Basler DECS-400 User manual

DECS-400 Digital Excitation Control System
SZF-5
9-10
• Microprocessor-based design
• Five Control Modes, with autotracking between modes
- Automatic Voltage Regulation (AVR) - Power Factor (PF)
- Field Current Regulation (FCR) - Field Voltage Regulation (FVR)
- Var Control
• 0.20% Voltage Regulation Accuracy
• Two pre-position set points for each mode
• Two Programmable Analog Outputs
• Setup from Front Panel HMI or by PC (local or remote)
• 40 Standard Stability Settings
• Time synchronization using IRIG or NTP (via Ethernet)
• Optional Integral Power System Stabilizer
- Dual input, integral of accelerating power (IEEE PSS2A/2B)
- Customer selectable speed-only sensing - Two wattmeter power measurement
- Optional Frequency Based Operation - Generator or Motor control modes
• Customizable Stability Setting with two PID setting groups
• Reactive Droop, Line Drop Compensation
• Generator Voltage Soft-Start during Buildup
• Real Time Metering for 19 Generator Parameters
• Voltage Matching
• Autotracking with Optional Backup DECS-400
• Flexible Remote Set point Control
- Contact inputs
- Proportional Analog input, ±10 Vdc or 4-20 mA
- Digital Communications
Local RS-232, ASCII, Modem Capabilities
RS-485, Modbus™, RJ-45 Ethernet
(continued on page 2)
TheDECS-400DigitalExcitationControlSystemisamicroprocessor-basedcontrollerthatprovidesexcitation
control, flexible logic control, and optional power system stabilization for synchronous machines in an
integrated package. The controller provides an analog output to control the DC output of an external rectifier
bridge and monitors machine parameters to control, limit, and protect the synchronous machine from
operating beyond its capability limitations.
The optional Power System Stabilizer is an IEEE-type PSS2A/2B, dual input, "integral of accelerating power"
stabilizerthatprovidessupplementarydampingforlow-frequencylocalmode,interarea,andinterunitpower
system oscillations.
Setup and initial operation are facilitated by Basler Electric's user-friendly BESTCOMS PC software that
incorporates real time monitoring test analysis, flexible oscillography, trending, and expanded testing
capabilities, including means for performing frequency response tests with a graphic display of results. This
replaces the need for an external Dynamic System Analyzer.
DECS-400
Digital Excitation
Control System
P. O. BOX 269 HIGHLAND, ILLINOIS, U.S.A. 62249 PHONE [phone] FAX [phone]
DESCRIPTION and
SPECIFICATIONS
Pages 2 through 6
FEATURES and
FUNCTIONS
Pages 6 through 9
FRONT VIEW
and DIMENSIONS
Page 9
INTERCONNECT
DIAGRAM
Page 10
BESTCOMS SOFTWARE
Pages 10 and 11
CUTOUT and ORDERING
Page 12
FEATURES
ADDITIONAL INFORMATION
INSTRUCTION MANUAL Request Publication 9369700990
WINDOWS®SOFTWARE
Interface for setting and communicating with Basler products
Request BESTCOMS-DECS400

DECS-400 Digital Excitation Control System
2
FEATURES, continued
DESCRIPTION
DECS-400 electrical and physical specifications are listed in the following paragraphs.
Operating Power
DECS-400 L: 24/48Vdc nominal (16-60Vdc), Burden=30W.
DECS-400 C: 120Vac nominal (85-132Vac, 50 or 60Hz), Burden=50VA.
125Vdc nominal (90-150Vdc), Burden=30W.
Generator Voltage Sensing Single-phase or three-phase line voltage, two ranges:
• 100V/50Hz nominal (85-127Vac), 120V/60Hz nominal (94-153V)
• 200V/50Hz nominal (170-254Vac), 240V/60Hz nominal (187-305V)
Bus Voltage Sensing Single-phase line voltage, two ranges:
• 100V/50Hz nominal (85-127V), 120V/60Hz (94 -153V)
• 200V/50Hz nominal (170 -254V), 240V/60Hz (187-305V)
SPECIFICATIONS
The DECS-400 Digital Excitation Control System is a
microprocessor-based controller that offers excitation
control, logic control, and optional power system sta-
bilization in an integrated package. The DECS-400 con-
trols field excitation by providing an analog signal used to
control the firing (output) of an external power bridge. The
DECS-400 monitors generator or motor parameters and
acts to control, limit, and protect the machine from operat-
ing outside its capability. The optional, onboard power
system stabilizer is an IEEE-defined PSS2A/2B, dual-input,
"integral of accelerating power" stabilizer that provides
supplementary damping for local mode, inter-unit and
inter-area power system oscillations.
