SINGLE-PHASE INDUCTION MOTOR 117

it is in the second case — lagging coil. In either case, the torque
efficiency is low, that is, the device is not suitable to produce
high starting-torque efficiencies, but its foremost advantage is
the extreme simplicity.

The voltage due -to the shaded portion of the pole, e%, is less
than that due to the unshaded portion, ei, and thus a somewhat
higher torque may be produced by shading more than half of
the pole: a > 0.5.

A larger air gap: 6 > 1, under the shaded portion of the pole,
or an external non-inductive resistance inserted into the shad-
ing coil, under certain conditions increases the torque somewhat —
at a sacrifice of power-factor — particularly with high-resistance
armature and low-resistance shading coil.

e0 = 100 volts; a = 0.5; b = 1; Y = 0.001 - 0.01 j.

X 10~2 X 10~2 per cent, per cent,

1-3/1-3/38.3 61.8 +1.9 1.97 +1-56 +4.07

2-2/40.3 60.2 +11.0 2.07 +9.28 +23.00

3-1/42.0 59.8 +21.5 2.17 +18.36 +43.70

2-2/1-3/37.2 62.9 -4.3 1.70 -3.52 -9.65

2-2/38.5 61.7 +6.2 1.76 +5.12 +13.60

3 - I/ 39.2 62.0 +17.3 1.80 +14.44 +37.40

3-1/1-3/37.6 63.0 -11.9 1.66 -9.76 -25.80

2-2/37.8 62.5 - 0.8 1.66 - 0.66 - 1.75

3-1/37.4 63.0 +10.3 1.64 +8.44 +22.60

Monocyclic Starting Device
76. The monocyclic starting device consists in producing ex-
ternally to the motor a system of polyphase voltages with single-
phase flow of energy, and impressing it upon the motor, which is
wound as polyphase motor.
If across the single-phase mains of voltage, e, two impedances
of different inductance factors, Z\ and Z2, are connected in series,
as shown diagrammaticaJly in Fig. 41, the two voltages, fli and
$2, across these two impedances are displaced in phase from each
other, thus forming with the main voltage a voltage triangle.
The altitude of this triangle, or the voltage, $0, b'etween the com-