This series low loss oil immersed transformers have the advantages of low loss, low noise, small temperature rise, high responsibility and freeness from hanging core for site use.
I. Iron core structure and process characteristics
A)The magnetic flux density of iron core is controlled and no magnetic saturation will occur even if at a voltage 1.1 times the rated value so that the iron core loss and noise can be controlled.
B)The height-width ratio of iron core is optimized to reduce the no-load loss and noise.
C)The structural design of iron core is optimized by 3D software to prevent the resonance of iron core.
D)All the silicon-steel sheets for the transformer iron core are 30ZH120 high permeability low loss grain oriented cold-roll thin silicon sheet imported from Japan
E)The iron core adopts a structure of 45 deg; Fully sloping step joints, stepping overlapping and circular section without punching and is bound with epoxy adhesive tape.
F)The clamping of iron core adopts a frame structure composed of trough type clamping pieces, tension links and beams that has a good mechanical strength.
The abovementioned measures have enabled the low loss transformers of the Company to reduce its no-load loss by more than 20%, its no-load current by more than 40% and its noise greatly.
II. Coil structure characteristics
A)The electromagnetic wire used for the coil is made of oxygen-free copper and has low resistivity.
B)The coil form is optimized.
C)The best coil structure and the insulation structure of the core and winding assembly are designed based on the computer-assisted calculation of electromagnetic field, temperature field and coil mechanical strength to enable coil ampere-turn balance, reliable insulation and rational heat dissipation so as to satisfy the requirements of transformer in insulation, temperature rise and short-circuit resistance
D)Subzone ampere-turn balance is realized in coil winding and pre-compression, and not only the equal height of inside and outside coils but also the equal height of ampere-turn subzones thereof are guaranteed, thus improving the resistance to short circuit of coils.
E)Constant pressure drying process is adopted for the coils to keep a relatively constant pressure in the vacuum drying of coils.
III. Core and winding assembly structure and general assembly
A)Manufacture of insulators
The insulators that are required to have mechanical strength such as insulation end rings, blocks and struts are hot-pressed.
B)Phase assembly process is adopted in core and winding assembling to make the coil into integrity with increased mechanical strength and resistance to short circuit.
C)The leads are fixed by wire clamps made of laminated wood.
D)The core and winding assembly of transformer is processed by advanced variable pressure vacuum drying to a residual vacuum of 25PA, thoroughly drying the transformer. Full vacuum oiling is adopted for the transformers, greatly increasing their insulation strength.
E)The processing of transformer oil is carried out in vacuum oil purification equipment.
F)Manufacture of oil tank, accessories and steel parts
The cutting of the steel sheet is carried out on CNC flame cutting equipment to ensure accurate dimensions of steel parts.
The upper and lower sections of oil tank are ground along their sealing surfaces and the key sealing surfaces of tank walls and cover are machined to guarantee the sealing effect.
The oil tank and parts will undergo fluorescent leakage test after welding on automatic welding equipment, ensuring the sealing reliability.
IV. Selection of main materials
A)Silicon steel sheet: Silicon steel sheet imported from Nippon Steel.
B)Insulation material: Insulating paper board imported from Weidmann
C)Coils: T2M copper foil imported from German Langboge
D)Transformer oil: 25# transformer oil produced in Karamay, Xinjiang.
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