APPLICATION
The DECS-400 is a digital excitation control system with optional Power System Stabilizer function that is used as the
primary controller in voltage regulator or main field excitation systems applied on a broad range of synchronous
generators or motors. The DECS-400 controls the generator output voltage, Var output or power factor by adjusting the
output of a semiconverter or full converter rectifier bridge that supplies DC power to the main or exciter field of the
generator. Because of its high level of flexibility and reliability, the DECS-400 is suitable for use in single or dual
controller systems on virtually any synchronous machine. The DECS-400 is at the heart of custom Basler Electric
excitation systems that typically include the digital controller, supplementary protective and control devices, a power
potential transformer and associated AC breaker or contactor, SCR firing circuits, and a power rectifier section, as-
sembled in suitable NEMA 1 excitation and power potential transformer enclosures.
• Built-in limiting functions
- Overexcitation Limiters - Summing Point or Takeover Type
- Underexcitation Limiters - 5 point user programmable or
internally generated, summing point or takeover
- Dual Slope Voltz/Hz Ratio or Underfrequency Limiter
- Stator Current Limiter (single phase or three phase)
• Built-in Protective Functions
- Field Overvoltage and Overcurrent
- Generator Undervoltage and Overvoltage
- Loss of Sensing Voltage
- Loss of Field (40Q)
- Field Overtemperature (for main field)
- Dual Slope Volts/Hertz (24)
- Exciter Diode Failure (for brushless exciters)
- Generator Frequency less than 10 Hz
• Sixteen Contact inputs - 10 user-programmable
• Eight Contact Outputs - 6 user-programmable
• Metering - Two 4-20mA meter drivers, customer programmable
• Four Communication Ports
• Data Logging, Sequence of Events Recording, Trending, real
time monitoring test analysis, and built-in frequency response test
capabilities
• UL Recognized, CSA certified, CE Compliant, GOST-R certified
per the relevant standards of Gosstandart of Russia, Byelorussian
certified
Integral programmable logic provides excitation system
control and annunciation based on DECS-400 contact
inputs, operating mode status, excitation system para-
meters and user-defined programming. Setup and initial
operation are facilitated by Basler Electric's user-friendly
BESTCOMS PC software that incorporates a test mode,
flexible oscillography, and a graphic display of PSS test
results.
The DECS-400 is designed for use with Basler's Interface
Firing Module (IFM) and semiconverter or full converter
power bridges. However, it will work equally well with any
power bridge with a firing circuit that is compatible with
the control signal output of the DECS-400.

DECS-400 Digital Excitation Control System
3
SPECIFICATIONS, continued
Generator Current Sensing Single or three phases; separate cross-current compensation input. 1 A ac or 5 A ac
nominal.
Sensing Burden Voltage: <1 VA per phase. Current: <1 VA. Parallel Compensation: <1VA.
Field Voltage and Current Field current and voltage values are provided by the Isolation Module.
Isolation Module Power +5 Vdc, ±12 Vdc from DECS-400.
Five field voltage sensing ranges: 63 Vdc, 125 Vdc, 250 Vdc, 375 Vdc, and 625 Vdc
Output: 0.9-9.1 Vdc (5.0 Vdc = zero field volts)
Two nominal shunt ranges: 50 mVdc and 100 mVdc
Output: 2.0-9.5 Vdc (2.0 Vdc = zero field current)
Contact Inputs
Sixteen contact inputs accept dry switch/relay contacts or open-collector outputs from a PLC. There are six fixed-
function contact inputs and 10 programmable contact inputs. Interrogation Voltage: 12 Vdc.
Fixed Function Inputs
• AVR* • FCR* • Lower** • Raise** • Start* • Stop*
*Functions activated by a momentary input.
**Functions active only when corresponding contact input is active.
Programmable Inputs
Any of the 10 programmable inputs can be programmed with the following functions. However, these are normally
preassigned by selecting one of the preprogrammed logic schemes.
• 2nd PID settings • Pre-Position • Reactive Droop Compensation Enable
• PSS Enable • PSS Motor Pump/Generator Mode • PSS Parameters Set Selection
• Phase Rotation • Unit/Parallel Operation (52 L/M) • Var/Power Factor Enable (52 J/K)
• Secondary Enable • Reactive Differential Compensation Enable • 2nd Pre-Position
Accessory Input (Remote Set Point Control)
Analog input for remote set point control. Select one of two configurations: ±10 Vdc or 4-20 mA dc.
