Times Of Electric

 What is the function of oil in transformer?   The oil used is purposed for two main reasons; 1.  Cooling 2.  Insulating   The oil used must possess the following properties. 1.  High dielectric strength 2.  Free from inorganic acid, alkali and corrosive sulphur to prevent injury to the conductor or insulation. 3.  Low viscosity to provide good heat transfer 4.  Free from sludging under normal operating conditions. 5.  Good resistance to emulsion so that the oil may throw down any moisture entering the tank.   Cooling The transformer windings dissipate waste heat, which needs to be removed. Transformer oil absorbs this heat from the windings and conducts it to the outside of the transformer, where it can be dissipated to the outside air. It is possible to build an air-cooled transformer. These are used where spillage of the insulating oil is an unacceptable hazzard. I.e., for indoor hazard.   Insulation All parts which might be...

  Why Transformer is rated in KVA?   Well there are different two reasons for this.   The first reason they normally use to explain for this is depending on the losses of the transformer. Consider a single phase transformer supplying a power VICosØ to the load. The two losses that occur in transformer are copper loss and core or iron loss. This copper loss depends on the current flowing through the conductor and iron loss depends on the voltage and not on the phase angle between voltage and current(cosØ). That is the losses are independent to the power factor of the load. Hence the total losses depends upon the volt-ampere(VA), the transformer is rated in VA or KVA or MVA.   The second reason is from the view point of manufacturer. The manufacturer doesn’t know the power factor of the load or the type of load connected at the consumer end. Since the power handled by the transformer depends on load pf., rated power(KW) of the transformer cannot be a satisfactory one. ...

Why we use stepped core in transformer?  Usually, rectangular core is used for small rated transformer while the coil can be either square or rectangular.  But for highly rated power transformer, we require circular coils only, so we have to use circular core(stepped core). Circular coil is preferred in power transformer due to its Superior mechanical characteristics.  On circular coils, the mechanical force acts radially, so the stress is less and shape of coil do not change, however if we use rectangular coils, then the mechanical forces acts perpendicular to the coil results in creating high stress which would deform the coil shape. This is the reason why circular coils are preferred over other coils for power transformer.  So the reason for circular core is that, if we use rectangular core, then the useful space is not utilized better resulting a air between the coil and core. This affects in increasing the length of mean-turn of the winding which further incr...