# Electric Machinery Fundamentals 5th edition

## Example 1-2:

Import the PyLab namespace (provides set of useful commands and constants like Pi)

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In [1]:

%pylab inline

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Populating the interactive namespace from numpy and matplotlib

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Define all the parameters:

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In [2]:

lc = 0.4                 # Length of iron core in m
lag = 0.0005             # Length of air gaip in m
a  = 0.0012              # Area of the core in m**2
ur = 4000                # Relative permeability
u0 = 4*pi*1e-7           # Permeability of free space in Vs/Am
n = 400                  # Number of turns on core
i = 0.6                  # Current in amps in A
fring = 1.05             # fringing factor

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Calculate the iron core reluctance:

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In [3]:

rc = lc/ (ur * u0 * a)
rc

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Out[3]:

66314.55962162306

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Calculate the airgap reluctance:

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In [4]:

rag = lag / (u0 * fring * a)
rag

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Out[4]:

315783.61724582413

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Calculate the total reluctance

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In [5]:

rtot = rc + rag
rtot

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Out[5]:

382098.1768674472

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Calculate the mmf

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In [6]:

mmf = n * i

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Finally, get the flux in the core:

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In [7]:

flux = mmf / rtot

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Calculate the fluc density in the airgap

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In [8]:

Bag = flux / (fring * a)

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Display the result:

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In [9]:

print('rc   = {} Vs/Am'.format(rc))
print('rag  = {} Vs/Am'.format(rag))
print('Flux = {} Vs'.format(flux))
print('Fluxdensity in airgap = {} Vs/m**2'.format(Bag))

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rc   = 66314.5596216 Vs/Am
rag  = 315783.617246 Vs/Am
Flux = 0.000628110822113 Vs
Fluxdensity in airgap = 0.49850065247 Vs/m**2

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(I'm using String Formatting in order to make the output above a bit nicer.)