1.            GENERAL

66 kV Circuit Breakers shall be outdoor type, comprising three identical single pole units, complete in all respects with all fittings and wiring. The circuit breakers and accessories shall conform to IEC-62271-100 or equivalent Indian Standard.

2.1         Circuit breaker shall be suitable for 3 phase, 50 Hz, 66 kV System. The circuit breaker shall meet the duty requirement of any type of fault or fault location, when used on 66 kV effectively grounded or ungrounded systems and perform make and break operations as per the stipulated duty cycles satisfactorily.
2.2         The rated transient recovery voltage for terminal fault and short line faults shall be as per IEC:62271-100.
2.3         The circuit breakers shall be reasonably quiet in operation. Noise level in excess of 140 dB measured at base of the breaker would be unacceptable. Bidder shall indicate the noise level of breaker at distance of 50 to 150 m from base of the breaker.
2.4         The Bidder may note that total break time of the breaker shall not be exceeded under any duty conditions specified such as with the combined variation of the trip coil voltage, pneumatic pressure and arc extinguishing medium pressure, etc.
2.5         While furnishing particulars regarding the D.C. component of the circuit breaker, the Bidder shall note that IEC-62271-100 requires that this value should correspond to the guaranteed minimum opening time under any condition of operation.
2.6         The critical current which gives the longest arc duration at lock out pressure of extinguishing medium and the duration shall be indicated.
2.7         All the duty requirements specified above shall be provided with the support of adequate test reports to be furnished along with the bid.
3.            Principle Technical Parameters: - The SF6 gas Circuit Breakers covered in this specification shall meet the technical requirement listed hereunder.

Type of circuit breaker
Outdoor SF6 type
Rated frequency
50 Hz
Number of poles
Three (3)
Reclosing duty cycle
O - 0.3 Sec. - CO – 15 Sec.-CO
Rated short circuit breaking current at rated voltage
31.5 kA with percentage of DC component as per  IEC56  corresponding  to  minimum opening  time  under  operating  conditions specified
Symmetrical interrupting Capability
31.5 kA rms
Short time current carrying Capability
31.5 kA rms for one (1) second
Rated normal current in amps.
800A (utility to customize based on actual requirement)
Total break (opening time)
60 m sec. (3 cycles)
Three phase high speed auto reclosing (as required)
Total closing time
100 ms
Trip and closing coil voltage
As per substation D.C.  Voltage
Auxiliary contacts
As required plus 8NO and 8NC contacts per pole as spare.  The  contacts  shall  have continuous  rating  of  10A  and  breaking capacity of 2A with circuit time constant of minimum 20 millisecond at 220V DC (Typ.)
Temperature rise over Ambient
As per IEC:62271-100
Type of operating mechanism
Spring charging
Rated ambient temperature
50 deg. Centigrade
Seismic acceleration
0.3g horizontal
Rated voltage
66 kV (rms)
Rated one minute power frequency withstand voltage (Dry and Wet)
170 kV rms
Rated lightning impulse withstand voltage (1.2/50 Micro-Sec.)
325 kVp
No. of Terminals in common control cabinet
All contacts to be wired to common control cabinet with 24 extra terminal blocks.

4.1            All making and breaking contacts shall be sealed and free from atmospheric effect. In the event of leakage of extinguishing medium to a value, which cannot withstand the dielectric stresses specified in the open position, the contacts shall preferably self-close. Main contacts shall be first to close and the last to open and shall be easily accessible for inspection and replacement. If there are no separately mounted arcing contacts, then the main contacts shall be easily accessible for inspection and replacement. Main contacts shall have ample area and contact pressure for carrying the rated current under all conditions. The interrupter sectional drawing showing the following conditions shall be furnished for information with the bid:

a)   Close position
b)   Arc initiation position
c)   Full arcing position
d)  Arc extinction position
e)  Open position.

4.2            All the three poles of the breaker shall be linked together electrically.

4.3            Circuit breakers shall be provided with two (2) independent trip coils, suitable for trip circuit supervision. The trip circuit supervision relay would also be provided. Necessary terminals shall be provided in the central control cabinet of the circuit breaker.

