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| Illustration 1 | g02860217 |
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SR5 generator similar to the frame families shown with controls and accessories. (1) Terminal box (2) Main stator (3) Main rotor (4) Rotor shaft (5) Permanent Magnet Pilot Exciter (PMPE) assembly (6) End bracket (7) Bearing (8 ) Exciter rotor (9) Fan (10) Bearing (11) Front bracket (12) Drive hub (13) Adapter | |
An engine supplies the power in order to turn the rotor shaft (4). The exciter rotor (8) and main rotor (3) are attached to the rotor shaft (4). The voltage regulator supplies DC voltage and DC current to the exciter field (stator). As the rotor shaft turns, the exciter rotor generates AC voltage and AC current. The rectifier components convert the AC exciter voltage and current to DC voltage and current.
This DC voltage and current is supplied to the main rotor windings. A magnetic field is created around the poles of the main rotor windings. As the main rotor turns with the rotor shaft, the magnetic field also rotates.
The magnetic field induces an AC voltage into stationary main stator (2). The main stator is a coil with multiple turns of wire. The current that flows through the main stator flows to the load.
The rectifier assembly will supply DC voltage and current to the main rotor (3). The main stator output voltage (load voltage) is controlled by the voltage regulator varying the DC current and the DC voltage that is supplied to the exciter field (stator).
Permanent magnet pilot excited (PMPE) is used for excitation on this SR5 generator.
Permanent Magnet Pilot Excited (PMPE) Generator
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| Illustration 2 | g03383477 |
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Generator wiring diagram for the SR5 (CR1 - CR6) Diodes (CR7) Varistor (L1) Exciter stator (L2) Exciter rotor (L3) Main rotor (L4) Main stator (L5) PMG stator (PM) Permanent magnet (R5) Resistor (RFA) Rotating field assembly (TR1) STD voltage droop transformer (T0, T1, T2, T3) Generator terminals and/or generator leads | |
Permanent magnet pilot excited (PMPE) generators provide power for the voltage regulator from a pilot exciter. The permanent magnet generator (PMG) components consists of a permanent magnet (PM) and a PMG stator (L5).
Refer to Illustration 2.
The pilot exciter operates independently from the generator output voltage. Constant excitation during a large load application is possible because the irregularities that occur in the generator output voltage do not affect the exciter.
The irregularities that occur in the generator output voltage are caused by load conditions. The independent exciter operation also allows the generator to sustain excessive currents for short periods of time.
When the engine starts turning the "Rotating Field Assembly "(RFA), the permanent magnet (PM) induces an AC voltage in the PMG stator (L5).
The PMG stator has three coils of wire. The PMG stator generates three phase alternating current (AC) voltage and current that powers the voltage regulator.
Within the voltage regulator, the three phase alternating current is rectified to direct current (DC). A controlled amount of the DC current is supplied to the exciter stator (L1) through terminals F1 and F2.
Direct current flows to the exciter stator (L1) which creates a magnetic field. The exciter rotor (L2) rotates in this magnetic field. The exciter stator and the exciter rotor generate three phase alternating current for the 3000 frame generators.
The AC current is then rectified by a three phase full wave bridge rectifier circuit. The rectifier assembly for the 3000 frame generators consists of diodes that are embedded in two rectifier blocks. This rectifier circuit is made of the following diodes: CR1, CR2, CR3, CR4, CR5 and CR6.
The DC output from the bridge rectifier is carried to the main rotor by the conductors for the (L3) windings. The conductors for the output from the bridge rectifier are routed through a groove that is in the generator shaft. Current through the main rotor windings creates the magnetic field within the generator.
As the main rotor windings rotate, the main field induces a three phase AC voltage in main stator (L4). This voltage is developed and is present across the following terminals: T0, T1, T2 and T3. These terminals are connections for the load.
In order to keep the output voltage constant with changing loads, the exciter current and exciter voltage must be controlled. The control of the exciter current and exciter voltage is the function of the voltage regulator.
The voltage regulator senses the generator output voltage directly at the T1, T2, T3, and the T0 terminals, or at the sensing transformers that are installed on the generators that are rated over 600 V.
The voltage regulator sends current to the exciter through wires F1 and F2. The amount of current is dependent on the sensed voltage.
Note: For more information on voltage regulation, see the appropriate voltage regulator service manual.
PMPE generators provide the magnetism for startup of the generator. A permanent magnet (PM) supplies the initial magnetism that is required at startup. Flashing the field is not required for startup of the generator.
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| Illustration 3 | g01614194 |
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Rectifier circuit for 3000 family generators (CR1 - CR6) Diodes (CR7) Varistor (L2) Exciter rotor (L3) Main rotor (R5) Resistor | |
The following diodes form a bridge rectifier circuit: CR1, CR2, CR3, CR4, CR5 and CR6. The bridge rectifier circuit receives three-phase alternating current from exciter rotor (L2). The bridge rectifier circuit rectifies the alternating current into direct current. The DC power is then routed to main stator windings (L3).
Diodes CR1 through CR6 are contained in the rotating rectifier blocks.
The SR5 3000 frame generator uses a three-diode rectifier block.
