ELECTRICAL THINGS

  What is Real Transformer ? Real transformer is a transformer with the following assumptions: Both the primary and secondary windings have finite non-zero resistances. Along with the mutual flux, there will be some amount of leakage flux in the core. Both types of magnetic losses, Hysteresis loss and Eddy current loss, will be present in the core. Operation of Real transformer under no-load Real transformer (1-phase) operation under no-load When an alternating voltage V 1   is applied to the primary terminals, a current I 1   flows through the primary winding as shown in the schematic diagram of above figure. This current produces the necessary MMF in the primary winding that creates an alternating flux in the core. This alternating flux generates a self-induced EMF e 1   in the primary winding and mutually induced EMF e 2   in the secondary winding. Different fluxes and its function :- The flux produced by the primary winding can actually be divided into two p...

 What is Ideal Transformer ? An ideal transformer is a transformer with the following assumptions: Permeability of transformer is infinite. Iron loss in the transformer core are zero. Resistance of transformer winding is zero. No magnetic leakage flux, so coefficient of coupling is  1 . Magnetization curve of transformer is linear. Operation of Ideal transformer under load Schematic diagram of an ideal, 1-phase transformer under load When a finite impedance load Z L   is connected across the secondary terminals of a 1-phase transformer as shown in above figure, the load current I 2   flows through the secondary winding and the load. load current I 2   is given by:- I 2  = V 2 / Z L How will MMFs Produce ? A voltage source V 1   is connected to the primary winding. Due to this voltage V 1  primary current I 1   flowing through N 1   number of turns in the primary winding produces an MMF  N 1 .I 1   which creates the flux Ⲫ in ...

What is Ideal Transformer ? An ideal transformer is a transformer with the following assumptions: Permeability of transformer is infinite. Iron loss in the transformer core are zero. Resistance of transformer winding is zero. No magnetic leakage flux, so coefficient of coupling is 1 . Magnetization curve of transformer is linear. Operation of Ideal transformer under No-Load 1-Phase transformer will have two coils, the primary and the secondary. The primary winding is supplied from an AC voltage source, while secondary winding terminals are connected to the load. By electrical load, it is meant the output current and thus no-load means that the output current is zero, i.e., the secondary terminals are open circuited. Schematic diagram of an ideal, single-phase transformer operation under no-load The output (secondary) current of a 1-Ⲫ transformer is   I 2 = V 2 / Z L   Where,     V 2 = Secondary terminal voltage            ...

  Mutual Flux and Leakage Flux Mutual flux and Leakage flux in a transformer Electrical energy in a transformer is first converted to magnetic energy in the core and then converted back to electrical energy in the secondary coil. The flux that is produced by the primary MMF actually carries the energy to the secondary side.  For proper operation of the transformer, it is thus necessary that the flux should find an easy path through the core so that it can link both the two coils. The magnetic core of a transformer including the limb and yoke, thus, must be made from good quality ferromagnetic material with low reluctance.  Such magnetic flux, which links both primary and secondary coils while passing entirely through the core, is termed as the useful flux or the mutual flux as shown in figure.  Apart from the useful flux, there are so called leakage fluxes , those complete their path through air or other nearby metal parts, thereby not linking primary and secondary ...

Electromagnetic induction Mutual coupling between two coils When two coils are placed close to each other (as shown in figure) with an AC source connected to one of the coils, electrical energy is transferred to the second coil through electromagnetic induction. Magnetic flux produced by the first coil (primary coil) links with the second coil (secondary coil), thereby energy transfer from the primary side to the secondary side of the transformer. To enhance the flux linkage between the two coils, a transformer will generally have a core made of high permeability magnetic material, onto which the two coils will be wound as shown in the figure below:- For a sinusoidal supply voltage, the primary supply current (magnetizing current I m ) is fundamentally a sinusoidal quantity given by:- I m = I max . sin(ωt) where, ω = 2𝜋f  radian/s ;  f is the supply frequency in Hz N 1 = Number of turns in primary coil In primary coil a sinusoidal voltage source is supplied and a sinusoid...

Different parts of the transformer are:- Transformer tank High voltage and low voltage bushings Cooling tubes / Fins / Radiator banks Cooling fans Conservator tank  Explosion vent Oil drain valve Oil inlet / filling valve Temperature / Pressure gauges Name plate Control panel and tap changer Transformer Tank The entire core and coil assembly of oil filled transformer is enclosed by metal tank made mostly of welded mild steel sheets or sometimes aluminum . Purpose of the tank is to hold the oil and to provide a protective causing around the internal parts. The tank is earthed so as to prevent external bodies from getting electrocuted and to prevent electromagnetic noise to escape from inside the transformer and interfere with outside equipments in the vicinity of the transformer. Transformer tanks must be air-tightly sealed for it to isolate its content from any atmospheric contaminants. Sufficient clearances are kept between the outer surface of outermost winding and inside walls ...

  Insulating Parts Insulation is essential to isolate the live parts inside a transformer from other live parts at different potential or from the grounded parts.   The desirable properties of an insulation material are: High resistivity High breakdown voltage (breakdown strength) High dielectric constant ( ɛ r ) Low dissipation factor (tan 𝛿) Thermal stability Chemical stability Mechanical stability The different MAJOR insulations in a transformer are: Between core and LV (press board) Between LV and HV (impregnated press board, oil) Between top and bottom of winding and yoke (impregnated press board) Between HV and tank (impregnated paper, cotton, oil) Bushings (Porcelain)- used to take out HV and LV coil terminals from inside the tank for external connections to overhead lines. The different MINOR insulations in a transformer are: Between conductors (enamel, varnish) Between turns (impregnated paper, cotton) Between layers (impregnated paper, cotton, press board) Between l...