The document discusses Alstom Grid's T155 gas-insulated switchgear (GIS) system. Key points: - The T155 GIS is suitable for 420-550kV networks and provides benefits like high reliability, availability, compact design, and accessibility. - It has over 44 years of experience with over 20,000 GIS bays installed worldwide. Components are designed and tested to high standards. - The T155 offers flexibility for different applications, layouts, and site constraints while minimizing space and costs. Its modular design also allows for future modifications and extensions.

1. Transmission networks are evolving into Smart Grids, integrating multiple
energy sources, optimising energy efficiency, and providing higher reliability and
availability. Alstom Grid T155 GIS offer solutions to face these new challenges.
GRID
T155
420 – 550 kV Gas-insulated Substations
The ALSTOM GRID T155 gas-insulated
switchgear (GIS) is ideal for such applica-tions
on 420 and 550 kV networks.
The T155 derives its extensive benefits from
ALSTOM GRID's active involvement in
SF6 switchgear technology for over 44 years,
during which over 20000 GIS bays have
been sold and installed around the world –
to the entire satisfaction of operators.
The T155 is continuously being upgraded,
reliably achieving all guaranteed ratings and
providing state-of-the-art technology.
Customer benefits
• High operational reliability
• Superior availability
• Excellent accessibility
• Modular design
• Increased compactness
Sustained improvements
ALSTOM anticipates the new requirements
resulting from changing market conditions
and customer priorities.
Research and development continuously
aims at improving the quality, performance
and reliability of products.
Using internationally recognised KEMA,
CESI and CERDA test laboratories, ALSTOM
closely follows-up technological develop-ments
and contributes to the technological
transformations of the future.
The ALSTOM quality-assurance system is
assessed and certified according to ISO 9001
and EN 29001 standards. It is subject
to unceasing improvements and is considered
an essential management tool throughout
the company.
Machining and manufacturing facilities use
the most modern technologies and ensure
the highest quality levels. From receipt of
order to delivery, thorough production and
engineering-flow planning associated with
computerised data-processing ensures that
deadlines and commitments are fully met.

2. Key system advantages
Proven design
T155 switchgear, based on its proven and
reliable ancestors, provides key customer
benefits. The main implemented tech-nologies
2
for enclosures, gaskets, insulators
and conductors have been validated by
several decades of field experience.
Optimal solutions
T155 switchgear is optimally suitable for all
types of single-line diagrams, arrangements,
building dimensions, environments and site
constraints.
All components have been designed to give
the T155 the highest flexibility:
• Individual customer solutions
• Clear and simple layouts
• Minimum space requirements
• Reduced substation construction costs.
Reliable operation
The T155's reliability can be attributed to
the following reasons:
• Professional experience and training of all
people involved in the industrial process,
from research and development designers
to site installation supervisors
• Minimum number of components and parts
GAS-INSULATED SUBSTATIONS T155
• Field-proven design principles
• Long-term experience – over 44 years
with GIS and over 50 years with circuit
breaker (CB) spring mechanisms
• ISO 9001 certified quality assurance
system
• Comprehensive development and labora-tory
testing.
Life cycle costs are dropped down to the
lowest.
Short manufacturing,
installation and commissioning
times
T155 advanced concepts make it possible to
reduce engineering, manufacturing, instal-lation
and commissioning times. Amongst
other reasons for these time reductions, the
following points deserve mentioning:
• Components and arrangements are highly
standardised, thus reducing engineering
lead times
• Support frames are simply bolted to the
concrete slab or floor by means of clas-sical
anchoring bolts, with no need of
embedded sectional rails, thanks to mini-mum
dynamic stresses
• Very little structural steelwork is neces-sary
• Proper sizing of transport units allows
convenient handling
• Most low voltage cables are fitted with
plug-in connectors
• Comprehensive factory tests ensure that
equipment is ready-to-operate.
Accessible components
The switchgear arrangement and the loca-tion
of the operating mechanisms (circuit-breakers,
disconnectors and earthing
switches) definitely provide the highest
degree of accessibility, thus bringing many
advantages:
• Safe operation
• Easy servicing with no use of heavy
equipment
• Convenient retrofits, changes and further
extensions
• Short dismantling and equipment adjust-ment
times, thanks to busbar coupling
elements.
