ECE 4501                POWER SYSTEMS                                                                              UMD                      S.NORR

 

MAGNETIC CIRCUITS

 

TERMS:

 

NAME:

SYMBOL / UNITS:

EQUATION:

Magneto-motive Force (mmf)

F    (Ampere – Turns) or

      (A-t)

F  = NI

Magnetic Field Intensity

H   (A-t/meter)

H = NI/l   (l = path length in

                   meters)

Flux Density

B    (Tesla)   yay!

      1Tesla = 1Wb/meter2

B = mH

Permiability

m    (H/meter)

m = mrmo     Where mr is the

               relative permeability

               of the material and

mo = 4p x 10-7  H/m     is the

       permeability of free space.

Flux

F    (Webers, Wb)

F = BA   (A is cross-sectional

              area in square meters)

Flux Linkage

l    (Weber-turns)

l  = NF

Inductance

L    (Henries)

L  = l/I = N2/Â

Reluctance

   (A-t/Wb)

 = l/mrmoA

 

 

Useful Relationships:

 

F = BA  = mrmoHA = mrmoANI/l  = NI/Â

 

 

OHM”S LAW ANALOGY:

 

If V = IR, then  F = FÂ

 

ELECTRICAL

MAGNETIC

Current

I   (Amps)

F  (Wb)

Flux

emf

V  (Volts)

F   (A-t)

mmf

Resistance

R  (Ohms)

  (A-t/Wb)

Reluctance

Conductivity

s   (S/m)  Siemans/meter

m   (H/m)

Permiability