Systems Operation

Usage:

Glossary

anode:: The positive end of a diode or rectifier.
blocking rectifier:: Permits current flow in only one direction. This keeps the polarity of the exciter in the correct direction.
bolted:: Use of a bolt to hold two or more parts together.
breaker:: An automatic switch used to open a circuit.
bridge:: A circuit used to change AC to DC and to measure small quantities of current, voltage or resistance.
build-up:: (Voltage) A gradual increase.
cathode:: The negative end of a diode or rectifier.
capacitance:: The measure of a capacitors ability to take and hold a charge.
circulating current:: The flow of current between two generators working in parallel.
commutator:: A part of the shaft used to remove DC voltage for excitation.
conduct:: Give path for current flow.
consideration:: factor.
continuity:: A circuit that is not open.
control:: One that controls.
controlled rectifier:: A rectifier that lets current flow only after it has "turned on."
DC controlled reactor:: Gives resistance to current flow to the rectifier according to the voltage droop setting. Same as saturable reactor, DC.
damping:: To smooth out.
de-energize:: To stop current from going to a component.
distribution winding:: An arrangement of windings, in groups that are in several slots, that go from one end of the core to the other end.
droop:: decrease.
effective:: Gives the desired effect.
elementary:: simple.
excitation:: DC current (controlled) used to make a magnetic field.
energize:: To cause current to go to a component.
electrostatic charges:: Electricity caused by friction.
exciter:: Gives DC current to the field windings of the generator.
field:: Magnetic lines of force around a conductor caused by current flow.
field windings:: Many turns of wire wrapped around an iron core. When a DC current flows through the field windings it causes a magnetic field (like that of a bar magnet).
flashing:: A process of putting DC current, from an outside source, into the field windings to get residual magnetism.
fluctuate:: change.
flux:: Magnetic lines of force.
full wave rectifer:: Changes AC to DC current.
gain:: A change in quantity of voltage.
gate:: An electronic part of a controlled rectifier (thyristor).
generate:: To make electricity.
grounded:: To make a connection to ground or to a component with similar effect.
impedance:: A combination of resistances.
induced:: caused.
interference:: Mixture of signals.
instrumentation:: Group of instruments.
insulated:: A component with insulation.
induce (to):: To send DC current to a coil and make a magnetic field.
layer wound:: Method of placing a large wire (instead of four small wires as in random wound) in uniform and parallel layers around a generator rotor.
lead:: wire.
line voltage:: The output voltage of the generator.
lock in:: When a contact closes to keep a solenoid energized.
lock out:: When a contact opens to keep a solenoid de-energized.
magnetic:: Having the characteristics of a magnet.
magnification:: make larger.
module:: An assembly of electronic components and circuits.
moisture:: The water content in the air.
oscillation:: A flow of electricity that periodically changes direction.
phase winding:: Group of generator stator coils in which electric power for the load is induced.
polarity:: The positive or negative characteristics of two poles.
pulsating:: Characteristic of rectified current similar to mechanical vibration.
radio suppresion:: Reduce the cause of radio frequency interference.
random wound:: A method of placing four small wires around a generator rotor. Each wire can cross the other while being wound.
reciprocating:: Movement in a straight line first one direction then the other.
regenerative power:: Power that works against the primary power.
reset:: To put a switch in a ready condition.
residual magnetism:: The characteristic of a magnet after removal of excitation.
saturable reactor:: Acts as a valve, as load changes, valve opens or closes to give more or less current to the rectifier.
saturated:: Magnetized to the point where an increase in current will give no increase in magnetic force.
satisfactorily:: correctly.
SCR:: Silicon Controlled Rectifier (semiconductor)
selinium (Se):: A metallic (like metal) element the with electrical characteristic of being a semiconductor.
semiconductor:: Components like, transistors, diodes, thyristors, etc. Has electrical characteristics between a conductor and insulation.
short:: Any connection between two or more components that is not desired.
shutdown:: When the engine is stopped either automatically or manually.
simultaneous:: At the same time.
solid-state:: An electronic component with no moving parts
surge:: A sudden increase in voltage or current.
tap:: Connection to get power from a circuit.
tested:: When a test has been made.
transfer:: change.
transient peak voltage:: A high voltage condition for a short time period.
trigger:: activate.
turn-on:: To start, as current flow through the controlled rectifier; to activate.
uniform:: Always the same form or pattern.
voltage droop resistor:: Variable resistor for control of voltage change from full load to no load.
voltage level resistor:: Gives wider range of voltage control.
voltage level rheostat:: Control for adjusting voltage output level.
voltage spike:: Temporary high voltage, lasts only a moment.
windings:: Layers of wire on a core.
wiring:: The wires of a circuit.
wound:: circled.

Identification

IDENTIFICATION PLATES (Typical)
1. Generator voltage location. 2. Generator group part number. 3. Sequence number location. 4. Serial No. Plate. 5. Caterpillar serial number location. 6. Caterpillar nameplate.

A sequence number (3) is stamped on the upper right hand side of the generator stator assembly located between the generator drive adapter face and the terminal box. This number will be stamped in a position below the generator voltage (1) and the generator group part number (2). These are stamped at the time of manufacture.

Caterpillar Tractor Co. will assign the Caterpillar serial number at the time of the generator use.

A serial number plate (4) will be attached to the generator by Caterpillar. This plate will be stamped with the generator model number, Caterpillar serial number, and the generator arrangement number.

Below the serial number plate, Caterpillar will stamp the Caterpillar serial number (5).

A Caterpillar data nameplate (6) is located below the stamped serial number.

