Which type of synchronous generators are used in Hydro-electric plants and why?

Salient pole Synchronous generators are used in hydoelectric  plant because: The majority of hydroelectric installations utilize salient pole synchronous generators.
Salient pole machines are employed  because the hydraulic turbine in the hydroelectric plants operates at low speeds compared to steam plants, therefore generators in hydro plant requires  large number of field poles to produce the rated frequency.
Rotor of synchronous generator requires  salient poles is mechanically best suited for low-speed applications

the type of the generator used is depends upon the HEAD availability.(height of dam).
For low head it is of Salient pole type and for high heads it is of Cylindrical core type generator.

salient pole three phase generator are used

As the speed of operation is low for hydro turbines use din Hydro-electric plants, salient pole type Synchronous generators are used.
These allow better ventilation and also have other advantages over smooth cylindrical type rotor.

siliant pole generator

What type of generator is used in hydro power plant

The majority of hydroelectric installations utilize salient pole synchronous generators. Salient pole machines are employed  because the hydraulic turbine in the hydroelectric plants operates at low speeds compared to steam plants, therefore generators in hydro plant requires  largenumber of field poles to produce the rated frequency. Rotor of synchronous generator requires  salient poles is mechanically best suited for low-speed applications, compared to round rotor machines which are employed in horizontal axis high-speed applications in turbo-generators. Round rotor or non salient pole synchronous generators are used in Thermal power plant because of high speed turbine.