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CRGO :

The core is build up firm interleaved low loss cold rolled, gain oriented silicon steel laminations. Individual stamping are coated on both sides with an insulating material, which is both oil & temperature resistant. The core limbs are securely bound with heavy-duty webbed cotton tapes & the yokes are family clamped between steel channels, all cores have mitered joints. Top & Bottom clamps are secured to each other by means of tie rods, which serve the dual purpose of securing the windings in place & of transferring the load from the bottom to the top clamps when the core & windings are lifted. This prevents tensile stresses being set up in the core legs, which could adversely affect the iron losses.
 
 

WINDINGS:

Transformer windings are designed to meet three fundamental requirements such as mechanical thermal & electrical. They are cylindrical in shape & are assembled concentrically. The low-tension windings are of the helical type, single or multiplayer, using flat copper strips, depending upon the size & current rating of the transformer. The high – tension winding consist of paper covered round & strips conductors depending upon the current rating of the transformer. For higher capacity continuous disc winding are used .

Pressboard washers & spacers rigidly support the winding. Interlayer cooling ducts are provided to ensure that the temperature gradient between windings & oil hence the hot temperature is minimized & high life expectancy is achieved. Insulation between layers & Tums is based upon the impulse test level of the voltage class of the winding as specified in IS 2026. Completed core coil assemblies are dried are prior to impregnation with transformer oil.

WINDING CONNECTIONS:

Tapping & lead are run in multi paper covered flexible conductors in press board half tubes, the phase leads being separated from he tapping leads by adequate barriers. These tubes are rigidly based to ensure that clearances between leads & tank sidewall are maintained when the transformer is position. Low voltage leads being of larger cross section are sufficiently robust, so supports are provided wherever necessary.

ISULATION & IMPREGNATION:

The principle components of insulation are pre-fabricated from pressboard sheet. All items subjected to compression in services are preshrunk & the slight recovery in dimension after preshrink age is compensated for windings during final drying of the completed transformer. The oil used for impregnation complies with IS 335 & every consignment received at works is tested before entry is permitted into the storage tanks.

SHORT CIRCUIT STRENGTH:

In order to prevent deformation when subject to shot circuit force, solid blocks & insulation, backed by substantial supporting frames, are utilized. Ensuring that design dimension is closely adhered during manufacturing procedure minimizes the axial end thrust under fault condition. Transformers are designed & constructed in such a way that they are capable of withstanding the effects of short circuit testing. Our transformers have been type tested CPRI.


TAPPINGS:

For the range of transformer covered in this Catalogue, tapping are provide on the H.T. Winding at +5% in steps of +2.5%. Other tapping ranges can be supplied on request. Tap selection is effected by means of an off circuit-tapping switch operated by an external handle. Tapping leads are brought away from the coil by the means of paper-insulated conductors. They are arranged in such a manner that the ampere-turn balance is maintained through the tapping range. ON LOAD TAP CHARGES are also provided depending upon customer’s requirement.
 

HT & LT TERMINATIONS

All bushing are of high quality porcelain or Epoxy complying as per IS 2099.
 
FABRICATED TANKS:

All tanks are made from mild steel, which is electrically welded. The design of the tank is such that the base & cover thickness is related to the size & weight of the finished product. The core & coil are fixed to the tank in such a way that the no damage will cause during transportation, loading & unloading. All tanks are oil pressure tested to a pressure of 0.4At plus the weight of oil contained.

The interior of the tank is painted with oil & heat resistant paints. Zinc chromate red oxide primer is applied to the exterior, before applying two coats of weather proof out door type synthetic enamel paint of shade IS: 631. Transformer tank & all other fabricated items are thoroughly cleaned before painting.

ROUTINE TESTS:

The following taste is carried out on all transitions. The numbers shown do not necessary indicate the sequence in which the test are carried out. All tests are in accordance with the latest revision of IS 2026.

 Resistance measurement of HV windings at normal tap position.
 Resistance measurement of LV windings.
 Ratio test on all tap connections.
 Polarity & vector group tests at normal tap.
 No load loss at rated current, at normal tap.
 Excitation current measurement at rated current, normal tap.
 Impedance & load loss measurement at rated current, at normal tap.
 Separate source voltage withstand test on HV & LV windings.
 Induced over voltage withstand test.
 Measurement of insulation resistance.
 Measurement of breakdown voltage of oil.
 Measurement of acidity value of oil.

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