3 Phase 4 Pole Generators

Generator And Regulator Components

GENERATOR REGULATOR HOUSING, FIG. 1.
1. Generator regulator assembly. TS1. Generator terminal strip.

GENERATOR REGULATOR ASSEMBLY, FIG. 2 (left side)

A2 Rectifier module

C1 RFI Suppression capacitor

C2 Suppression capacitor

CR11 Surge suppression diode

F1 Fuse

L2 SCR reactor

R1 Voltage droop potentiometer

R2 Voltage level rheostat

R3 Regulator gain rheostat

TP Thermal protector

NOTE: Earlier generators do not have a thermal protector.

GENERATOR REGULATOR ASSEMBLY, FIG. 3 (right side)

A1 Regulator module

C3 RFI Suppression capacitor

L1 Suppression reactor

R4 Regulator power resistor

R5 Damping resistor

T1 Voltage droop transformer

TS3 Voltage regulator terminal strip

A2 RECTIFIER MODULE, FIG. 4

CR9 Controlled rectifier

CR10 Field Rectifier

E3 SCR Heat sink

E4 Field rectifier heat sink

ROTATING FIELD ASSEMBLY, FIG. 5 (OUTSIDE BEARING TYPE RFA)

E1 Negative heat sink

E2 Positive heat sink

ROTATING FIELD ASSEMBLY, FIG. 6 (INSIDE BEARING TYPE RFA)

NEGATIVE HEAT SINK ASSEMBLY, FIG. 7 (OUTSIDE BEARING TYPE RFA)

E2 Negative heat sink

CR4,5,6 Rotating rectifiers

CR8 Surge suppression diode

POSITIVE HEAT SINK ASSEMBLY, FIG. 8 (OUTSIDE BEARING TYPE RFA)

E1 Positive heat sink

CR1,2,3 Rotating rectifier

CR7 Surge suppression diode

R6 Suppression resistor

EXCITER AND HEAT SINK ASSEMBLY, FIG. 9 (INSIDE BEARING TYPE RFA)

E1 Positive heat sink

E2 Negative heat sink

CR7,8 Surge suppression diodes

R6 Suppression resistor

NEGATIVE HEAT SINK ASSEMBLY, FIG. 10 (FROM OUTSIDE BEARING TYPE RFA)

CR4,5,6 Rotating rectifiers

CR8 Surge suppression diode

POSITIVE HEAT SINK ASSEMBLY, FIG. 11 (FROM OUTSIDE BEARING TYPE RFA)

CR1,2,3 Rotating rectifiers

CR7 Surge suppression diode

R6 Suppression resistor

ROTATING FIELD ASSEMBLY (RFA), FIG. 12 (OUTSIDE BEARING TYPE RFA)

L4 Exciter armature

L5 Rotating field

E2 Negative heat sink

NOTE: Earlier rotating field assemblies had two fans.

ROTATING FIELD ASSEMBLY (RFA), FIG. 13 (INSIDE BEARING TYPE RFA)

L4 Exciter armature

L5 Rotating field

END HOUSING, FIG. 14 (OUTSIDE BEARING TYPE RFA)

L3 Exciter field

L4 Exciter armature

EXCITER FIELD AND ARMATURE, FIG. 15 (INSIDE BEARING TYPE RFA)

L3 Exciter field

L4 Exciter armature

GENERATOR HOUSING, FIG. 16

L6 Stator

Operation of Generator

Introduction

The SR 4 Generator has no brushes and no commutator. This gives better performance and longer service life. It uses a solid-state, automatic voltage regulator. This regulator has only one moving part in the voltage build-up system. This part is a completely sealed relay that is activated only when the generator is started or stopped.

From the outside, the SR 4 Generator looks very similar to the SRCR generators.

Here are the design characteristics of the SR 4 Generator:

The windings of the alternator coils are the stator (L6). The windings of the alternator field coils are the poles of the rotor, shown in the wiring diagram as rotating field (L5). The rotating field assembly (RFA) also has:

1. Exciter armature (L4).

2. Rotating rectifiers (CR1 thru CR6).

3. Surge suppression diodes (CR7 and CR8).

4. Positive (E1) and negative (E2) heat sinks.

5. Suppression resistor (R6).

REAR OF GENERATOR

L3 Exciter field

L4 Exciter armature

All of these components are installed on the rotor shaft. The shaft is connected through a flexible plate-type coupling to the flywheel of the engine. The rear end of the rotor shaft uses an anti-friction bearing for support. The stationary exciter field (L3) has a six-pole distributive winding on a core that is part of the generator end housing. Both the field coils of the exciter and the alternator have their windings on magnetic steel. This metal keeps a small amount of residual magnetism.

Start Up Voltage Generation

When the engine starts turning the rotating field assembly (RFA), the residual magnetism in the exciter field (L3) causes a small amount of alternating current (AC) voltage to be generated in the exciter armature (L4). This voltage causes an AC current to flow which is changed to direct current (D.C.) by the three-phase full-wave bridge rectifier circuit (CR1 thru CR6). The DC current then goes to the rotating field (L5) of the alternator. Here it adds to the residual magnetism of the rotating field (L5). With this field turning, an AC voltage is generated in stator (L6) which causes a current to flow to the output terminals (T0, T1, T2 and T3). Part of this AC current is changed to half wave DC and is sent back to exciter field (L3). As a result, the magnetic field in the exciter becomes stronger. The flow of current back to (L3) is explained in more detail on the pages that follow.

