Basler DECS-100 Digital Excitation System Debugging Guide

Basler DECS-100 Digital Excitation Control System: A Complete Guide to Principles, Applications, and Field Debugging

Product Overview and Application Positioning

The DECS-100 Digital Excitation Control System launched by Basler Electric is a solid-state excitation regulation device designed based on microprocessors, specifically designed for excitation control of brushless AC generators. This device achieves precise control of the output voltage of the generator by adjusting the current of the excitation field of the generator. DECS-100 is encapsulated with epoxy resin and designed for installation behind panels, occupying minimal space in the generator junction box. Its compact and sturdy structure makes it particularly suitable for power generation applications that require strict space and reliability.

DECS-100 supports two excitation power supply modes - permanent magnet generator (PMG) power supply and self parallel excitation (taking power from the generator output), covering various application needs from small and medium-sized diesel generator sets to large industrial power generation facilities. The four quadrant control mode (AVR, FCR, PF, VAR) combined with programmable PID stabilization parameters enables the device to adapt to generators with different excitation system time constants and achieve precise adjustment of reactive power and power factor during grid connected operation.

Compared with large rack mounted excitation systems, the core advantages of DECS-100 lie in its highly integrated compact design (weighing only 1.1kg) and its adaptability to harsh environments with epoxy encapsulation - operating temperature range of -40 to+70 ℃, and passing MIL-STD-810E salt spray testing, making it an ideal choice for harsh working conditions such as ships, oil platforms, and remote power stations.

Core technical specifications

2.1 Control mode and adjustment accuracy

DECS-100 provides four control modes, which can be controlled through BESTCOMS ™ Software configuration:

AVR mode (automatic voltage regulation): The regulation accuracy is ± 0.25% (under rated power factor and constant frequency conditions); When using three-phase induction and 40% total harmonic distortion caused by six SCR loads, the accuracy still remains within ± 0.5%; The temperature drift is ± 0.5%/40 ℃; The response time is less than 1 cycle. The V/Hz slope can be adjusted from 0 to 3PU (0.01PU step), and the inflection point frequency can be adjusted from 40 to 65Hz.

FCR mode (manual/magnetic field current regulation): The regulation range is 0~7Adc (0.01A step), used for backup control or open-loop regulation of excitation current during the debugging phase when AVR mode fails.

VAR mode (reactive power regulation, optional): The regulation range is -100% absorption to+100% output, with 1% step, suitable for maintaining constant reactive power when operating in parallel with an infinite bus.

PF mode (power factor adjustment, optional): The adjustment range is 0.6 lag to 0.6 lead, 0.001 step, suitable for maintaining a constant power factor when parallel with the grid.

2.2 Field output and excitation power supply

Continuous rated output: 63Vdc/7Adc (minimum field resistance 9 Ω)

10 second strong excitation capability: 135Vdc/15ADC (suitable for 5 Ω field resistance) or 90Vdc/10ADC (9 Ω field resistance)

Input power supply: 88~250Vac, 50~400Hz (single-phase or three-phase), from PMG, generator output (self parallel excitation) or auxiliary winding

2.3 Inductive input and measurement accuracy

Generator voltage induction: three-phase or single-phase (terminals E1/E2/E3), maximum 600Vac, PT ratio 1-150 can be set

Bus voltage induction: single-phase (terminal B1/B3, only voltage matching optional model), variable ratio 1-150 can be set

B-phase current induction: 1A or 5A CT secondary optional (terminals CT1/CT2), CT transformation ratio 1~6000 can be set

Measurement accuracy (25 ℃): Voltage ± 0.5%, current ± 0.5%, frequency ± 0.2Hz, power factor ± 0.02 (CT input ≥ 10% rated value), phase angle ± 2.0 °

Attachment input (auxiliary adjustment): -3V to+3Vcd (1k Ω input impedance), ± 3V corresponds to ± 30% set value offset, used for remote automatic voltage regulator (AVR) or power system stabilizer (PSS) signal input

