Basler SR4A User manual

INSTRUCTION MANUAL
FOR
VOLTAGE REGULATOR
Model: SR4A & SR8A
Part Number: 9 01 00 XXX
Publication Number: 9 0177 00 990
Revision: R 09/97

i
INTRODUCTION
This manual provides information concerning the operation and installation of a SR4A & SR8A Voltage
Regulator. To accomplish this, the following is provided.
•Specifications
•Functional Description
•Installation Information
•Operation
•Maintenance
REV LMNPR
ECA 15609 15959 16057 16195 16334
WARNING
TO AVOID PERSONAL INJURY OR EQUIPMENT DAMAGE, ONLY
QUALIFIED PERSONNEL SHOULD PERFORM THE PROCEDURES
PRESENTED IN THIS MANUAL.
WARNING
All SR4A and SR8A Voltage Regulators are shipped factory preset
for 120 Vac sensing.

ii
First Printing: August 1971
Printed in USA
© 1997, Basler Electric Co., Highland, IL 62249
September 1997
It is not the intention of this manual to cover all details and variations in equipment,
nor does this manual provide data for every possible contingency regarding
installation or operation. The availability and design of all features and options are
subject to modification without notice. Should further information be required,
contact Basler Electric Company, Highland, Illinois.
BASLER ELECTRIC, BOX 269 HIGHLAND, IL 62249 USA
PHONE [phone] FAX [phone]
CONFIDENTIAL INFORMATION
OF BASLER ELECTRIC COMPANY, HIGHLAND, IL. IT IS LOANED
FOR CONFIDENTIAL USE, SUBJECT TO RETURN ON REQUEST,
AND WITH THE MUTUAL UNDERSTANDING THAT IT WILL NOT BE
USED IN ANY MANNER DETRIMENTAL TO THE INTEREST OF
BASLER ELECTRIC COMPANY.

iii
CONTENTS
SECTION 1.0 GENERAL INFORMATION.....................................................................1-1
1.1 Description...............................................................................................1-1
1.2 Specifications...........................................................................................1-1
Electrical Specifications ...........................................................................1-1
Physical Specifications ............................................................................1-2
1.3 Optional Features .................................................................................... 1-2
1.4 Accessories .............................................................................................1-3
1.5 Model Number Description and Selection ...............................................1-3
Typical Model Number .............................................................................1-4
Model Number Designations ....................................................................1-4
SECTION 2.0 PRINCIPLES OF OPERATION...............................................................2-1
2.1 Functional Circuits ................................................................................... 2-1
Overall Block Diagram .............................................................................2-1
2.2 Application Information ............................................................................ 2-1
2.3 Parallel Compensation............................................................................. 2-2
SECTION 3.0 INSTALLATION....................................................................................... 3-1
3.1 Mounting..................................................................................................3-1
Outline Drawing .......................................................................................3-1
3.2 Interconnection ........................................................................................ 3-2
Voltage Adjust Potentiometer P/N (03456) ..............................................3-2
Paralleling Potentiometer P/N (03469) ....................................................3-2
Brush Type Rotary Exciter Interconnection .............................................3-5
Brushless Type Rotary Exciter (or Static Exciter)
Interconnection ........................................................................................ 3-6
3.3 Parallel Compensation............................................................................. 3-6
3.4 Reactive Droop Compensation (Droop)................................................... 3-7
3.5 Reactive Droop Compensation (Cross-Current)...................................... 3-7
Reactive Differential (Cross-Current) Compensation CT
Interconnection ........................................................................................
3-8
Top View of Voltage Regulator................................................................ 3-8
SECTION 4.0 OPERATION............................................................................................ 4-1
4.1 General....................................................................................................4-1
4.2 Operation at Reduced Speeds ................................................................4-1
4.3 Voltage Shutdown....................................................................................4-1
4.4 Adjustments............................................................................................. 4-2
4.5 Wiring .....................................................................................................4-2
4.6 Initial Operation........................................................................................4-2
4.7 Field Flashing........................................................................................... 4-4
4.8 Parallel Operation.................................................................................... 4-4
SECTION 5.0 MAINTENANCE, REPLACEMENT PARTS AND
TROUBLESHOOTING........................................................................... 5-1
5.1 Preventive Maintenance .......................................................................... 5-1
5.2 Corrective Maintenance...........................................................................5-1
Operational Test ......................................................................................5-1
5.3 Replacement Parts..................................................................................5-2
Component Location and Identification ....................................................5-2
SR4A Replacement Parts ........................................................................5-3

