# POB4

 What is the basic function of a hydro-electric generator? Discuss the energy transfer process To take the rotational energy from the turbine shaft (mechanical energy), to spin a set of field windings carrying direct current, thus creating a rotating magnetic field that will induce an alternating current in the stator What type of machines does BC Hydro use for the majority of their energy production and why? BC Hydro uses large three-phase Alternating Current synchronous machines because of their ability to produce both active and reactive power In principle, how is an alternating current waveform generated by a hydro-electric generator? A DC current is applied to the field windings of the rotor. This DC current produces a magnetic field about the rotor. As the rotor turns, the magnetic field rotates and induces a voltage in the stator. The voltage induced in the stator causes current to flow out of the stator to the load connected to the generator. The magnitude of the voltage induced in the stator is determined by the strength of the DC current applied to the rotor field winding. What is the purpose of the DC being applied to the field coils on the roto DC current produces a magnetic field about the rotor What is the air gap? The gap between the Rotor and the Strator. There is a magnetic field across the air gap that relies, for its strength, on the width of the air gap being small What are the two types of rotors? Which are used on hydro-electric generators and why? Cylindrical rotors Salient pole rotors What formula represents the relationship between speed and frequency on a hydro-electric generating unit? RPM = 120*F/P  F= Frequency  P = number of poles on the rotor How fast does a 2 pole machine spin in a 60 Hz system? 3600 RPM In which component, the rotor or the stator, is the alternating current waveform induced? Stator Windings To get a 3 phase alternating current, the stator windings are spaced ___ degrees apart. 120 Degrees What is the purpose of bearings in a hydro-electric generator? To support the gravitational and rotation forces on generators and turbine runners What pump is used to supply lubricating oil between the thrust pad and collar during startups to prevent damage? Oil LiftPump Authorcpoitras23 ID166179 Card SetPOB4 DescriptionPOB4 Updated2012-08-15T20:46:38Z Show Answers