26 ELECTRICAL APPARATUS
As seen from Fig. 12, at the high speed, the motor performance
is excellent, but at the lowest speed, power-factor and apparent
efficiency are already low, especially at light-load.
The three current curves cross: at the lowest speed, the motor
takes most current at no-load, as the exciting current is highest;
at higher values of torque, obviously the current is greatest at
the highest speed, where the torque represents most power.
The speed regulation is equally good at all speeds.
Fig. 13 then shows the speed curves, with revolutions per
minute as abscissae, for the three numbers of poles. It gives
current, torque and power as ordinates, and shows that the
maximum torque is nearly the same at all three speeds, while
current and power drop off with decrease of speed.