| Certification: | ISO9001 |
|---|---|
| Shell Material: | Steel Plate |
| Voltage Level: | Medium Voltage |
| Installation: | Fixed |
| Structure: | Cabinet |
| Current: | AC |
| Customization: |
|---|
Suppliers with verified business licenses
Audited Supplier 7.0 Technical Specifications/ Requirements of 33KV GIS
7.1 General
This section of the document includes the design, manufacture, testing & inspection of 33 KV GIS as specified.
7.2 Climate Data
The distribution transformers to be supplied against this contract shall be suitable for satisfactory use under the following climatic condition:
Transformers as specified will be installed in a hot humid environment and presence of the insects and presence of the insects and vermin locations. The information is given as a guide for Tenders and no responsibility for its accuracy will be accepted, nor any claim based on the above be entertained.
7.3 System Particulars
7.4 Standards
The equipment specified in this Section shall conform to the latest edition of the appropriate IEC specifications and other recognized international standard. In particular:
British Standards
BS 159 Specifications for HV bus bars and bus bar connections
BS 1977 Specifications for high conductivity copper tubes for electrical purposes
BS 2898 Specifications for wrought aluminium for electrical purposes. Strip with drawn or rolled edges.
BS 3938 Specification for current transformers.
BS 5253 Specifications for AC disconnectors and earthing switches.
BS 6651 Lightning Protection
BS 7354 Code of practice for design of HV open terminal stations.
IEC Standards
IEC 62271-200 A.C. metal-enclosed switchgear and controlgear for rated voltages above 1KV and up to and including 52 KV.
IEC 62271-102 High-voltage switchgear and controlgear -Part 102:Alternating current disconnectors and earthing switches.
IEC62271-100 High-voltage switchgear and controlgear -Part 100:Alternating current circuit breaker.
IEC 694 Common clauses for high-voltage switchgear and control gear standards
IEC 298 A.C. metal-enclosed switchgear and controlgear for rated voltages above 1KV and up to and including 52 KV.
IEC 376 Specification and acceptance of new sulphur hexafluoride
IEC 480 Guide to checking of sulphur hexafluoride taken from electrical equipment.
IEC 60 High Voltage test techniques.
IEC 71 Insulation Co-ordination
IEC 99 Surge arresters
IEC 129 AC disconnectors (isolators) and earthing switches.
IEC 44-1 Current transformers.
IEC 44-2 Voltage transformers.
IEC 211 Tests on hollow insulators for use in electrical equipment.
IEC 265 HV switches.
IEC 56 HV alternating current circuit breaker
IEC 273 Characteristics of indoor and outdoor post insulators for systems with nominal voltages greater than 1000V
7.5.1 Switch gear-Design and Performance:
33 KV gas insulated switchgear shall be suitable for indoor location and capable of continuous operation under the climatic conditions existing on site. It shall be designed to comply with this Specification and relevant IEC and British Standards where applicable.
In all cases the ancillary plant necessary to complete installation of the equipment shall be included in the Contract.
The disposition of plant in any substation is to be such that the operation of any item of plant under the specified service conditions shall in no way create a condition that could adversely affect the performance of adjacent circuit breakers or any associated equipment.
The Contractor is to ensure that the complete substation installation will satisfy the requirements of this Specification and the appropriate Standards in respect of insulation, fault levels, mechanical stress etc., and any additional equipment found to be necessary to meet these requirements shall be deemed to have been included in the Contract Price.
The layout and design of plant and equipment on substation sites shall make provision for the future extensions shown on the layout drawings and shall provide for ready access for operation, maintenance and extension whilst the remaining sections of equipment are alive. Working clearances provided between isolated equipment and nearest live metal work shall not be less than the British Standard section clearances.
Insulation creepage distances shall not be less than 25mm per KV rated voltage between phases.
The Contractor shall be responsible for ensuring that insulation co-ordination in accordance with recommendation of IEC-71 is achieved. Dynamic and temporary over voltages shall be assumed to be in accordance with normally accepted IEC levels.
