Practical Guide to Basler DECS-300 Digital Excitation System

All editable parameters are password protected. The system provides two levels of permissions:

Global access (can change any parameter)

Set value access (only allows modification of operational parameters such as start stop, mode switching, set values, and preset positions)

The factory default password is "DECS3". If the user forgets the custom password, they can restore the default password by simultaneously pressing the "Edit" and "Reset" keys when powering on - but this operation will also restore all user settings to factory default values. It is recommended to save the configuration file through BESTCOMS in advance.

The timeout for editing sessions is 10 minutes without any keystrokes, and the timeout for secure access is also 10 minutes. If there is a timeout during the editing session, the modified parameters will be automatically saved to non-volatile memory (EEPROM).

BESTCOMS Software and Debugging Practice

4.1 Overview of Software Functions

BESTCOMS-DECS300-32 is based on Windows ® The PC application software of the platform (supporting Windows 2000/XP/Vista) communicates with DECS-300 through the front panel COM0 port (RS-232). Its core functions include:

Parameter reading, writing, and offline editing (can be saved as *. d3 files for rapid deployment on multiple devices)

Real time monitoring (refreshed approximately once per second)

Automatic calculation of PID parameters (based on generator time constant T'do and exciter time constant Te)

Step response analysis (AVR/FCR/VAR/PF mode)

Data recording and event sequence recording (SOE, supports COMTRADE format waveform viewing)

4.2 PID tuning engineering method

PID parameter tuning is a crucial step in the debugging of excitation systems. BESTCOMS provides two auxiliary tools:

Preset stability table: Built in 20 sets of recommended PID parameters for the excitation machine magnetic field and main magnetic field (based on T'do and Te combination), as shown in the typical value excerpt in the table below:

T’do (s) Kp Ki Kd

1.0 11.80 42.60 0.02

3.0 26.43 65.20 0.03

5.0 34.56 65.74 0.01

7.0 39.73 61.61 0.01

PID calculator: After the user specifies the time constants of the generator and exciter, the software automatically generates recommended PID parameters and can directly apply the results to the 21st group (user-defined group).

4.3 Key points of on-site debugging process

Off grid no-load debugging (turbine not rotating): Start at 20% rated excitation current in FCR mode, verify excitation, voltage building, and demagnetization functions, check magnetic field flicker logic and alarm output.

Off grid speed debugging: gradually increase the voltage to the rated voltage, conduct a 5% step response test, observe the overshoot and adjustment time. If the response is too slow, increase Kg (loop gain); If the overshoot is too large, reduce Kp (proportional gain) or increase Kd (differential gain).

Grid connected debugging: Verify the phase relationship between CT polarity and voltage transformer (B-phase current should lag E1-E3 voltage by 90 °), confirm that the air balance indicator light is always on, then switch to AVR mode, and test the OEL, UEL, SCL, and VAR/PF control functions separately.

4.4 Data Recording and Fault Analysis

DECS-300 supports up to 8 waveform records (in COMTRADE format), each of which can monitor 6 user-defined variables (such as Vab, Ifd, VAR, frequency, etc.). The sampling interval is adjustable from 4ms to 10s, and the maximum number of pre trigger points is 599. The triggering methods include software triggering, logic triggering, and level triggering. On site engineers can use this function to capture transient waveforms before and after faults, greatly reducing the time for troubleshooting.

Modbus communication integration

5.1 Communication Parameters

The DECS-300 supports Modbus RTU protocol through the RS-485 port (COM2) on the backplane, with default parameters of 9600 bps, 8 data bits, no checksum, and 2 stop bits. The slave address (1~247) and response delay (0~200ms) can be modified online through BESTCOMS or Modbus messages.

5.2 Supported Function Codes

03 (Read and hold register)

06 (Write a single hold register)

16 (Write multiple hold registers)

08 (Loop testing, including returning query data, restarting communication, and forcing slave stations to only listen for sub functions)

5.3 Register Space Organization

DECS-300 divides data into 15 information categories (C1~C15) by function, covering product information (C1), real-time measurement (C2), system configuration (C4), operating mode (C5), set value (C6), limiter (C8), PID gain (C9), protection parameters (C10), and relay configuration (C12).

Example of partial key register addresses:

47525-47526: Rated voltage of generator (R/W, floating point)

47529-47530: Rated magnetic field current of generator (R/W, floating point)

47621-47622: FCR mode setting value (R/W, floating point)

47623-47624: AVR mode setting value (R/W, floating point)

47861-47862: Main PID Stability Group Number (R/W, Floating Point)

48161: EEPROM Save Command (R/W, UI16)

Important note: Parameters written via Modbus will not be automatically saved to EEPROM. If permanent storage is required, the corresponding category flag values must be written to register 48161 (such as 0x0001 for C4 and C6, 0x0002 for C5 and C7, etc.).