6.1           Circuit breaker shall be operated by electrically spring charged mechanism.

6.2           The operating mechanism shall be anti-pumping and trip free (as per IEC definition) electrically and either mechanically or pneumatically under every method of closing. The mechanism of the breaker shall be such that the position of the breaker is maintained even after the leakage of operating media and/or gas.

6.3           The operating mechanism shall be such that the failure of any auxiliary spring will not prevent tripping and will not cause trip or closing operation of the power operated closing devices. A mechanical indicator shall be provided to show open and close positions of breaker. It shall be located in a position where it will be visible to a man standing on the ground with the mechanism housing door closed. An operation counter shall also be provided.

6.4           Closing coil shall operate correctly at all values of voltage between 85% and 110% of the rated voltage. Shunt trip coils 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 70% and 110% of rated voltage. If additional elements are introduced in the trip coil circuit their successful operation for similar applications of outdoor breaker shall be clearly brought out in the bid.

6.5           Working parts of the mechanism shall be of corrosion resisting material. Bearings requiring grease, shall be equipped with pressure type grease fittings. Bearing pin, bolts, nuts and other parts shall be adequately pinned or locked to prevent loosening or changing adjustment with repeated operation of the breaker.

6.6           Operating mechanism shall normally be operated by remote electrical control. Electrical tripping shall be performed by shunt trip coil. Provision shall also be made for local electrical control. ‘Local/remote’ selector switches and closes & trip push buttons shall be provided in the breaker central control cabinet. Remote located push buttons and indicating lamps shall also be provided.

6.7           Operating mechanism and all accessories shall be in local control cabinet. A central control cabinet for the three poles of the breaker shall be provided along with supply of necessary tubing, cables, etc.

6.8           Provisions shall be made on breakers for attaching an operation analyser to perform speed tests after installation at site to record contact travel against time and measure opening time.

6.9           The Bidder shall furnish curve supported by test data indicating the opening time under close-open operation with combined variation of trip coil and operating media along with the bid.

6.10        Spring Operated Mechanism
Spring operated mechanism shall be complete with motor, opening spring & closing spring with limit switch for automatic charging and other necessary accessories to make the mechanism a complete operating unit. Opening spring shall be supplied with limit switch for automatic charging and other necessary accessories.

As long as power is available to the motor, a continuous sequence of closing and opening operations shall be possible. The motor shall have adequate thermal rating for this duty. After failure of power supply to the motor, one close-open operation shall be possible with the energy contained in the operating mechanism.

Breaker operation shall be independent of the motor, which shall be used solely for compressing the closing spring.

Motor ratings shall be such that it requires not more than 30 seconds for fully charging the closing spring.

Closing action of the circuit breaker shall compress the opening spring ready for tripping.

When closing springs are discharged, after closing a breaker, closing springs shall automatically be charged for the next operation and an indication of this shall be provided in the local and remote control cabinet.

The spring operating mechanism shall have adequate energy stored in the operating spring to close and latch the circuit breaker against the rated making current and also to provide the required energy for the tripping mechanism in case the tripping energy is derived from the operating mechanism.

6.11        Fittings and Accessories

6.11.1        Following is list of some of the major fittings and accessories to be furnished as integral part of the breakers. Number and exact location of these parts shall be indicated in the bid.

6.11.2       Control unit/Central control cabinet shall be complete with:

a)     Double compression type cable glands, lugs, ferrules, etc.
b)     Local/remote changeover switch
c)     Operation counter
d)     Fuses, as required
e)     Anti-pumping relay/contactor
g)Rating and diagram plate in accordance with IEC including year of manufacture, etc.
h)     Gauges for SF6 gas pressure.
i) Gas density monitor with alarm and lockout contacts

8.           TESTS 
Any fittings, accessories or apparatus which may not have been specifically mentioned in this specification but which are usually necessary for the satisfactory operation of the equipment, shall be deemed to have been included in this specification.

10.      PACKINGS:
All material shall be suitably packed for transport, direct to site and Manufacturer shall be responsible for all damages/losses due to improper packing. All boxes shall be marked with signs indicating the up and down sides of the boxes along with the unpacking instructions, if considered necessary by the Manufacturers.

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