INSIDE GENERATOR HOUSING

E1 Positive heat sink

E2 Negative heat sink

L5 Rotating field

L6 Stator

FOR SR 4 GENERATORS - LINE TO NEUTRAL POWER FOR EXCITATION AND REGULATION^*

A1 REGULATOR MODULE

A2 RECTIFIER MODULE

C1,3 RFI SUPPRESSION CAPACITOR

C2 SUPPRESSION CAPACITOR

CR1-6 ROTATING RECTIFIERS

CR7,8 SURGE SUPPRESSION DIODES

CR9 CONTROLLED RECTIFIER

CR10 FIELD RECTIFIER

CR11 SURGE SUPPRESSION DIODE

E1 POSITIVE HEAT SINK

E2 NEGATIVE HEAT SINK

E3 SCR HEAT SINK

E4 FIELD RECTIFIER HEAT SINK

F1 FUSE

L1 SUPPRESSION REACTOR

L2 SCR REACTOR

L3 EXCITER FIELD

L4 EXCITER ARMATURE

FOR SR 4 GENERATORS - LINE TO LINE POWER FOR EXCITATION AND REGULATION ^**

^*Thermal protector is not found on some earlier models.

NOTE: Current production and replacement A1 modules (black in color) for the line to line generator regulators require a wiring change from that for regulators using earlier A1 modules (brown in color). The lead connections from L1 and C1 change their terminal connections from terminal 22 to terminal 20.

Excitation Circuit

Power for excitation comes from stator (L6) during the negative half cycle. That is, when (T0) is positive and (T8) is negative. The current flow is shown on the opposite page.

For SR 4 Generators with line to neutral power for excitation & regulation

From (T0) to terminal (26).

From terminal (26) through wire (26) to suppression reactor (L1).

For SR 4 Generators with line to line power for excitation & regulation

From the tapped connection of phase 1 of stator (L6) to terminal (22).

From terminal (22) through wire (22) to suppression reactor (L1).

For All SR 4 Generators

Through suppression reactor (L1) and wire (12) to suppression capacitor (C2).

From suppression capacitor (C2) through wire (12) to SCR reactor (L2).

Through SCR reactor (L2) and wire (19) to spade terminal (19) of rectifier module (A2).

GENERATOR REGULATOR ASSEMBLY

A2 Rectifier module

C2 Suppression capacitor

F1 Fuse

L1 Suppression reactor

L2 SCR Reactor

TP Thermal protector (if so equipped)

TS3 Voltage regulator terminal strip

From spade terminal (19) of rectifier module (A2) to heat sink (E3) and the anode terminal of controlled rectifier (CR9).

NOTE: To make this current flow through the controlled rectifier possible, a signal voltage must be sent to the gate of (CR9). Until this signal turns (CR9) on, the current puts a charge on suppression capacitor (C2). When the signal is sent to the gate, controlled rectifier (CR9) "turns on." Current flows through controlled rectifier (CR9).

From the cathode terminal of controlled rectifier (CR9) to heat sink (E4).

From heat sink (E4) to spade terminal (8) of recifier module (A2).

Through wire (8) to terminal (F1).

Through wire (F1) to the positive end of exciter field (L3).

Through exciter field (L3) to terminal (F2).

From terminal (F2) through wire (6) to fuse (F1).

From fuse (F1) through thermal protector (TP) and wire (24) to terminal (24).

From terminal (24) to connection on phase 2 of stator (L6).

A2 RECTIFIER MODULE

E3 SCR Heat sink

E4 Field rectifier heat sink

CR9 Controlled rectifier

FOR SR 4 GENERATORS
LINE TO NEUTRAL POWER FOR EXCITATION AND REGULATION ^*

A1 REGULATOR MODULE

A2 RECTIFIER MODULE

C1,3 RFI SUPPRESSION CAPACITOR

C2 SUPPRESSION CAPACITOR

CR1-6 ROTATING RECTIFIERS

CR7,8 SURGE SUPPRESSION DIODES

CR9 CONTROLLED RECTIFIER

CR10 FIELD RECTIFIER

CR11 SURGE SUPPRESSION DIODE

E1 POSITIVE HEAT SINK

E2 NEGATIVE HEAT SINK

E3 SCR HEAT SINK

E4 FIELD RECTIFIER HEAT SINK

F1 FUSE

L1 SUPPRESSION REACTOR

L2 SCR REACTOR

L3 EXCITER FIELD

L4 EXCITER ARMATURE

FOR SR 4 GENERATORS
LINE TO LINE POWER FOR EXCITATION AND REGULATION ^**

^*Thermal protector is not found on some earlier models.

Voltage Build-Up Circuit

To send the gate signal to controlled rectifier (CR9) to let voltage increase from residual magnetism, a circuit goes:

From spade terminal (19) of rectifier module (A2), through wire (19) to spade terminal (9) of regulator module (A1).

Through regulator module (A1) to spade terminal (10).

From spade terminal (10) of regulator module (A1) through wire (10) to spade terminal (10) of rectifier module (A2).

From spade terminal (10) on rectifier module (A2) to the gate terminal on controlled rectifier (CR9).

NOTE: The voltage build-up circuit in regulator module (A1) has a normally closed relay, a diode rectifier and a current limiting impedance in it.

When generator voltage at the relay coil is at pickup value (60 to 70% of rated voltage), the coil causes the relay contact to open. Another circuit in regulator module (A1) sends the gate signal to controlled rectifier (CR9) one time each cycle. When engine speed is lowered, voltage at the relay coil is lower. When the voltage is less than the drop-out voltage, the relay contact closes. Pickup voltage is generated at an engine rpm less than the factory setting of low idle rpm. The relay contact will open and close rapidly at an engine speed of approximately 800 to 900 rpm. If it is necessary to operate the engine at a speed less than the factory setting of low idle, either fuse (F1) must be removed or a single pole, single-throw toggle switch must be installed between fuse (F1) and terminal (24) in place of wire (24). The switch rating must be 250 volts, 15 amperes. When the fuse (F1) is removed or the switch is open, the voltage can not go up and no damage can come to the regulator.