2.4 Protection and restriction functions

Generator overvoltage protection: 100~120% rated voltage adjustable (1% step), delay 0-10s (1s step), configurable alarm output and/or hardware trip

Magnetic field overvoltage protection: adjustable from 0 to 250Vdc (1V step), fixed delay of 10s, configurable alarm output and/or hardware tripping

Loss of Sense Protection (LOS): It operates when the voltage is below 50% of the rated value or when the three-phase imbalance exceeds 20%. The delay time is adjustable from 0 to 25 seconds (default 10 seconds), and can be configured to turn off or switch to FCR mode

Over excitation limit (OEL): optional summation point or takeover type, current threshold 0-15Adc (0.01A step), delay 0-10s

Underexcitation limit (UEL): reactive power threshold 0~100% rated reactive power (1% step), delay 0~10s

Under frequency (V/Hz) limitation: The inflection point frequency is adjustable from 40 to 65Hz, with a slope of 0 to 3PU (0.01 step), and disabled below 12Hz

2.5 Soft start and voltage matching

Soft start time: adjustable from 1 to 7200s (1 second step), controls the generator voltage to climb from residual voltage to the set value, effectively suppressing voltage building overshoot

Voltage matching (optional): Match the output voltage of the generator with the bus voltage, with an accuracy of ± 0.5% and an adjustable speed of 1-300s (0.01s step), supporting both "hold" and "restore" modes

Front panel indication and operation

The DECS-100 front panel provides 8 red LED indicator lights (see Figure 2-1) for quick diagnosis:

Meaning of LED indicator light

Overexcitation Shutdown: The magnetic field overvoltage exceeds the set value for 10 seconds, and the device has been turned off (flashing for 5 seconds after power on)

Generator Overvoltage: The generator voltage exceeds the set value for 0.75 seconds, and the device has been turned off (flashing for 5 seconds after power on)

Loss of Generator Sensing detects a loss of sensation and outputs an alarm to close the contact (flashing for 5 seconds after power on)

Overexcitation Limiting: The excitation current exceeds the OEL set value (if it does not recover after the delay, it will be turned off and flash for 5 seconds after power on)

Underexcitation Limiting: Reactive power below UEL curve (if not restored after delay, turn off and flash for 5 seconds after power on)

Var/P.F. Mode Active VAR or PF control mode activation (requires 52J/K open contacts and software enabled)

Manual Mode Active FCR Manual Mode Activation

Underfrequency Active: The generator frequency is below the V/Hz inflection point setting and underfrequency adjustment is being performed

The flashing indicator function of all LEDs when powered on again after the fault is turned off provides a convenient means for on-site engineers to trace the fault history.

Function description and working principle

4.1 Hardware Architecture (Figure 3-1)

The signal flow of DECS-100 can be divided into the following paths:

Voltage induction path: The three-phase voltage connected to the E1/E2/E3 terminals is divided and anti aliasing filtered before being sent to the ADC for 96 samples per cycle. The VC-A signal is simultaneously sent to the zero crossing detection circuit for frequency measurement.

Current sensing path: The B-phase current at CT1/CT2 terminals is sent to the ADC through internal CT and conditioning circuits for calculating the effective current value and power/power factor.

Excitation power path: The AC power input from terminals 3/4/5 is rectified and filtered before being supplied to the power amplification stage. The microprocessor generates a PWM drive signal based on the PID calculation result to control the power switch and outputs it to the F+/F - terminals.

Auxiliary input path: The -3~+3Vdc signal from terminals A/B is sent to the ADC through a 1k Ω input impedance for remote setting value adjustment.

Contact input path: The 13Vdc internal power supply provides status signals through 5 dry contact inputs (6U/6D/52J/52K/52L/52M/VM), which are isolated by optocouplers and sent to the microprocessor.

4.2 PID Control Algorithm and Stable Parameters

The AVR/FCR loop of DECS-100 adopts PID (Proportional Integral Derivative) control algorithm:

Proportional gain Kp: The output is proportional to the error. If Kp is too small, the response will be slow, and if it is too large, overshoot will increase. Typical values range from 1 to 1000.

