The IS200EAUXH1A Exciter Auxiliary Interface Board is a core member of the I/O terminal board family within the General Electric (GE) EX2100e digital excitation control system. The EX2100e is GE's fourth-generation digital excitation platform, designed for steam, gas, and hydro turbine generators, and supports applications including static excitation systems, brushless exciter regulators, and Alterrex regulators. As a specific model of the Exciter Auxiliary Interface Board (EAUX), the IS200EAUXH1A serves as the central hub connecting the main controller to key peripheral equipment within the excitation system.
The IS200EAUXH1A communicates with the UCSx main controller via a High-Speed Serial Link (HSSL) and directly interfaces with the DC contactor, field flashing relays, generator circuit breaker status, de-excitation module, field ground detector, and AC and DC feedback signals. It centrally conditions and forwards a wide array of discrete control signals, analog feedback signals, and status monitoring signals, significantly simplifying system wiring and enhancing the modularity and control reliability of the excitation system.
System Positioning and Architecture Integration
Within the EX2100e control system, the control cabinet houses the controller boards, I/O boards, and power distribution modules. The IS200EAUXH1A is an I/O terminal board, typically installed in the control cabinet, and communicates via the High-Speed Serial Link Interface (HSLA) boards with the Compact High-speed Serial Link Expansion (CSLA) boards belonging to the M1, M2, and C controller sections. In a simplex control configuration, the IS200EAUXH1A interfaces only with the M1 controller; in a Triple Modular Redundant (TMR) configuration, it can interact with all three control sections—M1, M2, and C—simultaneously, enabling voting and redundant acquisition of critical signals.
The standout feature of the IS200EAUXH1A is its multi-function integration: a single board handles DC contactor driving, field flashing relay control, the generator 86G lockout signal input, de-excitation and Crowbar status monitoring, field voltage and current feedback reception, AC source feedback conditioning, and the field ground detection interface. This makes it the central information hub for the excitation system's auxiliary functions.
Detailed Core Functions
1. DC Contactor (41DC) Control
The IS200EAUXH1A directly drives the DC contactors 41A (and optional 41B) in the generator field circuit. The control signal originates from the UCSx controller, is transmitted via HSSL to the IS200EAUXH1A, and then output by the board's relay driver circuit to the contactor coils. The status of the contactors' auxiliary contacts is returned to the IS200EAUXH1A as feedback signals, forming a closed-loop monitoring system. The board supplies a wetted 125 V DC voltage for the contact inputs, ensuring reliable acquisition. For applications demanding higher response speeds, the IS200EAUXH1A supports the installation of an IS200EAUD daughterboard, which upgrades the standard 125 V DC coil driver to a high-speed contactor interface, providing approximately four times the forcing voltage for the initial 150 milliseconds, significantly shortening the contactor pickup time.
2. Field Flashing Relay (53A/53B) Control
During generator startup, a brief initial field current (approximately 10-20% of no-load field current) is required, which is supplied from the station battery through field flashing relays 53A and 53B. The IS200EAUXH1A receives the flashing command from the controller and, through its onboard driver circuits and contact voting logic, outputs a single control voltage that actuates the 53A and 53B relays in the auxiliary cabinet. In a TMR system, the drive signals from the three control sections are contact-voted on the IS200EAUXH1A to produce a single control level, ensuring that a single controller fault will neither falsely trigger nor fail to trigger the field flashing.
3. Generator 86G Lockout Signal Interface
The 86G is a dedicated generator protection contact input provided by the customer, typically a normally closed contact. The IS200EAUXH1A receives the 86G input and transmits its status to the controller via HSSL. When the 86G operates, the excitation system immediately disconnects from the generator field. Even if the controller software fails to respond correctly, this hardware loop guarantees a safe disconnect, achieving an independent fast protection function.