The 33 KV Gas Insulated switchgear with circuit breakers having vacuum interruption facility shall be Indoor, Metal clad, dust & vermin proof, factory assembled, type tested, protected against condensation and aggressive gases, double busbar and single phase or three phase encapsulated. All high voltage components/ parts must be fully gas insulated sealed hermetically and safe-to- touch. The Switchgear (primary section) panel shall be filled with insulating gas at sight or in factory and fitted with gas monitoring device with contact. SF6 may be used as an insulating medium, not for quenching.
All control and monitoring elements should be accessible from the front.
The arrangement of the Circuit-breaker in the panel must be such that in the event of any necessary inspections both the operating mechanism and the arc chambers can be removed and reinstalled from the front or back in a verifiably short time. The bus bars must remain in uninterrupted operation and there must be no reduction in either the insulation level (additional measures such as protective barriers are not permitted) or personal safety. Confirmation must be provided with the quotation.
Each sealed-off gas compartment must have its own pressure relief facility, which in event of arcing fault prevents uncontrolled rupturing of the compartment. The manufacturer must guarantee an adequate pressure reserve between the operating value of the pressure relief and the rupturing pressure of the vessels. The pressure relief facilities must limit the effects of a fault arc to one compartment. Gas escaping under pressure must divert in a direction that is not dangerous for operating personnel; the same applies to fixed parts (rupture diaphragms etc).
Pressure monitoring takes place with contact-making manometer gauges, which function independently for each bus bar section, three-position switch gas compartment or bus bar voltage transformer set respectively or temperature compensated gas sensors for each gas compartment, which shall be equipped with self-supervision and independent of availability of power/voltage source.
The gas compartments must be well sealed both mutually and to their surroundings. The gas loss must not exceed 0.1% per year and compartment. The filling pressure must be selected so that after thirty years of operation the full test voltages can still be withstand, without any topping up.
The use of plastics must be minimized, in order to likewise minimize the risk of fire in the event of a fault.
The Current transformer must be of the di-electrically non-stressed and must not be cable mounted.
The Voltage transformer shall be of plug-in-design and located outside of the gas enclosure and disconnect able by a three position isolation switch.
Cable termination shall be totally insulated. Provision should be kept for plug-in connection of at least two cables per phase.
The LV compartment shall be made of high quality sheet steel with powdered coated painting with sufficient space for mounting secondary equipment.
The complete switchgear must be compact in dimension as space is very limited.
Interlocking between the Circuit breaker and three position switch should meet the following conditions:
· To prevent the disconnector from switching under load, they may only be actuated with the circuit-breaker open.
· The three-position switch must be prevented from switching through from the closed state in to the "ready-to-earth" position.
· The three-position switch can only be brought into the earthing position if the circuit breaker is open.
· Closing of the circuit-breaker must be blocked for as long as the three position switch has not reached a definite switching position.
· For earthing of the feeder, reliable "interrogation interlocking" must be provided. Only the three-position switch is switched into the "ready-to-earth" position, feeder can be earthed and short-circuited by closing the circuit-breaker.
Gas compartment must be provided with gas pressure monitoring by pressure gauge with signaling contacts, to signal any increase drop of gas pressure.
The individual panels are to be connected by solid insulated, plug-in bus bars outside the SF6 Gas compartment. The bus bar is to be located in a metal-clad compartment. No gas handling at site is preferred.
The switchgear must be extendable at both ends of the bus bars.
The Vacuum Circuit Breaker as a making/breaking unit, including operating mechanism, must be maintenance free.
The three-position disconnector (ON-OFF-EARTH) is to reduce the number of functional elements within the encapsulation and together with the circuit breaker, provide make-proof earthing.
In order to reduce the number of mechanical parts within the encapsulation, the operating shafts are to be located outside the encapsulation. The switches are to be operated without a seal via gas-tight welded-in bushings.
The material of the SF6 containers is to consist of non-corroding high-quality metal/metal composition. The live parts are to be insulated against the earthed housing by SF6 gas.
The Transformers are to be exchangeable toroidal-core or ring type transformers which are to be used outside the SF6 encapsulation so that they are not exposed to dielectric stress.
The cable terminals of the 3-Phases are to be located horizontally next to one another on one level and are to be easily accessible from the front or rear.
Medium-Voltage Section
The Medium Voltage section must be maintenance free and immune to environmental influences.
