To separate suitable relations are assumed between D and L depending upon the type of the generator.

**Separation
of D and L: **Inner diameter and gross length of the stator can
be calculated from D^{2}L** **product obtained from the output
equation. To separate suitable relations are assumed between D and L depending
upon the type of the generator.

Salient
pole machines: In case of salient pole machines either round or rectangular
pole construction is employed. In these types of machines the diameter of the
machine will be quite larger than the axial length.

Round
Poles: The ratio of pole arc to pole pitch may be assumed varying between 0.6
to 0.7 and pole arc may be taken as approximately equal to axial length of the
stator core. Hence

Axial
length of the core/ pole pitch = L/τ_{p} = 0.6 to
0.7

Rectangular
poles: The ratio of axial length to pole pitch may be assumed varying between
0.8 to 3 and a suitable value may be assumed based on the design
specifications.

Axial
length of the core/ pole pitch = L/τ_{p} = 0.8 to
3

Using the
above relations D and L can be separated. However once these values are
obtained diameter of the machine must satisfy the limiting value of peripheral
speed so that the rotor can withstand centrifugal forces produced. Limiting
values of peripheral speeds are as follows:

Bolted
pole construction = 45 m/s Dove tail pole construction = 75 m/s Normal design =
30 m/s

Turbo
alternators: These alternators will have larger speed of the order of 3000 rpm.
Hence the diameter of the machine will be smaller than the axial length. As
such the diameter of the rotor is limited from the consideration of permissible
peripheral speed limit. Hence the internal diameter of the stator is normally
calculated based on peripheral speed. The peripheral speed in case of turbo
alternators is much higher than the salient pole machines. Peripheral speed for
these alternators must be below 175 m/s.

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Design of Electrical Machines : Synchronous Machines : Separation of D and L - Design of Synchronous Machines |

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