Control Outputs
Isolated analog output for set point control. Output drives external Firing Circuit/Rectifier Bridge. Select one of
three configurations: ±10 Vdc, 0-10 Vdc, or 4-20 milliamperes dc
Meter Drivers
Two programmable 4 to 20 mA analog meter drivers. Meter side isolated from DECS-400. Programmable to meter
field voltage or current, generator voltage or current, bus voltage, generator or bus frequency, active power,
reactive power, apparent power, power factor, field temperature, tracking error, position indication and PSS
parameters. 64 selectable parameters in all.
Contact Outputs
Two dedicated contact outputs and six programmable contact outputs.
Make 30 A for 0.2 seconds per IEEE C37.90; Carry 7 A continuous. Break (Resistive or Inductive) 0.3 A at 120 Vdc
or 250 Vdc (L/R = 0.04 maximum)
Dedicated Outputs Programmable Outputs (All programmed through integrated logic; however,
• Watchdog • DECS-400 Status they are normally preassigned when using one of the
• On/Off • Active Limiter Functions pre-programmed logic schemes.)
• Active Alarms
• Active Protective Functions
Communication Ports
COM 0 RS-232 front panel female DB-9, 1200-19200 Baud, 8N1 Full Duplex, ASCII commands
COM 1 RS-485 rear panel screw terminals, 4800-19200 Baud, 8N1 Half Duplex, ASCII commands
COM 2 RS-485 rear panel screw terminals, 4800-19200 Baud, 8N2 Half Duplex, Modbus™ protocol
J1 FCC Part 68 approved modem, rear panel RJ-11
RJ-45 Ethernet, Modbus TCP Protocol, 10 base T

DECS-400 Digital Excitation Control System
4
SPECIFICATIONS, continued
IRIG-B Time Sync
Standard: 200-98, Format B002, Demodulated (dc level-shifted digital signal) or NTP via Ethernet
Regulation Accuracy
AVR Mode Voltage regulation ±0.2% over the load range, at rated power factor and constant generator
frequency. Steady state stability is ±0.1% at constant load and frequency. Temperature
Stability ±0.5% between 0 to 50°C at constant load and frequency. Response Time <1
cycle.
FCR Mode Field Current Regulation is ±1.% of the nominal value for 10% of the rectifier bridge input
voltage change or 20% of the field resistance change. Otherwise, ±5.0%.
VAR Control Mode Reactive Power Regulation is ±2.0% of the nominal VA rating at the rated frequency.
PF Control Mode ±0.02 Power Factor for real power between 10 and 100% at rated frequency.
(e.g. set point PF = 0.8, PF regulation is between 0.78 and 0.82)
Metering Accuracy
Generator and Bus Voltage: ±1.0% Generator and Bus Frequency: ±0.1 Hz
Generator Line Current: ±1.0% Power Factor: ±0.02 PF
Field Current and Voltage: ±2.0% Aux. Voltage and Current Input: ±1.0%
Generator Power: Apparent Power (VA) ±2.0%; Active Power (W) ±2.0%; Reactive Power (var) ±2.0%
Power System Stabilizer (PSS)
Operating Mode: Generator or Motor, ABC or ACB phase sequence
Sensing Configuration: Power and Speed or Speed only
Power Measurement: 2 wattmeter method
Frequency Range: Responds to power oscillations from 0.1 to 5 Hz. Low-pass and high-pass
filtering prevents unwanted PSS action outside this range.
Soft Start Two sets of soft start settings are available when operating in AVR or FCR mode. Bias level is adjust-
able from 0-90% in 1% increments; time to reach nominal value is adjustable from 1-7,200 s in 1 s increments.
Sequence of Events Recording Events are time- and date-stamped and stored in volatile memory. 127 event
capacity, 50 ms scan interval. SER can be triggered by input/output status changes, alarms, or system operating
status changes.
Data Logging (Oscillography) Stores 6 records, with up to 6 variables per record. Sampling rate: 600 data
points per record, pre-trigger adjustable from 0 to 599 data points. Record interval adjustable from 4 ms to 10 s.
Trending Stores 1 record, with up to 6 variables per record. Sampling rate is 1200 data points per record, with
total record duration adjustable from 1 hour to 30 days.
Paralleling/Line Drop Compensation Can use either reactive droop or reactive differential (cross-current)
compensation. Droop adjustable from 0% to 30% in 0.1% increments. Parallel compensation burden is less than 1
VA. Negative droop settings provide line drop compensation. Adjustable from -30% to 0% in 0.1% increments.
Limiters
Underfrequency Compensation Choice: Underfrequency compensation with slope adjustable from 0 to 3.00 PU in
.01 PU increments and knee frequency between 15 and 90 Hz, or Volts/Hertz ratio limiter with slope adjustable
from 0 to 3.0 PU in 0.1 PU increments. Provisions for two levels of protection, with duration of high V/Hz limit
adjustable in the range of 0 to 10 s.
