8- 66 KV CIRCUIT BREAKERS, 66 KV CTS AND ISOLATORS
1.1
Circuit Breakers
1.1.1
Applicable Standards
1.1.2.
Parameters
1.1.3.1
1.1.3.2
:
IEC 62271-100/BS 5311 / IS 13118
:
a)
Type of circuit breaker
SF6,
Outdoor
b)
c)
d)
e)
f)
g)
h)
Rated current
Rated short circuit breaking
current
Short time withstand for 1 sec.
Auto reclosing
No. of poles
Operating duty
Rated breaking time
3 pole
O –0.3 sec. – CO – 3 min -CO
3 cycles
i)
Power system particulars
As per requirements
j)
No. of auxiliary contacts
6 NO+6 NC
k)
Out-of-phase breaking current
l)
Line charging breaking current
25 % of rated short circuit
breaking current
10A
m)
Auxiliary supplies
48 V DC
630 A
26.2 kA
26.2 kA
General Requirements
a)
Circuit breakers shall be three-phase type, supplied with a common
base; factory installed inter-phase wiring and common control
cubicle.
b)
Circuit breakers shall be capable of clearing short line faults with
the impedance behind the bus corresponding to the rated fault
current.
c)
Circuit breakers shall be suitable for 3-phase auto reclosing.
Operating Devices
a)
Anti-pumping features shall be provided with breaker.
b)
Two trip coils shall be provided for 66 kV breakers. The trip coils
shall have sufficient continuous rating to cater to the trip coil
supervision relay current.
c)
As specified for line breakers, operating mechanism shall be
suitable for high speed reclosing. It shall be non-pumping
electrically and mechanically, under every method of closing
(except during manual tripping of a breaker for maintenance).
d)
A mechanical indicator shall be provided inside the operating
mechanism box to show open and closed positions, visible through
a glass window from ground level. An operation counter shall also
be provided.
(a)
A closing release shall operate correctly at all values of voltage
between 80% and 110 % of the rated voltage. A shunt trip shall
operate correctly under all operating conditions of the circuit
breaker upto the rated breaking capacity of the circuit breaker and
at all values of supply voltage between 50 % and 110 % of rated
voltage.
(b)
Two stage pressure switches shall be provided to monitor SF6 gas
pressure inside the interrupting chambers. The first stage shall
initiate alarm of the breaker and blocking of closing. The second
stage shall initiate blocking of tripping.
(c)
Provision shall be made for attaching an operation analyser to
perform speed tests after installation of the breakers at site.
1.1.4
Operating Mechanism
1.1.4.1
Operating Mechanism shall be spring-operated type complete with motor,
opening spring, closing spring with limit switch for automatic charging
and all necessary accessories.
1.1.4.2
As long as power is available to the motor, a continuous sequence of at
least 10 closing and opening operations shall be possible. After failure of
power supply to the motor, at least one open-close-open operation of the
circuit breaker shall be possible.
1.1.4.3
Breaker operation shall be independent of the motor operation, which shall
be used solely for compressing the closing spring.
1.1.4.4
Motor rating shall be such that it requires a maximum of 15 seconds for
fully charging the closing spring.
1.1.4.5
Closing action of the circuit breaker shall compress the opening spring to
keep it ready for tripping.
1.1.4.6
When closing springs are discharged, after closing a breaker, they shall
automatically be charged for the next operation. Facility for manual
charging of closing springs shall be provided.
1.1.4.7
Mechanical interlocks shall be provided in the operating mechanism to
prevent discharging of closing springs when the breaker is already in the
closed position. Provision shall be made to prevent a closing operation to
be carried out with the springs partially charged.
1.1.5
Operating mechanism control
1.1.5.1
Operating mechanism shall normally be operated by remote electrical
control. Electrical tripping shall be performed by shunt trip coils.
Provision shall be made for local electrical control. 'Local/Remote'
selector switch shall be provided in the operating mechanism cubicle.
1.1.5.2
A conveniently located emergency tripping lever shall also be provided for
local tripping of the breaker. A local manual-closing device, which can
easily be operated from the ground, shall also be provided for maintenance
purposes. Direction of motion of handle shall be clearly marked.
1.1.6
Operating mechanism housing
1.1.6.1
Operating mechanism and all accessories shall be enclosed in a weatherproof mechanism cabinet of hot dip galvanised sheet steel construction,
the thickness of which shall not be less than 2 mm. Hinged doors giving
access to the mechanism at the front and sides shall be provided. Suitable
gaskets shall be provided to make the mechanism housing waterproof and
dust-proof. Padlock and duplicate keys shall be provided.