The installation must be resistant to accidental arcs.
All switches are to be operated from the front. The circuit breakers must be remotely controllable.
Capacitive dividers in the bushing to the bushing to the cable terminal compartment are to allow safe testing for dead state at the panel front. The degree of protection of the switchgear must not be reduced here.
Gas Compartment Technology
The sealed gas compartment must have its own pressure relief device which prevents uncontrolled bursting of the gas compartment when an accidental arc occurs. The manufacturer must guarantee a sufficient pressure reserve between the operating pressure of the pressure relief devices and the bursting pressure of the container.
The gas compartment must be tightly sealed. The filling pressure is to be such that at least 30 years service is guaranteed without the necessity of refilling.
The pressure of the SF6 gas is to be monitored inside the gas compartment by means of pressure-gauge manometer which to be temperature compensated sensor with self-supervision independent of any auxiliary power availability. In this way, complete temperature compensation can be achieved. Any pressure drop beyond the safe level as specified by the manufacturer shall be indicated in the form of sound and light alarm. Each Bus-section shall have individual pressure monitoring arrangement.
Locking Devices
Three-position disconnectors (ON- OFF- EARTH) must be mechanically locked against the circuit breaker
The inductive type Cast-resin insulated Voltage transformer shall be mounted outside the primary enclosure. The VTs can be plugged into the bus bar. The Voltage transformer on bus bar must be designed for 80% Power frequency withstand voltage so that repeat tests can be carried out on the bus bar without removal of the transformer. However, the voltage transformer on bus bar must be capable of withstanding over 100% power frequency withstand voltage under normal operating conditions.
Cable termination shall be totally insulated. Provision should be kept for plug-in connection of at least two cable per phase.
The LV compartment shall be made of high quality sheet steel with powdered coated painting with sufficient space for mounting secondary equipment.
The complete switchgear must be compact in dimension as space is very limited. Also the Switchgear should be suitable for future extension or replacement of panels without affecting the gas enclosures.
7.5.2 Current Ratings
Every current-carrying part of the switchgear including current transformer, busbars, connections, contacts and joints shall be capable of carrying its specified rated current at rated frequency continuously and in no part shall its temperature rise exceed that specified in relevant standards.
7.5.3 Corona
Equipment shall be designed so as to minimize corona or other electrical discharge and radio interference. Tests for corona and radio interference shall be carried out by the Contractor at his Works and on Site.
7.5.4 Local, Remote and Supervisory Control
Circuit breakers and motorized disconnectors shall be electrically controlled locally, remotely and by supervisory control.
Position indication of these devices shall be provided via auxiliary switches on their operating mechanisms and the Contractor shall include the supply and fitting of the necessary auxiliary switches.
For supervisory control, the interface between the automation devices and the control equipment being provided under this Contract if required.
7.5.5 Circuit Breakers
7.5.5.1 Type
33 KV Gas Insulated circuit breakers having SF6 interruption facility shall have spring operating mechanism.
7.5.5.2 Operating Duty and Performance
i) General
The requirements of IEC-2271-100 in respect of type tests, service operation and the making and breaking of fault currents shall apply to all types of circuit breakers. Designs shall be suitable for interrupting 3-Phase ungrounded faults.
ii) Test Certificates
Circuit breakers shall be covered by test certificates issued by a recognized testing laboratory certifying the operation of the circuit-breaker at duties corresponding to the rated breaking capacities of the circuit-breakers. The test duty shall not be less onerous than the requirements of BS 5311 or equivalent. Test certificates or equivalent shall be submitted with the tender.
Test certificates should conform with current standards for type test approval tests.
iii) Rate-of-Rise of Restriking Voltage
Attention is drawn to the requirements of the minimum inherent rates of rise of restriking voltage of test plant arrangements. Where not specifically stated in the test certificates submitted with the Tender, the Tenderer shall certify that the TRV to which the circuit-breaker was subjected during the short circuit tests was the most severe condition that could be imposed by the available test plant for a first phase-to-clear factor of 1.5.
