network which helps stabilize the
Functionally, transistor Q1 acts as a
C2, thus forming an RC circuit with a
Rectifier D6 is used to assist in the
variable time constant. If the transistor is
correct operation of the silicon
controlled rectifier (SCR).
charges at a relatively slow rate and does
Surge protector SP1 is used to limit
not reach the voltage level required to fire
the unijunction until late in the cycle.
The cross current compensation
Consequently, the SCR fires ]ate in the
(CCC) system consists of the
cycle and the control current supplied the
current transformer CCCT (fig.
S (C) winding is small. If the transistor
has a low resistance, capacitor C2
current transformers are mounted to
charges rapidly and reaches the required
the left of the reconnection panel
voltage level early in the cycle. This
assembly and the rheostat is
causes the SCR to fire early in the cycle,
mounted on the relay box.
supplying a relatively high value of control
Cross current compensation is
current to the S (C) winding.
required to minimize circulating
The silicon controlled rectifier (SCR),
unijunction semi-conductor Q2 and
operating in parallel.
transistor Q1 are all synchronized and
accomplished by using the current
power supplied by the 120 pulses per
transformer CC-CT to detect the
second rectified output of D5. Zener
zero power factor load of each
diode Z2 limits the voltage across the Q1
and the Q2 to a maximum of 18 volts
even though the output of D2 has a
maximum peak of nearly 200 volts.
The voltage difference is absorbed by
Control of the transistor Q1 (ie its relative
resistance) is established by the error
signal resulting from the difference in
voltage between the zener reference Z1
voltage seen across resistor R12. This
rectifier D1 and filtered by reactor L1,
capacitor C1 and resistors R6 and R12.
Voltage regulator adjustments are made
by means of a 250 ohm rheostat
VOLTAGE ADJUST mounted on the
control panel. The upper range of the
voltage control can be extended by
decreasing adjustable resistor R1.
The remaining circuit elements used in
Figure 125. CCCT, CT1, and CT3 transformer
the voltage regulator serve the following
resistors R10 and R11 form a