- The role of the core: the transformer is manufactured according to the principle of electromagnetic induction, the magnetic circuit is the medium of electric energy conversion, because the core is made of silicon steel sheet with high permeability, as long as the small excitation current is passed, the required magnetic flux can be obtained.
- The material of the iron core: the grade and lamination coefficient of commonly used cold-rolled silicon steel sheet are as follows. Because the surface of the silicon steel sheet has a good adhesion insulation film, it is not painted. The lamination coefficient depends on the thickness of the insulation film, the waviness, the difference of the same plate and the size of the burr.
- Core section shape: the cross-section shape of the core column is a circular stepped ladder, and the series of core diameter φ70~φ1600 is 6~26 (in 1/4 circle). When the core diameter is φ70~φ395, the cross section shape of the yoke is the same as that of the core column. When the core diameter is φ340~φ1600, the cross section shape of the yoke is D-shaped.
- Core diameter: D0=KDPzh0.25
Where: KD – diameter experience coefficient, cold rolled silicon steel sheet, copper wire KD=52~57
Pzh – Capacity per column (kVA)
- Magnetic flux density selection principle:
Core magnetic density general hot-rolled silicon steel sheet 1.4~1.47T; Cold rolled silicon steel sheet 1.6~1.75T
- No-load loss:
The loss measured by the transformer during no-load, no-load loss mainly includes the hysteresis loss (proportional to frequency) and eddy current loss (proportional to frequency square) in the core silicon steel sheet.
- No-load current:
The current measured when the transformer is no-load, no-load current is mainly the reactive component of the excitation current (proportional to the frequency) and the active component of no-load loss.
- Factors affecting no-load performance
8.1 Core material: the no-load loss and current of hot-rolled silicon steel sheet is larger than that of cold-rolled silicon steel sheet; The thicker the thickness of each sheet, the greater the no-load loss and current, but too thin will increase the additional coefficient of the process; Generally, the thickness of each piece is 0.23, 0.27, 0.3mm;
8.2 Core magnetic density: If the core magnetic density is too high, no-load loss and no-load current will increase.
8.3 Laminated form: If the number of each laminated is large, the no-load loss and no-load current will increase, generally 2 pieces are used in a stack.
8.4 Joint form: oriented cold rolled silicon steel sheet, generally adopt full oblique joints, such as the use of semi-straight semi-oblique joints, each increase in a direct joint will increase the no-load loss of about 3.5%;
8.5 Burr size: large burr, no-load loss and no-load current will increase, generally ≤0.03mm;
8.6 Clamping mode: The core screw is used than the adhesive tape and binding tape, and the no-load loss and no-load current are increased.
8.7 Manufacturing process: such as shear, handling, wrestling will produce stress, so that no-load loss and no-load current increase;
8.8 Degree of cleanliness: Keep the core clean without dust and foreign matter, otherwise it will also increase no-load loss and no-load current.