Regulator module (A1) is sealed in an insulation of epoxy. Inside the epoxy module (A1) are resistors, capacitors, rectifiers, zener diodes, transistors and amplifiers in circuits that are fastened to terminals (1 thru 11). This component is only available as a complete unit.

GENERATOR REGULATOR ASSEMBLY

A1 Regulator module

CR9 Controlled rectifier

F1 Fuse

FOR SR 4 GENERATORS
LINE TO NEUTRAL POWER FOR EXCITATION AND REGULATION^*

A1 REGULATOR MODULE

A2 RECTIFIER MODULE

C1,3 RFI SUPPRESSION CAPACITOR

C2 SUPPRESSION CAPACITOR

CR1-6 ROTATING RECTIFIERS

CR7,8 SURGE SUPPRESSION DIODES

CR9 CONTROLLED RECTIFIER

CR10 FIELD RECTIFIER

CR11 SURGE SUPPRESSION DIODE

E1 POSITIVE HEAT SINK

E2 NEGATIVE HEAT SINK

E3 SCR HEAT SINK

E4 FIELD RECTIFIER HEAT SINK

F1 FUSE

L1 SUPPRESSION REACTOR

L2 SCR REACTOR

L3 EXCITER FIELD

L4 EXCITER ARMATURE

FOR SR 4 GENERATORS
LINE TO LINE POWER FOR EXCITATION AND REGULATION^**

^*Thermal protector is not found on some earlier models.

Normal Voltage Generation

The DC current flow to exciter field (L3) causes a magnetic field in which the exciter armature (L4) is turning. The magnetic field of (L3) makes a three phase voltage in exciter armature (L4). The current flow caused as a result of this voltage is rectified (changed to DC) by rectifiers (CR1 thru CR6) on heat sink (E1 and E2). This rectified current is sent to rotating field (L5) and makes the magnetic field of the generator. As rotating field (L5) turns it induces a three phase AC voltage in stator (L6) that is sent to terminals (T1), (T2), and (T3) which are the connections for a load. To keep the output voltage constant with changing loads, it is necessary to control the excitation current. This control is made possible by controlled rectifier (CR9).

INSIDE GENERATOR HOUSING
E1 Positive heat sink. L3 Exciter field. L5 Rotating field. E2 Negative heat sink. L4 Exciter armature. L6 Stator.

Excitation Circuit Control

Controlled rectifier (CR9) is in effect, an on-off valve that will let current either flow through or can stop the flow of current to the exciter field (L3). A controlled rectifier, normally called an SCR, has the usual diode terminals, anode (1) and cathode (2) and a third terminal (3) that is used as a gate. When an electrical signal is sent to the gate, it takes approximately three microseconds (.000003 seconds) for a controlled rectifier to "turn on" and let current flow through. The controlled rectifier is "on" until the current flow through it stops, then it turns "off." After the gate signal turns the rectifier "on," there is current flow through it as long as the anode is positive and the cathode is negative. When the voltage at the anode goes to zero or becomes negative while the cathode is positive the controlled rectifier turns "off." Because during each cycle the voltage at (T0) is positive and then negative in comparison to (T8), controlled rectifier (CR9) is "off" once each cycle and a gate signal must be sent to (CR9) during the next half cycle.

CONTROL RECTIFIER SYMBOL
1. Anode. 2. Cathode. 3. Third terminal (gate).

The timing of the signal to the gate of controlled rectifier (CR9) is the function of regulator module (A1). An increase in load on the generator causes the regulator module (A1) to send the signal to the gate earlier in the cycle. This gives an increase to the excitation time for exciter field (L3) and makes the necessary additional excitation available to hold the voltage at the rated level under a higher load. A decrease in load on the generator causes the regulator module (A1) to send the signal to the gate later in the cycle. This gives a decrease in excitation time in exciter field (L3). While the controlled rectifier (CR9) is "off," the excitation current of exciter field (L3) is made to flow for the complete cycle by the circuit with field rectifier (CR10) in it. The average current flow of the full cycle in exciter field (L3) is in direct relation to the time that controlled rectifier (CR9) is "turned on."

GENERATOR REGULATOR ASSEMBLY
A1 Regulator module. CR9 Controlled rectifier.

FOR SR 4 GENERATORS
LINE TO NEUTRAL POWER FOR EXCITATION AND REGULATION^*

A1 REGULATOR MODULE

A2 RECTIFIER MODULE

C1,3 RFI SUPPRESSION CAPACITOR

C2 SUPPRESSION CAPACITOR

CR1-6 ROTATING RECTIFIERS

CR7,8 SURGE SUPPRESSION DIODES

CR9 CONTROLLED RECTIFIER

CR10 FIELD RECTIFIER

CR11 SURGE SUPPRESSION DIODES

E1 POSITIVE HEAT SINK

E2 NEGATIVE HEAT SINK

E3 SCR HEAT SINK

E4 FIELD RECTIFIER HEAT SINK

F1 FUSE

L1 SUPPRESSION REACTOR

L2 SCR REACTOR

L3 EXCITER FIELD

L4 EXCITER ARMATURE

FOR SR 4 GENERATORS
LINE TO LINE POWER FOR EXCITATION AND REGULATION^**

^*Thermal protector is not found on some earlier models.