Integral gain Ki: eliminates steady-state errors. Increasing Ki can accelerate steady-state convergence, but excessive Ki may lead to oscillation.

Differential gain Kd: Provides lead correction, suppresses overshoot and oscillation. Typical values range from 1 to 10 (0.01 steps).

Differential time constant Td: Filter out noise introduced by numerical differentiation, with a typical value of 0.01~0.03 (adjustable from 0~1).

Loop gain Kg: Roughly adjust the overall gain level of the PID algorithm to speed up or slow down the response speed.

The PID window of BESTCOMS provides the function of automatically calculating recommended PID parameters based on the generator time constant T'd0 and the excitation machine time constant Texc. Table 5-1 provides 20 sets of preset stable parameters - corresponding to T'd0 ranging from 1.00s to 10.5s (with a step of 0.5s), Texc is approximately T'd0/6.

4.3 52L/M and 52J/K contact logic

DECS-100 switches operating modes through two sets of external dry contacts:

52L/M status, 52J/K status, DECS-100 operating mode

Closed AVR mode activated, no droop, VAR/PF disabled (standalone/independent operation)

Open close droop mode activated, VAR/PF disabled (parallel to grid or islanded multi machine droop)

Disconnect VAR/PF mode activation (parallel to the grid, reactive power/power factor regulation)

The 52L/M terminal is usually connected to the auxiliary contact of the generator circuit breaker, which opens when the circuit breaker is closed, causing the DECS-100 to enter parallel operation mode. The 52J/K terminal is usually connected to the auxiliary contacts of the grid side circuit breaker - the contacts are disconnected during parallel operation, making the VAR/PF function available.

4.4 Loss of Sense Protection Logic and Precautions

When loss of sensitivity is detected, DECS-100 can be configured with two response modes:

Shutdown mode: After a set delay, the DECS-100 will shut off the excitation output and the alarm contact will close.

Switch to FCR mode: After a set delay, the DECS-100 will automatically switch to FCR (manual) mode for operation. Before enabling FCR conversion, it is necessary to pre evaluate and set appropriate FCR settings - inappropriate excitation current levels may cause serious damage to the generator.

Loss of sensation detection is triggered under the following three conditions:

Induced voltage below 50% of rated value (single-phase or three-phase induction)

Complete loss of any phase voltage (three-phase induction)

The difference between any line voltage and the three-phase average value exceeds 20% of the rated value (three-phase induction)

The desensitization function is automatically disabled when the frequency is below 12Hz or when a generator short circuit is detected (B-phase CT current exceeds 3 times the rated value), and is not activated during soft start.

Installation and wiring points

5.1 Mechanical Installation

DECS-100 is designed for panel installation (Figure 4-1, 4-2), and is screwed into the plastic housing of DECS-100 through the installation holes of the generator junction box with 6 # 12 self tapping screws (recommended torque 4.07-4.52N · m). The size of the front panel opening is 101.6mm × 101.6mm. The ambient temperature at the installation location should not exceed the range of -40~+70 ℃.

5.2 Terminal Wiring

All terminals of DECS-100 are located on the rear panel and use 1/4 inch quick connect terminals (Figure 4-3):

Power input (3, 4, 5): single-phase or three-phase 88~250Vac, 50~400Hz. A single phase can be connected to any two phases. When supplying power from a low impedance power source (such as station power or socket), ICRM-7 modules must be connected in series to prevent damage to DECS-100 caused by closing surge current.

Generator voltage induction (E1, E2, E3): Three phase connection E1/E2/E3 (ABC phase sequence), single-phase connection E1 (A phase), E2 and E3 are short circuited and then connected to phase C.

Bus voltage induction (B1, B3): Only voltage matching optional models are available. B1 is connected to phase A, B3 is connected to phase C (non phase sensitive).

B-phase current induction (CT1, CT2): CT1 is connected to CT secondary S1, CT2 is connected to S2. 1A or 5A CT is optional (see style number).

