It depends on the rotor structure. Generally, the iron core will have ventilation channels in sections. If the small rotor core does not have a ventilation channel, there will be an axial ventilation hole or slot in the middle of the core. The hydroelectric generator has a large magnetic pole rotor and ventilation and cooling channels between each magnetic pole. The turbine generator rotor will have ventilation channels designed into the slot wedges and rotor guide bars to connect to the cooling air path.
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