Hunting of Alternators

Author: E.E. Kimberly

The torque of a reciprocating engine is pulsating, and hence the power delivered to an alternator driven by it is pulsating. If such a power unit is operated in parallel with another power unit, an unstable condition may result as follows. When the torque of the engine is greatest, its alternator takes momentarily more than its average load and the other alternator takes less than its average load. When the engine torque is least, its alternator takes less than its average load. This oscillation of power, if too violent, may be cumulative; and, if the period of oscillation is too near the natural oscillating frequency of the rotor, the alternators may be thrown out of synchronism. Such oscillation is called "hunting." Destructive oscillation is prevented in alternators driven by internal-combustion engines by heavy amortisseur windings similar to the starting squirrel-cage windings of synchronous motors or by heavy flywheels or their equivalents.