Flyback Circuit

A circuit from the negative (-) end to the positive (+) end of the exciter field (L3) permits a current flow in the exciter field, when the controlled rectifier (CR9) is "turned off." That is, when (T0) is negative and (T8) is positive. The flow is as follows:

From the negative (-) end of exciter field (L3) through wire (F2) to terminal (F2).

From terminal (F2) through wire (6) to spade terminal (6) on rectifier module (A2).

From spade terminal (6) on rectifier module (A2) to the anode (terminal end) of field rectifier (CR10).

From the cathode (stud end) of field rectifier (CR10) to heat sink (E4).

From heat sink (E4) to spade terminal (8) on rectifier module (A2).

A2 RECTIFIER MODULE

CR9 Controlled rectifier

CR10 Field rectifier

E4 Heat sink

From spade terminal (8) on rectifier module (A2) through wire (8) to terminal (F1).

When the current flow goes through exciter field (L3) it causes a magnetic field around the coils of the field. The strength of the magnetic field is in relation to the current going through the exciter field. An increse in current flow makes the magnetic field stronger, and a decrease in current flow makes the magnetic field weaker.

When the current through the exciter field (L3) stops because controlled rectifier (CR9) has cut-off the flow, the magnetic field strength is maximum. The field now starts to collapse (grow weaker) back into the conductors of the coil. As a result of this, a voltage is induced in the coil. The voltage causes a current flow, as shown in the circuit schematic. This circuit helps to keep current flow through exciter field (L3) constant.

END HOUSING

L3 Exciter field

INSIDE GENERATOR HOUSING

L3 Exciter field

FOR SR 4 GENERATORS
LINE TO NEUTRAL POWER FOR EXCITATION AND REGULATION^*

A1 REGULATOR MODULE

A2 RECTIFIER MODULE

C1,3 RFI SUPPRESSION CAPACITOR

C2 SUPPRESSION CAPACITOR

CR1-6 ROTATING RECTIFIERS

CR7,8 SURGE SUPPRESSION DIODES

CR9 CONTROLLED RECTIFIER

CR10 FIELD RECTIFIER

CR11 SURGE SUPPRESSION DIODE

E1 POSITIVE HEAT SINK

E2 NEGATIVE HEAT SINK

E3 SCR HEAT SINK

E4 FIELD RECTIFIER HEAT SINK

F1 FUSE

L1 SUPPRESSION REACTOR

L2 SCR REACTOR

L3 EXCITER FIELD

L4 EXCITER ARMATURE

FOR SR 4 GENERATORS
LINE TO LINE POWER FOR EXCITATION AND REGULATION^**

^*Thermal protector is not found on some earlier models.

Output Voltage Sensing

Voltage sensing by regulator module (A1) is through a circuit from connections in phases 1 and 3 of stator (L6) to terminals (20) and (22). The circuit then goes:

From terminals (20) and (22) through wires (20) and (22) to spade terminals (1) and (2) on regulator module (A1).

Through regulator module (A1) to spade terminal (5).

From spade terminal (5) on regulator module (A1) through wire (5) through the red wire to voltage droop rheostat (R1).

From voltage droop rheostat (R1) to voltage level rheostat (R2).

From voltage level rheostat (R2) through wire (6) to fuse (F1).

Through fuse (F1), thermal protector (TP) and wire (24) to terminal (24).

From terminal (24) to the tapped connection in phase 2 of stator (L6).

The voltage divider in regulator module (A1) has a capacitive reactance. Since capacitive reactance will go up as frequency goes down or will go down as frequency goes up, the regulator module gives a voltage control on the basis of volts per hertz.

GENERATOR HOUSING

L6 Stator

GENERATOR REGULATOR ASSEMBLY

A1 Regulator module

F1 Fuse

R1 Voltage droop potentiometer

R2 Voltage level rheostat

TP Thermal protector

FOR SR 4 GENERATORS
LINE TO NEUTRAL POWER FOR EXCITATION AND REGULATION ^*

A1 REGULATOR MODULE

A2 RECTIFIER MODULE

C1,3 RFI SUPPRESSION CAPACITOR

C2 SUPPRESSION CAPACITOR

CR1-6 ROTATING RECTIFIERS

CR7,8 SURGE SUPPRESSION DIODES

CR9 CONTROLLED RECTIFIER

CR10 FIELD RECTIFIER

CR11 SURGE SUPPRESSSION DIODE

E1 POSITIVE HEAT SINK

E2 NEGATIVE HEAT SINK

E3 SCR HEAT SINK

E4 FIELD RECTIFIER HEAT SINK

F1 FUSE

L1 SUPPRESSION REACTOR

L2 SCR REACTOR

L3 EXCITER FIELD

L4 EXCITER ARMATURE

FOR SR 4 GENERATORS
LINE TO LINE POWER FOR EXCITATION AND REGULATION ^**

^*Thermal protector is not found on some earlier models.

Power Supply For Regulator Module A1

For SR 4 Generators with line to neutral power for excitation & regulation

The following circuit gives power to the regulator module (A1):

From neutral (TO) of stator (L6) to terminal (26).

From terminal (26) through wire (26) to regulator power resistor (R4).

Through regulator power resistor (R4) and wire (3) to regulator module (A1).

Through regulator module (A1) to terminal (6).

From terminal (6) of regulator module (A1) to potentiometer (R1) (voltage droop).

From potentiometer (R1) (voltage droop) to rheostat (R2) (voltage level).

From rheostat (R2) (voltage level) through wire (6), fuse (F1), thermal protector (TP) and wire (24) to terminal (24).

