The DS200SDCCG5A, or Drive Control Card, is explicitly defined as the main processor board within the EX2000 Digital Excitation System. It is not merely a simple input/output interface module but a central processing unit integrating the system's core algorithms, real-time control logic, and high-speed computing capabilities. Its design goal is to replace the complex discrete components and hard-wired logic of traditional analog excitation regulators with a highly integrated, programmable digital solution, offering more precise, flexible, and reliable excitation control.
Within the EX2000 system, the DS200SDCCG5A assumes the following core missions:
Executing Control Algorithms: Runs core control and protection algorithms such as Automatic Voltage Regulation (AVR), Manual Voltage Regulation (FVR), Overexcitation Limiting (OEL), and Underexcitation Limiting (UEL).
Processing Input/Output Signals: Manages and processes all signals from generator potential transformers (PTs), current transformers (CTs), bridge feedbacks (voltage, current), status inputs, etc.
Generating Control Commands: Calculates and outputs the firing pulses for the Silicon Controlled Rectifier (SCR) bridge, precisely controlling the excitation power output.
System Coordination and Communication: Acts as the hub for communication within the controller module and with peripherals (e.g., Operator Station, simulator).
In essence, the DS200SDCCG5A is the physical embodiment of the intelligence and high performance of the EX2000 excitation system. Its performance directly determines the static accuracy, dynamic response speed, and overall reliability of the entire excitation system.
2. Hardware Architecture and Design Features
The hardware design of the DS200SDCCG5A reflects the advanced, high-reliability industrial control concepts of its era (document publication period):
Multi-Processor Parallel Architecture:
The most notable feature of the DS200SDCCG5A is its use of three independent 16-bit microprocessors, efficiently coupled and sharing data via Dual-Ported Random Access Memory (RAM). This architecture offers multiple advantages:
Functional Separation and Specialization: Different processors can focus on different tasks (e.g., one for voltage regulation calculations, one for protection logic, one for communication handling), improving code efficiency and real-time performance.
Redundancy and Reliability: Critical functions can be cross-checked between processors, enhancing system fault tolerance.
High Performance: Parallel processing capability enables the real-time execution of complex control algorithms (e.g., PSS - Power System Stabilizer) and processing of numerous I/O signals.
Powerful Expansion and Interface Capability:
External Dual-Ported RAM Expansion: The card supports connecting two external dual-ported RAMs, greatly expanding data processing and storage capacity, reserving space for complex configurations and future functional upgrades.
General-Purpose Interface Circuits: Incorporates rich general-purpose interface circuits, allowing flexible connection with other printed wiring boards in the EX2000 system (e.g., DCFB, SLCC, NTB/3TB) to form excitation systems tailored to different application needs (terminal-fed, bus-fed, single/multi-bridge).
Customer I/O Processing: Directly controls and processes input/output signals related to customer equipment.
Watchdog and Reset Protection:
The card features comprehensive hardware watchdog protection that can automatically trigger a system reset if software operation becomes abnormal, preventing control system "runaways" that could lead to equipment incidents. Clear reset pathways are provided:
Hardware Reset: By pressing the onboard RESET button.
External Signal Reset: By applying +5 to +24 V dc to a customer interface point (connected to the NTB/3TB).
Important Safety Warning: The documentation specifically emphasizes that a hard reset must NOT be initiated when the unit is running, as it will cause a unit trip. This underscores its critical role in the operational safety chain.
Noise Immunity and Industrial-Grade Design:
As equipment intended for harsh industrial environments like power plants, the DS200SDCCG5A design inherently follows high-level Electromagnetic Compatibility (EMC) standards. It employs multi-layer board design, high-quality components, and rigorous testing procedures to ensure stable operation in environments with strong electromagnetic interference.
3. Software Functionality and Configurability
The power of the DS200SDCCG5A stems not only from its hardware but also from the software architecture it hosts. The EX2000 application software employs a modular "software block" design. These functional blocks (such as Proportional-Integral regulators, function generators, logic gates, signal level detectors, etc.) act like building blocks. They can be flexibly configured and interconnected using GE's proprietary "Control System Toolbox" to form complete control logic.
As the main processor, the DS200SDCCG5A is responsible for interpreting and executing these software blocks. Its primary implemented software functions include:
Automatic Voltage Regulator (AVR):
The core is a Proportional-Integral (PI) regulator. It compares generator terminal voltage feedback with a setpoint to generate an error signal, which is processed to output a control signal to the firing circuit.
Supports Reactive Current Compensation (RCC) for proper reactive power sharing between paralleled units. The compensation level can be easily adjusted via software parameters (e.g., EE.3791 ASPRCC) and can even be set negative for Line Drop Compensation (LDC).
Features advanced functions like preset values, anti-windup protection, and high/low gain switching (for hot backup systems).
Manual Voltage Regulator (FVR):
Takes over control when the AVR drops out (e.g., due to PT failure), directly regulating the exciter/bridge output voltage.