Adaptability
Not only is the T155 the ideal product to
design substations according to any single-line
diagram (single busbar, double busbar,
one circuit-breaker and a half, etc.), but it is
also optimal for gas-insulated modules.
OPTIGIM® T155 gas-insulated modules
enable the creation and/or extension of air-insulated
substations with lower space
requirements, while benefitting from safer
and more reliable gas-insulated switchgear.
The T155 GIS is also suitable for future
modications and extensions, thus optimi-sing
capital costs.
1 Circuit breaker
2 Spring-operated mechanism
3 Disconnector
4 High-speed earthing switch
5 Low-speed earthing switch
6 Current transformer
7 Cable connection

3. GAS-INSULATED SUBSTATIONS T155
3
Adapted aluminium enclosures
Enclosures are made of aluminium alloys,
cast or welded, each material being selec ted
for different reasons:
• Low electrical resistance, which mini-mises
touch voltage, creates an efficient
electromagnetic shielding (return current
and primary current are nearly equal) and
reduces resistive losses
• Non-magnetic behaviour which entails
no magnetic losses
• High resistance to corrosion, making it
unnecessary to paint enclosures and
internal surfaces and ensuring long-term
gas tightness and flange-to-flange con-tact
resistance quality (despite there
being no technical need to do so, external
surfaces are painted regardless, for a
long-lasting attractive look)
• Light weight, which makes handling easy,
minimises static loads and reduces civil
works.
Perfect SF6 sealing
The ALSTOM sealing system uses original
patented gaskets, which actually provide
three concentric seals and ensure that sub-station’s
gas leakage rate is less than
0.5% per year.
Safe insulators
Conductors and live parts are fitted to cast
epoxy-resin insulators, made of special
high-quality materials and manufactured
in ALSTOM's own workshops. Optimized
shapes and long creepage distances jointly
ensure the highest long-term voltage with-stand,
within resin and gas.
Components
Adequate SF6 accessories
Each SF6 compartment has a filling valve,
moisture absorber, safety pressure relief
valve and a temperature-compensated
density switch or sensor. Density thresholds
can be tested without depressurising the
main gas compartment. Digital monitoring
systems offer valuable solutions for SF6
management and trend analysis.
State-of-the-art circuit breaker
Each T155 circuit breaker pole is equipped
with its own spring mechanism. Each
pole contains two breaking chambers. The
chambers use high-performance breaking
technology with an optimum combination
of both puffer and thermal effects. The
use of two interrupting units per pole ensures
full compliance with the IEC's latest and
most stringent standards, even for high-level
ratings such as 550 kV and 63 kA. The
circuit breaker has been fully type-tested
under all operating conditions and conse-quently
can be used for all types of networks
and applications.
Grading capacitors ensure uniform voltage
distribution between the interrupting ele-ments.
Design, manufacture, assembly and
quality control provide the highest levels of
both mechanical and electrical endurance,
which means that no reconditioning is
required before at least 25 years, under
normal operating conditions.
High quality conductors
Connecting conductors are made of tubular
aluminium with high-grade, silver-plated
contacts at the ends. The sliding feature
allows thermal expansion without transmit-ting
mechanical stress to insulators.
Specific design provides ample angular
deflection for easier and shorter assembling
or dismantling operations.
Design, manufacturing and testing is per-formed
in accordance with most stringent
international standards, ensuring the
highest mechanical withstand and degree
of safety.
Technical data
Rated voltage kV 420 – 550
Rated frequency Hz 50/60
Rated lightning impulse withstand voltage kV 1425 – 1550
Rated power frequency withstand voltage kV 650 – 710
Rated current for busbars A up to 6300
or feeders A up to 4000
Rated short time current (3 s) kA up to 63
Rated breaking current kA up to 63
Application Indoor/ Outdoor
Other values on request

4. Superior spring mechanisms
ALSTOM’s experience with circuit breaker
spring mechanisms spans over 70 years
and amounts to more than 90000 units
produced – customers have repeatedly
expressed their deep satisfaction with them.
These mechanisms are called full-spring
mechanisms since they have no pressurised
(hydraulic or pneumatic) driving fluid.