From terminal (24) to the tapped connection of phase 2 of stator (L6).

For SR 4 Generators with line to line power for excitation & regulation

The following circuit gives power to the regulator module (A1):

From the tapped connected of phase 1 of stator (L6) to terminal (22).

From terminal (22) through wire (22) to regulator power resistors (R4,7).

Through regulator power resistors (R4,7) and wire (3) of regulator (A1).

Through regulator module (A1) to terminal (6).

From terminal (6) of regulator module (A1) to potentiometer (R1) (voltage droop).

From potentiometer (R1) (voltage droop) to rheostat (R2) (voltage level).

From rheostat (R2) (voltage level) through wire (6), fuse (F1), thermal protector (TP) and wire (24) to terminal (24).

From terminal (24) to the tapped connection of phase 2 of stator (L6).

GENERATOR REGULATOR ASSEMBLY

A1 Regulator module

F1 Fuse

R1 Voltage droop potentiometer

R2 Voltage level rheostat

R4 Regulator power resistor

TP Thermal protector

FOR SR 4 GENERATORS
LINE TO NEUTRAL POWER FOR EXCITATION AND REGULATION ^*

A1 REGULATOR MODULE

A2 RECTIFIER MODULE

C1,3 RFI SUPPRESSION CAPACITOR

C2 SUPPRESSION CAPACITOR

CR1-6 ROTATING RECTIFIERS

CR7,8 SURGE SUPPRESSION DIODES

CR9 CONTROLLED RECTIFIER

CR10 FIELD RECTIFIER

CR11 SURGE SUPPRESSSION DIODE

E1 POSITIVE HEAT SINK

E2 NEGATIVE HEAT SINK

E3 SCR HEAT SINK

E4 FIELD RECTIFIER HEAT SINK

F1 FUSE

L1 SUPPRESSION REACTOR

L2 SCR REACTOR

L3 EXCITER FIELD

L4 EXCITER ARMATURE

FOR SR 4 GENERATORS
LINE TO LINE POWER FOR EXCITATION AND REGULATION ^**

^*Thermal protector is not found on some earlier models.

Regulator Gain Circuit

Regulator gain is an adjustment to compensate for voltage drop caused by generator load or governor speed droop. A circuit to control regulator gain goes:

From spade terminal (7) of regulator module (A1) through wire (17) to regulator gain rheostat (R3).

From regulator gain rheostat (R3) through wire (18) to spade terminal (8) on regulator module (A1).

There is a feedback circuit to regulator module (A1). This circuit gives a voltage signal to regulator module (A1). The signal changes at the same rate as the voltage of exciter field (L3). The following circuit gives the signal voltage.

From the cathode of controlled rectifier (CR9) to terminal (11) on rectifier module (A2).

From terminal (11) through wire (11) to terminal (11) of regulator module (A1).

The input received by the regulator module is used by electrical circuits in the module to determine regulator gain.

GENERATOR REGULATOR ASSEMBLY

A1 Regulator module

A2 Rectifier module

CR9 Controlled rectifier

R3 Regulator gain rheostat

FOR SR 4 GENERATORS
LINE TO NEUTRAL POWER FOR EXCITATION AND REGULATION ^*

A1 REGULATOR MODULE

A2 RECTIFIER MODULE

C1,3 RFI SUPPRESSION CAPACITOR

C2 SUPPRESSION CAPACITOR

CR1-6 ROTATING RECTIFIERS

CR7,8 SURGE SUPPRESSION DIODES

CR9 CONTROLLED RECTIFIER

CR10 FIELD RECTIFIER

CR11 SURGE SUPPRESSSION DIODE

E1 POSITIVE HEAT SINK

E2 NEGATIVE HEAT SINK

E3 SCR HEAT SINK

E4 FIELD RECTIFIER HEAT SINK

F1 FUSE

L1 SUPPRESSION REACTOR

L2 SCR REACTOR

L3 EXCITER FIELD

L4 EXCITER ARMATURE

FOR SR 4 GENERATORS
LINE TO LINE POWER FOR EXCITATION AND REGULATION ^**

^*Thermal protector is not found on some earlier models.

Radio Frequency Interference (RFI) Suppression

When controlled rectifier (CR9) "turns on", it is very rapid (approximately three microseconds). This causes a shock load on the stator (L6). AC voltage shocks will cause harmonics (frequency multiplications) at radio frequencies. For many applications, these harmonics will cause electronic equipment to operate very badly.

The action of suppression capacitor (C2) and SCR reactor (L2) gives a reduction of the shock load on stator (L6). As said earlier, suppression capacitor (C2) gets a charge during the time (TO) is positive and (T8) is negative and controlled rectifier (CR9) is not "turned on". When a gate signal is sent to controlled rectifier (CR9) the first surge of current is caused by the voltage charge on (C2). The current increase time is made longer by SCR reactor (L2). Suppression reactor (L1) and RFI suppression capacitors (C1) and (C3) cause a reduction of interference with radio frequencies. Damping Resistor (R5) is connected in parallel with suppression reactor (L1) to prevent any voltage oscillations that start in (L1). RFI suppression capacitor (C1) is connected from neutral to (T8) on phase 2 of stator (L6). Suppression capacitor (C3) is connected from neutral to generator frame ground. To get the maximum effect from the RFI suppression capacitors, the generator frame must be connected to an earth or building (station) ground.

