Basler DECS-300 Digital Excitation Control System

Basler DECS-300 Digital Excitation Control System

Chapter 1 General Information

1. Core positioning and application

A fully digital excitation regulation device that outputs analog control signals to drive a thyristor rectifier bridge (output 20-5000A DC excitation), suitable for any capacity synchronous generator, single machine independent, multi machine parallel in power plants, and grid connected scenarios.

2. Four core operation control modes

AVR automatic voltage regulation: main operating mode, precise maintenance of terminal voltage, voltage regulation accuracy ± 0.25%;

FCR excitation current manual mode: constant excitation current control, maintenance/start stop standby, accuracy ± 1%;

VAR reactive power control: constant reactive power, suitable for grid connected stable reactive power;

PF power factor control: Constant power factor, commonly used in power plant grid connection.

3. Summary of core functions

Dual PID stable parameter group: two independent PID sets for main and auxiliary, with one click switching of external contacts; Built in 20 sets of prefabricated excitation PID parameters, supporting user-defined 21st group;

Pre position: Two sets of preset excitation settings, the circuit breaker automatically switches to the no-load excitation value when it opens, without disturbance switching;

Soft start and build up pressure: customizable boost slope and build up duration to suppress start-up overshoot;

Multiple limiters (OEL/UEL/SCL/V/Hz)

OEL overexcitation limit: divided sum type, tracking inverse time limit type, distinguishing between two sets of parameters: single machine offline/grid connected online;

UEL under excitation limit: built-in curve+5-point custom active reactive curve to prevent step loss;

Stator current limit: high and low level current limit+delay protection;

V/Hz limit, low frequency limit, to prevent iron core saturation;

Parallel matching functions: reactive power droop compensation, cross current differential current sharing, line voltage drop compensation;

Tracking disturbance free switching: internal (local four mode mutual tracking), external (dual redundant DECS master-slave tracking), mode switching fluctuation ≤ 0.5% excitation voltage;

Improve the protection system: 7 major categories of hard protection+programmable alarm output;

Data recording: Event sequence recording SOE, COMTRADE standard fault recording, can store 8 sets of recording curves;

Communication system: Three independent serial ports, local debugging, redundant interconnection, Modbus remote monitoring;

Supporting isolation module: dedicated isolation module collects excitation voltage and current, and isolates strong and weak electricity.

4. Key electrical accuracy indicators

AVR steady-state voltage regulation: ± 0.1% under constant load;

FCR constant current: ± 1% when the excitation bridge voltage/resistance fluctuates;

PF control: active power range of 10% to 100%, power factor error ± 0.02;

Measurement accuracy: Line voltage and current<0.5%, frequency ± 0.1Hz;

5. Sensor input specifications

Terminal voltage: single-phase/three-phase PT acquisition, with two levels of 100V/240V;

Bus voltage: single-phase PT, maximum 500kV primary side range;

Stator current: CT 1A/5A dual range;

Excitation signal: collected by isolation module, with 5 levels of excitation voltage (32/63/125/250/375V) and 2 levels of shunt (50/100mV);

Auxiliary analog input: -10~+10V or 4~20mA (compatible with PSS power stabilizer).

6. Output interface specifications

Analog control output: ± 10V/0~10V/4~20mA, choose one from three, drive SCR trigger cabinet;

8-way relay output: 4 fully programmable, 4 fixed functions (voltage building, voltage building failure, watchdog, start stop), contact 7A long-term load-bearing;

13 passive switch inputs (24V internal power supply), realizing logic such as start stop, mode switching, redundancy enable, PID switching, and pre positioning.

7. Communication port hardware

COM0 (front panel RS232): Local BESTCOMS software debugging, default 9600 baud, 8N1;

COM1 (Backplane RS232): Only used for redundant master-slave tracking interconnection of two DECS devices;

COM2 (Backplane RS485): Modbus RTU bus, remote upper control, PLC monitoring, adjustable addresses from 1 to 247.

8. Environmental and mechanical parameters

Working temperature: -40~+60 ℃ (LCD screen fails below -20 ℃);

Installation: Standard 19 inch rack with a height of 3U, optional cabinet door embedded panel;

Protection: Meets industrial EMC static electricity, surge, RF interference and anti-interference standards, UL/CSA/CE certification.

Chapter 2 Human Machine Interface HMI (Section 2)

1. Front panel hardware composition

64 × 128 backlit LCD display screen, 6 operation buttons, 6 status LEDs (zero tolerance, internal tracking, pre positioning, high and low limit indicator lights), COM0 debugging serial port; The buttons include up, down, left, right navigation, EDIT editing button, and RESET reset alarm button.

