I * 84 ELECTRICAL APPARATUS
^ I seen, power-factor and apparent efficiency rise to high values, and
I I even the efficiency is higher than in the straight induction motor.
!| . i> However, at light-load the power-factor and thus the apparent
-*\ ' \ efficiency falls off, very much in the same manner as in the con-
<j i catenation with a synchronous motor.
'1 i It is interesting to note the relatively great drop of speed at
^ , , light-load, while at heavier load the speed remains more nearly
II i constant. This is a general characteristic of anti-inductive im-
jl pedance in the induction-motor secondary, and shared by the
^ use of an electrostatic condenser in the secondary.
(i \ For comparison, on Fig. 28 the curve of apparent efficiency of
this motor couple is shown as CC.
if]
;| >
f\ \ Induction Motor with Condenser in Secondary Circuit
'! ! 55. As a condenser consumes leading, that is, produces lagging
I reactive current, it can be used to supply the lagging component
j of current of the induction motor and thereby improve the
power-factor.
/ Shunted across the motor terminals, the condenser consumes a
p constant current, at constant impressed voltage and frequency,
J'i and as the lagging component of induction-motor current in-
/i creases with the load, the characteristics of the combination of
, / motor and shunted condenser thus change from leading current
f< at no-load, over unity power-factor to lagging current at overload.
II As the condenser is an external apparatus, the characteristics of
j,( the induction motor proper obviously are not changed by a
| shunted condenser.
As illustration is shown, in Fig. 32, the slow-speed induction
motor Fig. 20, shunted by a condenser of 125 kva. per phase.
Fig. 32 gives efficiency, T?, power-factor, p, and apparent efficiency,
7, of the combination of motor and condenser, assuming an
efficiency of the condenser of 99.5 per cent., that is, 0.5 per cent.
loss in the condenser, or Z = 0.0025 — 0.5 j, that is, a condenser
just neutralizing the magnetizing current.
However, when using a condenser in shunt, it must be realized
that the current consumed by the condenser is proportional to the
frequency, and therefore, if the wave of impressed voltage is
greatly distorted, that is, contains considerable higher harmonics
—especially harmonics of high order—the condenser may produce
considerable higher-frequency currents, and thus by distortion