Overexcitation On-line and off-line limiters provided, each a choice between summing point and takeover type
controllers. Dual settings groups. Provisions to scale settings for both type limiters based on an auxiliary analog
input (by others) representing air temperature, hydrogen pressure, etc. Includes a cooldown feature to prohibit
repeated high forcing level operation that could be damaging to the rotor.

DECS-400 Digital Excitation Control System
5
Off-Line Level One – Highest current level set point adjustable from 0 to 11,999Adc in 0.1% increments of
the rated field current. Limiting occurs for a time period ranging from 0 to 60 seconds, settable in
1 second increments.
Level Two – Lowest current level set point adjustable from 0 to 11,999Adc in 0.1% increments of
the rated field current. Limiting occurs indefinitely.
Takeover Type OEL The Takeover OEL uses an I2t characteristic. Limiter response time is less than three
cycles.
On-Line High Level – High current level (instantaneous) set point is adjustable from 0 to 11,999 Adc in 0.1
Adc increments.
Low Level – Low current set point is adjustable from 0 to11,999 Adc in 0.1 Adc increments.
Limiting occurs indefinitely.
Time Dial – This setting determines the inverse time curve selected.
Off-Line High Level – High current level (instantaneous) set point is adjustable from 0 to 11,999 Adc in 0.1
Adc increments.
Low Level – Low current set point is adjustable from 0 to 11,999 Adc in 0.1 Adc increments.
Limiting occurs indefinitely.
Time Dial – This setting determines the inverse time curve selected.
Underexcitation Customer selectable summing point type of takeover type limiter. The UEL curve can be se-
lected either by specifying acceptable reactive power level at zero active power output, or by
entering a five point UEL characteristic. Dual settings groups available. UEL limiter adjusts
characteristics with changes in terminal voltage.
Stator Current Single or three phase stator current limiter, adjustable between 100% and 300% of nominal
generator output current. Includes a two-step limiter with a definite time delay for the higher limit
level, adjustable between 0 and 60 s. Summing point type limiter with PI control loop.
Protection Functions
Field Overvoltage Range 1 to 2000 Vdc, time delay 0.2 to 30 s, dual setting groups
Field Overcurrent Range from 0.1 to 9,999 Adc, time delay 0.1 to 20 s, dual setting groups
Generator UndervoltageRange from 0 to 34,500 Vac, time delay 0.5 to 60 s, dual setting groups
Generator Overvoltage Range from 0 to 34,500 Vac, time delay 0.1 to 60 s, dual setting groups
Loss of Sensing VoltagePickup level 0 to 100% with balanced or unbalanced conditions; time delay 0 to 30s
Generator Frequency <10 Hertz
Loss of Field (40Q) Range 0 to 3000 Mvar, time delay 0 to 9.9 s
Field Overtemperature Calculated from field voltage and current. Setting range from 0 to 572°C, time delay from
0.1 to 60s
Volts per Hertz (24) Range from 0.5 to 6 V/Hz, integrating reset range 0 to 9.9 V/Hz
Exciter Diode Failure Shorted and/or Open; Exciter to Stator Poles Ratio less than or equal to 10, generator
frequency range 40 to 70 Hz (for brushless exciter applications)
SPECIFICATIONS, continued
Summing Point Type OEL Limiter response time is less than three cycles.
On-Line Level One – Highest current level (instantaneous) set point adjustable from 0 to 11,999Adc in
0.1% increments of the rated field current. Limiting occurs for a time period ranging from 0 to 60
seconds, settable in 1 second increments.
Level Two – Medium current level set point adjustable from 0 to 11,999Adc in 0.1% increments of
the rated field current. Limiting occurs for a time period ranging from 0 to 120 seconds, settable
in 1 second increments.
Level Three – Lowest current level set point adjustable from 0 to 11,999Adc in 0.1% increments
of the rated field current. Limiting occurs indefinitely.

DECS-400 Digital Excitation Control System
6
FEATURES/FUNCTIONS
Voltage Regulation
The DECS-400 regulates the generator RMS voltage to
within 0.20% from no-load to full-load, utilizing digital
signal processing and precise regulation algorithms
developed by Basler Electric, using the experience
gained over longer than a decade of manufacturing
tens of thousands of digital voltage regulators.
Output
The DECS-400 supplies an isolated output signal of 4-
20 mA, 0-10 Vdc, or ±10Vdc to the firing or control
circuits of external power stages. The dc current
produced by the power stages provides excitation to
the field of the generator or the exciter. The DECS-400
can control virtually any bridge capable of accepting
these signals, that is suitable for use on synchronous
generators/motors.