1.1.6.2
Common marshalling box with necessary tubing and cables shall be
provided. A light point suitable for 11 W CFL lamp with pin type holder
and door switch and one 15A, 240 V, AC socket outlet shall be provided
in the housing.
1.1.7
Bushing/Insulators
1.1.7.1
Puncture strength of bushings/insulators shall be greater than the dry
flashover value. When operating at normal rated voltage, there shall be no
electric discharge between the conductors and bushing/insulator, which
would cause corrosion or damage to conductors, insulators or supports.
No radio interference shall be caused by the bushings/insulators when
operating at the normal rated voltage.
1.1.7.2
All iron parts shall be hot dip galvanised and all joints shall be airtight.
Surface of the joints shall be trued-up; porcelain parts by grinding and
metal parts by machining.
1.1.7.3
All current carrying contact surfaces shall be silver faced. Silver facing
shall not be less than one mil in thickness.
1.1.8
Fittings/Accessories
All the fittings and accessories necessary for ensuring satisfactory
operation as per design and O&M requirements shall be considered to be
part of Scope/Responsibility.
1.1.9
Tests
1.1.9.1
All routine tests shall be carried out as per the latest applicable standards
on the breaker and its accessories. Certificates of tests on bought out
items such as bushings shall be furnished for approval.
1.1.9.2
Type tests, if specified and routine tests shall also be carried out on all
associated equipment as per relevant standards.
1.1.9.3
In addition to the routine tests, the following tests shall be performed on
each breaker:
a)
b)
Lightning impulse withstand test
Radio Interference Voltage Test (for 66kV Breakers)
1.1.9.4
Speed curves for each breaker shall be obtained with the help of a suitable
Operation Analyzer to determine breaker contact movement during
opening, closing, auto-recessing and trip free operation under normal as
well as limiting operating conditions (of control voltage, pneumatic
pressure, etc). The tests shall show the speed of contacts at various stages
of operation, travel of contacts, opening time, closing time, shortest time
between separation and meeting of contacts at break-make operation, etc.
1.1.9.5
A copy of the test results shall be supplied for approval before shipment of
the circuit breakers. Bound copies of complete test results shall be
furnished with the circuit breakers. These shall include complete reports
and results of the routine test as also certified copies of type tests carried
out on circuit breakers of identical design.
2.1
Isolators
2.1.1
Applicable standards
:
IEC 62271-102/
IS 9921
Parameters
a)
b)
Voltage Class
Rated current
66kV
630 A
c)
e)
Rated SC breaking
Rated making current
of earth switch
Power frequency
withstand Voltage
20 kA
50 kA
f)
g)
h)
i)
j)
Installation
No. of poles
Mode of Operation
No. of auxiliary
contacts
k)
Line charging
70 kVp + altitude correction
Outdoor
3 pole
Motorised
12NO+12NC as spare for Client’s use
10 A
2.1.2
Base channels and other structural steel members such as operating pipes,
phase coupling rods, operating mechanism boxes, bolts, pins, etc. shall be
hot dip galvanised. All castings except current-carrying parts shall be
made of malleable cast iron or cast steel. Grey iron shall not be used in
the manufacture of any part. Manual operating handles shall be of
galvanised steel.
2.1.3
Live metal parts shall be of non-rusting and non-corroding metal. Current
carrying parts shall be of non-ferrous material such as aluminium or
copper. Bolts, screws and pins shall be provided with lock washers, keys
or equivalent locking facilities and, if on current carrying parts, shall be
made of non-rusting and non-corroding metal such as copper silicon alloy.
2.14
The isolator or earthing switch shall be provided with current carrying
contacts on the hinge and jaw ends and all contact surfaces shall be of
silver faced copper.
2.2.1
Earthing pads
2.2.2
Each pole of the isolator shall be provided with two earthing pads of noncorroding material at opposite ends, brazed to the channel base. Flexible
tinned copper earth connectors shall be provided for connecting operating
handles of isolators and earthing switches to the earthing system.
2.2.3
Earthing switch
2.2.3.1
Earthing switch shall form an integral part of each pole of the isolator.
Two independent earthing pads each with flexible tinned copper braids
and suitable connectors for the specified size of earth conductor lead shall
be provided at the hinge end of the switch.