4. De-excitation and Crowbar Status Monitoring
During a generator trip, the energy stored in the field inductance must be dissipated through the De-excitation module (EDEX). The IS200EAUXH1A forwards the de-excitation command from the controller to the EDEX board and simultaneously receives the de-excitation and Crowbar status feedback signals (including Hall effect conduction sensor signals) from the EDEX. After conditioning, these signals are uploaded to the controller to confirm whether the energy dissipation circuit has operated correctly. If both independent firing control circuits fail, the EDEX will self-fire on anode-to-cathode overvoltage; the IS200EAUXH1A will also capture and report this backup action.
5. Field Voltage and Field Current Feedback
The DC field feedback is sent from the EDFF (Exciter DC Fanned Feedback) board to the IS200EAUXH1A via a fiber-optic link in the form of frequency signals. This fiber-optic isolation method provides extremely high voltage isolation and noise immunity. The IS200EAUXH1A receives the field voltage and field current feedback signals forwarded by the EDFF through the EAUX, and then transmits them to the controller over the HSSL. These signals are used by control software for functions such as Automatic Voltage Regulation (AVR), Manual Excitation Regulation (FVR/FCR), and Overexcitation Limiting (OEL).
6. AC Source Feedback
The three-phase AC voltage from the excitation transformer is measured by the EBAC (Exciter Bridge AC Feedback) board. After being stepped down by isolation transformers, the output signals are sent to the IS200EAUXH1A. The IS200EAUXH1A conditions these synchronization signals and fans them out to the M1, M2, and C controllers for synchronizing the firing pulses of the thyristor bridge. In a TMR configuration, the signals are fanned out on the IS200EAUXH1A to ensure each control section receives consistent voltage zero-crossing information.
7. Field Ground Detection Interface
Field ground detection is a vital protective function of the excitation system. The IS200EAUXH1A works in conjunction with the EXAM (Exciter Attenuation Module): the EAUX generates a low-frequency square wave signal (±50 V, 0.2 Hz), which is applied through the EXAM between the electrical midpoint of the generator field winding and ground. If a field ground fault occurs, leakage current flows through a sense resistor in the EXAM, and the resulting voltage signal is sent back to the IS200EAUXH1A via a nine-conductor cable. The IS200EAUXH1A digitizes this voltage signal and transmits it to the controller over HSSL, where software determines the ground fault presence and resistance value. In a redundant system, the test signal can be supplied by either M1 or M2, with the C controller managing a relay in the EXAM to switch the signal source, ensuring continuous ground detection even if one controller fails.
8. Power and Communication Interface
The IS200EAUXH1A is powered by the EDIS (Exciter Power Distribution) module. Its typical operating voltage is 28 V DC, derived from the EDIS's 125 V DC bus via a 28 V power supply module. The board integrates a High-Speed Serial Link (HSSL) interface, which connects through the HSLA board to the CSLA expansion port of the controller, enabling real-time data exchange.
Redundancy Support and Reliability Design
The IS200EAUXH1A is available in two groups to accommodate different system redundancy levels:
Group H1: For TMR redundant control, interfaces with the M1, M2, and C control sections. Critical I/O signals are voted upon among the three sections.
Group H2: For simplex control, interfaces only with the M1 controller.
In TMR applications, the IS200EAUXH1A, working with the redundant controller architecture, ensures that critical functions like DC contactor control and field flashing relay driving continue to operate normally even if one controller fails. This greatly enhances system availability. According to system design, the EX2100e redundant system can achieve a Mean Time Between Forced Outages (MTBFO) of 175,000 hours. As a key component within this system, the high-reliability design of the IS200EAUXH1A is fundamental to achieving this benchmark.
Environmental Adaptability and Physical Specifications
The IS200EAUXH1A is designed for installation inside the EX2100e control cabinet. Its operating ambient temperature range is 0 to 40 °C (32 to 104 °F), with a humidity range of 5 to 95%, non-condensing. The control cabinet is typically rated NEMA 1 or IP20, with an optional NEMA 12/IP54 sealed cabinet available, providing effective industrial environmental protection for the board. The board itself complies with GE's industrial control board design specifications, requires Electrostatic Discharge (ESD) protection during handling, and must be replaced using a grounding wrist strap and anti-static packaging.