Any device incorporated in a circuit breaker to limit or control the rate of rise of restriking voltage across the circuit breaker contacts shall likewise be to the Engineer's approval and full descriptions of any such device shall be given.
iv) Interrupting Duties
In addition to the requirements of IEC 56 for interrupting terminal faults, circuit-breakers shall be capable of coping with the interrupting duties produced by the switching of low inductive currents associated with reactors or transformer magnetizing currents, or by the switching of capacitor currents associated with overhead line-charging, cable-charging or capacitor banks as may be applicable.
Circuit breakers shall be capable of interrupting currents associated with short-line faults and the out-of-phase switching conditions that may occur in service.
v) Break Time
Attention is drawn to the specification Clause-5.2 wherein the overall fault clearance times (i.e. relaying time plus circuit breaker time) are specified.
Insulation Coordination
The insulation strength across the open circuit breaker shall be at least 15 per cent greater than the line to ground insulation strength for all impulse, switching surge and power frequency voltage conditions.
7.5.5.3 General Arrangement
Outdoor circuit breakers shall be suitable for mounting directly on concrete pads and shall include any necessary supporting steelwork. For indoor sub-station circuit breaker shall be suitable for mounting directly on the cubicle.
Evidence shall be provided that enclosures subject to pressures in excess of normal atmospheric pressure during service operation have withstood approved pressure tests without leakage, permanent distortion or any temporary distortion such as might cause maloperation of the circuit breaker.
7.5.5.4 Operating Mechanisms
Circuit-breaker mechanisms shall be "trip free" as defined in IEC Publication 56-1 and BS 5311:1976. It is recognized that it may be necessary for contacts to close momentarily prior to opening to ensure satisfactory current interruptions.
Each part of the operating mechanisms shall be of substantial construction, utilizing such materials as stainless steel, brass or gunmetal where necessary to prevent sticking due to rust or corrosion. The overall designs shall be such as to reduce mechanical shock to a minimum and shall prevent inadvertent operation due to fault current stresses, vibration or other causes.
An approved mechanically operator shall be provided on each circuit-breaker operating mechanism to show whether the circuit breaker is open or closed. Each phase shall incorporate a mechanical indicator or other approved means of position indication where operating mechanism designs do not utilize mechanical coupling between phases.
Where circuit breakers comprise three independent units it shall be possible to make independent adjustments to each unit. For 3-Phase operation the three units shall make and break the circuits simultaneously. In the event of any phase failing to complete a closing operation, provision shall be made for automatic tripping of all three phases of the circuit breaker.
Power closing mechanisms shall be recharged automatically for further operations as soon as the circuit-breaker has completed the closing operation and the design of the closing mechanisms shall be such that the cannot be operated inadvertently due to external shock forces resulting from short circuits, circuit-breaker operation or any other cause.
Circuit-breaker operating mechanisms capable of storing energy for at least two complete closing and tripping operations, local to the equipment and without recharging, are preferred. Mechanisms incapable of storing energy for at least two complete operations shall utilize the substation DC supply for recharging the mechanism.
7.5.6 Operating Cubicles
Circuit-breaker operating mechanisms, auxiliary switches and associated relays, control switches, control cable terminations and other ancillary equipment shall be accommodated in aluzinc/anodized coated sheet aluminum vermin-proof and weatherproof cubicles. Where appropriate the cubicles may be free standing. Cubicles are to be painted with RAL 7044 & RAL 7032 colour.
Cubicles shall be of rigid construction, preferably folded but alternatively formed on a framework of standard rolled steel sections and shall include any supporting steelwork necessary for mounting on the circuit breaker or on concrete foundations. Bolts or carriage keys shall not be used to secure the panels or doors. All fastenings shall be integral with the panel or door and provision made for locking. Doors and panels shall be rigid and fitted with weatherproof sealing material suitable for the climatic conditions specified.
Cubicles shall be well ventilated through vermin-proof louvres comprising a brass gauge screen attached to a frame and secured to the inside of the cubicle. Divisions between compartments within the cubicle shall be perforated to assist air circulation. In addition, thermostat controlled anti- condensation heater of an approved type shall be provided and controlled by a single pole switch mounted within the cubicle. In addition, thermostat controlled anti-condensation heater of an approved type shall be provided and controlled by a single pole switch mounted within the cubicle.
