Basler DECS-250 Excitation System Debugging Guide

Basler DECS-250 Excitation System Debugging Guide

Product Overview and Technical Specifications

DECS-250 adopts a 24Vdc control power supply, with a continuous excitation power output of 15Vdc (forced 30Adc/10 seconds), and can provide 32/63/125Vdc excitation voltage according to the input voltage (60/120/240Vac). Its key functions include:

Adjustment modes: AVR (Automatic Voltage Regulation), FCR (Field Current Regulation), PF (Power Factor Regulation), Var (Reactive Power Regulation)

Protection functions: Generator over/under voltage (59/27), over/under frequency (81O/81U), over excitation voltage (59F), demagnetization (40), reverse reactive power (40Q), reverse power (32R), rotating diode monitoring, etc

Parallel compensation: Droop, Cross current compensation

Limiters: Voltage/Hertz (V/Hz), Over Excitation Limit (OEL), Underexcitation Limit (UEL)

Synchronization: single/double bus, single-phase/three-phase, with built-in dead bus closing judgment

Redundancy: Dual machine hot standby, tracking set values through RS-232 serial port to achieve undisturbed switching

All parameters are read and written through the Schedule/Unscheduled data table of Logix PLC, without the need for specialized debugging software.

Installation and wiring points

2.1 Environment and Mechanical Installation

DECS-250 must be installed vertically, leaving 63.5mm on the left and right, and 101.6mm on the top and bottom for heat dissipation. The ambient temperature is -40~+70 ℃, and the humidity is 5-95% without condensation. Suitable for Class I Division 2 and Zone 2 hazardous areas, it needs to be installed in cabinets with IP54 or higher.

2.2 Power Wiring

Control power supply: Terminal 47 (BAT+), 48 (BAT -), DC 18-32V, power consumption 30W.

Operating power supply (excitation power): terminals 49, 50, 51 (PMG A/B/C), can be connected to single-phase or three-phase, and the voltage range depends on the required excitation voltage (see Table 8-1). If self parallel excitation (Shun) is used, power is taken from the generator end through PT. Note: If a single-phase 300Hz PMG is used in a redundant system, only one DECS-250 can be connected at a time, otherwise a contactor needs to be added for switching.

2.3 Wiring of Voltage and Current Transformers

Generator voltage: terminals 13-16 (V GEN A/B/C/N), supporting single-phase, open delta, three-phase three wire, and three-phase four wire.

Bus voltage: terminals 17-20 (V BUS A/B/C/N), also supporting multiple wiring options. When using dual busbars, select the "Dual Breaker" configuration and only use single-phase.

Generator current: Terminals 36-41 (I1+/I1-, I2+/I2-, I3+/I3-), CT secondary 1A or 5A. Note: If only one CT is used, it must be connected to phase B.

Crossflow compensation CT: Terminal 42 (ID+), 43 (ID -), usually connected to phase B. The circuit resistance should be less than 0.1 Ω (internal load 1 Ω). If the resistance is too high, a resistor can be added in series at terminals 33 and 34 (ID RES+/-) to adjust the gain.

Remote voltage regulation input: terminals 24 (VREF -), 25 (VREF+), ± 10Vdc, used for power system stabilizers (PSS), etc.

2.4 Excitation output and relay

Excitation output: Terminals 54 (EXC+) and 55 (EXC -) require twisted pair shielded wires. In redundant systems, 3-4 flywheel diodes need to be connected in series outside the excitation winding on site to avoid measurement errors caused by intermittent current during switching.

Fault relay: Terminals 29 and 30 (FLT RLY), normally open contacts, can be configured to close when any protection action is taken.

Redundant relay: terminals 31 and 32 (RD RLY), with the main machine closed, used to control the external contactor to output excitation to the magnetic field.

Cross current relay: Terminals 27 and 28 (ID RLY), close when the cross current function is not activated, short-circuit the cross current CT input.

2.5 Load sharing and redundant communication

Active load sharing: Terminal 1 (LS+), 2 (LS -), 0-5VDC signal, all parallel units LS+and LS - are connected in parallel.

Redundant communication: DB9 (RS-232) uses a null modem cable to connect two DECS-250 devices for setting value tracking.

RSLogix 5000 configuration steps

DECS-250 exchanges data with Logix PLC through ControlNet or EtherNet/IP, and all configurations are completed in RSLogix 5000.

3.1 Adding Modules

Under I/O Configuration, right-click on 1756-CNB (R) (ControlNet Bridge) and select "New Module".

Select "1407-CGCM" (a compatible model of DECS-250) and click Create.

Enter Major Revision (host firmware major version, such as 4), which cannot be changed thereafter; Minor Revision corresponds to the firmware sub version (such as 25).

Set the module name, ControlNet node address (MAC ID), and select the electronic lock method (recommended Compatible Module or Exact Match).

3.2 Configuration Tab

Double click the module to open the properties dialog box, and configure the following tabs in sequence:

Generator tab

Rated Frequency (50/60Hz), Rated Voltage (line voltage) Rated Current、Rated Power（kVA）、Rated Field Voltage、Rated Field Current—— Fill in according to the generator nameplate.