Basler Electric DECS-400 Digital Excitation Control System

INTRODUCTION

The DECS-400 Digital Excitation Control System is a microprocessor-based controller that offers

excitation control, logic control, and optional power system stabilization in an integrated package. The

DECS-400 controls 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 operating outside its capability.

The optional, onboard power system stabilizer is an IEEE-defined PSS2A, dual-input, “integral of

accelerating power” stabilizer that provides supplementary damping for low-frequency, local mode and

power system oscillations.

Integral programmable logic provides excitation system control and annunciation based on DECS-400

contact inputs, operating mode status, excitation system parameters, 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 Electric’s Interface Firing Module (IFM) and SSE or SSE-N

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.

FEATURES

DECS-400 features and capabilities are listed below. The paragraphs following the list describe major

DECS-400 features and functions in more detail.

• Five excitation control modes

− Automatic Voltage Regulation (AVR)

− Field Current Regulation (FCR)

− Field Voltage Regulation (FVR)

− Power Factor (PF)

− Var

• Two pre-position setpoints (with adjustable traverse rate) for each excitation control mode

• Two PID groups

• Programmable analog control output selectable for 4 to 20 mAdc, –10 to +10 Vdc, or 0 to +10 Vdc

• Remote setpoint control input accepts analog voltage or current control signal

• Real-time metering

• Integrated power system stabilizer (PSS)

− Generator or motor control modes, accommodates phase rotation changes between modes

− Speed and power sensing or speed-only sensing

− Two-wattmeter or three-wattmeter methods of power measurement

• Soft start and voltage buildup control

• Four limiting functions

− Stator current

− Overexcitation

− Underexcitation

− Underfrequency compensation

− Reactive power

• Ten protection functions

− Field overvoltage

− Field overcurrent

− Generator undervoltage

− Generator overvoltage

− Loss of sensing voltage

− Generator frequency less than 10 hertz

− Loss of field (40Q)

− Field overtemperature

− Volts per hertz (24)

− Exciter diode failure

• IRIG time synchronization

• Sixteen contact inputs

− Six fixed-function inputs: AVR, Manual, Lower, Raise, Start, and Stop

− Ten user-programmable inputs

• Eight contact outputs

− Two fixed-function outputs: Watchdog, On/Off

− Six user-programmable outputs, configurable for maintained, latched, or momentary operation

• Four communication ports

− Front RS-232 port for interface with PC running BESTCOMS software

− Rear RS-485 port for dedicated communication with secondary, redundant DECS-400

− Rear RS-485 port using Modbus™ protocol for communication with remote terminal

− Rear RJ-45 port connects to onboard modem that provides dial-in and dial-out capability

• Data logging, sequence of events recording, and trending

Generator Voltage Regulation

By utilizing digital signal processing and precise regulation algorithms, the DECS-400 regulates the

generator rms voltage to within 0.2% of the setpoint from no-load to full-load.

Control Output

The DECS-400 supplies an isolated control output signal of 4 to 20 mAdc, 0 to 10 Vdc, or ±10 Vdc 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, motor, or exciter. The DECS-400 can control virtually any bridge

that is capable of accepting these signals and is suitable for use on synchronous generators or motors.