Electrical Engineering ⇒ Topic : Self Inductance

Gaurav
 
SELF INDUCTANCE When the current in a coil is changing, the flux linked with the coil is also changing. In this case, an e.m.f. is produced in the coil. If the permeability of the coil is assumed to be constant, the induced e.m.f. of the coil is proportional to the rate of change of current, i.e., ................. (1) In Eq. (1), L is the constant of proportionality and it is known as self inductance of the coil. According to Faraday's law of electromagnetic induction, the induced e.m.f. in a coil having N turns is given by ............... (2) From Eqs. (1) and (2), it can be written as: .................. (3) If (Φ) versus i graph is taken as linear, Eq. (3) can be expressed as: ................. (5) ............... (6) where S is the reluctance of the coil and is equal to l/μA. From Eq. (6), it can be given as: ................ (7) Using Eq. (7), it can be obtained from Eq. (5) as: .................... (8) Equation (8) suggests that the inductance of any coil depends on the length and the area of crosssection of the coil. From Eq. (5), self inductance can be defined as the flux linkage of the coil per ampere current flow through it. The unit of self inductance is Henry (H).  
 
Sachin
 
Selfinductance (L) The property of a coil that opposes any change in the amount of current flowing through it is called its selfinductance or inductance. This property (i.e. inductance) is due to the selfinduced e.m.f. in the coil itself by the changing current. If the current in the coil is increasing, the selfinduced e.m.f. is set up in such a direction so as to oppose the rise of current i. e. direction of selfinduced e.m.f. is opposite to that of the applied voltage. Similarly, if the current in the coil is decreasing, selfinduced voltage will be such so as to oppose the decrease in current i.e. selfinduced e.m.f. will be in the same direction as the applied voltage. It may be noted that selfinductance does not prevent the current from changing ; it serves only to delay the change  
 
Amir
 
Two coils C_{1} and C_{2} are shown separately in Figure (a). Assume that the coil / having N_{1} turns carries a current of /_{1} amperes and links with a flux of Φ_{1} Wb. Similarly, let coil 2, having N_{2} turns carry a current of I_{2} amperes and link with a flux of Φ_{2} Wb. Then, the selfinductance of coil l(L_{1}) will be the number of flux linkages with the same coil due to its own current of /_{1 }amperes. Thus ................1 Similarly, the selfinductance of coil 2 (L_{2}) is
FIGURE (a) Selfinductance of a coil ..............2  
 
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