Access doors or panels shall be glazed where necessary to enable instruments to be viewed without opening the cubicles. The arrangement of equipment within the cubicle shall be such that access for maintenance or removal of any item shall be possible with the minimum disturbance to associated apparatus.
Circuit breaker control position selector and circuit-breaker operating control switches as specified in the Specification shall be installed in the cubicle. Circuit-breaker control from this position will be used under maintenance and emergency conditions only.
Where practicable an approved schematic diagram of the part of the control system local to the circuit-breaker, identifying the various components within the cubicle and on the circuit-breaker and referring to the appropriate drawings and maintenance instructions, shall be affixed to the inside of the cubicle access door. The diagram shall be marked on durable non-fading material suitable for the specified site conditions.
7.5.7 Voltage Transformers
Voltage transformers shall comply with IEC 60044-2 and IEC 60186 and the requirements of this specification.
Separate sets of fuses or MCBs shall be provided at the VT for :
a) Each protection scheme
b) Instruments, recorder etc.
c) Synchronizing
The circuits for each main protection scheme shall be segregated in separate multicore cables from the VT to the protection panels. An (VT failure) alarm shall be provided for each set of fuses and MCB s.
The 33 KV voltage transformers shall be of the following specifications and ratings:
KV//V Burden = 15VA, 0.2% acc. for each phase accuracy class 0.2 and 3P
The insulation value of the PT shall be rated maximum system voltage 36 KV and nominal 33 KV, BILL-170 KV and power frequency withstand voltage for 1 min.70 KV.
7.5.8 Current Transformers
Current transformers shall comply with IEC 60044-1 and the requirements of this Specification.
Primary winding conductors shall be not less than 100sq. mm section and shall have a one second short time current rating not less than that of the associated switchgear. Secondary windings of each current transformer shall be earthed at one point only.
Magnetization and core loss curves and secondary resistance shall be provided for each type and rating of current transformer. Where the Contractor wishes to provide current transformer ratios differing from those specified, he shall first obtain approval in writing from the Engineer for each specific instance.
Current transformers for balanced protective schemes, including neutral current transformers where appropriate, shall have identical turns ratio and shall have magnetization characteristics for each specific instance.
Current transformers shall be capable of withstanding, without damage, the peak and rated specific short-time currents of their associated equipment. They shall also withstand continuously a current equal to 1.2 times the CT ratio, except for transformer circuits when 1.5 times shall apply.
Current transformers provided for protective gear purposes shall have over current and saturation factors not less than those corresponding to the design short circuit level of the system. The output of each current transformer shall be not less than 15 VA with an accuracy limit factor of 20 and it shall be ensured that the capacity of the current transformers provided is adequate for operation of the associated protective devices and instruments. Where double ratio secondary windings are specified, a label shall be provided at the secondary terminals of the current transformer indicating clearly the connection required for either ratio. These connections and ratio in use shall be shown on appropriate schematic and connection diagrams.
The accuracy class of all protection CTs shall be 5P or better and that of metering CTs shall be 0.2 or better.
Current transformers for all unit type protection shall be of the low reactance type and their performance shall be stated in terms of the Class X parameters of IEC standard (low reactance current transformers are preferred for all forms of protection). Current transformers may be shown to be low reactance by virtue of their construction as per IEC Standard.
If all the constructional requirements are not met, then type tests will be required to prove that the current transformers are low reactance; the primary test current shall not be less than the through fault(stability) current of the protection.
The CT cores for each Main protection scheme shall be segregated in separate multi-core control cables from the current transformer through to protection panels.
Where double ratios are specified with multiple windings, it shall be possible to select either ratio for each winding without alteration to the number of primary turns.
Neutral current transformers shall be of the outdoor totally enclosed, porcelain bushing type complete with suitable mounting steelwork/cast resin insulation as specified and complete with terminal box for secondary connections.
The Contractor shall provide details of their method of calculating the outputs of the current transformers for each type of protection specified and shall submit calculations for all the current transformers to the Employer before starting manufacture.
Current transformer shall be capable of withstanding without damage at full load, peak and rated short time current.
