PASCAL
TECHNICAL DESCRIPTION OF 12kV VCB PANEL TYPE PSI
1.0
INTRODUCTION
PSI medium voltage panel is primarily designed to meet all types of switching applications
encountered in public distribution systems and medium industries up to fault level of 26.3kA,
rated current of 1250A and Busbar rating of 2000A. This panel has been developed in
consultation with several utilities and in particular with the field operating staff and attempts
to take care of all real life operating problems in a safe, reliable and operator friendly way.
2.0
APPLICABLE STANDARDS
PSI panel has been completely type tested as per latest IEC/IS Standards;
IS 13118 and IEC 62271-100 (2008) for Circuit Breaker
IS 3427 and IEC62271-200/IEC (2008) for Indoor Panels
3.0
BASIC RATINGS
Type Designation
Rated Operating Duty
Type of Breaker and Classification
Rated Voltage
Rated Current
Rated Frequency
Rated Symmetrical Short Circuit Breaking Current
Rated Asymmetrical Short Circuit Breaking Current
Rated Short Time Current
Rated Cable Charging Breaking Current
Rated Single Capacitor Bank Switching Current
Rated Bus Bar Current
Rated Internal arc current
Power frequency withstand voltage
1.2/50 micro sec impulse withstand voltage
*
PSI
O – 0.3s – CO – 3m – CO*
Vacuum, Category M2, E2
12 kV
1250 A*
50 Hz
26.3 kA
DC component > 48%
26.3 kA - 3 sec
25 A
400 A
2000 A
26.3 kA
28 kV* for 1 min
75 kV* peak
Higher ratings/duty optional
4.0
SWITCHING APPLICATIONS
The circuit breaker is designed to meet all types of switching applications relevant to public
distribution network and medium industries. These include;
Standard duty O-0.3s-CO-3m-CO under normal and fault conditions
Auto reclosing duty O-0.3s-CO-15s-CO-3m-CO
Low Inductive Current Switching
Single Bank Capacitor Switching
Motor Switching
High DC component (>48%) short circuit switching
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5.0
GENERAL DESCRIPTION OF THE SWITCHGEAR
Basic Switchgear has two components
Moving Component – Vacuum Circuit Breaker Truck / Cassette
Fixed Component – Switchgear Cubicle
5.1
VACUUM CIRCUIT BREAKER
The Circuit Breaker is mounted on a truck and is of
horizontal isolation and horizontal draw out type. Cassette
type design can also be provided as an option. The basic
design is simple and sturdy and the truck is of lowest
volume and weight when compared to other circuit breakers
of equivalent rating.
Movement of truck is on special non metallic nylon wheels
and special guides are provided inside the panel making
insertion and removal smooth and easy.
Vacuum Circuit Breaker Truck
The Vacuum Interrupter is of ABB make – VG series, suitable for 26.3kA short circuit
Breaking currents at 12kV. Due to innovative and compact design, the
mechanical and electrical endurance of the interrupter is very high:
- Number of operations at no load - 50000
- Number of operation at rated current – 30000
- Number of operations at rated short circuit current – 100
ABB VI
The operating mechanism is spring charged, stored energy type. This is time tested; proven
mechanism and more than 15000 mechanisms are in use all over the country for over 15
years.
The closing springs and opening springs are specially designed
and aligned with the operating characteristics of the
interrupter. This ensures repeated reliability; low stress and
lower requirement of operating energy. Dashpots are further
mounted to reduce vibrations during opening of the moving
contacts.
Mechanism under automated
testing for 10000 operations
These features make the mechanism suitable for 10000
mechanical operations without any change of components. The
life of operating mechanism with maintenance and
replacement of components is more than 35000 operations,
matching with vacuum interrupter life.
Use of ABB interrupter and driven by MK Engineering operating mechanism, the breaker is
designed for M2, E2, C2 category.
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The truck has an aesthetically designed front fascia where mechanical actuating and indicating
devices are brought directly from the circuit breaker, providing user friendly operator
interface. These are :
o Mechanical emergency push to trip button
o Mechanical push to close push button where required with lock
o Breaker ON/OFF indicator
o Spring CHARGED/DISCHARGED indicator
o Mechanical operation counter
o Other requirement can also be considered.
