Based on the design data of the stator and rotor of an induction motor, performance of the machine has to be evaluated.

**Performance Evaluation:**

Based on
the design data of the stator and rotor of an induction motor, performance of
the machine has to be evaluated. The parameters for performance evaluation are
iron losses, no load current, no load power factor, leakage reactance etc. Based
on the values of these parameters design values of stator and rotor can be
justified.

Iron
losses: Iron losses are occurring in all the iron parts due to the varying
magnetic field of the machine. Iron loss has two components, hysteresis and eddy
current losses occurring in the iron parts depend upon the frequency of the
applied voltage. The frequency of the induced voltage in rotor is equal to the
slip frequency which is very low and hence the iron losses occurring in the
rotor is negligibly small. Hence the iron losses occurring in the induction
motor is mainly due to the losses in the stator alone. Iron losses occurring in
the stator can be computed as given below.

(a) Losses in stator teeth:

The
following steps explain the calculation of iron loss in the stator teeth

(i)
Calculate the area of cross section of stator tooth
based on the width of the tooth at 1/3^{rd} height and iron length of
the core as A'** _{ts}**= b'

(ii)
Calculate the volume all the teeth in stator V_{ts}
= A'** _{ts}** x h

(iii) Compute
the weight of all the teeth based on volume and density of the material as

W_{ts}
= V_{ts} x density. ( density of the material can be found in DDH) (7.8
x 10^{-3} kg/m^{3})

(iv)
Corresponding to the operating flux density in the
stator teeth of the machine iron loss per kg of the material can be found by
referring to the graph on pp179 of DDH.

(v)
Total iron losses in teeth= Iron loss /kg x weight
of all teeth W_{ts} ie result of (iii) x (iv)

(c)
Losses in stator core

Similar
to the above calculation of iron loss in teeth, iron loss in stator core can be
estimated.

(i) Calculate
the area of cross section of the core as
A_{cs} = d_{cs} x *l*_{i} m^{2}

(ii)
Calculate the mean diameter of the stator core
below the slots as D_{mcs}= D + 2 h_{ts} + dcs m

(iii)
Compute the volume of stator core as V_{cs}
= A_{cs} x π D_{mcs} m^{3}

(iv)
Calculate the weight of the stator core as W_{cs}
= V_{cs} x density

(v)
Corresponding to the operating flux density in the
stator core of the machine iron loss per kg of the material can be found by
referring to the graph on pp 179 of DDH.

(vi)
Total iron losses in core = Iron loss /kg x weight
of core W_{cs} ie result of (iv) x (v)

Total
iron losses in induction motor = Iron loss in stator core + iron losses in
stator teeth.

In addition
friction and windage loss can be taken into account by assuming it as 1- 2 % of
the out put of the motor.

Hence
total no load losses = Total iron losses + Friction and windage loss.

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Design of Electrical Machines : Induction Motors : Performance Evaluation - Design of Induction Motors |

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