Contrary to hydraulic or pneumatic mecha-nisms
4
(even when the fluid is used for
transmission only), ALSTOM’s spring
mechanisms are not likely to leak, they
forever store their energy and do not prema-turely
age due to frequent motor starts and
pressure top-ups. Operation times do not
depend on temperature and pressure, thus
making the right use of synchronising relays
(see below). The use of a spring mechanism
at such voltages and ratings is only possible
due to ALSTOM's long-term experience in
the fields of spring-operated mechanisms
and circuit breakers.
Control of switching surges
Depending on overhead line (OHL) para-meters
and network ratings, OHL switching
surges may be mitigated by using one or
several of the following means:
• Synchronising relay
• Additional surge arresters
• Insertion closing resistor.
For reactor switching, a synchronising relay
may be associated with the mandatory
surge arresters required for protection of
this sensitive equipment.
Thanks to its spring mechanism, the T155
circuit breaker features perfect timing
stability, a pre-requisite to its association
with a synchronising relay.
Safe disconnectors
All three disconnector (DS) poles are con-nected
to a common 3-pole electrical
mechanism via a sturdy mechanical linkage.
Clear and safe indication of the main con-tacts
position is provided by a reliable indi-cator
directly fitted to the linkage. This indi-cator
is well-visible from the operating level.
Totally safe insulation between energised
and de-energised sections of the substation
is provided thanks to long gaps between
open contacts and proper dielectric design.
Disconnectors reliably switch capacitive
currents which occur when switchgear sec-tions
are energised or de-energised, as well
as commutation currents caused by busbar
transfers. All performances have been
demonstrated according to the latest appli-cable
standards.
High power earthing switches
Earthing switches (ES) may have switching
capabilities or not. Those with these capa-bilities
are fast-operated (high-speed type),
not only on closing but also on opening, by
means of a spring released at the end of
both operations. High-speed ES are there-fore
capable, not only of making the full
short-circuit current, but also of interrupting
(according to most stringent standard spe-cifications)
currents associated with parallel
overhead lines. The latter capability is widely
and reliably achieved thanks to the specific
high-speed opening feature of the T155
earthing switch. Properly selected ES, either
high or low-speed, may be electrically
insulated from the enclosures by removing
an external link, thus conveniently enabling
current or voltage injection tests for timing,
resistance measurement or protection check
purposes.
All three ES poles are connected to a com-mon
3-pole electrical mechanism via a
sturdy mechanical linkage. The contact
position indicator, which is common to the
three poles of low-speed ES and fitted to
each pole of high-speed ES, is reliable and
clearly visible at operating level.
Field-proven busducts
Tens of kilometres of ALSTOM gas-insulated
busducts are installed around the world,
thus demonstrating an unsurpassable field
experience. Not only can these busducts
match all physical constraints, but the GIS
and its high voltage terminations can also
be arranged in the most suitable way.
ALSTOM spring mechanisms have few
moving parts, require almost no maintenance,
need no on-site adjustment and stand
out due to their long service life. Sturdy
design assures superior reliability. Adapted
travel curve and damping entail low dynamic
loads on the floor and adjacent GIS com-ponents.
Therefore, mechanical ageing is
sharply reduced and civil works are less
expensive.
GAS-INSULATED SUBSTATIONS T155

5. GAS-INSULATED SUBSTATIONS T155
5
Busducts can be installed either above
ground, or in trenches, tunnels, or shafts. This
makes it possible to locate HV substations
within underground power plants for instance,
thus enabling operators to locate step-up
power transformers underground too.
Thermal expansion is dealt with by means
of suitable sliding supports, bellows, special
steel frames, etc.
Customised current and
voltage transformers
T155 current and/or voltage transformers
are suitable for all protection and metering
purposes and cover a very large range of
ratings. Most often, instrument transformers
are conventional, inductive types.
Non-conventional instru-ment
transformers (NCIT)
can also be provided. The
ALSTOM non-conventio-nal
current transformer
is based on the Rogowski
principle, which avoids
any magnetic saturation
concerns. Thanks to ALSTOM's original
design, even the most demanding metering
ratings, up to 0.2 accuracy class, can be
achieved with very low primary currents.
The non-conventional voltage transformer
is a capacitive-type and may even be com-bined
with the CT. The ALSTOM NCIT deli-vers
standard analog and/or digital signals.