2. The seven main branches of the menu tree (complete 7-page hierarchical structure)

OPER operation interface: start stop, AVR/FCR/PF/VAR mode, compensation, tracking main switch;

SETPOINT fixed values: benchmark values for each mode, upper and lower limits, and two sets of pre positioning parameters;

LOOP GAIN control gain: main/auxiliary PID complete set of KP/KI/KD, limiter gain;

METER measurement: real-time multi parameter display, fault alarm list;

Protection: All protection on/off, threshold, and delay settings;

LIMITED limiter: OEL/UEL/SCL, V/Hz curve parameters;

SYSTEM system parameters: generator/excitation/transformer model, relay logic, lifting rate, tracking parameters;

Generic: baud rate, clock, screen contrast.

3. Permission and Password Mechanism

Two level access permissions:

Global permission: can modify all parameters, default password DECS3;

Setpoint: Only allows start stop, mode switching, and modification of benchmark values, and cannot modify core parameters such as protection and PID;

Power off and long press Edit+Reset to restore all factory defaults (losing custom parameters).

4. Measurement and alarm functions

Custom measurement window with 3 columns on the screen, which can display more than 20 types of quantities such as voltage, current, reactive power, power factor, excitation temperature, etc;

The alarm list can store up to 6 latest faults, which are automatically refreshed and divided into self-locking faults (requiring manual reset) and self resetting faults (automatically cleared when the fault disappears);

LED status prompt: Tracking ready, reaching pre positioning, excitation upper and lower limits triggered.

5. Edit operation rules

To modify parameters, you need to enter the Edit session. If there is no operation for 10 minutes, it will automatically time out and save; Parameter modifications can take effect immediately, but they need to be saved to the non-volatile EEPROM again by pressing Edit, and the Reset button will abandon the modification and revert back to the original value.

Chapter 3 Functional Principle Description (Section 3)

1. Hardware architecture

The whole machine consists of 13 switch inputs, multiple analog acquisition channels, 12 bit ADC, DSP signal processor, main control MCU, DAC analog output, 8 relays, three serial ports, real-time clock RTC, and isolation module interface; DSP is responsible for high-speed data acquisition, filtering, and excitation regulation operations, while MCU is responsible for protection, communication, and human-computer interaction.

2. Switch input logic (13 24V passive contacts)

Key priority rule: Stop shutdown>Start startup; FCR manual mode>AVR automatic mode; The combination of 52L/M (grid connected circuit breaker) and 52J/K (reactive power mode) contacts determines the operation mode and online/offline OEL switching.

3. Function of simulation acquisition and isolation module

The isolation module isolates strong and weak electricity through optocouplers, collects excitation DC voltage and shunt current, converts them into standardized 0.9~9.5V analog signals, and sends them to the host; Simultaneously provide ± 12V isolated power supply for the host.

4. Logic of the four major adjustment modes

AVR: closed-loop stable terminal voltage, supporting soft start and voltage matching grid connection;

FCR: open-loop constant excitation current, reliable operation without voltage sensing;

VAR: Closed loop constant reactive power output;

PF: Closed loop constant power factor;

The mode supports automatic tracking within the machine and switches without disturbance.

5. Seven types of standard protection functions (all can be turned on or off, threshold delay can be adjusted)

Excitation overvoltage FOV; 2. Excitation overcurrent FOC (inverse time curve); 3. Excitation overheating; 4. Generator overvoltage; 5. Generator undervoltage; 6. demagnetization protection (alarm for excessive absorption of reactive power); 7. Loss of voltage sensing (can automatically switch FCR to ensure the operation of the unit);

Additional auxiliary protection: frequency below 10Hz alarm, V/Hz limit, low frequency limit.

6. Detailed principles of the four major limiters

OEL overexcitation limit

Sum up type: offline high and low level, online high, medium, and low level current threshold+segmented delay;

Tracking type: with inverse time characteristics, suitable for frequent fluctuating loads;

Offline/online parameters are automatically switched by the contacts of the grid connected circuit breaker.

UEL under excitation limit: Built in curve or custom 5-point active reactive power boundary to prevent phase loss, FCR mode only alarms without restrictions.

SCL stator current limit: high and low current levels+delay to avoid stator overheating.

Low frequency/V/Hz limit: Automatically reduce excitation at low frequencies to prevent iron core saturation.

7. Data recording and waveform recording function

SOE event sequence: 50ms scan capture switch, protection, mode change, with timestamp;

Fault waveform recording: compatible with COMTRADE power standard, with a maximum of 600 points per segment, can pre trigger and record the waveform before the fault, with adjustable sampling time of 4-10ms, used for fault analysis.

8. Redundant tracking mechanism

Two DECS are interconnected through COM1, and the parameters of the main regulator are synchronized in real-time to the standby machine; The excitation fluctuation is minimal during switching, meeting the requirements of a disturbance free redundant excitation system design.