The contact arms of the circuit breaker are fitted with well
proven tulip isolating contacts. This ensures maximum surfaces
contact and therefore efficient transfer of current at very low
resistance. The spring loaded contacts also provide flexibility and
strength during passage of short circuit currents.
.
Circuit Breaker Pole with
Isolating Contact
5.2
SWITCHGEAR CUBICLE
]
The switchgear cubicle is categorized as Metal Clad, Metal Partition (PM) design as
specified in latest IEC/IS. The air insulated cubicle has four distinct compartments
separated by metal partition which is earthed. The automatic safety shutters are also
metallic and earthed.
.
5.2.1 BASIC CONSTRUCTION AND DESIGN
The basic cubicle is constructed using only CRCA sheet steel. Sheet steel is fabricated
using CNC turret punch press and then undergoes complete surface treatment process.
Finally it is painted through powder coating painting process. This ensures complete
accuracy which facilitates smooth operation in the field over prolonged period. This also
provides scratch, pickling and rust resistant, long lasting, aesthetic surface.
The entire construction is weld free and either bolted or riveted depending upon the
design requirement. This ensures predictable behavior during internal arc and also a
distortion free appearance.
The cubicle is designed to withstand internal arc faults in any of its three high voltage
compartments, that is, breaker, bus bar or CT & Cable compartment. A pressure release
flap is provided on top of each of these compartments which open in the event of
internal fault in order to guide fumes and smoke generated by the internal arc. All other
surfaces of the l, including the door are designed to withstand the pressures and other
effects generated by internal fault.
Transfer of current from Circuit Breaker to Busbar and CT is through uniquely designed
bus bar spouts and circuit spouts. This provides more strength and rigidity during short
circuit operation and also acts like a bushing between two compartments.
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A continuous copper earth bus of size 50X6 mm runs across the entire length of the
switchboard. All doors, partitions, covers and non current carrying metallic parts are
earthed to achieve earth potential for the entire enclosure. Instrument casings, cable
armor and others points which need to be earthed are also connected to this earth bus.
Terminals are provided at each end of the earth bus to connect to the grid earthing.
The earth bus is designed to carry rated short circuit current for 1 sec.
One of the key features of the panel is accessibility to all functions to the operators in
most user friendly way:
Simple access to CT maintenance and for current injection tests.
o Access to bus bars for authorized persons for maintenance.
o Easy access to draw out PT and associated fuses.
o Sufficient headroom and space for cables termination and access.
o Operating instrument and indicating functions at convenient height.
The standard cubicle is designed for IPH 4X and IPH 5X protection as defined in IEC. Higher
degree of protection, if required can be provided as an option.
The cubicle offers lowest Width and Depth (600mms X 1740 mms) as well as lower overall
weight compared to other panels of equivalent rating, making it most economical in terms
of sub station space requirement and associated civil works cost.
5.2.2 CIRCUIT BREAKER COMPARTMENT
The circuit breaker compartment encloses the draw out circuit breaker truck. Special
guides are provided to rack in and rack out the circuit breaker truck with easily.
The compartment has a distinct test position and service position and it is not possible to
operate the circuit breaker in any intermediate position. The breaker is inserted from test
position to service position through an operating handle with the door closed, providing
additional operator safety.
The safety shutters are metallic and earthed. Both, the bus side shutters and circuit side
shutters have independent operating mechanisms which operate only through the
movement of the circuit breaker truck. When the circuit breaker is withdrawn, the safety
shutters close so that no live parts are accessible. The shutters can be locked in the
closed position.
The compartment has a hinged door with unique multi point locking with sufficient
strength to withstand effects of internal arcing.
The electrical low voltage connection between the fixed cubicle and draw out circuit
breaker is established via a multi pin connector of sufficient number of pins depending
upon the requirement. The connector base is fixed and integral part of the cubicle. The
connector top is flexible and integral part of the circuit breaker truck.
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5.2.3 BUS BAR COMPARTMENT
A spacious bus bar compartment is provided on top of the cubicle. This houses rectangular
electrolytic copper or aluminum bus bars. Cross section depends upon the current rating.