iv
CONTENTS - Continued
SECTION 5 MAINTENANCE, REPLACEMENT PARTS, AND
TROUBLESHOOTING - Continued
SR8A Replacement Parts ........................................................................5-3
Wiring Diagram .........................................................................................5-4
5.4 Warranty and Repair Service...................................................................5-5
5.5 Troubleshooting........................................................................................5-5
Tr
oubleshooting Chart ..............................................................................5-6

1-1
a. The SR4A and SR8A Voltage Regulators precisely control the output voltage of an ac electric
generating system by controlling the amount of current supplied to the exciter (or generator) field.
This includes brushless rotary exciters, brush type rotary exciters or direct excitation into the
generator field of machines within the regulator's power rating.
b. The regulators consist of silicon controlled rectifiers (SCR's) transistors, transformers, silicon
diodes, resistors and capacitors. The voltage regulators contain no electrolytic capacitors and are
relatively unaffected by temperature, humidity, vibration and shock.
Table 1-1 provides the electrical specifications of the SR4A and SR8A while Table 1-2 provides the
physical specifications. Table 1-1. Electrical Specifications.
Input Power:
SR4A:
SR8A: 95 - 139 Vac (±10), 50/60 Hz, 840 VA.
190 - 277 Vac (±10), 50/60 Hz, 1680 VA.
Output Power:
SR4A:
SR8A:
63 Vdc @ 7 A Maximum Continuous, 90 Vdc @ 10 A One Minute
Forcing.
125 Vdc @ 7 A Maximum Continuous, 180 Vdc @ 10 A One
Minute Forcing.
Input Sensing:
SR4A:
SR8A:
NEMA Standard 60 Hz: 100 - 110/190 - 200 - 208/220 - 230 -
240/380 - 400 - 415/500 Vac; ±10%.
NEMA Standard 60 Hz: 120 - 139/208/240/416/480/600 Vac;
±10%.
Input Sensing Burden:
SR4A:
SR8A: 10 VA.
10 VA.
Parallel Compensation: 5 A Input; 25 VA Burden. Droop adjust to 6%.
Minimum Field Resis-
tance:
SR4A:
SR8A: 9 Ω
18 Ω
Voltage Regulation: <±1/2% (Average voltage).
SECTION 1
GENERAL INFORMATION
1-1. DESCRIPTION
1-2. SPECIFICATIONS

1-2
Table 1-1. Electrical Specifications (con’t).
Response Time: <17 mS on 60 Hz systems; <20 mS on 50 Hz systems.
Voltage Adjust Range: ±10% on nominal.
Power Dissipation (Max): 60 Watts
Temperature Coefficient: ±1/2% for a 40°C (104°F) change.
Table 1-2. Physical Specifications.
Operating Temperature
Range: -55°C (-67°F) to +70°C (+158°F).
Storage Temperature
Range: -65°C (-85°F) to +100°C (+212°F).
Vibration: Tested to withstand 5 G's from 20 to 260 Hz.
Mounting: Designed for operation when mounted directly to an engine
generator set. It is strongly recommended that the voltage
regulator be mounted vertically for optimum cooling.
Overall Dimensions:
Height:
Width:
Depth:
11.5 inches (292 mm).
8.38 inches (213 mm).
5.0 inches (127 mm).
Weight: 13 lbs. (5.8 kg.).
The internal voltage regulator optional features listed below are designated by a combination of
letters and numbers in the complete model number. (See Table 1-3 and/or contact the factory for
additional variations).
a. Parallel compensation
c. Voltage build up relay
b. Single or three-phase sensing.
d. Sensing Voltage
e. Cover
f. Voltage adjust rheostat
g. Type of stability circuit
1-3. OPTIONAL FEATURES

