Generators; Prepackaged; Ac Generators - Guardian 4721 Repair Manual

SECTION 2.1
DESCRIPTION AND MAJOR COMPONENTS
1
BLACK
1
4
RED
4
Figure 2. Brush Holders and Brushes
THE EXCITATION CIRCUIT
AC output from the stator excitation (DPE) winding is
delivered to the voltage regulator, via a thermal pro-
tector (TP), Wire No. 2, an excitation circuit breaker
(CB1), Wire No. 162, and Wire No. 6. This is "unregu-
lated" excitation current.
DPE - STATOR EXCITATION WINDING
CB2 - EXCITATION CIRCUIT BREAKER
VR - VOLTAGE REGULATOR
TP - THERMAL PROTECTOR
6
WIRE
5
NUT
2
DPE TP
Figure 3. Schematic - Excitation Circuit
THERMAL PROTECTOR:
This normally closed thermal switch protects the stator
windings against excessively high internal tempera-
tures. The switch is physically imbedded in the stator
windings and electrically connected in series with the
DPE winding AC output to the regulator. If internal sta-
tor temperatures exceed a safe value, the switch con-
tacts will open and the DPE output to the voltage regu-
lator will be terminated. Without excitation current flow
to the rotor, generator AC output voltage will drop to a
value commensurate with rotor residual magnetism.
Page 22
+ -
BLACK
1
RUSH WITH RED LEAD
RED
6
VR
162
6
(BYPASS)
162
CB2
PART 2
The thermal protector is self-resetting. That is, when
internal stator temperatures drop to a safe value, its
contacts will re-close and normal DPE output to the
regulator will resume.
Wire No. 5 is a thermal protector "bypass" lead. If the
thermal switch has failed in its open position, it can be
bypassed. The Wire No. 5 bypass lead is brought out
of the stator and has a wire nut on its end.
TP
Figure 4. The Thermal Protector
EXCITATION CIRCUIT BREAKER:
This circuit breaker protects the regulator against high
voltage surges. If the breaker has tripped open, loss
of excitation current will occur. Stator power winding
AC output voltage will then drop to a value commen-
surate with residual magnetism in the rotor. The
breaker is self-resetting.
Figure 5. Excitation Circuit Breaker
VOLTAGE REGULATOR:
See Figure 6. Unregulated AC output from the stator
DPE winding is delivered to the voltage regulator, via
Wires No. 6 and 162. Stator power winding AC volt-
age and frequency signals are delivered to the regula-
tor, via "sensing" Wires No. S15 and S16. The regula-
tor rectifies the DPE output and, based on the sensing
lead signals, regulates the DC current output. An LED
(light emitting diode) is incorporated on the regulator.
This red light senses the "sensing" (S15/S16) input.
PREPACKAGED LIQUID
COOLED AC GENERATORS
162
2