7 - GAS INSULATED SWITCHGEAR
1.0
SCOPE
1.1
The scope shall be for the design, engineering, manufacture, assembly, testing at
manufacturer's works before dispatch and services for supply, insurance,
transportation, delivery at project site, handling, storage and preservation at store/site,
transport to place of installation, complete work of site assembly, erection, testing at
site and commissioning of 36 kV SF6 Gas Insulated Switchgear (GIS). The
equipment shall comprise of:
a)
b)
c)
d)
e)
g)
h)
i)
j)
k)
l)
Circuit Breakers
Bus Bars – Single bus
Current Transformers
Voltage Transformers
Transition between SF6 GIS and XLPE Cable terminations, operating
mechanism for each equipment
SF6 Gas and Hydraulic Oil for first filling plus 10% extra
Standalone Partial Discharge Monitoring System along with its accessories
Supporting steel structures
Embedment, ladders and walkways for erection and maintenance,
Complete earthing system etc.
Any other item which is not covered above and but required for the operation
of the switchgear shall be supplied.
1.2
Any other equipment not explicitly mentioned herein/in the schedule of requirements
but is necessary for completeness of works specified shall also be included in the
scope without any extra cost. The equipment shall be suitable for climatic conditions
and altitude as mentioned in the technical specifications.
2.0
STANDARDS
2.1
The GIS switchgear shall comply to the following standards:
IEC - 56 (Parts 1 to 6) : AC High Voltage circuit breaker.
IEC - 68 (Part III) : Seismic test methods for equipments
IEC – 71 : Insulation coordination.
IEC – 137 : Bushing particulars.
IEC -185 : Current transformers.
IEC -186 : Voltage transformers.
IEC -267 : Guide to testing of circuit breakers.
IEC -270 : Partial discharge measurements.
IEC - Rec. 376 : SF6 Gas.
IEC - 427: Synthetic testing of high voltage AC circuit breaker.
IEC – 480 : Guide to the checking of SF6 taken for electrical equipments.
IEC – 506 : Switching impulse test on HV insulators.
IEC - 694: Common Clauses for HV switchgear.
IEC - 859: Cable connections for gas insulated metal enclosed switchgear.
IEC - 1639: Direct connection between power transformer and SF6 GIS.
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ANSI/IEEE: Guide for safety in AC substation grounding (Std. 80-1986).
2.2
If there are, in the opinion of the bidder, any contradictions between the above
standards and these specifications, such contradictions shall be brought to the
attention at the time of bidding.
3.0
RATINGS
3.1
The ratings and general characteristics of the GIS shall be as follows:
(The ratings applicable to specific items of equipment are indicated in the applicable
sections dealing with the equipment).
(a)
Type of Switchgear
36 kV Three phase, metal
enclosed, SF6 gas insulated
switchgear
(b)
Location
Indoor
(c)
Frequency
50 ± 3% Hz
(d)
Rated voltage class, kV rms
36
(e)
Highest System voltage
36 kV rms
(f)
Number of phases
Three
(g)
Full wave impulse withstand voltage
(1.2/50 micro sec.)
170 kVp
(h)
Rated one minute power frequency with
stand voltage
Phase to earth
Across open contacts
70 kV rms
70 kV rms
System earthing
Effectively grounded
(i)
(ii)
(i)
(j)
Rated normal current
(i) Transformer Incoming circuits
(ii) Out going feeder circuits
(iii) Bus coupler circuits
630A
630 A
630 A
(k)
Rated short circuit withstand current at
rated maximum voltage for three second
Not less than 25 kA rms
(symmetrical)
(l)
Rated breaking capacity of circuit breaker
(min)
Rated making capacity (min)
25 kA rms
(m)
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40 kAp
(n)
(p)
Prospective transient recovery voltage
appearing across the circuit breaker
terminals
Partial discharge level at
1.1 Un/√ 3
Material of enclosure
(q)
(r)
Material of bus bar
Insulation medium
Aluminium alloy or Nonmagnetic material
Aluminium alloy
SF6 gas
(s)
(i)
(ii)
(iii)
SF6 relative pressure at 20ºC
Filling
Alarm
Lockout pressure
6 kgf/cm2
5.5 kgf/cm2
5 kgf/cm2
(o)
As per IEC 56
10 pico coulombs or less
3.2
All current carrying components of the equipment specified shall be capable of
continuous operation at the specified rated current without exceeding the maximum
temperature rise specified in the relevant IEC/IEEE standards.
