Transformers

Outdoor Oil Cooled Voltage Transformers

Outdoor Voltage Transformers are of mostly dead tank Design. They may be either of single phase (Three single phase VT's to be connected in star connection) or Three phase.

Single phase electromagnetic Voltage Transformer (EHV) is manufactured of two types.
    A) Single Pole (To connect between line and earth) suitable for HV Neutral earthed system. The single pole may be of both types- Hollow Insulator type and Transformer Insulator type.
    B) Double Pole (To connect between line and line) suitable for isolated Neutral earthed system.

Three phase Voltage Transformers are of star/star connected or Four Pole, star/ star/open delta connection (Residual Voltage Transformer).

General Description:

CORE: Core is made of High permeable, low loss. Grain oriented silicon steel. They are designed to operate in low operating flux density to ensure that the ratio and phase angle error are well within limits over a wide voltage range. Three limb construction is used for three phase and core type/ shell type construction is used for single phase to minimize leakage reactance. Five limb construction is used for Residual voltage Transformer.
PRIMARY AND SECONDARY: Enameled Copper wire is used for primary and Secondary winding. Winding is of trapezoidal form with winding of each layer selected such that surge voltage is distributed equally in all layers of winding. Multilayer craft paper insulation is provided between layers to avoid interlayer shorts. Stress equalizing shield is given in the final layer of the primary winding. Primary terminal is brought out through metallic pipe. Capacitance grading is done in the whole insulation to distribute dielectric stress. Winding and taping is done is done free dust free atmosphere. Secondary winding is separately wound and inserted in the primary winding as per the requirement.
INSULATION: High quality Crepe paper and Kraft paper is used for insulating VT Primary and secondary. The high Voltage Connection is brought out through paper condenser formed on metallic galvanized pipe using fine grading of insulation. Semi conducting Shield is used to give linear distribution of electric stress along the length of the bushing. The paper insulation is dried under very high vacuum and strictly controlled conditions. Filtered and degassed oil is filled in VT.
TRANSFORMER OIL: Transformers are filled with high quality Power Oil ( Conforming to IS 335) free from Polychlorinated biphenyls and terphynyls ( PCB and PCT). The oil is filtered, degassed, dehydrated in high vacuum till achieving desired BDV before filling.
PORCELAIN INSULATOR: The Porcelain Insulator used is of reputed/ customer approved make. They are brown glazed with required creepage as per customers request! ambient climate and air pollution at the place of installation. TANKS: M.S Tanks undergoes seven tank process and coated with oil insoluble paint on the inside. Outside of the tank is applied with 2 coats of zinc Primer and 2 coats of Polyurethane paint of required shade. Hotdip galvanized tank can be provided on request.
PRIMARY TERMINALS: Primary Terminals are generally 30mm dia of length 80mm (as per IS). Material would be aluminum or electrolytic copper duly tinned/nickel chromium plating or silver plating on customers requirement.
SECONDARY TERMINALS: Normally M6 Brass studs with three nuts and two washers are offered. Terminal Blocks can be offered on request.
GASKETS: Gaskets are made of moulded nitryl butyl rubber which has good properties with both Transformer oil and atmospheric conditions.
ACCESSORIES: All accessories including oil filling/drain plug, oil level indicator, PRV/ Explosion Vent are tightened with '0' rings which are positioned in properly dimensioned grooves. SS hardwares may be supplied on request.
Oil VOLUME COMPENSATION: Normally nitrogen cushioning is done in the top to avoid oil Volume Compensation due to temperature variations. SS Bellows may be supplied on request.