Stability
The DECS-400 utilizes proportional (P), integral (I) and
derivative (D) stability control. DECS-400 has
preprogrammed stability (PID) settings for both main
field (20 settings) and exciter field (20 settings)
applications. Thus, a suitable standard stability set is
available for most machines and applications. The
DECS-400 also provides an additional setting group
that can be customized to provide optimum generator
transient performance. Setup software includes a PID
selection program to assist in choosing the correct
PID settings. The DECS-400 also provides for custom-
izing the stability and transient performance of the
minimum and maximum Excitation Limiters, the VAR/
PF controllers, and the stator current limiter, by
providing additional stability adjustments.
Two PID Setting Groups
The DEC-400 provides for two sets of PID settings to
optimize performance under two distinct operating
conditions, such as with a Power System Stabilizer
(PSS) in or out of service. A fast controller provides
optimum transient performance with the PSS in
service, while a slower controller can provide improved
damping of first swing oscillations with the PSS off line.
Optional Power System Stabilizer
The DECS-400 may be purchased with an integral
Power System Stabilizer function that duplicates the
excellent performance of the Basler PSS-100 Power
System Stabilizer without the complications of an
additional control device. The PSS provides damping
for local mode, inter-area and inter-unit oscillations in
the 0.1 to 5.0 Hz range. The PSS incorporated in the
DECS-400 is a dual-input, IEEE type PSS2A/2B
stabilizer that utilizes the "integral of accelerating
power" algorithm. The PSS can also be programmed
to respond to frequency only if required for unusual
applications. Required inputs include three phase
voltages and two or three phase line currents.
Underfrequency Limiter
or V/Hz Ratio Limiter
DECS-400 includes a customer selectable choice of an
Underfrequency Limiter or a V/Hz Ratio Limiter to avoid
overfluxing the generator or other connected magnetic
devices. The under-frequency limiter slope can be set
at 0-3 PU Volts/Hz in 0.1 PU increments, and the
frequency roll-off kneepoint can be set across a range
of 15 to 90 Hz, in 0.1Hz increments, with fixed voltage
above the knee frequency. The V/Hz Ratio Limiter
regulates voltage based on a customer defined V/Hz
SPECIFICATIONS, continued
Type Tests
Shock: IEC 60255-21-2 Vibration: IEC 60255-21-1
Humidity: IEC 68-1, IEC 68-2-28 Dielectric Strength: IEEE 421.3
Transients: IEEE C37.90.1-1989 Impulse: IEC 60255-5
Surge Withstand Capability: IEEE C37.90.1-1989 Radio Frequency Interference: IEEE C37.90.2
Electrostatic Discharge: IEEE C37.90.3 Draft 2.3
Agencies CE Compliant
UL recognized per Standard 508 and Standard CAN/CSA-C22-2
Number 14-M91, UL File Number E97035.
GOST-R certified per the relevant standards of Gosstandart of Russia
Byelorussian certified
Environment Operating Temperature: -40 to 60°C (-40 to 140°F)
Storage Temperature: -40 to 85°C (-40 to 185°F)
Physical Weight:6.1 kg (13.5 lb)
Size: See Figure 1 on page 9 for DECS-400 dimensions.

DECS-400 Digital Excitation Control System
FEATURES/FUNCTIONS, continued
Overexcitation Limiters
Overexcitation limiters monitor the field current output
of the voltage regulator or static exciter and act to limit
the field current to prevent field overheating. The
Overexcitation Limiter (OEL) function includes a
cooldown feature to avoid damage to the rotor caused
by repeated high forcing. The OEL is active in all
modes except FCR mode. In FCR mode, limiter action
is optional. The DECS-400 provides a choice of two
types of overexcitation limiters: Summing Point and
Takeover. The output of the Summing Point type
limiter is applied to the summing junction of the AVR
control loop in addition to the AVR controller output,
while the output of a takeover type limiter overrides the
normal AVR output.
Summing Point Type OEL
Three OEL current levels are defined for on-line
operation - high, medium, and low. The generator can
operate continuously at the low OEL current level and
for programmed times at the high and medium OEL
current levels. Two OEL current levels are defined for
off-line (main breaker open) operation - high and low.
The generator can operate continuously at the low
OEL current level and for a programmed time at the
high OEL current level.
