2. transformer on No load.pptx

transfomer

1. Transformer on No load

2. Transformer on-no load

3. Transformer on-no load The primary winding draws a small amount of alternating current of instantaneous value i , called the exciting current , from the voltage source. The exciting current establishes flux ϕ in the core all of which is assumed to be confined to the core i.e., there is no leakage of flux. Applying kvl on the primary winding,  

4. Transformer on-no load The primary winding will have flux linkages This flux induces an emf in the primary winding which will be given as  

5. Transformer on-no load The induced emf, and the flux will be sinusoidal just as the voltage source Where is the maximum value of the core flux =2 π f in rad/s (f =frequency of voltage source) The emf induced in the primary winding will be The rms Value of the induced emf will be given by  

6. Transformer on-no load Since , then Maximum Flux will be given as So the maximum flux in a transformer is determined by the voltage/frequency ratio at which it is operating Equation (1) is true for any electromagnetic device operating with sinusoidally varying ac assuming all other assumptions are the same. The flux produced in the primary also links the secondary coil and induces an emf of and are in Phase as both are induced by the same flux.  

7. Example The Primary of a transformer has 200 turns and is excited by a 60 Hz, 200V source. What is the maximum value of the core flux? If the supply frequency is reduced to 50Hz, what will be the maximum value of the core flux

8. Transformer on-no load The Excitation current will be made up of two components, and is the component of exciting current that is magnetizing in nature and is proportional to the sinusoidal flux and in phase with it. It lagging the induced emf by 90°.  

9. Transformer on-no load The component comes about due to the presence of Hysterisis and phenomenon of eddy currents. It is in phase with E 1 Thus, the exciting current lags the induced emf by an angle θ slightly less than 90° as shown in the phasor diagram  

10. Transformer on-no load

11. Transformer on-no load From the phasor diagram , the core-loss is given by From the no-load phasor diagram, the parallel circuit model of exciting current can be easily imagined where in conductance Gi accounts for core-loss current Ii and inductive susceptance Bm for magnetizing current Im . Both these currents are drawn at induced emf E 1 = V 1 for resistance-less,

12. Transformer on-no load

13. Example A transformer on no-load has a core-loss of 50 W, draws a current of 2 A (rms) and has an induced emf of 230 V (rms). Determine the no-load power factor, core-loss current and magnetizing current. Also calculate the no-load circuit parameters of the transformer. Neglect winding resistance and leakage flux.