GENERATOR REGULATOR ASSEMBLY

C1,3 RFI Suppression capacitors

C2 Suppression capacitor

CR9 Controlled rectifier

L1 Suppression reactor

L2 SCR Reactor

R5 Damping resistor

Protection Of Generator Circuits

The SR 4 Generator regulator and excitation circuits use many components for protection. Fuse (F1) is the type that opens very rapidly and gives protection against secondary damage caused by another component failure. This type of fuse is used because it is specifically made to work in circuits that have semiconductors. If the fuse needs replacement, it is important that the same amperage rating and type is used. A larger amperage rating or a fuse that does not open rapidly will not prevent damage to other components.

F1 FUSE

Surge suppression diode (CR11) prevents too high voltages that are abnormal (not normal) and transient (temporary) from causing damage to controlled rectifier (CR9) or field rectifier (CR10). Inside of rectifier module (A2) there are resistance-capacitance circuits connected from anode to cathode of both controlled rectifier (CR9) and field rectifier (CR10). These circuits give added protection for abnormal transient peak voltages that can cause damage at (CR9) or (CR10).

GENERATOR REGULATOR ASSEMBLY
A2. Rectifier module. CR9. Controlled rectifier. CR10. Field rectifier. CR11. Surge suppression diode.

Surge suppression diodes (CR7) and (CR8) are connected in parallel, electrically. CR7 is installed on the positive heat sink (E1) and CR8 is installed on the negative heat sink (E2). These diodes are connected in parallel to give the current capacity needed for suppression of any abnormal transient peak voltages that can cause damage to the rotating rectifiers (CR1 thru CR6).

ROTATING FIELD ASSEMBLY (RFA)
E1. Positive heat sink. E2. Negative heat sink. R6. Suppression resistor.

E1 POSITIVE HEAT SINK
R6. Suppression resistor.

Suppression resistor (R6) gives a low resistance circuit from the insulated windings to the shaft and cores of the revolving field assembly (RFA). If this resistor was not installed, air friction on the windings and heat sinks can cause electrostatic charges. These charges can cause voltages to become high enough to destroy the insulation. Resistor (R6) is a 27,000 ohm resistor that lets these electrostatic charges run off as they are generated and prevents any voltage build-up. Because of the value and power rating of resistor (R6), a ground failure at any point on the revolving field assembly (RFA) will not prevent the generator from operating normally and it will not cause damage to (R6).

Regulator Adjustment

GENERATOR VOLTAGE ADJUSTMENT CONTROLS
4. Voltage droop control. 5. Voltage level control. 6. Regulator gain control.

Adjustment of voltage level rheostat (R2) is done with voltage level control (5). This is done when an increase or decrease of the generator voltage is necessary to get correct line voltage. Adjustment of regulator gain rheostat (R3) is done with regulator gain control (6). Adjustment of regulator gain rheostat (R3) and voltage level rheostat (R2) must be made in sequence to get exact generator voltage regulation when the engine is equipped with either a mechanical speed droop or an isochronous (0% speed droop) governor. Do the steps that follow:

1. Remove the access panel on the left side of the generator. Loosen the locknuts on the voltage adjustment controls. Turn voltage droop control (4) fully counterclockwise.

2. Start the engine. Increase engine speed to nameplate rating.

3. Adjust voltage level control (5) to give nameplate rated voltage. Put a normal load on the generator. Let the generator warm up to normal temperature for operation.

4. Remove the load from the generator. Adjust the voltage level control if necessary. Put a normal load on the generator. Check generator voltage. If the voltage stays at nameplate rating, regulator gain control (6) is adjusted correctly. Tighten all locknuts.

5. If generator VOLTAGE INCREASES, turn the regulator gain control a small amount counterclockwise. If generator VOLTAGE DECREASES, turn the regulator gain control a small amount clockwise. Remove the load. Adjust the voltage level control if necessary.

6. Put a normal load on the generator. If the voltage does not stay at nameplate rating see Step 5. If it does, tighten all locknuts and install the access panel.

NOTE: Generator sets equipped with a control panel on top of the generator have the voltage level rheostat in the control panel. The yellow wire from terminal 7 on the terminal strip of the regulator assembly is disconnected. The voltage level rheostat on the control panel is then connected to terminals 6 and 7 on the terminal strip. The same sequence of adjustments must be made.

In order to get an even distribution of reactive load and to keep circulating currents to a minimum when two or more generators are operated in parallel, it is necessary to have a specific decrease in voltage, at each generator, with an increase in generator load. This decrease in voltage is the voltage droop. Adjustment of voltage droop potentiometer (R1) is done with voltage droop control (4). Correction to the voltage droop can be made by turning (R1) from counterclockwise for no voltage droop to clockwise for an increase in voltage droop. Adjustment of voltage droop control (4) must be in sequence with voltage level control (5) and regulator gain control (6). See OPERATION GUIDE for engine.

Series Boost Attachment

Series boost lets SR 4 generators stay on the line, for approximately 10 seconds, when there is a short in the generating or load circuits. This gives circuit breakers a chance to trip in sequence. When circuit breakers trip in sequence, there is less chance for a loss of power to all of the electrical system.

The series boost panel group has a control module A3, voltage sensing transformer T3 and series boost heat sink E5. Current transformer T2 is external to the panel group.

Voltage sensing transformer T3 gets power from the same terminals on the regulator terminal strip as exciter field L3 (terminals 24 and 22 on 580 frame generators and terminals 24 and 26 on all others). Voltage sensing transformer T3 gives power to control module A3. The electrical action of control module A3 causes a gate signal through wire 34 to the triac on series boost heat sink E5. The triac short circuits current transformer T2. This prevents any series boost effect during normal operation.

