Ans. The term surging is given to describe the current fluctuations produced by hunting.
The mechanical analogy of hunting illustrated in fig. 1,611 will help to an understanding of this phenomenon. In alternating current circuits a precisely similar action takes place between the alternators and synchronous motors, or even between the alternators themselves.
CHARACTERISTICS OF SYNCHRONOUS MOTORS
Starting.—The motor must be brought up to synchronous speed without load, a starting compensator being used. If provided with a self-starting device, the latter must be cut out of circuit at the proper time. The starting torque of motor with self-starting device is very small.
Running.—The motor runs at synchronous speed. The maximum torque is several times full load torque and occurs at synchronous speed.
Stopping.—If the motor receive a sudden overload sufficient to momentarily reduce its speed, it will stop; this may be brought about by momentary interruption of the current, sufficient to cause a loss of synchronism.
Effect upon Circuit.—In case of short circuit in the line the motor acts as a generator and thus increases the intensity of the short circuit. The motor impresses its own wave form upon the circuit. Over excitation will give to the circuit the effect of capacity, and under excitation, that of inductance.
Power Factor.—This depends upon the field current, wave form and hunting. The power factor may be controlled by varying the field excitation.
Necessary Auxiliary Apparatus.—Power for starting, or if self-starting, means of reducing the voltage while starting; also, field exciter, rheostat, friction clutch, main switch and exciter switch, instruments for indicating when the field current is properly adjusted.