1-3
a. The following is a partial list of accessories that are available for use with the SR4A and SR8A
Voltage Regulators.
(1) Underfrequency protection.
(2) Excitation support systems.
(3) EMI suppression filters.
(4) Low and medium voltage power isolation transformers.
(5) Paralleling current transformers.
(6) Manual Voltage control modules.
(7) Volts per hertz sensing modules.
(8) DC sensing modules.
(9) 400 hertz regulator.
(10) Voltage regulators operating from 60 hertz power on 400 hertz generators
(11) Wide range voltage adjust circuit components.
(12) VAR/Power Factor Controller.
(13) Overvoltage protection.
(14) Control switches.
(15) Motor operated controls.
(16) Line drop compensators.
(17) Voltage transient suppression filters.
b. Information covering these accessories may be obtained by consulting the applicable instruction
manual and product bulletin, or by contacting your nearest Basler Electric Sales Representative or
the factory.
c. An external voltage adjust rheostat may be obtained from a source other than Basler Electric.
This rheostat must be a minimum of 2 watts in size. The nominal required resistance is 175 ohms.
Although any value from 150 ohms to 250 ohms may be used, a slight change in the voltage adjust
range will occur.
The model number of the voltage regulator is a combination of letters and numbers indicating the
features which are included in the regulator. An example of a model number, showing the manner in
which the various features are designated, is shown in Figure 1-1. A complete list of various
features and their description is given in Table 1-3.
1-4. ACCESSORIES
1-5. MODEL NUMBER DESCRIPTION AND SELECTION

1-4
Figure 1-1. Typical Model Number.
Table 1-3. Model Number Designations.
Sample Model Number
SR4 A 2 B 15 B 3 A
SR4
SR8
A-Surface
mounted.
2-Parallel
provisions with
adjustable
slide wire
resistor.
B-Build-up
Relay. 15-Selectable
1-phase
sensing.
16-Selectable
3-phase
sensing w/
Faston
connectors.
B-Cover. 3-Voltage
Adjust
Rheostat
supplied
separately
with
regulator.
A-For use on
all brush-type
and most
brushless
exciters on
generators
rated over
150 kW.
E-For use
with
brushless
exciters
(primarily on
generators
rated 150 kW
or less) or
with all rotary
exciters.
The above style chart represents our standard product offering.
MODEL AND POWER RATING
VOLTAGE BUILD-UP PROVISIONS
PARALLEL PROVISIONS
SINGLE-PHASE SENSING
ENCLOSURE
TYPE OF VOLTAGE ADJUSTMENT
TYPE OF STABILITY CIRCUIT
SR4A 2 B 15 B 3 E
D2556-06
02-20-97

1-5
The following styles are available on a special order basis.
Sample Model Number
SR8A A 3 B 15 B 4 E
SR4
SR8 A-Surface
mounted. 1-No parallel provisions.
2-Parallel
provisions
with
adjustable
slide wire
resistor.
3-Parallel
provisions
with external
parallel
rheostat.
A-No relay.
B-Build-up
relay.
C-
Hermetically
sealed relay.
15-
Selectable 1-
phase
sensing.
16-
Selectable 3-
phase
sensing w/
Faston
connectors.
B-Cover. 2-Voltage
adjust
rheostat
internally
installed.
3-Voltage
adjust
rheostat
supplied
separately
with
regulator.
4-Voltage
adjust
rheostat
internally
installed
with locking
shaft.
A-For use
on all brush-
type and
most
brushless
exciters on
generators
rated over
150 kW.
B-For use
as static
exciter.
E-For use
with
brushless
exciters
(primarily on
generators
rated 150
kW or less)
or with all
rotary
exciters.