In automatic mode, the FVR output precisely tracks the AVR output, ensuring bumpless transfer between auto and manual modes.
Limiting and Protection Functions:
Overexcitation Limiter (OEL): During online operation, monitors rotor winding heating via an I⊃2;t (current squared time) model, providing inverse-time protection. Offline, it provides simple overcurrent limiting to prevent overfluxing. The DS200SDCCG5A runs the associated Protection Inverse Time block (PRIT1) and signal level detection logic.
Underexcitation Limiter (UEL): Prevents the generator from entering an unstable operating region or stator end-core overheating. A software-implemented UEL curve (five-segment piecewise linear function) works in conjunction with a PI regulator to dynamically limit the lower bound of excitation current.
Volts per Hertz (V/Hz) Limiter: Prevents magnetic saturation of the generator and connected transformers due to excessive voltage-to-frequency ratio during start-up and shutdown.
Instantaneous Overcurrent Trip (IOC): Rapidly blocks firing pulses when the bridge current exceeds a preset instantaneous threshold, protecting power semiconductors.
Firing Pulse Generation:
The DS200SDCCG5A ultimately takes the outputs from the AVR, FVR, or FCR (Field Current Regulator), passes them through a "minimum value gate," and combines this with statuses like start/stop and IOC to generate the final SCR bridge firing code. This function is implemented via high-speed output circuits, ensuring precise pulse synchronization and timing.
4. System Integration and Collaborative Operation
The DS200SDCCG5A does not operate in isolation; it is the core member of the EX2000 controller module ecosystem:
Interaction with the Feedback System: Receives bridge DC voltage and current signals (attenuated via the SHVI/SHVM board) and generator voltage/current signals (from the PTCT board) via the DCFB (DC Power and Feedback Board). The DS200SDCCG5A is responsible for the software scaling and offset correction of these raw counts, converting them into the standardized per-unit values used by the internal control system.
Interaction with the Communication System: Communicates with the Operator Station (IOS or Innovation Series) and engineering stations (PCs running the Control System Toolbox) via the SLCC (LAN Communications Card) or the integrated communication functions on the LDCC. This enables remote monitoring, parameter modification, and fault diagnosis.
Interaction with the Terminal Interface: Connects to numerous customer digital and analog I/Os, as well as relay outputs, via the NTB/3TB (Drive Terminal Board).
Integration with the Simulator: The DS200SDCCG5A supports access to the internal simulation model generated by the TCCB (Microprocessor Application Board). By setting software jumpers (e.g., EE.570.0=1), the control system can be disconnected from the actual generator and use mathematical models for offline testing, personnel training, and fault rehearsal, greatly facilitating commissioning and maintenance.
5. Diagnostics, Maintenance, and Troubleshooting
The DS200SDCCG5A possesses powerful self-diagnostic capabilities, forming the cornerstone of the EX2000 system's high maintainability:
Built-in Diagnostic Tests:
Using the "Programmer module" (keypad and display) connected to the SLCC, maintenance personnel can run a series of diagnostic tests (e.g., Test 10 to view software revisions, Test 31/11 to monitor key variables, Test 13 for board tests).
Key variables (e.g., field voltage VFG, field current IFG) can be routed to the DAC1/DAC2 or MET1/MET2 test points on the NTB/3TB board for observation with an oscilloscope or multimeter.
Fault Indication and Classification:
When the DS200SDCCG5A detects an internal or external fault, it reports it via code on both its ten onboard diagnostic LEDs and the Programmer display. The fault code range is extensive (1 to 1023), covering everything from power anomalies and communication loss to software checksum errors and processor watchdog timeouts.
Faults are finely categorized as: Trip Faults (immediate shutdown), Filtered Faults (shutdown after delay), Non-latched Annunciated Faults, Latched Annunciated Faults, Locked Faults (require hard reset), etc. This classification helps maintenance personnel quickly assess fault severity and prioritize responses.
Commissioning and Parameter Tuning:
All control parameters (e.g., Kp, Ki of PI regulators, settings for various limiters, scaling factors) are stored in EEPROM as "EE Values." Authorized personnel can use the Control System Toolbox or the Programmer module to modify these parameters online or offline to optimize system performance or adapt to specific unit characteristics.
6. Application Value and Conclusion
As the heart of the EX2000 Digital Excitation System, the DS200SDCCG5A delivers multiple values to users:
Exceptional Control Performance: Based on high-speed multi-processors and advanced control algorithms, it provides fast and precise voltage and reactive power control, enhancing grid stability.
Extremely High Reliability: Hardware watchdog, multi-processor cross-checking, and a detailed fault diagnostic system minimize the risk of unplanned downtime.
Outstanding Flexibility: Modular software and configurable hardware allow easy adaptation to generators of different capacities and connection schemes.
Powerful Maintainability: The built-in simulator, rich diagnostic tools, and clear fault codes significantly reduce Mean Time To Repair (MTTR).
Future-Oriented Design: Expanded RAM and modular architecture provide potential for future functional upgrades (e.g., more complex PSS, additional protection logic).
