Transformer concept

Transformer
1.1 Classification of the transformer, the basic structure, ratings
1.1.1 Classification of the transformer
Transformers: the use of electromagnetic induction principle, to an AC power voltage into another voltage of the same frequency AC power.
(To raise or lower the voltage of a static energy conversion devices)
Structural principles: the two sets of windings insulated from each other in a common core, the magnetic coupling between them only, no electricity connection.
One side: the side which leads to alternating current, which absorb  energy side. One side of the pass into the current of the alternating magnetic flux, then EMF.
Secondary side: on the load side, that side of the output power. And the primary magnetic flux generated by cross-linking, and produce EMF.
Principle: e1/e2 = N1/N2 ≈ U1/U2 (drawn diagram)
1. Classification by purpose: power transformers, special transformers, instrument transformers, voltage regulators, high voltage transformer test
2. Divided by the number of winding: two-winding, three-winding, multi-winding transformer and autotransformer
Structure according to core points: the heart-type, shell type transformer
Divided by number of phases: single-phase transformers, three-phase transformer
By sub-cooling and cooling medium: air-cooled dry-type transformers and oil-cooled oil-immersed transformers.
1.1.2 The basic structure of the transformer
Main structure: core, winding, tank, insulated casing.

The role of material structure parts name
The formation of magnetic core 0.27, 0.3, 0.35mm thick cold-rolled silicon steel heart-type: coil core surrounded by a simple
Shell: core surrounded by coils, square coils
Winding transformer circuit part cylindrical copper or aluminum wire, cake-type, continuous and spiral coil. Low-voltage winding assembly by the core
Tank insulation, heat
Lead insulation transformer bushing porcelain multi-part umbrella. 1.1.3 Series and voltage levels on the rating of the transformer
Rated capacity SN1 = SN2 = SN (VA, kVA, MVA)
Rated voltage: one side of the U1N, secondary U2N: one side of the applied voltage, the secondary side of the load voltage is the U2N.
Rated current: one side I1N. Secondary I2N.
Rated frequency: 50HZ
Rated temperature rise, impedance voltage, join groups, load loss, short-circuit loss and so on.
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Single-phase transformer: SN1 = I1NU1N = SN2 = I2NU2N = SN
Three-phase transformer: Note: Rated line voltage, rated line  current
          Y Winding Connection:
          Δ winding connection:
1.2 Transformer no-load operation
1.2.1 No-load run-time flux, induced electromotive force
At this point, the secondary side open, one side of the access to AC voltage, resulting in current i0, create magnetic force F0, the magnetic field are:
Main flux: with both primary and secondary cross-linking, and closed down the core. Nonlinear magnetic circuit. Main flux is the energy transfer medium.
Leakage flux: only cross-linked with the winding itself through the oil or air closed. Linear magnetic circuit.
Potential main sensing:, assuming current frequency is f,, then,
Potential capacity of RMS recovery: (behind the flux of 90 degrees)
Induced leakage potential:
Sinusoidal steady state,
This shows that EMF can use leak compression leak down to that. And is constant (magnetic permeability of the leakage constant).
   1.2.2 The voltage balance equation, the transformation ratio
According to Figure 3.7 can be:
Sinusoidal steady state:
Z1 is a winding leakage impedance, constant.
Variable ratio defined: E1/E2 = N1/N2 ≈ U1/U20 (as E1 ≈ U1, E2 = U20)
1.2.3 No-load current
Transformer analysis, the magnetic potential and magnetic flux to meet the law; voltage, current, induced voltage to meet the circuit's law; flux and induced voltage to meet the law of electromagnetic induction.
No-load current waveforms
    Transformer no-load operation, load current established by the main magnetic flux, so the load current is the magnetizing current. Since the nonlinear magnetization characteristics of magnetic materials used to create the magnetic field excitation current waveform and core size and the degree of saturation are directly related.
(1) circuit is not (2) saturation, (3). If u sine wave, (4) is φ sine wave, (5) i0 is sine wave
(6) saturation, (7) φ and i0 nonlinear. U still the sine wave power supply, (8) φ sine wave, (9) i0 as peaked wave distortion.
(10) Moreover, the more saturated magnetic core, (11), themore serious the excitation current waveform distortion.
(12) because the magnetic circuit is saturated, (13) is able to obtain sine wave potential, (14) requires sine wave flux, (15) therefore have the potential spire wave excitation current.