4.0
GENERAL DESIGN AND SAFETY REQUIREMENTS
4.1
The GIS assembly shall consist of completely separate pressurized sections in order
to de-pressurize one gas compartment for inspection, maintenance or if necessary for
repair while keeping the adjacent compartments in healthy uncharged condition.
These compartments shall be such that maintenance on one feeder may be performed
without de-energizing the adjacent feeders. These compartments shall be designed to
minimize the risk of damage to adjacent sections and protection of personnel in the
event of a failure occurring within the compartments. Stainless steel carbon
impregnated or nickel plate rupture diaphragms with suitable deflectors shall be
provided to prevent uncontrolled bursting pressures developing within the enclosures
under worst operating conditions.
Sections of GIS shall be supplied filled with dry Nitrogen or SF6 gas at a positive
pressure and hermetically sealed to protect the dielectric system during transportation.
4.2
The workmanship shall be of the highest quality and shall conform to the latest
modern practices for the manufacture of high technology machinery and electrical
switchgear.
4.3
The switchgear, which shall be of modular design, shall have complete phase
isolation. The conductors and the live parts shall be mounted on high graded epoxy
resin insulators. These insulators shall be designed to have high structural strength
and electrical dielectric properties and shall be shaped so as to provide uniform field
distribution and to minimize the effects of particle deposition either from migration of
foreign particles within the enclosures or from the by-products of SF6 breakdown
under arcing conditions.
4.4
Gas barrier insulators and support insulators shall have the same basis of design. The
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support insulators shall have holes on both sides for proper flow of gas.
4.5
Gas barrier insulators shall be provided so as to divide the GIS into separate
compartments. They shall be suitably located in order to minimize disturbance in case
of leakage or dismantling. They shall be designed to withstand 1.5 times full rated
pressure on one side while vacuum is exerted on the other side. They shall be
designed to withstand any internal fault thereby keeping an internal arc inside the
faulty compartment. Due to safety requirement for working on the pressurized
equipment, whenever the pressure of the adjacent gas compartment is reduced, it
should be ensured by the Supplier that adjacent compartment would remain in
uncharged condition with reduced pressure. The gas tight barriers shall be clearly
marked on the outside of the enclosures.
4.6
The material and thickness of the enclosures shall be such as to withstand an internal
flash over without burn through for a period long enough (500 ms) till the backup
relay protection clears the fault. The material shall be such that it has no effect of
environment as well as from the by-products of SF6 breakdown under arcing
condition.
4.7
Sufficient inspection windows/access openings shall be provided at the switchgear to
ensure that each switchgear component can be inspected/monitored during
installation and future maintenance. Each section shall have plug-in or easily
removable connection pieces to allow for easy replacement of any component with
the minimum of disturbance to the remainder of the equipment.
4.8
The material used for manufacturing the switchgear equipment shall be of the type,
composition and have physical properties best suited to their particular purposes and
in accordance with the latest engineering practices. All the conductors shall be
fabricated of aluminium tubes of cross sectional area suitable to meet the normal and
short circuit current rating requirements. The finish of the conductors shall be smooth
so as to prevent any electrical discharge. The conductor ends shall be silver plated
and fitted into finger contacts or tulip contacts. The contacts shall be of sliding type to
allow the conductors to expand or contract axially due to temperature variation
without imposing any mechanical stress on supporting insulators.
4.9
Each pressure filled enclosure shall be designed and fabricated to comply with the
requirements of the applicable pressure vessel codes and based on the design
temperature and design pressures as defined in IEC 517.
4.10
The manufacturer shall guarantee that the pressure loss within each individual gasfilled compartment shall not be more than one percent per year.
4.11
Each gas-filled compartment shall be equipped with static filters, density switches,
filling valve and safety diaphragm. The filters shall be capable of absorbing any water
vapour, which may penetrate into the enclosures as well as the by-products of SF6
during interruption. Each gas compartment shall be fitted with separate non-return
valve connectors for evacuating and filling the gas and checking the gas pressure etc.
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4.12
The switchgear line-up when installed and operating under the ambient conditions
shall perform satisfactorily and safely under all normal and fault conditions. Even
repeated operations upto the permissible servicing intervals under 100% rated and
fault conditions shall not diminish the performance or significantly shorten the useful
life of the switchgear. Any fault caused by external reasons shall be positively
confined to the originating compartment and shall not spread to other parts of the
switchgear. Routine maintenance to any of its external components including the
protective relays and instrument transformers shall not be required in less than five
years intervals. The internal components shall be maintenance free for at least 10
years. Routine replacement of insulating gas shall not be required in intervals of less
than ten years.
