Hydro Generator- Part 3

Out-puts from a Generator - Governors

•

• •Governor ensures frequency at a set value by increasing / decreasing the fuel input
  
  Two types of Governors :
  Pneumatic : Fuel flow is controlled by valve position control. Control Input : DC Voltage

          Electronic : Fuel flow is controlled by a total servo mechanism. Control input : DC Voltage pulses 

 

Out-puts from a Generator - Voltage

• •Voltage is induced in the stator winding
•  Terminal voltage depends upon :

1.   No. of conductors in series per winding
2.   Speed at which magnetic field cuts the winding
3.   Strength of the magnetic field
   

 Voltage Control

• •Nominal Voltage = 415 V, 11 kV 
• Voltage can vary due to load fluctuations 
• Terminal voltage is controlled by

varying the Strength of magnetic field

          = varying the current through the field coil
          = varying the voltage applied to the field coil (Exciter control)

 

Typical Exciter

 

Read more in coming posts... 

Hydro Generator- Part 2

Generator components

Prime Mover

• Source of mechanical power for relative motion
• Two classes of Prime movers :

                            High Speed : Steam & Gas Turbines
                            Low Speed : IC engines, Water turbines and DC motors

• Type of prime mover plays an important role in a generator installation. Many characteristics of alternator and its construction depend upon Speed at which the rotor is turned. 

 Rotors

• Two types are used in rotating field alternators

            - Turbine driven rotor ( used where prime mover is a high speed turbine)

            - salient pole rotor( used with low speed prime movers)

Stator

Many types based on

                   - Power out put
                   - Voltage output
                  - Type of cooling
                  - Number of phases

Simplified schematic of 3 ph. Stator

• Three single phase windings displaced by 120 degrees
• Star or Delta connection
• Neutral may or may not be brought out
• No. of terminals can be 3,4, or 6

Out-puts from a Generator

• Three phase ac power at :

                 -Rated Voltage
                 -Rated Frequency

Common Ratings

• Small Generators : 25 kVA to 300 kVA
• Medium Size Generators : 500 kVA to 1 MVA
• Large size Generators : 1 MVA to 25 MVA
• Power Plant Generators: 110 MW to 500 MW

Frequency

• Frequency depends up on the Speed of Rotation ( direct proportion)
• F = PN / 120 where F = frequency in Hz, P = No. of poles, N = speed of rotation in RPM, ( 120 is a constant to convert minutes to seconds and poles to pole pairs)
• Nominal frequency = 50/60 Hz
• Generator frequency can vary due to load fluctuations
• Frequency Regulation is mainly by adjusting the speed
• speed is controlled by varying the fuel input to the prime mover ( Governor control)

Read more in coming posts...