Two different blocks are required. One block is positive and the other block is negative.
Rectifying the current creates heat. The rotating rectifier blocks are fastened to heat sinks. These heat sinks spread the heat and allow the rotating rectifier blocks to operate at a cooler temperature.
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| Illustration 4 | g01757734 |
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(13) Positive rectifier block
(14) Negative rectifier block | |
Three-diode rectifier blocks are used only for SR5 3000 Frame Generator Applications
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| Illustration 5 | g01322040 |
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(15) Varistor
(16) Three-diode rectifier blocks | |
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| Illustration 6 | g01613997 |
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Three-Diode Rectifier Block Wiring (17) Positive rectifier block (18) Negative rectifier block (19) Main rotor wire passageway (20) Heat sink assembly (21) Resistor (22) Exciter rotor wire passageway (23) Varistor | |
In order to form a bridge rectifier circuit, two similar three-diode rectifier blocks are connected. Each of the three-diode rectifier blocks contain three diodes. Positive rectifier block (17) contains diodes CR1, CR2, and CR3. Negative rectifier block (18) contains diodes CR4, CR5, and CR6.
Both of the three-diode half-wave rectifiers must be wired correctly. Refer to Illustration 6. Each "AC" terminal connects to an "L2" wire from the exciter rotor. The "+" diode terminals connect together internally. The "+" terminal connects to one "L3" wire of the main rotor winding. The "-" terminal connects together internally. The "-" terminal connects to the other "L3" wire of the main rotor winding.
The positive rectifier block (17) and the negative rectifier block (18) are mounted to the heat sink assembly (20). The heat sink assembly is on the end of the generator shaft. The heat sink assembly (20) also contains a varistor (23) and resistor (21). The varistor and the resistor are used to protect the generator excitation and rectification circuits. Refer to Generator Operation, "Generator Circuit Protection".
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| Illustration 7 | g01991774 |
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PMPE Generator Wiring Diagram (CR1 - CR6) Diodes (CR7) Varistor (L1) Exciter Stator (L2) Exciter Rotor (L3) Main Rotor (L4) Main Stator (L5) PMG Stator (PM) Permanent Magnet (R5) Resistor (RFA) Rotating Field Assembly (TR1) Optional Voltage Droop Transformer (T0, T1, T2, T3, T7, T8, T9) Generator terminals and/or Generator Leads | |
The varistor protects the diodes by suppressing any abnormal transient peak voltages. The varistor is a separate component that mounts on the heat sink assembly.
The varistor can be the first component to fail. The varistor can fail in adverse operating conditions due to out of phase paralleling and voltage spikes due to unbalanced loads. The varistor must be checked for proper operation at regular intervals.
The resistor is a separate component that mounts on the heat sink assembly. The resistor provides a low resistance circuit from the insulated windings to the shaft and cores of RFA.
The resistor is a 27000 ohm resistor. Air friction on the windings can cause an electrostatic charge. If this resistor is not installed, these charges can cause voltages to become high enough to destroy the winding insulation. The resistor allows charges to dissipate as the charges are generated. This resistor also prevents any buildup of voltage.
Due to the resistance value and power rating of the resistor, a ground failure at any point on the RFA will not prevent the generator from operating normally. A ground failure will not damage the resistor.
The voltage regulator and related components also protect the generator. The PMPE exciters utilize fuses that will stop the current flow to the voltage regulators. The fuses open rapidly. If no voltage is applied to the exciter, then the generator output voltage is reduced to a low level.
The fuses protect against secondary damage that is caused by other component failures. If any fuse is replaced, use only a fuse of the same type and amperage rating. A larger amperage rating or a fuse which does not open rapidly will not prevent damage to other components.
All voltage regulators have built in excessive current protection circuits that also open the excitation circuit.
Note: For more information on voltage regulation, see the appropriate voltage regulator service manual.
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| Illustration 8 | g01991814 |
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Location of the Space Heater (31) End Bracket (32) Heater Element (33) Exciter Stator (34) End Bearing | |
The space heater is attached to the rear bearing bracket. The space heater is located at the exciter end of the generator.
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| Illustration 9 | g01516042 |
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Simplified diagram of space heater connections | |
The SR5 generator can operate in high humidity conditions without problems. The humidity can be as high as 100% non-condensing humidity. However, problems can occur when the generator is idle and the surrounding air is warmer than the generator. Moisture can form on the windings. Moisture will result in poor performance or even damage to the windings. Whenever the generator is not active, the space heaters should be operated.
An external source is required to operate the space heaters. This source must be 230 VAC 60 Hz or 200 volts 50 Hz. Both of these sources must be single phase. Refer to Illustration 10.
The Caterpillar control system requires that a 230 (200) volt supply is used as the space heater supply. The 230 (200) volt supply must be used to operate with the circuit breakers and relay contacts that are used for the space heater. The circuit breakers and relay contacts are located in the AC control panel. The heater system is designed to turn off automatically when the engine is running.
Space Heater Connections - Optional
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| Illustration 10 | g03535316 |
| (40) AC-C4 connector | |
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| Illustration 11 | g03535357 |
| (41) AC-C4 connector | |