Questions & Answers About SYNCHRONOUS GENERATOR


1.    Name the two types of alternators depending on the rotor construction.
         The two types of rotors are used in alternators.
  •                        Salient pole type
  •                        Smooth cylindrical type.
2.    What are the various functions of damper winding provided with alternator?
3.    Explain the meaning of synchronous reactance.

               Terminal voltage is decreased from its no-load value Eo to V.
  •      Drop due to armature resistance, IRa.
  •     Drop due to leakage reactance, IXL.
  •     Drop due to armature reactance, IXa.
              The drop in voltage due to armature reaction may be accounted Xa in the armature                 winding .voltage drop IXa.
             The leakage reactance XL and armature Xa may combined to give synchronous                        reactance Xs.
Xs= XL+ Xa.
               Voltage drop in an alternator under load
   = IRa+jI Xs
   = I (Ra+jI Xs)
   = IZs.
                Zs is synchronous impedance.

4.    Define voltage regulation of an alternator.

  •  Regulation of an alternator is defined as the rise in terminal voltage when the
     load is thrown of keeping speed and excitation constant.
%Regulation =        o E -V
V      x100
                  Regulation is positive (inductive loads) and negative (capacitive loads).

5.    What is load characteristic?
The ZPF saturation curve is one special case of load characteristic curves. The                        other curves represent conditions as ZPF at other than rated load or saturation  at  pf.s             other than zero.

6.    State the condition required for paralleling two synchronous generators.

For satisfactory parallel operation of alternators the following three conditions must be fulfilled.
(i) The terminal voltage of the incoming alternator must be same as the bus- bar                   voltage.
(ii) Frequency of the generated voltage of the incoming alternator should be equal                 to the bus-be frequency.
(iii) Phase sequence of the voltages of the incoming alternator should be the same                  as that of the bus bar.

7.    What is meant by synchronizing?

A synchronous generator can be put to share the load, it should be properly connected in         parallel with the common bus-bar.

8.Write down the equation for frequency of emf induced in an Altenator.

Frequency of emf induced in an Alternator,f ,expressed in cycles per second or
Hz, is given by the following equation
F = (PN)/120 Hz,
Where P- Number of poles
N-Speed in rpm

9. How are alternators classified?

According to type of field system
•    Stationary field system type
•    Rotating field system type

According to shape of field system
•    Salient pole type
•    Smooth cylindrical type

 10.Name the types of Alternator based on their rotor construction.

Alternators can be classified into the following two types according to its rotor construction
•    Smooth cylindrical type alternator
•    Salient pole alternator


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