*
40/63/80/125*
16/25/31.5
40/63/80
16/25
40/63
Breaking capacity (kA)
16/25/31,5/40
16/25/31,5
16/25
25
25
25
IP 3X(1)
IP 3X(1)
IP 3X(1)
2150/2350
625/825
2150/2350
625/825
2450/2650
750/950
650(3)/800(2)
800
900
900
650(3)/800(2)
800
900
900
800/1000(2)
1000
1000
1100
1260
1460
1460
1420
1420
1550
500
550
600
Rated withstand voltage
50/60 Hz - 1 min (kV rms)
Lightning impulse (kVp)
Rated current
Cubicle (A)
Busbar (A)
Internal arc withstand (kA 1s)
(kA 0.15s)
Degree of protection of the enclosures
Height with low voltage compartment (mm)
Height of low voltage compartment (mm)
Width (mm)
Depth (mm)
≤ 1250
1600
2000
2500
A
A
A
A
(4)
16-25 kA
31.5 kA
40 kA
Approximate weight of a cubicle
excluding voltage transformer (kg)
40
* Excepted earthing switch 1sec - 100 kAp - (1) for any other degree of protection, please contact us - (2) equipped with withdrawable voltage transformers
(3) short time current ≤ 25 kA - (4) forced ventilation for 2500A - Please contact us.
8
VISAX : a complete range
Incoming (or outgoing) unit fitted with withdrawable Voltage Transformers (VT) and surge arrester
(fixed VT also available).
Load break switch - fuse unit (ISR type load break switch).
Metering/measurement unit with fixed VT and busbar earthing.
Coupling - bus riser unit with withdrawable VT.
9
The essential components of the VISAX concept
Compartment for inter-unit low voltage
cableway, with customer terminal block
accessible.
Busbar compartment
Optional: the compartment may be partitioned
between units and the busbars isolated.
Multipurpose bushing. (1)
Hot gases extraction duct (standard)
A duct collecting the gases from the ducts of a
series of units is proposed as an option.
Cable compartment
From 1 to 4 single core cable per phase
(according to power handled) may be connected
to the multipurpose bushings.Three-core cables
may also be connected.
(1)
(3)
(2)
Earthing switch. (2)
Voltage transformer. (3)
The multipurpose bushing performs
the following functions:
• location of ring type current
transformers,
Incoming/outgoing and
coupling/bus riser units may be
fitted with voltage transformers, with
or without fuses.
• power connection between circuit
breaker and cable compartments,
• section for the connection of
medium voltage cables,
They are available in two formats,
fixed, easy to dismantle, or
withdrawable, which can be
extracted from the front face of the
unit.
• capacitor divider for signalling
the presence of voltage on the
cables.
VISAX is fitted with an earthing
switch with making capacity on
short circuit current.
10
The isolating circuit breaker
The BLV circuit breaker constitutes
the key element in VISAX units.
During isolation, the assembly
comprising the poles and the
operating mechanism rotates. The
circuit breaker is a self-supporting
module which only exerts minimal
forces on the mounting points.
Consequently, the various
operations only require low energy
and the long-term reliability is
further enhanced.
Fig. 1 - Operating mechanism.
The elements making up the
BLV circuit breaker
The circuit breaker is fitted with a
spring-loaded mechanical
operating mechanism (fig. 1)
specially developed and optimised
for the specific characteristics of the
vacuum interrupters. Its design
based on a single shaft and spiral
spring for both opening and
closing operations guarantees
exceptional reliability and safety.
The vacuum interrupters are located
in single-pole enclosures (fig. 2).
These enclosures, made of synthetic
resin, provide not only the required
level of insulation, but also the
complete protection of the
interrupters from external damage.
Fig. 2 - Pole.
(A)
BLV type self-isolating rotative vacuum
circuit breaker
(B)
(D)
(C)
Fig. 3 - Vacuum interrupter.
11
The vacuum interrupters (fig. 3) use
the most advanced technology to
control the arc: the axial magnetic
field. They are essentially made up
of a sealed ceramic enclosure
containing the highly pure copper
contacts. One of these contacts is
fixed (A), the other moving (B) by
means of a metal bellows (C). A
screen (D), located around the
contact zone, collects the metal
vapours created by the arc.
ALSTOM Transmission & Distribution - Appareillage moyenne tension - Boulevard de la Résistance - B.P. 4019 - 71040 Mâcon Cédex 9
Tel. : +33 (0)3 85 29 35 00 - Tlx : 800878 F - Fax : +33 (0)3 85 29 35 01 - www.alstom.com
A067 - AMT - 12/2000 - © - ALSTOM - 2000. ALSTOM 2000 - The logo ALSTOM and their frameworks are trademarks and service trademark applications of ALSTOM. The other names mentioned, registered or not, are the property of their respective companies - COMIMPRESS - 03 85 32 25 40