For case 1 where field current was 6A we found that Ea is 268V. Its also given that load current is 126A so Ia becomes 126-6=120A. Now 120*0.03 is 3.6V. From the equation V(t)=Ea + Ia*Ra we find Ea is 250-3.6=243V. How come are we getting two different values for Ea.
Dear Varun, the Armature Current is assumed to be constant here for calculation, but as we've seen the same increases with increase in Field Resistance; what'd have been the way of calculation then? Please tell.
sir as armature current is constant so Ea will be constant then ratio of Ea1 and Ea2 should be always 1 in this problem?? also sir motor is on load so how can we use magnetization curve data since curve is on No load?? kindly guide me sir
Field current remains constant in a given machine unless we change field resistance for speed control and flux remains constant irrespective of the load when compensating winding is used ( flux weekning is neutralized),so we take the no load emf for the corresponding field .In the next case we increase arm resistance here flux decreases back emf decreases armature current increases new armature current has to be used (but we assumed it as constant for calculation) Ea1 Ea2 are not same as it corresponds to two different field current.
Sir, the ratio phi1/phi2 is also equal to If1/If2 which is equal to 6/5. WHY did we use the ratio of Ea01/Ea02?
For case 1 where field current was 6A we found that Ea is 268V. Its also given that load current is 126A so Ia becomes 126-6=120A. Now 120*0.03 is 3.6V. From the equation V(t)=Ea + Ia*Ra we find Ea is 250-3.6=243V. How come are we getting two different values for Ea.
Dear Varun, the Armature Current is assumed to be constant here for calculation, but as we've seen the same increases with increase in Field Resistance; what'd have been the way of calculation then? Please tell.
The graph is for open circuit terminal voltage. Why ? Did they make a mistake? Shouldn't it be Ea?
Sir, Why didn't we take If1/If2 as the ratio for phi1/phi2?
sir as armature current is constant so Ea will be constant then ratio of Ea1 and Ea2 should be always 1 in this problem??
also sir motor is on load so how can we use magnetization curve data since curve is on No load??
kindly guide me sir
Field current remains constant in a given machine unless we change field resistance for speed control and flux remains constant irrespective of the load when compensating winding is used ( flux weekning is neutralized),so we take the no load emf for the corresponding field .In the next case we increase arm resistance here flux decreases back emf decreases armature current increases new armature current has to be used (but we assumed it as constant for calculation) Ea1 Ea2 are not same as it corresponds to two different field current.
i think i havent understood this video