2.2.3
Interlocks
2.2.3.1
Isolators and earthing switches shall be provided with padlocking facility
to lock them in fully open or fully closed positions. Padlock with keys
shall be supplied with the isolator.
2.2.3.2
Isolator and earthing switch shall be mechanically interlocked such that it
will not be possible to close the earthing switch when the isolator is closed
and vice versa.
2.2.3.3
Isolator shall be provided with electrical interlocking feature. This shall
be in the form of bolt interlock comprising an interlock coil of latch-in
type to lock the isolator-driving shaft and thus prevent isolator operation
in the latch-in condition. It shall be possible to release the latch by
energising the interlock coil when certain preset conditions of external
interlocking scheme are fulfilled. For this purpose the Contractor shall
provide facilities for wiring external interlocking contacts both in isolator
opening and closing circuits. Further, a separate bypass switch or a
similar facility shall be provided on the local control cabinet to facilitate
emergency manual operation of isolator.
Electrical interlocking
arrangement shall be fail-safe type.
2.2.3.4
Typical isolator interlocks such as breaker open for opening and closing of
isolator and earth switch, earth switch closing when the respective isolator
is open and ensuring the bus is dead before closing the earth switch for bus
earthing shall be provided.
2.2.4
Insulators
2.2.4.1
Insulators used in the assembly of isolators shall be of porcelain and of
brown colour. Insulator cap and base shall be of high-grade cast steel or
malleable steel casting and they shall be machine faced and galvanised.
2.2.5
Operating Mechanism and Controls
2.2.5.1
The ganging mechanism shall be provided with sufficient adjustment to
allow for final alignment of the isolator blades for simultaneous operation.
Adjustable stops shall be provided to prevent over-travel in both
directions. The mechanism shall provide quick, simple and effective
operation.
2.2.5.2
The manual operating handles shall be mounted on the base of supporting
structure. Guide bearings shall be provided, if necessary, at a height of
1250 mm above grade level. Where isolator is required to be connected to
high level buses, the operating rod shall be provided with guide bearings
at an interval of 3 metres. All members necessary for attaching the
operating mechanism and operating handles to the supporting structure
and foundations shall be supplied as an integral part of the isolator.
Rustproof pins and bearings of the brass bushing, ball and roller type, shall
be furnished. All bearings shall be weather protected by means of covers
and grease retainers.
2.2.5.3
A weather-proof galvanised sheet steel cabinet with gasketed hinged door
and padlocking facility shall be provided to house driving mechanism,
motor starters, control valve solenoids, auxiliary switches, etc., as
applicable. All cabling from operating mechanism and auxiliary contacts
to operating mechanism box shall be in the scope of supply of the
Contractor and shall be carried out using 1100 V grade, 1.5 sq. mm.
stranded copper conductor, PVC insulated, armoured, multicore cables or
single core cables laid in heavy gauge galvanised steel conduits, unless
otherwise specified.
2.2.5.4
In addition to the limit switch contacts required for control of power
operated isolators, the number of spare auxiliary contacts as mentioned
above (6 NO + 6 NC) shall be provided for Employer's use. The auxiliary
contacts shall be of silver faced copper. The contacts shall be designed to
carry 10 A continuously. All contacts shall be suitable for breaking an
inductive current of 0.2 A at 220 V DC.
2.2.5.5
A local isolating switch-fuse unit/MCB for disconnection of power supply,
a local/remote selector switch and a set of open/close push buttons shall be
provided in the operating mechanism box for power operated isolators.
2.2.5.6
The control of power operated isolators shall be so arranged that the
desired operation shall be completed when corresponding push button is
pressed even momentarily. The control circuit shall be so arranged that
necessary interlocks with associated breaker and earthing switch can be
incorporated.
2.2.5.7
Arrangement shall be provided to permit manual operation of power
operated isolators. The arrangement shall be such that when manual
operating handle is in the engaged position, the power operation is made
inoperative. Padlocking facility shall be provided for the manual
operating handle. One detachable manual operating handle for every
group of four (4) power operated isolators shall be provided.
2.2.5.8
The operating mechanism design shall be such that during the operation of
the isolator, especially manual operation, when the moving blades reach
the sparking distance, springs take over to give a quick, snap action
closing so that the isolator closing is independent of manual efforts.
Similarly, the springs must assist during the opening operation to give
quick breaking feature.
2.2.5.9
Motors shall be totally enclosed, weatherproof, outdoor universal type and
tropicalised. Magnetic contactor type of starters suitable for direct-on-line
duty shall be provided for control of motors.