Takeover Type OEL
The Takeover-style Overexcitation Limiter, determines
the field current level at which limiting occurs using an
inverse time characteristic. Two current levels and a
time dial setting are defined for the takeover-style
OEL. Separate curves may be selected for on-line and
off-line operation. If the system enters an
overexcitation condition, the field current is limited and
made to follow the selected curve. The selection of on-
line or off-line OEL levels and curves is determined
by an OEL option selection. 7
slope adjustable between 0.0 and 3.0 PU, and includes
two limiting levels to permit operation above the
primary V/Hz range for a customer adjustable time limit
to inhibit limiter response to transient frequency or
voltage excursions.
Soft-Start Voltage Buildup
The DECS-400 includes a voltage soft-start feature with
a user-adjustable setting to control the rate at which the
generator voltage is allowed to build up and to prevent
voltage overshoot during start-up of the generator
system. The soft-start feature is active in both AVR and
FCR modes.
Reactive Droop and Line Drop Compensation
The DECS-400 has provisions for paralleling two or
more generators using reactive droop or for using
reactive differential compensation with the addition of
an external current transformer with secondary currents
of 1 or 5A ac. The current input burden is less than
1VA, so existing metering CTs can be used. Inputting a
negative value for droop provides Line Drop Compen-
sation to offset line or transformer impedance drops
and move the regulation point beyond the terminals of
the machine.
Set Point Control
DECS-400 includes means for external adjustment of
the set point of the controlling mode of operation using
raise/lower contact inputs or an auxiliary analog input
of 4-20 mA or ±10Vdc. The active mode set point may
also be adjusted using BESTCOMS Windows®based
software in a PC connected to the RS-232 communica-
tion port, or using Modbus™ protocol (floating point) to
communicate digitally using the RS-485 port. The
traverse rates of all modes of operation are indepen-
dently adjustable, so the operator can customize the
rate of adjustment and "feel" to meet his/her needs.
Dual Pre-position Inputs
DECS-400 provides the added flexibility of two cus-
tomer-adjustable sets of predetermined operating
points for each mode of operation. On startup and with
the appropriate contact inputs to the DECS-400, the
operating mode is driven to one of two preset operat-
ing or regulation levels, depending on the configuration
of the system. This allows the DECS-400 to be config-
ured for multiple system and application needs.
Field Current & Voltage Regulation Operating
Modes
DECS-400 provides a manual channel of operation
called Field Current Regulation (FCR) Mode. In this
mode, DECS-400 regulates the DC output current of
the power bridge. It is not dependent on the generator
voltage sensing input to the DECS-400 and, therefore,
provides backup excitation control when loss of
sensing is detected. In FCR mode, the operator must
manually vary field current to maintain nominal gen-
erator voltage as load varies.
Field Voltage Regulation: This mode (FVR) is similar to
FCR. Instead of regulating field current, field voltage is
being maintained.
VAR/Power Factor Controller Operating Mode
DECS-400 has two additional control modes for use
when the generator is operating in parallel with the
utility power grid. In the VAR control mode, the DECS-
400 can regulate the VAR output of the generator at an
operator adjustable VAR setting or, in the Power
Factor mode, it can control the VAR output of the
generator to maintain a specific power factor as the
kW load varies on the generator.

DECS-400 Digital Excitation Control System
FEATURES/FUNCTIONS, continued
8
Stator Current Limiter
The stator current limiter (SCL) senses the level of
stator current and limits it to prevent stator overheat-
ing. The SCL operates in all modes except FCR. In
FCR mode, the DECS-400 provides indication that a
stator overcurrent condition exists, but limiter action is
inhibited. Two SCL current levels are provided: high
and low. The generator can operate continuously at
the low SCL level, but only for a programmed time at
the high SCL level.
Autotracking Between DECS-400 Operating Modes
DECS-400 is an intelligent device that can provide
autotracking (autofollowing) of the controlling mode by
the non-controlling modes. This allows the operator to
initiate a controlled, bumpless transfer of the DECS-
400 between operating modes with minimal distur-
bance to the power system. This feature can be used
in conjunction with a set of protective relays to initiate a
transfer to a backup mode of operation, such as FCR
mode, upon the detection of a system failure or fault,
such as loss of sensing.
Autotracking between DECS-400 Units
The DECS-400 is also designed to automatically track
a second DECS-400 unit using dedicated communica-
tion ports on the two units. A backup DECS-400
controller can be placed in service and programmed
to track the control output of the primary DECS-400. In
the unlikely event of a failure of the first DECS-400,
protective relays can initiate a transfer of control from
the first to the second DECS-400 with minimal system
disturbance.
Protective Functions
The protective functions built into the DECS-400 may
be used as backup to the primary protection relays
and can be assigned to up to six programmable output
contacts via the PC software. The protection features
offer fully adjustable tripping levels and time delays.
