All primary fuses are, high capaicty, inrush time delay, 1 amp fuses.
All secondary fuses are low capacity, one time, 2 amps fuses.
PT 1, 2 & 4, 5 are connected open delta., The primary line to line is 460 volts and secondary line to
line is 115 volt. Phase B is grounded on all secondaries for proper fuse protection and common A.C.
reference voltage between circuits.
PT 3 is the bus potential transformer connected on lines A & B.
PT 6,7,8 are connected wye to wye. The primary line to ground is 265 volts and the secondary is 110
Current Transformers (CT)
The current transformers are mounted so that the generator phase wires must run through them,
therefore, all load currents are sensed and converted to a smaller current that can be easily handled
by switches and meters.
Current transformers are constant current devices which means the current remains constant with
various loads. When the load on a current transformer changes the voltage reduces and the current
remains the same. It is easy to see that when a current transformer secondary terminals are open (no
current) the voltage will rise high. For this reason, the secondary terminals on the current
transformers are either connected to the Ammeter and reverse power relay or shorted out by means
of the Ammeter switch. This is done to prevent arcing at the switch contacts and high voltage at the
current transformer terminals.
Generator Run Lights
120 Volt lamp operates from PT1 which is connected to the respective generators phases A & B.
Breaker Position Lights
120 volt breaker closed light operates through the breaker auxiliary contact a which closes when the
breaker is closed.
120 volt breaker open light operates through the breaker auxiliary contact b which closes when the
breaker is open.
The breaker auxiliary contacts are mounted inside the breaker case and wired out to terminal strips
TB B located directly behind the breaker pan.
Under Voltage Relay (UVR)
Each breaker has a separate under voltage relay that shunt trips the breaker upon loss of generator
Each generator under voltage relay operates at 120 volt from PT1 which is connected to the
respective generators phases A & B.
The 120 volt input to each generator undervoltage relay has a normally closed contact of the reverse
power relay in series. When a reverse power occurs the breaker is shunt