Current transformers shall be located on the non busbar side of the circuit breaker except where current transformers are provided on both sides of the circuit breaker. The current transformer shall comply IEC185 with latest revision
The 33 KV feeder panel CTs shall have two cores and transformer feeder panel CTs shall have three cores for protection and metering. The capacity, ratio and accuracy class of the CT will be of the following specification and rating:
800-400/5-5-5A, 1st core 15 VA, acc. 0.2% FS>5 for metering
2nd core 15 VA, acc. 5P20 for protection.
3rd core 15 VA, acc. Class X for protection.
1600-800/5-5A, 1st core 15 VA, acc. 0.2% FS>5 for metering
2nd core 15 VA, acc. 5P20 for protection.
800-400/5-5-5A, 1st core 15 VA, acc. 0.2% FS>5 for metering
2nd core 15 VA, acc. 5P20 for protection.
3rd core 15 VA, acc. 5P20 for protection.
The insulation value of the CT shall be rated maximum system voltage 36 KV and nominal 33 KV, BIL-170 KV and power frequency withstand voltage for 1 min.70 KV.
7.5.9 Interlocking Facilities
Disconnectors, earthing switches, circuit breakers, etc., shall be provided with an interlocking system, which ensures safe operation of the equipment under all service conditions.
The items of plant supplied under this Contract shall be complete with all interlocking facilities needed for the final arrangement, avoiding the need for future modifications.
Where mechanical key interlocks are employed, they shall be effective at the point where hand power is applied so that stresses cannot be transferred to parts remote from that point.
Tripping of the circuit breaker shall not occur if any attempt is made to remove a trapped key from the mechanism. Emergency tripping devices shall be kept separate and distinct from any key interlocking system and shall be clearly labeled, suitably protected from inadvertent operation but readily accessible.
Circuit breakers shall be interlocked so that, except under maintenance conditions, it is not possible to close a circuit breaker unless the selected bus bar and circuit disconnectors are closed.
Except as stated below, disconnectors shall be so interlocked that they cannot be operated unless the associated circuit breaker is open.
All electrical interlocks shall so function as to interrupt the operating supply, and an approved system of interlocks shall be provided which shall cover the emergency hand operation of apparatus which is normally power operated. Failure of supply (or its restoration after an outage) or of connections to any electrical interlock shall not produce or permit faulty operation. Electrical bolt interlocks shall be energized only when the operating mechanism is being operated. Visible indication shall be provided to show whether the operating mechanism is locked or free. Approved means, normally padlocked, shall be provided whereby the bolt can be operated in the emergency of a failure of interlock supplies.
7.5.10 Auxiliary Switches and Contactors
Circuit-breakers, disconnectors and earthing devices and circuit selector disconnectors shall be provided with suitably rated auxiliary switches and contactors, where permitted, to relay circuit information for the purpose of control, protection, indication and metering at the substation site as required by the relevant section of the Specification. In addition they shall be provided with auxiliary contacts for position indication to the central system control room via the remote supervisory system. Disconnector auxiliary switches are not to be used for current transformer switching circuits.
Auxiliary contactors shall be provided only where the circuit requirement cannot be met by the auxiliary switch arrangements and multiple contractors and relays will not be accepted in lieu of the auxiliary switches except as specifically approved by the Engineer. Auxiliary switches and contractors shall comply with the requirements of this Specification and in particular shall be capable of operation within the same voltage limits as specified for the associated circuit-breaker close and trip coils.
The connections of all auxiliary switches, including spares, and contractors as well as the associated coil connections and interconnections between auxiliary switches, shall be wired to a terminal board located in the operating cubicle or other approved position.
Auxiliary switches and contractors shall be mounted in an approved accessible position clear of the main operating mechanism but with a minimum of additional mechanical linkages and housed in a substantial weatherproof enclosure. Where adjustable linkages are provided to facilitate the timing of the auxiliary switches with respect to the main equipment, approved locking devices shall be fitted.
Auxiliary switch contacts shall be positively operated, make with a wiping action and, where necessary, discharge resistors shall be provided to prevent arcing when breaking inductive circuits.
Except for the contacts employed for control and interlocking, the requirements for auxiliary switches in respect of timing shall be as follows :
For Circuit Breakers
Normally open contacts, with the exception of two sets of this type, shall close in about 10 milliseconds after the making of the main circuit-breaker contacts and shall open in about 10 milliseconds before the separation of the main circuit-breaker contacts whilst the two remaining sets shall close in about 5 milliseconds before the making of the main circuit breaker contacts and open simultaneously with the main circuit contacts.