2-1
Refer to the Block Diagram, Figure 2-1. The voltage regulator senses the generator voltage, com-
pares a rectified sample of that voltage with a reference diode (zener) voltage and supplies the field
current required to maintain the predetermined ratio between the generator voltage and the
reference voltage. This unit consists of five basic circuits. These are a sensing circuit, an error
detector, an error amplifier, a power controller and a stabilization network.
Figure 2-1. Overall Block Diagram.
a.
Starting large motors or providing fault current for selective breaker tripping
.
(1) For generators equipped with brushless exciters or for static excited generators the field power is
taken from the generator output voltage. A heavy load, such as a large motor, can cause the
generator voltage to decrease substantially at the first few cycles after load applications. A short
circuit on the generator output could reduce the voltage from the generator to zero. Either of these
conditions can cause reduction of the available field power to a level which will not sustain generator
voltage. Accessory excitation support systems are available which take advantage of the generator
line currents as a source of excitation power during either condition.
(2) For brush-type rotation excited generators, the exciter armature connections can be used as an
alternate source of excitation during either of the conditions described above to provide excitation
SECTION 2
PRINCIPLES OF OPERATION
2-1. FUNCTIONAL CIRCUITS
2-2. APPLICATION INFORMATION

2-2
support. See Figure 3-2 for a typical interconnection diagram. This scheme uses the other contact
on the buildup relay to connect dc voltage from the exciter armature directly to the exciter field. As
an alternative, the regulator could be used as described in paragraph 2-3a. with an excitation support
system accessory.
a.
Reactive Droop Compensation (Droop) or Reactive Differential Compensation
(Cross-Current)
(1) Parallel operation requires additional components in the regulating system. These are resistor
R25, transformer T3 and a current transformer CT1. Two of the components are included in a
parallel equipped voltage regulator. These are R25 and T3. Current transformer CT1 is a separate
item and must be interconnected as shown in Figures 3-2 or 3-3.
(2) These components allow the paralleled generators to share reactive load and reduce circulating
reactive currents between them. This is accomplished in the following manner.
(3) A current transformer CT1 is installed in phase B of each generator. It develops a signal that is
proportional in amplitude and phase to the line current. This current signal develops a voltage
across resistor R25. A slider on R25 supplies a part of this voltage to the primary of the transformer
T3. The secondaries of T3 are connected in series with the leads from the secondary of the sensing
transformer T1, and the sensing rectifiers located on the printed circuit board. The ac voltage
applied to the sensing rectifier bridge is the vector sum of the stepped down sensing voltage
(terminals E1 and E3) and the parallel CT signal supplied through T3 (terminals 1 and 2). The
voltage supplied to the sensing rectifiers by the parallel CT is very small in relation to the signal
supplied by the sensing voltage. The regulator input sensing voltage (terminals E1 and E3) and the
parallel compensation signal (terminals 1 and 2) must be connected to the generator system so as to
provide the correct phase and polarity relationship.
(4) Regulators with single-phase sensing provide about 8% maximum droop while three-phase
sensing regulators provide 6% droop. When generators are paralleled on the same bus and have
different type sensing, care must be taken to compensate for these differences using the slide wire
adjustment on the droop resistor R25.
(5) When a resistive load (unity P.F) load is applied to the generator, the voltage that appears across
R25 (and T3 windings), leads the sensing voltage by 90°, and the vector sum of the two voltages is
nearly the same as the original sensing voltage; consequently, almost no change occurs in generator
output voltage.
(6) When a lagging power (inductive) load is applied to the generator, the voltage across R25
becomes more in phase with the sensing voltage and the combined vectors of the two voltages
results in a larger voltage being applied to the sensing rectifiers. Since the action of the regulator is
to maintain a constant voltage at the sensing rectifiers, the regulator reacts by decreasing the
generator output voltage.
3$5$//(/&203(16$7,21

