Non-salient pole rotor

It is used for stream turbine-driven alternator i.e. turbo-alternators,which run at very high speeds. The rotor consists of a smooth solid forged steel cylinder, having a number of slots milled out at intervals along the outer periphery (and parellel to the shaft) for accomodating fields coils. Such rotors are designed mostly for 2-pole (or 4-pole) turbo generators running at 3600 r.p.m. Two (or four) regions corresponding to the central polar areas are left unslotted.

The central polar area are surrounded by the field windings placed in slots. The field coils are so arranged around these polar areas that flux density is maximum on the polar central line and gradually falls away on either side. It should be noted that in this case, poles are non-salient i.e. they do not project out from the surface of the rotor. To avoid excessive peripheral velocity, such rotors have very small diameters (about 1 meter or so). Hence, turbo-generators are characterised by small diameters and very long axial (or rotor ) length. The cylindrical construction of the rotor gives better balance and quieter-operation and also less windage losses

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