Chapter 4 Installation Guide (Section 4)

1. Mechanical installation

19 inch standard rack 3U, optional cabinet door embedded installation accessories; The isolation module is independently wall mounted and does not require any openings; Provide complete hole dimensions and installation hole location drawings.

2. General wiring specifications

The back of the whole machine is divided into A/B/C three row terminal blocks, equipped with three D-Sub serial ports and a 15 pin isolation module dedicated interface; The minimum wire size is 14AWG, and the grounding terminal must have a separate 12AWG thick copper wire.

3. Wiring rules for various types of terminals

Power terminal: AC 120Vac, DC 125Vdc/24-48Vdc, supports dual power redundancy, DC anti reverse connection;

Voltage/current transformer terminals: machine end PT, bus PT, stator CT phase separation wiring, CT circuit must not be open circuited;

13 control inputs: passive contacts for start stop, mode switching, PID group switching, pre positioning, alarm reset, etc;

8-way output relay: programmable alarm+fixed function voltage building, watchdog, etc;

Auxiliary Analog Input (PSS), Analog Control Output (SCR trigger);

15 pin P1 interface: Connect the isolation module to transmit excitation voltage/current acquisition and power supply.

4. Communication wiring

COM0 front panel RS232: directly connected to computer serial port;

COM1 backplane RS232: dedicated dual machine redundant interconnect cable;

COM2 backplane RS485 Modbus: twisted pair, up to 1219 meters long, with 120 Ω terminal resistors at both ends of the bus.

5. Parallel compensation wiring

Complete schematic diagram of reactive power sag, cross differential current sharing (dual generator parallel dedicated CT wiring), and line voltage drop compensation; Provide standard wiring diagrams for SSE and SSE-N excitation systems.

Chapter 5: Operation and Debugging Steps of the Whole Machine (Section 5)

Complete standardized process for on-site operation, consisting of three stages: separation line (unit not running), offline turning, and grid connection with load:

Preparation before debugging: record the rated parameters of the generator, prepare the recorder, and install BESTCOMS;

Software parameter configuration process (BESTCOMS)

System options → Rated parameters → Transformer ratio → AVR/FCR setting → VAR/PF parameters → Soft start → OEL/UEL/SCL limit → Protection threshold → Relay logic;

Offline static testing (turbine stationary)

Remote/panel/software start stop testing, mode switching, lifting excitation, alarm circuit verification;

Empty load debugging of turning gear

FCR manual start-up, boost testing, AVR switching, PID parameter tuning (providing recommended values for two sets of standard PID for excitation machine/main excitation), soft start waveform observation;

Grid connected load debugging

Synchronous voltage matching verification, OEL/UEL/SCL limit action test, reactive power/power factor control performance test, parallel current sharing verification;

PID tuning method: Adjust KP/KI/KD through step response waveform to solve overshoot, oscillation, and slow response problems;

After all tests are completed, the parameters will be permanently stored in EEPROM.

Chapter 6 BESTCOMS Supporting Upper level Software (Section 6)

1. Software function

Windows platform specific debugging and monitoring software, features: online real-time measurement, full parameter reading and writing, PID automatic calculation, step response analysis, fault recording/event export, parameter file saving and reuse.

2. Operating conditions for software and hardware

Compatible with Win2000/XP/Vista, not supported by older NT/95/98; Connect the PC serial port to the DECS front panel COM0 and install the software CD.

3. Core operating procedures

Establish serial communication and enter password (default DECS3);

Seven major configuration interfaces: system configuration, setting value adjustment, gain setting, protection logic, data analysis, waveform recording, real-time monitoring;

Functional modules:

PID calculator: Input the generator time constant to automatically generate recommended parameters;

Analysis interface: AVR/FCR/PF/VAR step response curve observation;

Recording settings: custom triggering conditions (level/logic shift), recording variables;

Parameter import and export, batch copying configuration for multiple units;

Communication settings: independent configuration of three-way serial port baud rate, Modbus address, and parity check.

Chapter 7 Maintenance

The document only reserves a maintenance chapter framework, which includes regular inspection items, internal component checks, serial communication maintenance, and basic methods for fault location. It combines HMI alarm codes and waveform data to troubleshoot common faults such as excitation abnormalities, voltage regulation oscillations, frequent action restrictions, and communication interruptions.

Chapter 8 Modbus Communication (Section 8)

Backplane COM2 RS485 adopts Modbus RTU standard, defining all register addresses:

Real time metering registers: voltage, current, reactive power, power, excitation quantity;

Running status register: current mode, limit trigger, alarm status;

Parameter read-write registers: AVR constant value, protection threshold, PID gain;

Remote control register: remote start stop, mode switching, up and down excitation;

Support remote monitoring of upper computer, PLC, and remote adjustment of excitation.