During hunting phenomena in alternators, does the speed only oscillate about its normal value or does the rotor actually oscillate about a fixed point? Is the slip in the alternator also affected during hunting?
Power produce in alternator depends on torque angle of alternator, due to hunting torque angle will increase and decreases(rotter oscillates around pole axis) depending on the disturbance(instant rise/fall in load).Rotter rotates at same synchronous speed and the oscillation will damp out slowly by damper winding provided on pole.
The rotor speed oscillates around base synchronous speed. In case of Synchronous motor or generator on sudden load connection, it can be easily visualized using Stroboscopic RPM meter.
In such cases, as the rotor speed increases beyond synchronous speed the slip is negative the damper bar produces a negative induction torque causing it to slow down and maintain the base speed.
But when the rotor speed decreases slightly below base speed, slip is positive and damper bar produces a positive induction motor torque causing it to maintain the base speed.
These oscillations will be absent if damper bars are not present.
Physically the rotor poles are locked with the the poles created by the rotating magnetic fields. In the event of hunting phenomenon, the two poles tries to slip away.
In that case, on the shaft you have to write using ckalk or paste a paper with marking either 1 2 3 4 5 or any thing you can write.
When the shaft is rotating, you will not visualize what you have written on it, until you use stroboscopic effect. In stroboscope the flickering light has a frequency of ON /OFF, when this frequency is matching with the frequency / speed of shaft , you will find what you have written. The shaft , though rotating will appear to be stationary-standstill.
Now if sudden load is applied on synchronous motor- image of what you have written on shaft will appear to swing from where is appeared to be standstill. Do not change the frequency of Stroboscope.
It says the minor swinging of speed due to hunting.
You require a stroboscope and a synchronous motor connected to a DC generator or a load of belt & pulley.
When DC generator is loaded a counter torque appears on the motor shaft.
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