The operation of the output circuit is centered
closing switch contacts) in series with transistors Q1 and
around the operation of Q1. In order to operate the
Q2. The K1 relay provides an electrical interlock
circuit breaker being monitored by the synchronizing
through the closing circuit of the generator circuit
monitor (fig. 8-28) on.
breaker. The electrical interlock will prevent an
operator from electricaly closing the circuit breaker
Two circuits affect the bias voltage of Q1:
unless the necessary conditions have been met. The
circuit breaker closing contacts must be open to energize
1. The phase difference monitoring circuit, which
includes resistor R6. When a voltage of
the K1 relay. Also, Q1 and Q2 must be ON. With proper
sufficient magnitude is developed across R6, the
circuit breaker line up, the first condition is met. The
base to emitter bias of transistor Q1 is reversed.
monitoring circuits must provide the current signals to
This turns off Q1.
Q1 and Q2 to turn them on. The functions of the devices
2. The voltage difference monitoring circuit. This
in the output circuit are shown in table 8-7.
circuit is connected across the base to the emitter
Table 8-7.--Devices in the Output Circuit
of transistor Q1. When transistor Q5 conducts,
this circuit disables Q1 by shorting the base to
emitter of Q1. This removes the bias reference
supply.
Q1 can conductor be biased on only when these two
circuits are off. The action by the Q1 transistor is similar
to that of a switch.
A transistor can be used to act like contacts that are
either closed or opened. This is done by using a large
enough base current signal that can drive the transistor
into saturation. At this point, the transistor acts like a
short circuit (equivalent to closed contacts). If the base
current signal is weakened, reversed, or eliminated, the
transistor then acts as an open circuit (equivalent to open
contacts).
The operation of the transistor circuit is as follows:
Relay K1 is energized when transistors Q1 and Q2 are
biased on, and circuit breaker switch contacts connected
between 2K and 2L are closed.
PHASE DIFFERENCE MONITORING
CIRCUIT
The phase difference monitoring circuit (fig. 8-29)
prevents energizing of the K1 relay if the phase
difference between the bus and the oncoming generator
is more than -30 and 0. It does this by reducing and
comparing both input voltages, using its output to
control transistor Q1.
Look at the schematic in figure 8-30. The
secondary winding X1 and X3 of T2 and X1 and
X3 of T3 are connected so the output voltages of
T2 and T3 subtract from each other. For instance,
assume that the voltages are in phase, as shown in
8-37