2-3
(7) When a leading power factor (capacitive) load is applied to the generator, the voltage across R25
becomes out of the phase with the sensing voltage and the combined vectors of the two voltages
results in a smaller voltage being applied to the sensing rectifiers, then the regulator reacts by
increasing the generator voltage.
(8) When two generators are operating in parallel, if the field excitation on one generator should
become excessive and cause a circulating current to flow between generators, this current will
appear as a lagging power factor (inductive) load to the generator with excessive field current and a
leading power factor (capacitive) load to the other. The parallel Compensation circuit will cause the
voltage regulator to decrease the field excitation on the generator with the lagging power factor load,
and increase the field excitation on the generator with the leading power factor load, so as to
minimize the circulating currents between the generators.
b.
Reactive Droop compensation (Droop)
.This action and circuitry is called reactive droop com-
pensation (droop). It allows two or more paralleled generators to proportionally share inductive loads
by causing a decrease or droop in the generator system voltage.
c.
Reactive differential compensation (cross-current)
.
(1) Reactive differential compensation allows two or more paralleled generators to share inductive
reactive loads with no decrease or droop in the generator system output voltage. This is accom-
plished by the action and circuitry described previously for reactive droop compensation, and the
addition of cross connecting leads between the parallel CT secondaries as shown is Figure 3-4. By
connecting the finish of one parallel CT to the start of another, a closed series loop is formed, which
interconnects the CT's of all generators to be paralleled. The signals from the interconnected CT's
cancel each other when the line currents are proportional and in phase. No system voltage de-
crease occurs. These regulators provide the necessary circuit isolation so that parallel reactive
differential compensation can be used. The reactive differential circuit can only be used when all the
generators connected in parallel have identical paralleling circuits included in the loop.
(2) Reactive differential compensation cannot be used when paralleled with the utility or other infinite
(utility) bus. When reactive differential compensation is to be used on an isolated bus that may
parallel with the utility bus, an auxiliary contact on the breaker used to connect the isolated bus to the
utility bus must be used to open the reactive differential interconnecting loop any time the isolated
system is connected to the utility. Contact the factory for additional information.

3-1
The voltage regulator will operate when mounted in any position, however, it should be vertically
mounted to obtain optimum cooling when operating near its full rated output. The regulator can be
mounted in any location where the ambient temperature does not exceed its ambient operational
limits. Due to its rugged construction, the regulator can be mounted directly on the generator.
The overall and mounting dimensions are shown in Figure 3-1. The mounting dimensions of the
associated potentiometers are shown in Figures 3-2 and 3-3.
Figure 3-1. Outline Drawing.
SECTION 3
INSTALLATION
3-1. MOUNTING

3-2
Figure 3-2. Voltage Adjust Potentiometer (P/N 03456).
Figure 3-3. Paralleling Potentiometer (P/N 03469).
3-2 INTERCONNECTION
CAUTION
Meggers and high potential test equipment must not be used.
Incorrect use of such equipment could damage the semiconductors
contained in the regulator.

