Lecture Outline : Production of Induced Force on a Current carrying wire Induced Voltage On A Conductor moving in a Magnetic Field A Linear DC Machine. - презентация

1 Lecture Outline : Production of Induced Force on a Current carrying wire Induced Voltage On A Conductor moving in a Magnetic Field A Linear DC Machine –Simple Example Starting The Linear DC Machine Linear DC Machine As A Motor Linear DC Machine As A Generator

2 Production Of Magnetic Field/Magnetic Circuits Electric Circuit Magnetic Circuit Electric Flux ? EMF ? Resistance ? Current ? Magnetic Flux ? MMF ? Reluctance? Flux Conductance ? Permeance ? V=IR Reluctance obeys same rules of addition as resistance

3 Magnetic Behavior OF Ferromagnetic Materials

4 Production of Induced Force on a wire A conducting wire of length l and a current i passing through it, placed in a uniform magnetic field density experiences a force on it. Direction of force can be determined by right hand rule. Magnitude of this force is given by F = i Bl Sine θ

5 Induced Voltage On A Conductor Moving in a Magnetic Field If a conducting wire moves through a magnetic field a voltage is induced in the wire. For a wire of length l moving with speed V in a magnetic field B, induced voltage e is given by e ind = (V B ). l Note: L is taken as vector length pointing along the direction of motion of wire. The voltage is induced so that positive end of wire is in the direction vector V B.

6 The Linear DC Machine A simplest linear DC machine is consists of a battery and a resistance connected to a frictionless rail of conductors while the rail track is placed in a uniform magnetic field.

7 Starting The DC Machine The operation of a DC machine can be explained through four basic equations :- Force on a current carrying conductor : F= (B L )i Voltage induce on a wire moving in a magnetic field: e ind = (V B ). l Kirchhoff's Voltage Law for the machine: V b = e ind +iR Newtons Law for the applied force on metal bar: F=ma

8 Starting The DC Machine (cntd..) Switch on the machine, current starts flowing that can be calculated using KVL V b = e ind +iR i = V b - e ind / R As the current starts flowing through the bar it is ? F=Bil As soon as the force is applied and the conductor starts moving next equation is applicable ? e ind = V B l As the velocity of block increase induced voltage increases Causing the current to fall down i = V b - e ind / R why ?

9 Starting The DC Machine (cntd..) Ultimately, bar moves with a constant speed causing the force to become zero F=ma ? The bar will keep on moving in no load steady state condition until an external force is applied The speed of bar is given by V b = e ind = V speed B l V speed = V b / B l

10 Linear DC Machine As -Motor e ind = V speed B l i = V b - e ind / R F=Bil ?

11 Linear DC Machine As -Motor A load is applied Net force changes F net = F ind – F load Decrease in force decrease the speed of bar that in turn decreases induced voltage e ind = V speed B l Decrease in induced voltage increase I i = V b - e ind / R Increase in i increases force on bar F=Bil That increases speed and thus the induced voltage until the bars attains a constant speed again Transforming power from electrical domain to mechanical domain P= e ind i

12 Linear DC Machine As -Generator ?