SERIES BOOST ASSEMBLY

A3 CONTROL MODULE

C68 SERIES BOOST CAPACITOR

E5 SERIES BOOST HEAT SINK

T3 VOLTAGE SENSING TRANSFORMER

If there is a short circuit that causes the voltage to voltage sensing transformer T3 to drop to a low value, control module A3 will stop the gate signal to the triac. Current from current transformer T2 will go through the bridge rectifier on heat sink E5, be rectified and flow through wire 9 to exciter field L3. This field current will be enough to give at least three times full load current into a short circuit. After approximately 10 seconds electrical action of control module A3 will again cause a gate signal through wire 34 to the triac on series boost heat sink E5. The triac will short circuit current transformer T2. Current flow to exciter field will be zero until the short circuit is corrected.

Series boost connections are not the same for all generator sets. Make reference to Fig. 1 or Fig. 2 for series boost to regulator connection. For series boost current transformer T2 connection, make reference to Fig. 3, Fig. 4, Fig. 5 or Fig. 6.

NOTE: For current transformer connection of machines not shown, make contact with Service Engineering; Caterpillar Tractor Co.

CURRENT TRANSFORMER T2

FIG. 1 SR 4 GENERATOR WITH SERIES BOOST
[Includes: 447, 448 & 449 frame (layer wound rotor - 208 V only); and all other frames (random and layer wound rotors) except 580 frame and 447, 448, and 449 frame (with layer wound rotor).]

FIG. 2 SR 4 GENERATOR WITH SERIES BOOST
[Includes: 580 frame and 447, 448 & 449 frames (with layer wound rotor) except 447, 448 & 449 frames with layer wound rotor - 208 V.]

FIG. 3 TRANSFORMER CONNECTIONS DIAGRAM

1. Generator.

2. Transformer (in series boost).

3. Load line leads (generator).

4. Load line leads (tranformer).

5. Series boost terminal strip.

6. Heat sink (for connection to terminal strip, make reference to secondary transformer connections chart).

7. Wire from excitation field.

8. Terminal strip on generator regulator.

LINE LEAD CONNECTIONS FOR SR 4 GENERATORS IN FIG. 3

FIG. 4 TRANSFORMER CONNECTIONS DIAGRAM

1. Generator.

2. Transformer (in series boost).

3. Load line leads (generator).

4. Load line leads (tranformer).

5. Series boost terminal strip.

6. Heat sink (for connection to terminal strip, make reference to secondary transformer connections chart).

7. Wire from excitation field.

8. Terminal strip on generator regulator.

LINE LEAD CONNECTIONS FOR SR 4 GENERATORS IN FIG. 4

FIG. 5 TRANSFORMER CONNECTIONS DIAGRAM

1. Generator.

2. Transformer (in series boost).

3. Load line leads (generator).

4. Load line leads (tranformer).

5. Series boost terminal strip.

6. Heat sink (for connection to terminal strip, make reference to secondary transformer connections chart).

7. Wire from excitation field.

8. Terminal strip on generator regulator.

LINE LEAD CONNECTIONS FOR SR 4 GENERATORS IN FIG. 5.

FIG. 6 TRANSFORMER CONNECTIONS DIAGRAM

1. Generator.

2. Transformer (in series boost).

3. Load line leads (generator).

4. Load line leads (tranformer).

5. Series boost terminal strip.

6. Heat sink (for connection to terminal strip, make reference to secondary transformer connections chart).

7. Wire from excitation field.

8. Terminal strip on generator regulator.

LINE LEAD CONNECTIONS FOR SR 4 GENERATORS IN FIG. 6

Manual Voltage Control Attachment

The location of the manual voltage control panel can be up to 76 ft. (23.2 meters) from the generator. Make reference to the chart.

The manual voltage control can be used to control generator voltage when there is a failure in the generator regulator assembly. It will manually control the rate at which control rectifier CR9 is turned on. For information on CR9 operation make reference to OPERATION OF GENERATOR.

NOTE: CR9 and CR10 must be able to operate correctly for the manual voltage control to work.

The manual voltage control has a switch (1), voltage control rheostat (2), flash button (3) and a control assembly.

VOLTAGE CONTROL PANEL
1. Switch (OFF, AUTO and MAN positions). 2. Voltage control rheostat. 3. Flash button.

Switch (1) is used to make the selection between AUTO, MAN and OFF. In the "AUTO" position the generator regulator assembly controls the generator voltage. In the 'OFF" position the generator voltage will go to zero. In the "MAN" position generator voltage is controlled by voltage control rheostat (2).

Flash button (3) is used when the generator voltage does not build up. With switch (1) in the "MAN" position push flash button (3) until the generator voltage starts to build up.

Show/hide table

NOTICE

Press the flash button only until the generator voltage starts to build up. If the button is held too long the voltage will increase to above the capacity of the generator. This can cause the line circuit breaker to trip or the regulator fuse to open.

When flash button (3) is pushed AC current from the generator is rectified by a diode on the manual volage control panel. This rectified (DC) current goes directly to the generator exciter field. It does not go through control rectifier CR9.

CONTROL ASSEMBLY
4. Trigger module. 5. Terminal strip. (4 and 5 are not serviced separately - lowest serviceable level is Manual Voltage Control Assembly)

The control assembly is on the back side of the mounting bracket for regulator module A1. The control assembly has terminal strip (5) and trigger module (4). When switch (1) is in the "MAN" position, the action of electrical circuits in trigger module (4) control the amount of "on" time for control rectifier CR9.

WIRING DIAGRAM
4. Trigger module. 5. Terminal strip (control assembly). 6. Terminal strip (voltage control panel). A1. Regulator module. F1. Terminal (regulator terminal strip).