Integrated surge arresters
Gas-insulated surge arresters minimise sub-station
footprints, improve equipment
reliability and reduce the number of outdoor
insulators. Thousands of units are installed
in high and extra-high voltage air and
gas-insulated substations. T155 zinc-oxide
resistors have very high ratings which mini-mise
residual voltages, thus perfectly pro-tecting
the equipment and dissipating the
very high energies associated with the
longest lines and cables. Proper grading
of the electrical field inside the enclosure is
achieved with special stress shields. A
leakage current meter and/or a discharge
counter may also be connected.
High-voltage terminations
The T155 can be directly connected to high
voltage cables, transformers and/or over-head
lines.
Reliable SF6-air bushings
The GIS connects to overhead lines by
means of busducts and SF6-air bushings,
the insulator of which, (porcelain or compo-site)
is filled with SF6 at substation rated
pressure. Electric field grading is natural,
based on sole SF6 insulation, which pro-vides
an excellent voltage surge withstand.
This limits the risk of ageing too. A range
of insulators allows external creepage
distances to meet specific customer require-ments.
Composite insulators are also explosion-proof
and thus bring a valuable safety
feature.
Direct connection
to power transformers
In order to remove any air-insulated part,
the T155 can be directly connected to
power transformers and reactors by means
of gas-insulated busducts and a specific
enclosure which houses the gas-tight
oil-SF6 bushing. The latter is provided by
the transformer or reactor manufacturer
and must be as per IEC standards. Proper
design easily manages the positioning tole-rances
of the power transformer or reactor.
The transformer or reactor may be discon-nected
from the substation via a removable
connection during GIS high voltage tests.
Standard HV cable connection
A specific enclosure is used to connect the
switchgear to the cable termination, whose
insulator provided by the cable supplier
must be as per IEC standards. Such a ter-mination
fits any type of HV cable, irre-spective
of insulation type (XLPE, paper-oil,
etc.) or conductor section.
The cable can be disconnected from the
switchgear via a removable conductor,
to allow separate GIS and cable high voltage
tests. Tools and testing means for HV cable
testing must be provided by the cable supplier.

6. Condition monitoring
Monitoring
Despite its superior reliability, T155 switch-gear
6
availability can be further enhanced by
means of condition monitoring systems
which have the following features:
• Predictive, instead of preventive mainte-nance
• Early warnings
• Time-tagged event recording.
SF6 , circuit breaker and partial discharge
monitoring are the most valuable systems.
Precise
circuit breaker monitoring
Circuit breaker monitoring can be provided
too. Travel curves and electrical wear are
recorded and can report on circuit-breaker
conditions in order to trigger servicing only
when it is strictly necessary.
For both SF6 and CB monitoring, ALSTOM
deploys modular electronic devices, whose
reliability is supported by hundreds of
thousands in operation around the world in
all types of critical industrial processes. These
devices are permanently self-monitoring
and any failure is immediately signalled.
These devices have successfully undergone
extremely severe and extensive qualication
tests. Due to their proximity to high voltage
and high current equipment, electro-magnetic
compatibility (EMC) withstand is
thoroughly checked: not only do these devi-ces
fully comply with the upper class of the
tests (electromagnetic fields, fast transients,
electrostatic discharges, radiated radio
waves, etc.) defined in IEC 1000/EN 61000
standards, but they also experience no
misoperation during the same tests. Display
is provided by user-friendly human-machine
interfaces.
GAS-INSULATED SUBSTATIONS T155
UHF monitoring
Internal partial discharges may be signs of
possible problems. It may be therefore
useful to monitor the ultra-high frequency
(UHF) electromagnetic waves generated by
the partial discharges. Associated with the
high voltage tests, this is the most effective
way to ensure full GIS integrity after instal-lation
or heavy maintenance. UHF sensors
transmit electromagnetic waves, the fre-quency
of which may reach 1 GHz. Sensors
(i.e. antennas) are properly located inside
the enclosures. On commissioning staged
and regular inspections, sensors are con-nected
to a portable UHF analyser.
A trained operator may then observe the
signals and determine switchgear status.
