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Elettrorecnica Industriale Gritti | Transformers, electric motors, electric pumps particolare trasformatore elettrico

Catalogo motori elettrici

Oil transformers

TECHNICAL CHARACTERISTICS - All the transformers are manufactured in accordance with the following specifications:
- CEI 14-4/EN 60076
- CEI - UNEL 21010/21014 CENELEC
- IEC 60076-11
- 89/336/CEE

The respect of the application of such norms is guaranteed from the organisation of business quality: ISO 9001:2008 NET N IT-55187 RINA N 16239/07/S

The core is constituted of a magnetic cold-roller and grainsoriented sheet, isolated on both sides by a thin inorganic coating. The magnetic circuit in formed by three supporting columns arranged on the same plane and connected by two rectilinear yokes at their ends.
The interpolated joint type of connection bet ween columns and yokes, cutting at 45°, allows a better utilization of the magnetic specification of the sheet, by achieving lower losses and less no load current. The columns and yokes section is incremented in variable number, according to transformer’s power. Uniform pressing stiffness and solidity of the columns is assured by bands made of special insulating materials, while the yokes pressing is obtained with well-dimensioned structural steel connect ed together by vertical tie-rods that allow a perfect performance of voltage. An optimised design, whether magnetic or mec hanical, permits reduction of no load losses and to obtain a low noise


The primary and secondary oil transformer windings are norm ally made with electrolytic copper, with insulation of conduct ors in pure cellulose paper or in double enamel for wires of sm all diameter. These windings are circular section and are a concentric type, coaxial to the core columns.
The low voltage winding is hel ically wound in over lapped alternate strata, norm ally with one or more metal strips in parallel. The high voltage winding is made with a wire or a metal strip, helically wound with more strata or with continuous disc in relationship to the working voltage and the transf ormer’s power. Every high and low voltage winding elements, assure undeformability in case of short-circuit.
Particular attention is paid to adjustment engagements, in relationship to the const ructive type and to the use of voltage winding, in order to avoid strata is insulated with pure cellulose paper sized in such a way as to bear any mechanical and electric stress; the oil’s circulation and necessary cooling are assured by wide channels placed between the windings strata. Insulation between high and low voltage and between the latter and the core is made with precompressed cardboard cylinders with a thickness, which conforms, to the respective insulating voltage, and with well-sized oil channels. A specific and design consents obtainment of uniform distribution of i mpulsive type over voltage and stresses. A perfect winding locking is assured by use of cardboard spacers and evaporated beech that, along with the pressing deformations due electrodynamics stress. All windings are successively dryer in an oven to definitively remove the remaining moisture and they are impregnated under vacuum for a perfect tightness to electric stresses.

The adjustment or variation of primary volt age is done with linear top changers in an oil bath and manoeuvrable with a transformer disconnected from the network by using knobs placed on the cover. The tap changers allow fitting the primary winding to the main voltage’s variation to obtain the nominal secondary voltage. The tap changers for the variation of primary voltage allows, on the contrary, obtainment of an immediate commutation when the transformers are foreseen to act to different work voltage without the problem of having to raise the core of the transformer caring out the passage of one tension to another.
To avoid an incorrect positioning of a tap changers, some holes are foreseen in correspondence with each indication notch of the various positions that allow a secure housing of the knob; in addition, it is possible to apply a padlock to avoid accidental or unaut horized manoeuvres.


The high and low bushing insulators are oil-filling type in enamelled brown porcelain, and conform to UNEL standardisation. The insulators are fixed on the cover with special frames and can be replaced without removing the core from the case. The high voltage bushings are provided with spark grap rods.

Tanks can be: HERMETIC or NORMAL WITH CONSERVATORS. For transformer up to the power of 2000 KVA we make type tank which guarantee the absorption an oil expansion and its increase of volume and doesn’t need a spread tank. Transformers with a higher power have tanks with radiators construct red of cold rolled steel plate. Radiators are singularly tested before their assembly. The transformers have a tank, which allows the spread of hot oil. For transformers up to 2000 KVA it’s possible the solution with total filling without conservator.
The inside walls of tanks are protected, prior to sand blasting, with special pants insoluble to hot oil. The outside walls are protected with paints suitable to the strictest environmental conditions.

The filling of the transformers is obtained with mineral oil, without PBC, dried and degassed, with electrical and chemical specifications, which conform to the CEI and IEC standards; the filling is done under-vacuum for a perfect seal to the impulsive voltages.

- Oil conservator
- Oil filling plug
- Oil level
- Overpressure device
- Conservator oil drain device
- Dryer connection device
- Air dryer
- Thermometer pocket
- Tank oil drain valve
- Grounding terminal
- Lifting lugs
- Truck with sliding wheels
- Rating plate

- 2 Contacts dial thermometer
- 2 Contacts gas relays dgpt2
- Press filter connection device
- Overpressure flow-off device
- Protection case of low and hing voltage cases
- Hing and low voltage cable boxer
- Hing voltage disconnectable terminals
- Check valve to remove the cooling elements without freeing oil
- Cooling elements oil drain valves
- Cooling elements hoisting eyebolts
- Auxiliary circuits centralized box
- Anti-condensate resistance for centralized box
- Thermostat for anti-condensate resistance driving
- Air pressure switch
- Pt 100

All transformers are tested in our test -room according to CEI 14-4 and IEC 76 norms. They are equipped of a manual, that contains a test bulletin, all the accessories and a copy of fisrt filling oil.

The transformers are guaranteed 24 months.

ELETTROTECNICA INDUSTRIALE GRITTI di Gritti L. & C. snc - Sede: Via Torricelli, 18/20 - Molinetto di Mazzano (BS) - P. Iva: 02164260172
Filiale: Via Torricelli, 21/23 - Molinetto di Mazzano (BS) Tel. + 39 030 26 29 480 / 030 21 20 850 - Fax +39 030 21 20 536 - E-mail: info@grittielettrotecnica.it