Alternators Flashcards
Name the two other names for Alternators.
Synchronous Generators
Alternating current generators
Describe a rotating field alternator.
Has rotating field windings
Excitation current is supplied through brushes and slip rings from an external dc source
Armature directly connected to an external load
The two distinct types of synchronous-generator rotating field structures are?
Cylindrical - smooth exterior, long, well balanced
Salient (projecting) - shorter in length, wide
What sort of conversion of energy happens in the armature winding?
Mechanical to Electrical
A one-turn stator winding in an alternator generates one-quarter the voltage of a comparable four-turn winding. T or F?
True
E•G
One Turn Coil= 30V
Four Turn Coil= 120V
In regards to a parallel delta-connected, three-phase, twelve-lead alternator, how would you find the current in a winding?
Divide Iphase by two to get the current per winding
How do you reduced Hysteresis Losses?
Alloys such as silicon steel or iron with silicon in it are used in the core material.
Heat losses produced by current in windings of the alternator are called?
Copper Losses
The power required to drive the built-in cooling fan of an alternating current generator is known as what type of losses?
Mechanical Losses
In an alternator, the slip rings are stationary. T or F?
False. Slip rings are attached to the rotor.
The Output Voltage of an Alternator is due to three factors:
Armature: Resistance, Reactance & Reaction
A solid state rectifier is an example of a external dc supply. T or F?
True
In a brush-type, self-excited alternator, a small shunt is mounted on the same alternator shaft that supports the main alternator rotor and field windings. T or F?
True
A brushless excitation system does not require a commutator. T or F?
True
Four conditions must be met before syncing two parallel alternators. State them:
Phase Sequence
Terminal Voltages
Frequencies
Phase Position
Using the “three-dark lamp method” the lamps must be suitable for what rating?
Twice the alternators phase voltage value
A synchroscope indicates what values?
Frequency and Phase Position of the incoming alternator relative to the running alternator or supply voltage
If a synchroscope pointer moves CCW, what does that indicate?
The frequency of the incoming alternator is lower than that of the running alternator.
The 12 o’clock position of a synchroscope means the frequency and phase position have all matched up. T or F?
True
How do you transfer the power load of ALT 1 to ALT 2 without changing frequency?
Increase the power input or the torque of the prime mover of ALT2 and simultaneously decrease the power input to ALT1
To increase the output voltage of a system supplied by two paralled alternators, the field excitation of both alternators needs to be increased. T or F?
True
A heavy flywheel reduces hunting. What other application reduces hunting?
Embedded amortisseur (dampen) windings in the surface of the alternator’s rotor pole faces produce an induced current that opposes and limits the action of hunting.
