Order list DO 04.12.17

Construction FeaturesConstruction Features

FABRICATION:

  1. Frames, Load bearing members, large doors: 2 mm thick Small doors, shrouds,
  2. Partitions: 1.6 mm thick
  3. Bases and Gland Plates : 3 mm thick

The complete structure is rigid, selfsupporting, free from flaws, twists and bends. All cutouts are true in shape and devoid of sharp edges.

Wherever single core cables are used, gland plates are non-magnetic made of 4 mm thick aluminium sheet.

PAINT: Powder coated RAL 7032 (Siemens grey) throughout.
PRE-TREATMENT PROCESS

CABLE ENTRY: From bottom / top (As required)

REAR ACCESS: Essential

CABLE GLANDS: Not included

CABLE LUGS: Not included

BUSBARS: Electrolytic grade of aluminium) with coloured heat shrink sleeves (joints/connections are bare).
EARTH BUS: 6mm x 50 mm GI throughout the length provided at the bottom.

DEGREE OF PROTECTION: The MCC is dust and vermin – proof construction and provided with degree of protection of IP:52 as per IS:13947. However, the bus bar chambers having a degree of protection of IP:42 are also possible. Provision is made in all compartments for providing IP:52 degree of protection, when circuit-breaker or module trolley has been removed. All cutouts are provided with synthetic rubber gaskets.

CONTROL WIRE: PVC insulated

DOORS / COVERS :

  • Feeder compartments: hinged with quarter turn bakelite knobs (unshrouded). All panel edges and cover/door edges are reinforced against distortion by rolling, bending or by the addition of welded reinforcement members. All equipment associated with an incomer or outgoing feeder are housed in a separate compartment of the vertical section. The compartment is sheet steel enclosed on all sides with the withdrawable units in position or removed. The front of the compartment is provided with hinged single leaf door with captive screws for positive closure.
  • Cable alley: A full height vertical cable alley of minimum 250 mm width is provided for power and control cables. Cable alley door is hinged.
  • Busbar chamber: A completely enclosed bus bar compartment is provided for the horizontal and vertical bus bars. Bolted covers are provided for access to horizontal and vertical bus bars and all joints for repair and maintenance which is feasible without disturbing any feeder compartment. Auxiliary and power bus bars are in separate compartments. Vertical bus bars are behind the feeder compartment. In case of double front, each side has its own vertical bus bars. Bus bars & vertical droppers are provided with heat shrinkable PVC sleeves, except at the tap off and stab in contact plates. Silver plated spring loaded earthing strip in the trolley is provided.

BOLTED CONSTRUCTION: The design of switchgear vertical panels is such that:-

  1. It is possible to extend the panel horizontally on both ends i.e. adequate matching slots/holes are provided. Also, the main horizontal bus bars could extend on either side, adequately outside their end supports.These end extended bus bars have predrilled holes & nuts/bolts / washers etc for future extension.
  2. It is possible to increase /decrease the size of feeder compartment without cutting/rewelding and repainting any of the structural members. It is possible to shift upwards / downwards the module separator without cutting /rewelding.

DRAWOUT CONSTRUCTION:

  • When a feeder is committed in DRAWOUT construction, it will be mounted in a withdrawable chassis which can be cranked into service position by a suitable tool. Sliding will be on telescopic rails. Connections from bus bars will be via stab in self aligning contacts of adequate rating.
  • When the trolley is cranked out, the body still remains earthed till the power is ON. This is achieved by an earth strip which is always in touch with metal body.
  • The trolley has 3 positions :-
    1. Service: In this position all the power/control contacts remain in service.
    2. Test: In this position power contacts are disconnected while controls are connected.
    3. Isolated: Both power & control is OFF.All the above three positions are marked on the trolley for proper positioning.
  • Power Contacts are made of silver plated copper. These are spring loaded & tested for 50 kA / 1 sec. Short circuit fault level. These are mounted on SMC supports in such a way that while cranking in / out the contacts do not have too much of play. These contacts have male / female arrangement and be plugged in the ‘L’ shaped silver plated copper contacts connected to VBB. Single finger contact is used for 63 A. Multiple finger contacts are used for 125 A & above. These contacts are available upto 600 A. The design of contacts is such that the grip actually increases during short circuit faults. The spring used is hardened spring steel, which does not deteriorate even under continuous operation.Power contacts male/female have enough play and are spring loaded. However, no wire springs is used. All stab in contacts are located with the help of at least two location holes / rivets as any of these current carrying parts, after heating get dislocated from their position. For higher rating contacts are multifinger type for adequate current carrying capacity. The design of contacts is such that the grip actually increases during any fault. Hardened spring steel is used for contact pressure.
  • Control Contacts are made in blocks of five way secondary isolating contacts. These also have male / female & are spring loaded so that fixed contacts remain in touch with movable position so that control supply remains ON in test position. Positioning is done in such a way that controls get disconnected only in isolated position.
  • Safety Shutters: These are made of insulating sheet. Fixed into position in such a way that when a trolley is withdrawn, the safety shutter falls & isolates all live parts.
  • Auxiliary Door: All control / indications/ instrument are mounted on a separate auxiliary door, which is a part of drawout trolley. When the trolley is withdrawn all control push buttons / indicating lamps/ammeters etc are withdrawn. These equipments are not mounted on the fixed door obviating the necessity of disconnecting wires from these control equipments.
  • Earth: Specially designed spring loaded scraping type earth contact is provided in the trolley in such a way that earth “makes” before & “breaks” after power contacts.
  • The equipments pertaining to a Drawout type incomer or feeder module are mounted on a fully withdrawable chassis which can be drawn out without having to unscrew any wire or cable connection. Suitable arrangement with cradle / rollers and guides shall be provided for smooth movement of the chassis. For modules of size more than half the panel height, double guides are provided for smooth removal or insertion of module.
  • The safety shutter, in case the module is withdrawn from its trolley properly covers the stab in power contacts and vertical droppers. The safety shutter is without any spring arrangement.

SPACE HEATER: 1 set of thermostatically control space heater in each vertical section will be provided.

INTERCHANGEABILITY: The idea of having draw out switchgear is to have lowest possible downtime. For this there should be complete interchangeability between similar rated/sized feeder trolleys so that in case of a defective feeder, spare trolley can be plugged in and defective ones cranked out in a short time of 2/3 minutes without shutting off the entire board.

All contacts are suitable for “ON” load working, however, the trolley can be cranked in / out only when that particular switch fuse / MCCB is in “OFF” position. It means the load of the particular feeder remains OFF but the vertical bus bar is ON thereby not affecting other feeders on the particular bus. Also, bus connections need not be disturbed as the same are not hard wired but connected through male female plug/socket arrangement.

All identical module chassis of same size are fully interchangeable without having to carryout any modifications. Withdrawable chassis is cranked in position by a suitable tool. Cranking in / out of the trolley is smooth without any jerks. Incoming & outgoing power contacts as well as control contacts are automatically isolated with the movement of module without manual disengagement.

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