A more sophisticated online monitoring
system may also be supplied for more
critical installations, for the permanent
supervision of switchgear dielectric con-ditions.
remote
monitoring
communication
communication
with control
equipment
monitoring
gateway
bay
gateway
&
SF6
monitoring
module
condition
monitoring
module(s)
digital links
A/D – D/A
converters
Complete SF6 monitoring
Apart from the usual density
thresholds (refilling request
and minimum operating
density), ALSTOM SF6 moni-toring
digital
position
sensors
digital
SF6
analogue sensors
on/off sensors
inputs
on/off
outputs
Control room
LCC
Switchgear
can also provide many
valuable functions:
• Accurate density display
• Filling overpressure alarm
• SF6 liquefaction detection
• Sensor status control
• Early warning
• Calculation of leakage rate
• Internal failure detection
• Historical record.
These functions help
operators to make proper
decisions and dramatically
increase substation
availability.
LAN

7. GAS-INSULATED SUBSTATIONS T155
7
Local control
A local control cubicle is generally asso-ciated
to each T155 circuit breaker bay.
This cubicle may provide all or part of the
following functions:
• Control, i.e. means of opening and closing
all switches (circuit breaker, disconnectors
and earthing switches)
• LV supply protection
• Display of switch position
• Alarm display (SF6 thresholds, supply
voltage, etc.)
• Safety electrical interlocks (using CB, DS
and ES auxiliary contacts)
• Current / voltage meters
• Interfacing terminals for remote control.
Assembly & maintenance
Reliable type and routine tests
Type tests are carried out according to
latest IEC standards. For some features, IEC
requirements are even supplemented by
additional tests, or more severe conditions,
to meet ALSTOM’s own superior standards
of quality. Despite our modern workshops,
which include a dustfree assembly hall, the
same rigorous policy is applied for routine
tests. For instance, partial discharge mea-surement
is performed at a much higher
voltage than required by IEC standards.
Simple transport and
on-site tests
Shipping units are filled with SF6 or N2 gas
at a slight overpressure, to prevent moisture
and dust ingress during transport. After site
erection, the equipment undergoes rigorous
inspections to ensure all required perfor-mances.
Site tests include severe resistance
measurements and mechanical and voltage
withstand tests.
Minimal maintenance
The T155 has a near-zero maintenance
concept – where reliability and availability
mean inspections at distant intervals and
where long life duration for mechanical and
electrical parts is guaranteed. The ALSTOM
Service team remains at the customer’s
disposal for any assistance and service,
however. An inspection and maintenance
plan can also be established to support the
equipment throughout its entire life cycle.
Comprehensive services
ALSTOM provides a global service offer,
supported by local resources:
• Network consulting
• Equipment expertise and diagnosis
• Erection and commissioning supervision
• Maintenance and spare parts management
• Repairs and emergency support
• Renovation and refurbishment
Dedication to customer satisfaction is
ALSTOM’s first guideline to its employees,
a testimony to the will of shapping a better
future.
The implemented technology can be con-ventional
(based on electromechanical
relays) or digital (based on electronic micro-processors).
The ALSTOM local control cubicle may also
incorporate the bay control unit (BCU) of a
substation digital control system (DCS)
and/or the protection relays themselves.

8. Applications
GRID
Hybrid module
Displayed OPTIGIM includes
one circuit breaker with:
1 current transformer
1 earthing switch
1 disconnector
1 SF6 -air bushing on both sides.
Length 10 m
Bushing terminal height 7.5 m
Alstom Grid Worldwide Contact Centre
www.grid.alstom.com/contactcentre/
Tel: +44 (0) 1785 250 070
www.grid.alstom.com
One circuit breaker and a half substation with 4 feeders
Building width 10 m, length 34 m
Double busbar layout with 6 feeders and 1 coupler
Building width 10 m, length 25 m
Grid-Products-L3-T155_Range-70627-2010_12 - EN © Copyrights Alstom 2010, the Alstom logo and any alternative version thereof are trademarks and service marks of Alstom. The other names mentioned, registered or not, are the property of
their respective companies. The technical and other data contained in this document are provided for Information only. Neither Alstom, its officers nor employees accept responsibility for or should be taken as making any representation or warranty
(whether express or implied) as to the accuracy or compIeteness of such data or the achievements of any projected performance criteria where these are indicated. No liability is accepted for any reliance placed upon the information contained in this brochure.
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GAS-INSULATED SUBSTATIONS T155