3-3
a.
General
.The regulator must be connected to the generator system as instructed in this section
and as shown in the basic interconnection diagrams (Figures 3-4 and 3-5). Number 16 gauge wire
(or larger) should be used for all connections to the regulator.
b.
Regulator Sensing (Terminals El, E2, and E3)
.
(1) The voltage regulator(s) contain an internal sensing transformer(s) T1 (T2) provided with taps for
various input sensing voltages. These sensing voltages are: 120, 208, 240, 416, 480, and 600 Vac
(refer to Figure 3-7). The model number of the unit designates single-phase (T1) or three-phase
(T1 and T2) sensing. For operation with generator voltages above 600 Vac, a potential
transformers(s) must be used to supply the regulator sensing voltage. The regulator sensing circuit
load is less than 10 VA and correct polarity must be maintained to the regulator sensing input.
(2) On single-phase sensing models, the voltage sensing leads are connected to terminals E1 and
E3. For three-phase sensing, terminals E1, E2 and E3 are used. For precise voltage regulation, the
sensing leads should be connected as close as possible to the point where regulation is desired.
The regulator regulates the voltage that is applied to its sensing terminals. Therefore, it cannot
correct for voltage drop in leads that may occur at points other than where the regulator sensing
leads are connected. The leads that supply regulator sensing should not be used to supply power to
any other equipment or to the regulator power stage (terminals 3 and 4).
(3) SR4A & SR8A Voltage Regulators are factory preset for 120 Vac sensing voltage. If the
sensing voltage needs to be changed for your installation, perform the following steps.
Step 1 . Remove the cover if applicable.
Step 2 . Remove 9 hex screws.
Step 3. Remove the printed circuit board without disconnecting the wires.
Step 4. Locate transformer(s) T1 for single-phase sensing units (T1 and T2 for three-
phase sensing units). These transformers are equipped with Faston connectors
for changing sensing taps.
Step 5. For single-phase sensing units, move the wire that is factory connected to T1-120
terminal to the T1 terminal labeled with the desired sensing voltage.
Step 6. For three-phase sensing units, move the wire that is factory connected to T1-120
terminal to the T1 terminal labeled with the desired sensing voltage. Also, move
the wire from T2-120 terminal to the T2 terminal labeled with the desired sensing
voltage.
(4) If the generator is to be operated in parallel with other generators, the phase relationship of
sensing voltage and the paralleling current transformer is very important. (See paragraph 3-3 for
further information.)
WARNING
The SR4A & SR8A Voltage Regulators are shipped factory
preset for 120 Vac sensing.

3-4
c.
Field Power (Terminals F+ and F-)
.
(1) The model number prefix (SR4A or SR8A) of the regulator, defines the amount of power the unit
is capable of delivering (See Table 1-1).
(2) The dc resistance of the field to which the regulator is connected (terminals F+ and F-) must be
equal to, or greater than, 9 Ωfor an SR4A and 18 Ωfor an SR8A. If the resistance is less than the
specified minimum, a resistor must be added in series with the field. This resistor value plus the field
resistance, must exceed the minimum preceding values.
(3) Good generator voltage stability usually results when the regulator output is above 10 Vdc at no
load (20 Vdc SR8A). Should the voltage be less and a voltage stability problem exists, it may be
necessary to add resistance in series with the field. This resistance raises the regulator output
voltage, thereby increasing the stability signal.
(4) When adding resistance in series with the field, the resistor value must not restrict field forcing
during full load conditions. The following example explains how to compute the proper resistance:
d.
Interconnecting Regulator with Brush Type Rotary Exciters (Terminal A-)
.
(1) When making connections on brush type rotary exciter applications, it is very important to
observe the polarities of the exciter field, exciter output and the generator field as shown in Figure
3-4. If these polarities are not known, the system should be operated on manual voltage control and
the polarities accurately determined, before connecting the voltage regulator into the system. The
voltage regulator could be damaged if interconnection is attempted before this data is known.
(2) When manual voltage control is desired on brush type exciter applications, a MANUAL-OFF-
AUTO switch and a field rheostat are used. (See Figure 3-4.) When this feature is not desired, the
output of the exciter can be connected directly to the regulator (terminal A-), to allow self-excitation
during short-circuit or overloads.
(3) When large motor starting or short circuit sustaining capability is not required it is not necessary
to use A- terminal.
e.
Input Power (Terminals 3 and 4)
.
(1) The model number prefix (SR4A or SR8A) of the regulator defines the maximum input power
requirements. (See Table 1-2.) The current requirement of the field, to which the regulator is
operating into, will determine the actual input current. The nominal voltage applied to the regulator
input power stage (terminals 3 and 4) must be 120V for the SR4A and either 208 or 240V for SR8A.
The input power may be taken from any generator lines that provide the correct voltage (line to line
or line to neutral). The phase relationship of this input in relation to other circuits is not important.
EXAMPLE: An SR4A voltage Regulator is required to operate into an
exciter field that has a dc resistance of 4 Ωand current requirement of
2.5 Adc at no load and 6 Adc at full load. Since the SR4A requires a
minimum field resistance of 9 Ω, a resistor of at least 5 Ωmust be con-
nected in series with the field. The regulator output will be 9 Ωtimes 2.5
A or 22.5 Vdc at no load, and 9 Ωtimes 6 A or 54 Vdc at full load. This
conforms to the 10 volt minimum at no load and provides a sufficient
amount of forcing at full load (up to 90 Vdc).

