Ingersoll-Rand Thermo King SGCM 4000, Maintenance Manual

Page: 147 / 181

Alternator Operation and Diagnosis
146
Alternator Function
Starting Excitation
The initial excitation for the alternator is supplied by residual magnetism in the main field. Residual main
stator voltage provides initial excitation power to the digital simplified regulator (DSR) from a separate
2-lead stator winding. The SG+ controller energizes Quad Relay 2 minutes after the engine starts.
Energizing the Quad Relay starts current flow from the DSR to yellow wire. The yellow wire sends the
current through the exciter field to build voltage in the stator windings. The exciter field current then
returns through the blue wire to chassis ground.
Running Excitation and Control
When the alternator output reaches the rated voltage, excitation is provided by the alternator excitation
winding. The magnetic field that was formed in the exciter field winding by the DSR induces voltage in
the exciter rotating winding. This voltage is changed from three-phase ac to dc by the rotating rectifier.
The dc current is transferred to the rotating main field winding. The rotating main field now becomes
magnetized. The magnetic field formed in the rotating main field winding induces a voltage in the
alternator stator windings. This voltage is sent out of the alternator stator leads to the power plug and
load. 460 Vac, 3-phase output can be measured at the power plug. In addition to being powered from the
stator excitation winding, the DSR monitors the stator output for voltage control purposes. The DSR
controls the voltage fed to the exciter field, and therefore, the main field, to maintain the alternator output
voltage within specified limits.
Overload
For temporary overloads (such as refrigeration unit start up), the DSR controls the voltage fed to the
exciter field to maintain the alternator output voltage. Over voltages caused by open circuit sensing
terminals are avoided by loss detection sensing circuitry that reduces the alternator terminal voltage to a
safe fixed level.
Overload Shutdown
The overload shutdown is provided by the controller.
If an overload condition becomes more than temporary, the reduction in alternator output voltage due to
the overload causes the DSR to increase field current through yellow wire. The DSR senses the overload
current and sends a signal out through the Open Collect circuit. The controller reads this signal and shuts
down the engine. A 20 minute restart is initiated.
If the controller shuts down unit operation, it indicates one of the following:
1. There is a malfunction in the load causing the load to fail to start or to draw single phase current.
2. The engine speed or power is low due to improper speed adjustment, fuel supply problems or other
mechanical conditions while the generator is supplying motor starting current to the load.
3. Internal component failure in the excitation control system, resulting in excessive field current. This
includes possible malfunction of protective elements in the excitation control.
4. Failure in the alternator rotating elements (exciter armature, rotating diode assemblies or main field)
can cause the regulator to supply excessive exciter field current.
5. Engine shutdown on low engine oil level, low oil pressure or high water temperature.