4.13
Bracings shall be provided for all mechanical components against the effects of short
circuit currents. The arc faults shall be positively confined to the originating
compartment and shall not spread to the other parts of switchgear.
4.14
The thermal rating of all current carrying parts shall be minimum for one second at
33kV for the rated symmetrical short-circuit current. If the maximum short-circuit
time is extended, the I2t value shall remain constant.
4.15
The switchgear shall be of the free standing, self-supporting with easy accessibility to
all the parts during installation and maintenance, dead front design with all highvoltage equipment installed inside gas-insulated metallic and earthed enclosures,
suitably sub-divided into individual arc and gas-proof compartments at least for:
(i)
(ii)
(iii)
(iv)
(v)
Busbars.
Intermediate compartment.
Circuit breakers.
Current Transformers.
Voltage Transformers.
4.17
The arrangement of the individual switchgear bays shall be such so as to achieve
optimum space-saving, neat and logical arrangement and adequate accessibility to all
external components.
4.18
It is required that the three phases of each switchgear bay be arranged side by side.
Segregated phase blocks of equipment in which one phase of each switchgear bay is
mounted in a separate block are not acceptable. The arrangement of the equipment
offered must provide adequate access for operation, testing and maintenance.
4.19
All the elements shall be accessible without removing support structures for routine
inspections and possible repairs. The removal of individual enclosure parts, or entire
breaker bays shall be possible without disturbing the enclosures of neighboring bays.
4.20
It should be impossible to unwillingly touch live parts of the switchgear or to perform
operations that lead to arcing faults without the use of tools or brute force.
4.21
All interlocks that prevent potentially dangerous mal-operations shall be constructed
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such that they cannot be operated easily, i.e. the operator must use tools or brute force
to over-ride them.
4.22
The actual position of circuit breakers must be positively displayed by mechanical
indicators visible from the operating position.
4.23
In general the contours of energized metal parts of the GIS and any other accessory
shall be such, so as to eliminate areas or points of high electrostatic flux
concentrations. The surfaces shall be smooth with no projection or irregularities,
which may cause visible corona.
4.24
The fabricated metal enclosures shall be of aluminium alloy or stainless steel and
have high resistance to corrosion, low electrical losses and negligible magnetic losses.
All joint surfaces shall be machined and all castings shall be spot faced for all bolt
heads or nuts and washers. All screws, bolts, studs and nuts shall conform to metric
system.
4.25
The breaker enclosure shall have provision for easy withdrawal of the interrupter
assemblies. The removed interrupter assembly must be easily and safely accessible
for inspection and possible repairs.
4.26
The enclosures of the same phase shall be electrically interconnected and at proper
points they shall be connected to the other phases thus entailing a return current
almost equal to the current circulating in the conductors.
4.27
The enclosure shall be designed to practically eliminate the external electromagnetic
field and thereby electro-dynamic stresses even under short circuit conditions.
4.28
The elbows, bends, cross and T-sections of interconnections shall include the
insulators bearing the conductor when the direction changes take place in order to
ensure that live parts remain perfectly centered and the electrical field is not increased
at such points.
4.29
The ladders and walkways shall be provided wherever necessary for access to the
equipment.
4.30
Wherever required, the heaters shall be provided for the equipment in order to ensure
the proper functioning of the switchgear at specified ambient temperatures. The
heaters shall be rated for 230V AC supply and shall be complete with thermostat,
control switches and fuses, connected as a balanced 3-phase, 4-wire load. The
possibility of using heaters without thermostats in order to achieve the higher
reliability may be examined and accordingly decided during detailed design stage but
it shall be ensured that the temperature rise of different enclosures where heating is
provided should be within safe limits as per relevant standards. The heaters shall be
so arranged and protected as to create no hazard to adjacent equipment from the heat
produced.
4.31
The provision shall be made for maintenance of equipment so that a mechanic 1780
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mm in height and 80 kg in weight shall be able to climb on the equipment.
4.32
The sealing provided between flanges of two modules/enclosures shall be such that
long term tightness is achieved.
4.33
Alarm circuit shall not respond to faults for momentary conditions. The following
indications including those required elsewhere in the specifications shall be generally
provided in the alarm and indication circuits.
4.34
Gas Insulating System
a)
b)
c)
Loss of gas density.