3-5
Figure 3-4. Brush Type Rotary Exciter Interconnection.
(2) When the generator output voltage is different than the preceding values and exceed the values
specified in Table 1-2, a power transformer must be used to match the generator voltage to the
regulator input. If excessive voltage is applied to the regulator input (terminals 3 and 4), the regulator
may be damaged.
CAUTION
Without the use of this transformer, a ground at any point in the field
circuit and another ground in the generator output, could result in
failure of the regulator.

3-6
Figure 3-5. Brushless Type Rotary Exciter (or Static Exciter) Interconnection.
(3) If the field or field flashing circuit is grounded, a power transformer must be used to isolate the
regulator input from ground.
a. In addition to the regulator provisions, a 25 VA current transformer (CT) is required (See Figure
3-4 and 3-5). This CT is connected in a generator line and should deliver from 3 to 5 A secondary
current at rated load.
b. The phase relationship of CT signal to the regulator sensing voltage must be correct or the system
will not parallel properly. On three-phase sensing models the CT must be installed in the line that
3-3. PARALLEL COMPENSATION (Terminals 1 and 2)

3-7
supplies sensing voltage to regulator terminal E2. For single-sensing phase models it must be
installed in the line of the three-phase generator that does not supply sensing to the regulator.
c. Figures 3-4 and 3-5 show the correct CT polarity for A-B-C phase rotation sequence. If the phase
rotation sequence is A-C-B, the CT's secondary leads must be interchanged.
a. For reactive droop compensation, connect the CT to its respective regulator as shown on Figures
3-4 and 3-5.
b. A unit-parallel switch shorts the parallel CT secondary to prevent any droop signal from being
injected into the regulating system during single unit operation. The switch may not be required on
parallel droop compensation applications where a voltage drop is not objectionable.
a. On parallel reactive differential compensation applications a contact should be used to short out
the paralleling CT secondary when that generator is not paralleled to the bus. If the switch is not
used, a voltage droop will be introduced into the system. This is due to the unloaded generator
parallel CT not supplying its compensating signal, but allowing a voltage drop to occur across it. Lack
of this shorting contact will also cause the voltage of the incoming generator to fluctuate prior to
paralleling. Ideally, this contact is an auxiliary on the circuit breaker contactor that opens when the
circuit breaker is closed.
b. For reactive differential compensation, connect each CT to its respective regulator. Then connect
the finish of the first CT to the start of the second CT, the finish of the second CT to the start of the
third CT, etc. Continue until all CT's are connected in series. The final step will be to connect the
finish of the last CT to the start of the first CT. (See Figure 3-6).
c. Reactive differential compensation cannot be used when paralleled with the utility or any infinite
bus. If this compensation system is used, a switching circuit must be used to convert the system to
a reactive droop compensation system. Contact the factory for additional information.
3-4. REACTIVE DROOP COMPENSATION (DROOP)
3-5. REACTIVE DIFFERENTIAL COMPENSATION (CROSS CURRENT)