The protective features are as follows:
• Generator Overvoltage* • Microprocessor Watchdog
• Generator Undervoltage* • Loss of Field Isolation Transducer
• Field Overvoltage* • Volts/Hertz Protection
• Field Overcurrent* • Exciter Diode Open
• Field Overtemperature* (Brushless App.)
• Loss of Field* • Exciter Diode Shorted
• Loss of Voltage Sensing (Brushless App.)
The functions marked with an asterisk (*) have dual setting groups.
Integrated Logic
The DECS-400 utilizes integrated logic functionality in
the form of multiplexors, AND gates, OR gates, NOT
gates, and timer gates. Inputs to the logic are in the
form of discrete information including switching inputs,
system status data, protection status data, limiter status
data, alarm status data, and PSS status data. The
outputs of the logic module can be used to control the
relay outputs as well as various other functions inside
the DECS such as control functions (start/stop, mode
select, etc.), protection functions (Field Overvoltage
Enable, Field Overcurrent Enable, etc.), limiter func-
tions (OEL enable, UEL enable, etc.), and PSS func-
tions. BESTCOMS includes tools for customizing the
system control logic for specific applications.
Metering
The DECS-400 is provided with two programmable 4 to
20 mA analog meter drivers for the customer's use. The
meter side is isolated from the DECS-400 circuitry.
Either can be programmed to meter a broad range of
generator and system parameters. 64 parameters are
available.
Sequence of Events Recording (SER)
A sequence of event report (SER) is a very powerful
tool for reconstructing the exact timing of an event or
disturbance. The DECS-400 monitors its contact inputs
and outputs for changes of state, system operation
changes, and alarm conditions. If any of these events
occurs, the DECS-400 will log that event with a date
and time stamp using IRIG B or NTP and an internal
clock with optional battery backup, allowing the user to
analyze a chain of events with accurate information
regarding the sequence in which they occurred. The
DECS-400 can store 127 events in volatile memory,
and those events are retrievable using BESTCOMS.
Oscillography
The data recording feature can record up to six (6)
oscillographic records stored in volatile memory. A
battery backup comes standard to maintain operation
of the real-time clock in the event that control power is
lost. The user can select up to six (6) variables to be
monitored when triggered by the DECS-400
BESTCOMS, a Logic Trigger, or a Level Trigger.
Variables that can be selected are: generator voltage,
Minimum Excitation Limiter
The Minimum Excitation Limiter prevents the excitation
being supplied to the field of the generator from
dropping below safe operating levels. This prevents
the machine from possibly slipping poles and damag-
ing the machine. This action also limits the amount of
VARs being absorbed by the machine, based on user-
definable settings. An internally generated Under-
excitation Limiting (UEL) curve based on a
permissable VAR level at 0kW can be utilized, or a 5
point UEL curve can be created to match specific
generator char-acteristics. UEL Limiter action is
optional in FCR mode.

DECS-400 Digital Excitation Control System
9
Figure 1 - Dimensions,
Front view
Depth: 11.14" (283.0mm)
current (single phase), frequency, kW, Power Factor,
field voltage, and field current. The user can utilize the
DECS-400 BESTCOMS to trigger and save a record of
a voltage step response during commissioning. Once
commissioned, a logic trigger or level trigger can be
used to activate the data recorder to capture the
occurrence for review at a later time. DECS-400 alarms
can also be used to start the data recorder. When an
alarm condition occurs, an oscillographic record can
be stored. A level trigger will initiate a record to be
saved when a variable exceeds a predetermined
setting, such as when the exciter field current exceeds
a predetermined setting.
The oscillographic records are recorded in accordance
with the IEEE Standard Common Format for Transient
Data Exchange (COMTRADE) or Log file format. Basler
Electric provides BESTWAVE, a COMTRADE viewer,
that allows the user to view the oscillography records
saved by the DECS-400.
Real Time Monitoring
The DECS-400 also provides for real time monitoring
for any of the parameters available for oscillography.
The real time monitoring screen will display two param-
eters at a time, and data can be stored in a file for later
examination.
Internal Testing Provisions
Using BESTCOMS, the operator can set up and run
both frequency and step response tests to facilitate
commissioning or to demonstrate system performance.
The frequency response test has a frequency range
from 0.1 to 10 Hz, and gain/phase information is
generated in the form of a Bode plot. The DECS-400
also allows injection of test signals at various points in
the PSS/voltage regulation loop for a high level of
testing flexibility. This feature eliminates the need for an
external Dynamic System Analyzer (DSA) and associ-
ated transducers.