Loss of heater power.
Any other alarm necessary to indicate deterioration of the gas insulating
system.
5.35.2 Operating System
a)
Low operating pressure.
b)
Loss of Heater Power.
c)
Loss of operating power.
d)
Loss of control.
e)
Pole disordance.
6.0
CIRCUIT BREAKERS
6.1
Type and Rating
6.1.1 The circuit breakers being supplied shall be suitable for operation with Transformers
and 33 kV Sub-transmission lines.
6.1.2
SF6 gas-insulated circuit breaker shall conform to IEC-56 and have the following
performance characteristics and ratings, in addition to those stated in Clause 4.0 of
this document.
(i)
Type of breaker
36 kV single phase, metal
enclosed, SF6 gas insulated,
hydraulically operated
(ii)
Rated frequency
50 Hz
(iii)
Rated normal current: (Minimum)
• Bus coupler breaker
• Transformer incomer
breaker
• Out going line breaker
(iv)
Number of poles
630 A
630 A
630 A
3
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(v)
Installation
Indoor
(vi)
Temperature rise
As per IEC 694
(vii)
Rated short time withstand current
kA (rms value of ac component)
minimum
Rated short circuit making current,
kA (peak) Minimum
25 kA for 3 second
(viii)
40 kA
(ix)
Rated out-of phase breaking current 25 kA
(rms)
(x)
Rated short circuit breaking current
-
Rated short circuit current
- Percentage of DC
component
25 kA (rms)
>70%
(xi)
System Earthing
Effectively earthed
(xii)
First-pole-to clear factor
> 1.3
(xiii)
Rated duration of short circuits
3 seconds
(xiv)
Total break time for any current
upto the rated breaking current
Not exceeding 60ms
(xv)
Closing time
< 100ms
(xvi) -
Maximum difference of time at
opening of series contacts within
one pole
- Maximum difference of time at
opening between phases
- Maximum difference of time at
closing between phases
(xvii)
Rated transient recovery voltage for
terminal faults
±3ms
±3ms
±3ms
As per IEC 56
(xviii)
Rated operating duty cycle
0-0.3 s-CO-3 min-CO
(xix)
Rated line charging
500 A with maximum
breaking current permissible
switching over voltage not
greater than 2.0pu
(xx)
Operating mechanism
Hydraulic operating
mechanism
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(xxi)
(xxii)
Rated supply voltage of closing and 48 V DC
opening devices and auxiliary
circuit
Number of auxiliary contacts
6 NO and 6 NC on each pole
wired to terminal blocks in
control cabinet
(xxiii)
- Number of trip coils
- Number of closing coils
2 per pole
2 per pole
(xxiv)
SF6 gas characteristics for SF6
circuit breaker
As per IEC 376
(xxv)
Main contact material
Copper with silver plate
7.1.3
The governing data for the selection of circuit breakers shall not be limited to the
above mentioned parameters but shall also take into account various provisions
contained in these specifications and relevant standards. The circuit breakers to be
supplied must be suitable for the intended services i.e. for no load, full load, inductive
and capacitive duty and fault service conditions.
8.0
INSPECTION AND TESTING
All the routine and acceptance tests as specified in the applicable standards shall be
carried out on the GIS switchgear. Test reports pf all the bought items shall be
reviewed during testing. Type test of the switchgear which has been carried out
within 5 year shall be submitted by the successful bidder during drawing approval.
9.0
COMPLETENESS OF THE EQUIPMENT
Any fittings, accessories or apparatus which may not have been specifically
mentioned in these specifications but are necessary for completeness of the
equipment shall be deemed to be included and shall be supplied without any extra
charges to the Employer. All plants and equipments shall be complete in all respects
even if the details regarding all the items are not mentioned in these specifications.
10.0
SPARES
The BPC shall have option to order recommended essential spare parts as per the
terms and conditions of the contract. The spare parts shall be interchangeable and
shall be of same quality as that of original components.
11.0
TOOLS/SPECIAL TOOLS, TACKLES & SLINGS, CONSUMABLES.
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All the tools/special tools, tackles and slings required for assembly, erection and
maintenance of the equipment shall be supplied. Consumables required for the
erection shall be supplied without any extra cost.
12.0
GENERAL REQUIREMENTS
The Constructional features, CTs, PTs, Meters. Cable terminations, control wiring,
relays and protection shall be as per the technical requirements section 2 B of the 33
kV and 11 kV indoor switchgear.
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