Radar System Engineering

SEC. 14.6] SPEED REGULATORS 571
different manufacturers. In general, a voltage-sensitive element, consisting
of a solenoid coil and a movable armature, is connected to a
multiple contactor. Movement of the armature from the closed to the
open position progressively short-circuits steps of resistance connected
to the contacts. It is necessary to choose the resistance steps withthe
field-excitation characteristic of the alternator in mind, so that each
progressive step of resistance produces an approximately equal change
of output voltage. The incremental change in output voltage produced
by one step of resistance determines the limit of sensitivity of the regulator.
An air dashpot is usually provided to damp any oscillation or
hunting of the armature.
Regulating Anti.hunt r.,hfi.
‘coil – coil “fi~””
A-
m
Voltage
adjusti.Ing
-
.hmfict ,!O.-”=tat
m
m F
I 1 1
1 I
I
Exciter
1
A+
Rect
n
@
Rect
tr?
FIc+.1415.-Schematic diagram of a General Electric voltage regulator Type GEA.2-B2
and 3-phase 230-volt alternator with exciter.
In field service, the usefulness of the finger-type regulators was
limited by the tendency of the contacts to stick and burn, and by corrosion
of the contacts due to moisture and salt air. In addition, the device
is very difficult to repair in the field. Consequently, finger-type regulators
have been used on radar systems only rarely.
14.6. Speed Regulators.—The a-c frequency generated by motoralternator
sets varies over a wide range with changes in input voltage,
load, altitude, and temperature. At high altitude, low temperatures and
air densities are encountered. The low temperature tends to lower the
speed by reducing the resistance of the motor field circuit, whereas low
air density allows the speed LOincrease because of lower windage losses.
The following test data indicate the conditions for maximum and minimum
frequency of the 1500-va PE-218-C and PE-218-D inverters.