Communications
DECS-400 comes complete with Windows®based PC
software designed to make the programming and cus-
tomization of the DECS-400 easy and fast. The software
includes a PID selection program that allows the user
to select stability settings quickly and easily in a user-
friendly format. The PC software has monitoring
screens that allow the user to view all settings, meter-
ing screens for viewing all machine parameters, and
control screens for remote control of the excitation
system.
The rear-mounted RS-485 port supports Modbus™
(floating point) communications protocol. This is an
open protocol with all registers and operating instruc-
tions available in the instruction manual, to make it
simple for the user to develop custom communications
software. A rear-mounted modem is also provided to
facilitate access to DECS-400 settings and alarms from
remote locations.
Ethernet communication is another standard feature
available on the DECS-400 via an RJ-45 port. This pro-
tocol supports Modbus TCP in 10 Base T transmission
speeds. It also gives users the ability to synchronize
time via NTP and download records created from Oscil-
lography, Sequence of Events, and Trending Logs.
Depending on system and preference, Modbus com-
munications is user-configurable to work through the
default modem (RS-485) or Ethernet (RJ-45) ports via
ASCII. Updated hardware designs maintain drawout
capabilities of the DECS-400, without having to discon-
nect wires.
Password Protection
All DECS-400 parameters are viewable via the front
panel LCD display, the PC software, or via Modbus™
without the need of a password. If the user wishes to
change a setting, the proper password must be en-
tered to allow access to the parameter. Two levels of
password protection exist, one for global access to all
parameters and one for limited access to parameters
normally associated with operator control.
FEATURES/FUNCTIONS, continued

DECS-400 Digital Excitation Control System
10
EXAMPLE CONNECTIONS
Figure 2 - Typical AC Connection Example
BESTCOMS SOFTWARE
Protection Underexcitation Limiter
The DECS-400 is supplied with BESTCOMS PC-based software to facilitate system setup and testing. As shown
in the Protection screen, below left, choices are made using drop-down screens, and parameters are familiar.
Reminders are also provided at the bottom of the screen for input units and available parameter range. Tabs
identify general functions, and related functions are on adjacent pages. As shown on the Underexcitation Limiter
Screen, below right, graphics are also used to help visualize input parameters.

DECS-400 Digital Excitation Control System
11
BESTCOMS SOFTWARE, continued
Metering Real Time Monitoring
Example of Multiple Screen Capability
As shown in the metering screen, above left, a broad range of machine and system parameters can be dis-
played, along with key system status information, such as operating status, operating mode, and key parameter
set points. Adjustments to the current operating mode set point can also be made from this screen.
On-line PSS and AVR testing can also be performed using screens such as the Test Signal screen, which can
initiate pre-programmed tests that may be monitored using the Real Time Monitoring function illustrated in the
Analysis screen, above right.
BESTCOMS for the DECS-400 also incorporates greater “Windows” functionality, as shown in the screen shot
below. The screen simultaneously displays the systems status and alarms window, other available systems
screens using the familiar Explorer View, along with other screens, such as the metering display, the protection
screen and the UEL settings screen shown. Multiple screens can be tiled, cascaded or otherwise manipulated
using familiar Windows commands.

DECS-400 Digital Excitation Control System
HOW TO ORDER
ACCESSORIES
• Front panel mounting bracket for DECS-300 retrofit applications, Basler P/N 9369707009
• Mounting bracket for 19" rack mount, Basler P/N 9365207030 (two required for mounting)
• Control Power Isolation Transformer
• The IDP-800 Interactive Display Panel is a high-resolution, 7.5 inch (diagonal), color touch screen HMI that permits the operator to monitor
Basler Electric's DECS-400 excitation systems status, perform control operations, and make routine adjustments to various set points.
This next generation HMI can be placed locally on the exciter cabinets or remotely in a control room, via two-wire RS-485 (4000 feet
maximum distance from DECS) or RJ-45 Ethernet communication. For more details, see Product Bulletin SZV.
Figure 4 - Front Panel Cutout Dimensions,
front panel mounting bracket
Figure 3 -Dimensions, Isolation Transducer
DECS-400 U
PSS
1) Integrated power
system stabilizer
2) None
POWER SUPPLY
L) 24/48 Vdc
C) 125 Vdc/120 Vac
CURRENT SENSING
1) 1 A CT secondary
5) 5 A CT secondary
BATTERY BACKUP
U) Battery backup for
real-time clock
MODEL NUMBER
NOTE:
Effective January 2008, battery backup feature is standard.
Printed in U.S.A.Printed in U.S.A.
Printed in U.S.A.Printed in U.S.A.
Printed in U.S.A.
www.basler.com
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