ABB PCD235 excitation controller unit (Unitrol/AC800PEC series)
PCD235 is a high-performance excitation controller/CIO unit designed by ABB specifically for generator excitation control. It belongs to the core module of Unitrol excitation system and AC800PEC platform, and is used for automatic voltage regulation (AVR), excitation control, power system stability (PSS), and excitation protection of synchronous generators.

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1、 Product Information
Model: PCD235 (commonly used: PCD235A101/3BHE03205R0101, PCD235B1101, PCD235C101)
Series: Unitrol (excitation), AC800PEC (power control) Symphony Plus
Manufacturer: ABB
Core functions: Generator excitation regulation AVR、PSS、 Excitation protection, synchronous grid connection control
Software tools: PCM600 (Protection and Control Configuration), Control Builder M (IEC 61131-3 Programming)
Safety level: meets the SIL2/SIL3 excitation protection requirements of the power system
2、 Technical parameters and specifications
1) Core performance
Processor: PowerPC+FPGA, 100 μ s control cycle (fastest 25 ns task)
Memory: 32 MB RAM/512 MB Flash
Control algorithm: AVR (PID/Fuzzy) PSS2A、 Overexcitation/underexcitation limit, V/Hz limit, demagnetization protection (40), excitation overcurrent (51)
2) I/O interface (excitation specific)
Analog input AI: 3 channels, ± 10 V/± 20 mA, accuracy ± 0.1% (collecting terminal voltage, excitation voltage/current, rotor temperature)
Analog output AO: 3 channels, ± 10 V, accuracy ± 0.2% (output excitation current command, PSS signal)
Digital input DI: 8 channels (24 VDC), used for switch values, synchronization signals, and protection contacts
Digital output DO: 8 channels (relay/24 VDC), used for excitation switching, alarm, and tripping
Temperature interface: 3-channel PT100/PTC, monitoring excitation winding/rectifier bridge temperature
3) Communication and Redundancy
Ethernet: 2 × 10/100 Mbps (IEC 61850, Modbus TCP, DNP3)
Serial port: RS485 (Modbus RTU), RS232
Fiber optic: 1 set of 3 fiber optic cables (primary and backup redundant synchronization, delay ≤ 100 μ s)
Redundancy: 1:1 hot standby (undisturbed switching, meeting the requirements of critical units)
4) Electrical and Environmental
Power supply: 24 VDC (18-30 VDC), power consumption approximately 4 W
Working temperature: 0 ℃~+60 ℃ (industrial grade)
Storage temperature: -40 ℃ to+85 ℃
Protection level: IP20 (installed inside the cabinet)
Dimensions (width x height x depth): 119 mm x 186 mm x 135 mm (same as AC800M rack)
Weight: Approximately 1.2 kg
3、 Usage scenarios
Thermal power/gas-fired power generation: excitation control of steam turbine generators AVR、PSS、 Grid connection and reactive power regulation
Hydropower: excitation system for hydro generators, low/over excitation protection, voltage and reactive power optimization
Nuclear power/thermal power: synchronous generator excitation, grid stability control, excitation fault diagnosis
Industrial power generation: precise control of voltage/reactive power for self owned power plants and islanded operating units
Power system stability: PSS suppresses low-frequency oscillations and enhances the transient stability limit of the power grid
4、 Related models (PCD235 series)
PCD235A101 (3BHE032025R0101): Standard excitation controller, basic AVR/PSS, most commonly used
PCD235B1101 (3BHE03205R101): Enhanced, Extended I/O+Advanced Excitation Protection
PCD235C101 (3BHE057901R0101): High performance model, Gigabit Ethernet+high-speed fiber redundancy, SIL3 certification
PCD231B101: Compact excitation CIO, suitable for small and medium-sized units
PCD335: Excitation expansion module, adding I/O and communication interfaces
5、 Core advantages
Dedicated excitation algorithm: Built in AVR/PSS/excitation protection, plug and play, no need for complex programming
High speed real-time control: FPGA+multi-core, 100 μ s level response, adapted to transient processes
High reliability redundancy: native 1:1 hot standby, fiber optic synchronization, disturbance free switching, ensuring that the unit does not shut down
Complete power communication: IEC 61850/Modbus/DNP3, seamlessly integrated with power plant DCS/monitoring system
Wide temperature anti-interference: industrial grade temperature and EMI protection, suitable for strong electromagnetic environment of excitation cabinet