Crompton Greaves AC Motors

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Crompton Greaves AC Motors

MECHANICAL FEATURES
General Enclosure
Frames 63 to 100 L with prefixes AD are of diecast aluminum. Foot mounted stators have integral feet. TEFC & TE motors have integral longitudinal ribs for effective heat transfer. Specially designed roller table motors for steel plants have circular ribs to avoid deposition of dust & slags between the ribs.
The stator & end shields are machined to close tolerances for providing perfect alignment&fits.
Terminal boxes of frames up to 132M are of diecast aluminum alloy. Frame 160 & above have cast iron terminal box. All joints in terminal box are sealed with gaskets. Motors above frame 160 have drain holes at their lowest position as a standard features.

Core
Both stator and rotor cores are made of high quality magnetic steel

Windings
Stator and rotor (for SR motors) windings consists of modified polyester enamel covered copper wire. Frame 280 and above are wound with dual coat copper wire as per IS: 13730-13. Motors wound with double glass covered conductors are also available on order for frame 160 and above only.

Insulation
All motors are made with class F insulation as a standard feature. The slot liners are either provided with double cuffing or edge binding at the slot mouth portion to strengthen the insulation. For frame 160 & above class F varnish or resin with vacuum pressure impregnation is used for impregnating the winding. Epoxy gel coat is sprayed on all winding overhangs (in frames 200 and above) to provide mechanical rigidity to the winding to withstand the electrical and mechanical stresses. Surge testing is carried out on all windings in addition to all other tests ensuring healthiness of windings. The overhangs of SR rotors are banded with resi-glass tape under controlled tension, to prevent flaring under centrifugal force caused by over speed.

Rotor
The rotor of SCR motors are made of pressure diecast aluminum (or alloy in case of special designs) up to frame ND355L. Rotors of specific polarity are made of electrolytic copper & copper alloy bars & rings connected by high quality silver brazing. The rotors of SR (slipring) motors are wound with copper wire or strip. (See in winding and insulation).

Slipring And Brushgear
SR motors are provided with slipring and brush gear arrangement. The Sliprings are moulded in epoxy-based insulation and have excellent stability at high temperature and have very good anti tracking property. Fabricated Sliprings as per Steel Plant's specification (IPSS) are also available on request for frames 160&above. 3 Nos. brush holders with 2 nos each metal graphite carbon brushes are provided- one on each ring phase. The grade of carbon brush is M15E of Assam carbon or equivalent. Each carbon brush is marked with its grade and the line of wear, which helps in identifying replacement need. The brush holders are made of brass. For 160 to 200, self tension adjustment brush holders are used . Frames 225 and above have adjustable arms to suit the range of slipring diameter. This always facilitates angular adjustment of arms for radial placement of brushes even after reduction in diameter of slipring, resulting out of any rework carried out in service. The brush tension is adjustable with the help of adjustable nuts provided on the brush arm. The sizes of brush and recommended force for all frames are as given in the table:


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