2.2.5.10
Limit switches for motor control shall be fitted on the isolator shaft, within
the cabinet, to sense open and close positions of the isolator.
2.2.5.11
Adequate no. of spare terminals shall be provided in the operating cabinet
for the purpose of external interlocks.
2.2.6
Supporting structures
2.2.6.1
Supporting structures for isolators shall be of hot dip galvanised steel. The
Contractor shall furnish detailed dimensioned drawings indicating weights
and all fixing details and relative locations of chassis, operating
mechanism box and operating handles, etc. after the award of the work.
2.2.6.2
Insulators used in the isolators shall be of the sleek solid core post type
made of porcelain to withstand a mechanical force of 1600 N.
2.2.6.3
Terminations shall be suitable for connection of compression terminal lugs.
2.2.
Tests
2.2.7.1
All routine tests shall be conducted on completely assembled isolators,
earthing switches, their operating devices and auxiliary equipment in
accordance with the applicable standards.
2.2.8
Current Transformers
2.2.8.1
Applicable Standards
:
IEC 60044-1, 60186 /BS 7625 &
7626/IS 2705, 3156
2.2.8.2
Parameters for CTs
a)
Type
i.
66 kV CTs
:
Outdoor Oil filled
b)
Power System details
:
As per protection and
metering requirements
c)
Class of insulation
:
A or better
d)
Rated extended primary
current for CTs
:
120% of rated primary
current
e)
Parameters such as no. of
:
cores, output, accuracy class,
current and voltage ratios, etc.
Will be finalized after award
of contract
2.2.8.3
Specific requirements
2.2.8.3.1
Secondary terminals of voltage and current transformers shall be brought
out in a weatherproof terminal box. Facility shall be provided for shortcircuiting and grounding the CT secondary at the terminal box. Glands
and lugs for terminating external cable connections shall be provided.
2.2.8.3.2
Terminal and polarity marks shall be indelibly marked on each VT and CT
on the associated terminals and these marks shall be in accordance with
relevant standards.
2.8.3.3
Current transformers shall be provided with the following accessories
including but not limited to:
a)
H.V. connectors for the HV conductor.
b)
Two earthing terminals on tanks on opposite sides for connecting
to the station earthing conductors.
c)
Oil level gauge.
d)
Filling and draining plugs.
e)
Power factor testing terminal.
f)
Facility for lifting bushings and tanks.
g)
Insulating oil required for first filling plus 10% excess. Power
factor of the transformer oil shall not exceed 0.005. Insulation oil
shall comply with applicable standards.
h)
Rating and diagram plate as per relevant standards.
2.2.8.4
The temperature rise shall not exceed the figures given in applicable
standards for operation under ambient temperature conditions specified.
2.2.8.5
The tanks/base and all exposed ferrous parts shall be hot dip galvanised
conforming to applicable standards.
2.2.8.6
In the case of multi-core CTs, it shall be possible to adjust the tap settings
on any core independent of the setting on the other cores, for which
purpose these tappings will have to be provided on the secondary
windings.
2.2.8.7
All CT cores under this Specification shall be of low reactance type.
2.2.8.8
No turn’s compensation shall be used in case of class 'PS' CTs.
2.2.8.9
In case of multiratio CTs, the minimum specified requirements in respect
of VA, accuracy, Knee Point Voltage (KPV) and maximum secondary
resistance specified shall be met at all taps.
2.2.8.10
Magnetising characteristics (extending well beyond KPV) and secondary
impedance values shall be furnished in Schedule of particulars for all
protection cores.
2.2.9
Insulators/ Bushings
2.2.9.1
Insulators/Bushings shall conform to applicable standards and shall be
made of homogeneous vitreous porcelain, the glazing of which shall be of
uniform brown or dark brown colour.
2.2.9.2
Oil filled insulator/ bushings shall be hermetically sealed to prevent
ingress of moisture. A cushion of nitrogen gas shall be provided to allow
for expansion.
2.2.10
Tests
2.2.10.1
Certificates of type tests carried out on similar CTs and VTs shall be
furnished with the Bid.
2.2.10.2
All routine tests as per applicable standards shall be carried out on CTs in
the presence of the Employer's representative.
2.2.10.3
Optional tests, where applicable shall be carried out by mutual agreement
between the Employer and the manufacturer.
2.2.10.4
In addition, the following tests shall be carried out on CT and VT of each
type
a)
b)
c)
Temperature rise test
Lightning impulse test
Determination of errors