Excitation output (F+, F -): connected to the excitation field of the generator. Output continuous 63Vdc/7Adc, strong excitation 135Vdc/15Vdc (10 seconds).

Alarm output (AL1, AL2): normally open contacts, 7Aac/ADC continuous, closed in case of fault.

Contact inputs: terminals 6U/7 (up), 6D/7 (down), 52J/52K (VAR/PF enabled), 52L/52M (parallel enabled), VM/VMC (voltage matching enabled) - all contacts are dry contacts powered by the internal 13Vdc of DECS-100.

5.3 CE/EMC compliant installation requirements

For CE and EMC compliant installation, DECS-100 must be installed inside a grounded metal enclosure (junction box). The wires connected to the following terminals must use shielded wires, with the shielding layer grounded outside the junction box:

Inductive voltage terminals E1/E2/E3

Alarm output AL1/AL2

External adjustment terminal 6D/7/6U

VAR/PF Enable 52J/52K

Parallel compensation of 52L/52M

Excitation output F+/F-

Power input 3/4/5

Voltage matching VM/VMC

In addition, it is necessary to install ferrite clamps (specifications shown in Table 4-5/4-6) at the wire outlet (25-76mm away from the connector), wound twice, to suppress radiation in the 31-300MHz frequency band.

5.4 Special precautions for power supply in programming state

The PWM power stage input terminal of DECS-100 has a large capacitance, and when powered on from a rigid power source (>120Vac), it will generate a high closing impulse current, which may damage the device. The power supply voltage of DECS-100 in programming state should be limited within the range of 30-120Vac (50/60Hz), and the connection between the F+and F - terminals and the generator magnetic field should be disconnected.

If the power supply voltage exceeds 120Vac during programming, a current limiting resistor -20 Ω/20W (briefly overloaded during impact, with minimal power consumption afterwards) or 10 Ω/50W - must be connected in series between the power supply and DECS-100.

In addition, 24Vdc can also be used for DECS-100 power supply for programming purposes only. Normal operation (PMG or self excitation) is not subject to the above restrictions, but applications powered by station electricity must use ICRM-7 modules to protect DECS-100.

BESTCOMS Software Operation Guide

6.1 Software installation and communication establishment

BESTCOMS-DECS100 software runs on Windows XP/Vista/7/8/10 environment and communicates with DECS-100 through the rear DB-9 RS-232 serial port (default 9600 8N1). The factory default password is "decs". After establishing communication, the software updates the measurement values approximately once per second.

6.2 Setting value modification and storage

All set values can be modified by following these steps: select the corresponding tab → click on the set value field → enter the new value → click on the SendToDECS button (or press Enter) → click on the EEPROM button to save to non-volatile memory. Attention: The erase and write life of non-volatile memory is about 10000 times, and it is necessary to plan frequent write operations reasonably.

6.3 Key Setting Parameters

System Configuration: Induced voltage type (single-phase/three-phase), limiter enable (OEL/UEL), OEL type (summation point/connection), generator frequency (50/60Hz), PT/CT ratio

Setting Adjustments: AVR setting value, FCR setting value, VAR/PF setting value, droop percentage (0-10%), fine voltage regulation bandwidth (0-15%)

Control Gain: Stable range (1-20 preset groups or 21 custom), PID parameters (Kp/Ki/Kd/Td/Kg)

Protection: overvoltage/overexcitation/loss of inductance/underexcitation protection threshold and delay, hardware shutdown enable

Startup: Soft start time, under frequency inflection point frequency and slope, voltage matching speed and mode

6.4 Step Response Analysis Tool

The Analysis screen supports step response testing in four modes: AVR, FCR, VAR, and PF (Figure 5-10 to 5-13). Users can set step increments/decrements of 0-10%, observe real-time responses of Vrms, Ifd, reactive power, and power factor, and use six alarm signals for on-site PID parameter optimization verification.

