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.

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.

instrumentation:

Group of instruments.

insulated:

A component with insulation.

induce (to):

To send DC current to a coil and make a magnetic field.

leads:

Wires.

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.

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 suppression:

Reduce the cause of radio frequency interference.

regenerative power:

Power that works against the primary power.

reset:

To put a switch in a ready condition.

saturable reactor:

Acts as a valve, as load changes, valve opens or closes to give more or less current to the rectifier.

reciprocating:

Movement in a straight line first one direction then the other.

residual magnetism:

The characteristic of a magnet after removal of excitation.

saturated:

Magnetized to the point where an increase in current will give no increase in magnetic force.

satisfactorily:

Correctly.

SCR:

Silicone 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.

transient peak voltage:

A high voltage condition for a short time period.

turn-on:

To start, as current flow through the controlled rectifier; to activate.

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.

windings:

Layers of wire on a core.

wiring:

The wires of a circuit.

wound:

Circled.

Identification

TYPICAL SRSE REGULATOR
1. Exciter reactors.

All Statically Regulated Statically Excited (SRSE) generators have three large exciter reactors as a part of the regulator assembly.

The generator serial number, on the nameplate, tells four things about the generator:

1. The first group of numbers is the approximate kW rating on 60 cycle generators. On 50 cycle generators it is usually one less than that for 60 cycle generators.

2. The letter S is the symbol for Caterpillar Statically Regulated Statically Excited generator.

3. The next letter gives an indication of the voltage rating. See chart.

4. The last group of numbers is the actual serial number of the generator in its kW and voltage rating.

NOTE: If a generator is connected to give performance different from that shown on the nameplate, a new nameplate should be installed on the generator. Mark the new nameplate to show the present method of connection and rated capacities.

The chart that follows gives the basic characteristics of each SRSE generator.

Principles Of Operation

SRSE 240-480 VOLT GENERATOR WIRING DIAGRAM

A. Voltage droop transformer.

B. Voltage droop control switch.

C. Saturable reactor.

D. Full wave rectifier.

E. Stator.

F. Rotating field.

H. Voltage level resistor.

J. Voltage level rheostat.

N. Power rectifier.

P. Heat sink.

Q. Voltage control choke.

R. Exciter reactor.

R. Trimmer resisitor.

T. Trimmer choke.

U. Relay N.C.

The Statically Regulated Statically Excited Generator gives improved performance and longer service life by applying a method of excitation which is controlled by an automatic voltage regulation system that contains no moving parts. The generator voltage buildup system uses only one moving part; a relay, which operates only when the generator is started or shut down.

The generator is constructed with the armature coils wound on the stator (E) and the field coils wound on the rotor, designated in the wiring diagram as the rotating field (F). The field coils are wound on magnetic steel that will retain a small amount of residual magnetism. The rotating field is connected directly to the engine flywheel through the generator shaft and coupling.

As the engine turns the rotating field, a small amount of AC voltage is generated in the stator by the influence of the residual magnetism in the rotating field. This AC voltage is directed to the power rectifier (N) which changes it to DC voltage. The DC voltage is then applied to the rotating field, through brushes and collector rings. The DC voltage, when applied to the rotating field, produces a magnetic field which adds its strength to the residual magnetism in the rotating field. As the field strength increases, higher voltage is generated by the stator. This process of increasing voltage builds up to the rated voltage, at which point the voltage is limited by the exciter reactors (R) placed in series with the stator, the power rectifiers and the rotating field.

Each exciter reactor (R) has four separate coils wound around a common iron core. The "H" and "Z" coils have magnetic polarity in one direction and the "X" and "Y" coils have magnetic polarity in the opposite direction. The "H" and "Z" coils are excitation coils and the "X" and "Y" coils are regulation coils which control the amount of excitation. The regulator circuit incorporates a saturable reactor (C), a full wave rectifier (D), a voltage control choke (Q) and one of the coils in each exciter reactor (R).

GENERATOR EXCITER AND REGULATOR
C. Saturable reactor. D. Full wave rectifier. N. Power rectifier. Q. Voltage control choke. R. Exciter reactor.

The saturable reactor increases the sensitivity of the regulator circuit so any small increase in generator voltage will cause a large increase in regulator current; conversely, any small decrease in generator voltage will cause a large decrease in regulator current. The full wave rectifier in the regulator circuit changes AC current (from the stator) to DC current. The voltage control choke dampens the pulsations in the regulator circuit DC current. The regulator circuit has no moving parts and automatically limits and regulates the generator voltage from no load up to and including full generator load, regardless of generator loads.

The relay (U) has the only moving part in the excitation and regulating circuit and is in operation only when the generator is being started or stopped. When the generator is being started, there is only a small amount of residual magnetism in the rotating field, while there is high resistance in the exciter reactor. This resistance must be minimized so that the voltage generated by residual magnetism can force enough current through the field to increase the magnetism of the field and cause the generator voltage to increase. Thus, more current must be applied to the rotating field to allow the generator to build-up voltage. To establish normal voltage build up quickly, the relay will allow the excitation current from the stator to by-pass two of the exciter reactors and allow rapid build-up of voltage. As the generator reaches approximately 60% of its rated voltage, the coil (2) in the relay, connected to a circuit from the stator, actuates and opens the relay contact points (1) to allow the excitation current to pass through all three of the exciter reactors. The DC relay converts generator AC voltage to DC voltage by means of rectifier (3) and applies this voltage to relay coil (2). The AC relay applies generator voltage directly to the relay coil (2). The generator voltage continues to increase until the regulator circuit limits the generated voltage to its rated value.

DC RELAY
1. Relay contact points. 2. Coil. 3. Rectifier.

AC RELAY
1. Relay contact points. 2. Coil.

The voltage rheostat (J) is a manual control for adjusting the output voltage of the generator to correct for tolerances in the components or to provide desired small changes in the generator output voltage level. To prevent the possibility of short circuiting the rectifier (D) with zero voltage level rheostat adjustment, the voltage level resistor (H) is placed in series with the voltage level rheostat.

VOLTAGE LEVEL ADJUSTMENT
H. Voltage level resistor. J. Voltage level rheostat.

When two or more generators are to be operated in parallel, it will be necessary for the voltage of each generator to decrease a specified amount as the generators are loaded. This decrease in voltage, as a generator is loaded, is called voltage droop. Voltage droop in generators is necessary in order to obtain stable parallel operation. A voltage droop transformer (A) is placed in series with the lead lines from the generator. The AC current being supplied to the load first passes through the primary of the voltage droop transformer. The secondary has ten different points to tap off voltage from the voltage droop transformer to the voltage droop control switch (B). When the switch is placed on zero, the transformer is completely out of the generator regulator circuit. When the voltage droop control switch is moved from zero, a portion of the voltage droop transformer secondary winding is placed in the generator voltage regulator circuit. As the generator is loaded, the voltage regulator circuit obtains extra voltage from the voltage droop transformer which will lower the amount of excitation current to the rotating field and the generator output voltage drops. The amount of voltage droop is increased by moving the voltage droop control switch to a progressively higher number.

VOLTAGE DROOP ADJUSTMENT
B. Voltage droop control switch.