Eddy Current Loss
Consider a coil wound on a core. If this coil carries an
alternating current i.e. current whose magnitude varies with respect to time,
then flux produced by it is also of alternating nature. So core is under
the influence of the changing flux and under such condition according to the
Faraday's law of electromagnetic induction, e.m.f. gets induced in the
core. Now if core is solid, then such induced e.m.f. circulates currents
through the core. Such currents in the core which are due to induced
em.f. in the core are called as eddy currents. Due to such currents there is
power loss(I2R) in the core. Such loss is called as eddy
current loss. This loss, similar to hysteresis loss, reduces the
efficiency. For solid core with less resistance, eddy currents are always
very high.
Eddy
current loss depends on the various factors which are
i)Nature of the material
It
has been found that loss can be considerable reduced by selecting high
resistivity
magnetic material like silicon. Most popular method used to
reduce eddy current loss is to use laminated construction by stacking thin
pieces known as lamination. The lamination are insulated from each other
by thin layers of insulating material like varnish, paper, mica. This
restrict the paths of the eddy currents, to respective lamination only.
So are through which current gets reduced considerably.
The
loss may also be replace by grinding the ferromagnetic material to a powder and
ixing it witg a binder that effectively insulates the particles one from
other. The mixture is then formed under pressure into the desired shape
and heat treated. Magnetic cores for use in communication euqioment are
frequently made by this process.
This
loss is quantified by using the expression,
Eddy
current loss=Ke(Bm)2f2t2*Volume
watts
where, Ke = A characteristic constant of material
Bm = Maximum flux density
f = Frequency
t = Thickness of the lamination
No comments:
Post a Comment