6.5 Firmware Upgrade

The embedded firmware of DECS-100 is stored in programmable flash memory and can be upgraded online through BESTCOMS' DECSLoad function (communication needs to be turned off first). Interruption of power or communication during the upgrade process will result in the inability of DECS-100 to recover. Before upgrading, the current setting value file (. de1) must be saved, and the F+/F - terminals must be disconnected to avoid accidental excitation output.

Common troubleshooting guide

Troubleshooting steps for fault phenomena

Generator voltage cannot be established ① Check all wiring (Figures 4-6 to 4-10); ② Confirm that the generator has reached its rated speed; ③ Check the input power supply during PMG power supply (refer to the specification sheet); ④ Check if the residual voltage during self excitation is ≥ 6Vac (if not, magnetize); ⑤ Check if there is a blown fuse; ⑥ Confirm that the over excitation turn off LED is not on (if it is on, check the load, power off for 1 minute and reset); ⑦ Confirm that the overexcitation limit LED is not on; ⑧ Check if the soft start setting value is too long; ⑨ Replace DECS-100

Low generator voltage ① Check if the voltage setting value is too low; ② Check if the set value of the underfrequency inflection point is higher than the actual frequency; ③ Confirm that the generator has reached its rated speed; ④ Check the input power supply voltage during PMG power supply; ⑤ Check the PT ratio and capacity during self excitation; ⑥ Confirm that the overexcitation limit LED is not on; ⑦ Check the impact of inductive loads in droop mode; ⑧ Check if the attachment input has changed the set value; ⑨ Replace DECS-100

High frequency motor voltage ① Check if the voltage setting value is too high; ② Check if the induction PT ratio is correct; ③ Check the impact of capacitive load sagging; ④ Check the impact of attachment input; ⑤ Replace DECS-100

Unstable voltage regulation (traveling block) ① Confirm that the casing is well grounded (GND terminal); ② Check if the excitation lead is grounded; ③ Check the grounding of PMG leads during PMG power supply; ④ Confirm that the load is not lower than the underfrequency inflection point; ⑤ Confirm that it is not affected by sagging mode; ⑥ Check if the Stability Range is correct; ⑦ Check if the Stability Level is correct; ⑧ Replace DECS-100

Overexcitation shutdown indicator ① Check if the generator is overloaded; ② Confirm that the excitation voltage requirement is compatible with the DECS-100 output; ③ Replace DECS-100; ④ Check for generator malfunction

Loss of sensitivity indicator ① Check the connection of voltage sensing leads; ② Confirm that E2 and E3 are connected to phase C simultaneously during single-phase induction; ③ Check the sensing PT ratio and function; ④ Confirm the balance of three-phase voltage; ⑤ Replace DECS-100

No sagging ① Confirm that the 52L/M contact is disconnected; ② Confirm that the 52J/K contact is closed or the VAR/PF function software is disabled; ③ Confirm that the sag setting value is greater than 0%; ④ Check that there is no open circuit in the CT1/CT2 circuit; ⑤ Confirm that the wiring is correct; ⑥ Confirm that the load contains inductive components; ⑦ Confirm CT ratio matching (1A CT for 5A input without droop); ⑧ Replace DECS-100

No voltage matching ① Confirm that the voltage matching option is selected and the software is enabled; ② Confirm that the wiring is correct; ③ Confirm that the VM/VMC contacts are closed; ④ Confirm that the B1/B3 terminals have the correct bus reference voltage; ⑤ Confirm that the set value of the generator is within 10% of the bus voltage range; ⑥ Replace DECS-100

BESTCOMS cannot communicate ① Check the RS-232 cable connection (Figure 4-5); ② Confirm that the COM port settings are correct; ③ Confirm that the password input is correct (default decs); ④ Check if DECS-100 is powered on

Maintenance and Storage

DECS-100 is equipped with long-life aluminum electrolytic capacitors inside. For equipment stored as spare parts for a long time, it is recommended to run it on for 30 minutes every year to extend the lifespan of the capacitor. When powered on, the power should be supplied within the range of 88~250Vac and 50~400Hz. When powered from a low impedance power supply, the ICRM-7 module must be used.