Normally closed contacts shall close 10 milliseconds after the opening of the main circuit-breaker contacts and open at least 10 milliseconds before the making of the main circuit-breaker contacts.
For Bus Bar Disconnectors
The operating sequence of any disconnector auxiliary switches used in D.C. circuits for high impedance bus bar zone protection shall be such that the auxiliary switches operate:-
a) Before reaching the pre-arcing distance on closing the disconnector.
b) After the pre-arcing distance has been exceeded on the opening of the disconnector.
For Earthing Switches
As for Bus bar disconnector auxiliary switches, Auxiliary switches shall be adjustable from normally-open to normally-closed or vice-versa.
7.5.11 Surge Arresters
Surge arresters shall be of the type employing non-linear metal oxide resistors without spark gaps. The contractor shall demonstrate by calculations that the surge arresters will adequately protect the switchgear arrangement proposed.
Arresters shall be designed and tested in accordance with the requirements of EN 50181. Any departure shall be the subject of agreement between the Engineer and the Contractor. Routine tests shall be carried out in accordance with the requirements of the Specification.
Surge arresters shall be plug-in-type designed to withstand extremes of the environment described. The insulation shall have a minimum creepage distance of 25mm/kV rated system phase to phase voltage. Porcelain shall comply with IEC 233. The method of sealing against the ingress of moisture shall be of a type well proven in service and the manufacturing procedures shall include an effective leak test which can be demonstrated to the inspecting engineer if required.
The internal components of arresters shall be arranged to minimize radial voltage stresses, internal corona and to ensure minimal capacitive coupling with any conducting layer of pollutant on the outside of the porcelain housing. Except where approved, organic materials are not permitted.
Good electrical contact shall be maintained between resistor blocks taking account of any thermal expansion and contraction of the block or mechanical shock during transport and erection, by installing a well proven clamping system.
Metal oxide arresters installed outdoors shall be able to dissipate, when new, twice the energy generated in the resistor blocks when energized at their maximum continuous operating voltage immediately having been subjected to the discharge duties specified in IEC 99-4 and assuming that the porcelain housing and the surrounding air is at least 5 degree centigrade higher than the maximum ambient air temperature specified.
Good quality control of the manufacturing process of the resistor elements (or ZnO blocks) shall be ensured by rigorous testing procedures. The procedures shall ensure that the characteristics of the blocks are, and will remain, within the specified limits when new and throughout the anticipated life of the arresters. Samples may be selected at random by the Engineer for special tests to be agreed with the manufacturer.
All surge arresters shall be fitted with a pressure relief diaphragm which shall prevent explosive shattering of the porcelain housing in the event of an arrester failure and the arrester shall have been tested according to the high and low current tests specified in IEC 99-1.
Arresters shall be supplied complete for installation in an outdoor switchyard, including insulating bases and surge counters, one per phase, and, if applicable, grading rings. The material used for terminals shall be compatible with that of the conductors to which they are to be connected.
Each arrester shall be identified by a rating plate in accordance with the requirements of IEC 99-4. In addition an identification mark shall be permanently inscribed on each separately housed unit of a multi-unit arrester so that units can be replaced in the correct position in the event of them being dismantled.
Surge counters shall have an internal assembly which is matched to the line discharge capability of the arrester and shall include a leakage current meter with a bi-linear scale for ease of reading. Auxiliary contacts are to be provided to signal remote indication of counter operation.
Surge arrester shall have suitable earth terminal to connect surge counter with insulated cable.
7.5.12 A.C. Motors
Motors shall be wound for nominal 400 volt, 3-pahse, 50 Hz, 3 wire or 230 volt, single phase supply and be capable of operating under frequency variations of + 5 Hz. and/or voltage variations of + 10% starting is to be direct on line.
Motors shall be either of the squirrel cage induction or commutator type. Where squirrel cage motors are to be used, cast rotor construction is preferred. Maximum starting current shall not exceed six times full load current.
Suppliers with verified business licenses
Audited Supplier 
){kind=link}
){kind=link}