However, adequate space is available to carry bus bar current of 2000 A.
A uniquely designed epoxy bus bar spout supports the bus
bar and provides the seal off bushing between bus bar
compartment and circuit breaker compartment. The epoxy
used is both non-hydroscopic and anti tracking.
The bus bars are insulated by either standard HT insulated
PVC sleeves or heat shrinkable sleeves. The busbar and tap
off joints are also color coated for easy identification. All
copper to copper joints are either silver plated or tin plated.
.
Bus bars and epoxy spouts arranged in
bus bar compartment
For maintenance, the bus bar compartment is accessible by opening the cover only with
special keys. This prevents accidental and unauthorized access to the bus bars.
Another unique feature of the design is, the pressure release valve in busbar chamber is
unaffected while mounting PT on top.
5.2.4 CABLE & CT (C&CT) COMPARTMENT
The C&CT compartment is located on rear bottom of the cubicle and accommodates
current transformers and cables.
Standard design is for cable entry from below. Special designs are available for bus duct
entry or cable entry from top.
Sufficient head room and space is available to accommodate 9nos. 1CX630 sq. mm or 3
nos. 3CX300 sq. mm cables in a standard panel and this is generally adequate for current
rating of the panel. Additional cables can be accommodated by extending the chamber
depth wise.
Specially designed split gland plate design is provided on the floor of the compartment
which makes it very easy for removal / sturdy fitting of power cables and resists undue
swing due to forces encountered during short circuit.
The standard compartment can accommodate metering, protection and PS class CTs for
most of the ratings. The CTs can be of bar primary or wound type. Higher requirement of
CTs can also be accommodated by extending depth of the panel.
The C&CT compartment is equipped with bolted cover on the rear of the panel. Opening
the cover through special keys provides easy access to the CTs.
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5.2.5 LOW VOLTAGE COMPARTMENT
Located in front top of the cubicle, the low voltage compartment houses customer specific
relays, meters, lamps and other control and indicating instruments. Compartment has a
hinged door to access the wiring.
Best practices are used for wiring and layout in standard panel;
o Control wires are 1.1kV grade standard with conductor size to match requirement.
With ferrules at both ends, wires are neatly bunched together and routed through
PVC trough.
o Stud terminals and ring type crimping lugs offer best protection against accidental
wire tugs. Disconnecting link type is used on CT & PT terminals.
o Layout is neat and orderly for easy identification.
o All operating instruments are maintained at a height of 1700 mms.
o All reading equipment is maintained at a height of 2000 mms.
Low voltage compartment is available in two height versions. The standard height
accommodates most of the customer requirement. This height can be increased, in case if
higher requirement.
5.3
OTHER ARRANGEMENTS
5.3.1
POTENTIAL TRANSFORMER
As a standard feature, draw out PT is provided on top of the panel. The PT and all fuses
are easily accessible for maintenance.
This design has two unique features;
o In this arrangement, PT can be connected either to the bus side or the circuit side
of the power supply.
o The arrangement of the PT does not interfere with internal arc protection
capabilities of the cubicle, unlike most other designs.
PT can also be accommodated in a separate panel with the PT mounted on draw out truck
for easy maintenance and fuse replacements.
5.3.2
SAFETY INTERLOCKS
Standard Safety Interlocks
o Circuit Breaker can be operated only in service/test position and not in any
intermediate position, besides fully isolated condition.
o Circuit Breaker cannot be inserted into service position in closed condition and
cannot be removed from service unless it is in open condition.
o Circuit Breaker cannot be moved from test position to service position unless
auxiliary plug is engaged and auxiliary plug cannot be disengaged if the circuit
breaker is in service position.
Additional optional safety interlocks
o Circuit Breaker cannot be inserted from test position to service position if the
front door is open.
o The front door cannot be opened unless circuit breaker is Open and brought to
Test position.
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Doc: COM 007 080510 REV 00
Development is a continues process in the organization and panels offered may differ slightly from what described. Details given in specific proposal to
customer will prevail in case of deviation from this general description.