GE IS200EXAMG1AAB Exciter Attenuation Module

The IS200EXAMG1AAB is an Exciter Attenuation Module (EXAM) manufactured by GE Energy as part of the EX2100™ and EX2100e™ excitation control systems. This module provides the essential attenuation interface between the high‑voltage field bus of the exciter power bridge and the ground detection system. The EXAM works in conjunction with the Exciter Ground Detector Module (EGDM) in EX2100 systems, or with the Auxiliary Interface Board (EAUX) or Regulator Auxiliary Board (ERAX) in EX2100e systems, to detect ground faults in the generator field circuit.

The IS200EXAMG1AAB mounts in the High Voltage Interface (HVI) module located in the auxiliary cabinet. It senses high DC and AC voltages from the bridge (field bus and power potential transformer inputs) and scales them down to a usable level for the ground detector electronics. Only one EXAM module is required for both simplex and triple‑modular redundant (TMR) applications. The module contains no test points, fuses, or LED indicators; its status is inferred from the control system diagnostics.

The suffix AAB indicates a specific revision (likely EXAM_B or later) that includes the test relay function, which is used for verifying the ground detector’s operation by temporarily inserting a known ground resistance. This module is designed for high reliability and is built to withstand the harsh electrical environment of excitation systems.

Functional Description

The IS200EXAMG1AAB provides attenuation between the exciter field bus and the ground detector electronics (EGDM in EX2100, or EAUX/ERAX in EX2100e). The field bus voltages range from 125 V dc to 1000 V dc, and the AC line‑to‑line PPT (power potential transformer) voltages range from 120 V rms to 1300 V rms. The module uses precision resistor networks to divide these high voltages down to levels that can be safely processed by the ground detector.

In EX2100 systems, the EGDM generates a ±50 V square‑wave signal that is applied to one end of the sense resistor on the EXAM. The resulting voltage drop, which is proportional to the leakage current to ground, is fed back to the EGDM. The EXAM also contains a relay that selects which master (M1 or M2) controls the ground detection in TMR configurations. The default state of the relay (de‑energised) feeds back to the M1 section; when energised, it feeds back to the M2 section. The relay coil operates on 24 V dc with diode suppression, requiring less than 20 mA.

In EX2100e systems, the EAUX or ERAX board provides the ±50 V square‑wave signal and also controls a test relay on the EXAM. The test relay (present on EXAM_B and later versions, which includes this IS200EXAMG1AAB) temporarily inserts a known resistance to ground, allowing the system to verify the integrity of the ground detection function. The control system can initiate this test periodically or on demand.

The module also interfaces with the field flashing circuit via connector J1, which carries the 53B contact high and low signals from the flashing relay auxiliary contact. This connection ensures that the square‑wave signal is removed during field flashing to avoid interference.

The EXAM provides two selectable filter capacitance settings via jumpers JP1 and JP2:

• For PPT voltages less than 750 V rms – jumper across pins 2‑3

• For PPT voltages greater than 750 V rms – jumper across pins 1‑2

Additionally, jumper JP3 selects the filter range for lower PPT voltages:

• For PPT voltages less than 375 V rms – jumper across pins 2‑3

• For PPT voltages greater than 375 V rms – jumper across pins 1‑2

These settings optimise the module’s noise rejection and response time for the specific system voltage.

Hardware Characteristics

Physical Form Factor and Mounting

The IS200EXAMG1AAB is a small printed wiring board designed to mount on a Glastic® bracket inside the High Voltage Interface (HVI) module, which is located in the auxiliary cabinet. The board does not use a backplane; instead, it connects to external circuits via stab‑on connectors (E1, E2), plug connectors (J1, J2), a ground terminal (TB1), and is secured to the bracket via mounting pins. The board is not online‑replaceable; the exciter must be de‑energised before replacement.

Connectors and Terminals

J2 Connector Pin Signals (Ground Detector Connector)

J1 Connector Pin Description

E1 and E2 Stab‑on Connector Descriptions

Jumpers

Three adjustable jumpers (JP1, JP2, JP3) are used to configure the module for different PPT secondary voltages.

LED Indicators

The IS200EXAMG1AAB has no onboard LEDs. Status is indicated by the EGDM or EAUX/ERAX LEDs and the control system diagnostics.

Installation and Replacement Procedures

Handling Precautions

• Static sensitivity – The IS200EXAMG1AAB contains static‑sensitive components. Always wear a wrist grounding strap and handle the board at a grounded workstation. Store the board in its antistatic bag when not in use.

• De‑energise before handling – To prevent electric shock, turn off power to the exciter and verify zero voltage on all circuits before touching the board or any connected cables. Follow all local lock‑out/tag‑out procedures. Refer to GEH‑6631 (EX2100 Installation and Startup Guide) or GEH‑6780 (EX2100e Installation and Startup Guide).

• Do not remove or insert connections with power applied – Doing so may cause equipment damage or personal injury.

• Avoid dropping hardware – Mounting hardware or screws dropped into the cabinet can cause short circuits.

Replacement Procedure (De‑energised System)

The EXAM module is not online‑maintainable. The exciter must be de‑energised before replacement.

1. De‑energise the exciter following the appropriate installation and startup guide.

2. Open the auxiliary cabinet door and test for zero voltage on all circuits using high‑voltage testing equipment.

3. Label all cables connected to the EXAM board (J1, J2, stab‑on connectors E1 and E2, and TB1 ground wire) to simplify reconnection.

4. Carefully disconnect:

   • The two stab‑on connectors (E1, E2) by pulling them straight off.

   • The J1 locking connector (squeeze the latch to release).

   • The J2 9‑pin D‑sub cable (unscrew the thumbscrews).

   • The wire from TB1 (loosen the screw terminal).

5. Unseat the board from the Glastic bracket by gently lifting it off the mounting pins.

6. Before installing the replacement board, verify that the jumpers (JP1, JP2, JP3) are set to the same positions as on the original board (based on the system’s PPT voltage ratings).

7. Seat the new IS200EXAMG1AAB firmly onto the Glastic bracket, ensuring the mounting pins align with the board holes.

8. Reconnect all cables and the ground wire in the reverse order:

   • E1 (VBUS‑P) and E2 (VBUS‑N) – ensure they are fully seated.

   • J1 (flashing relay auxiliary) – listen for the latch click.

   • J2 (9‑pin ground detector cable) – tighten the thumbscrews finger‑tight.

   • TB1 (shield ground) – tighten the screw.

9. Close the auxiliary cabinet door and restore power. Verify that the ground detector function operates correctly (check control system diagnostics for any EXAM‑related alarms).

Ordering Information

When ordering the IS200EXAMG1AAB, use the complete part number exactly as shown. The part number follows GE’s convention:

• IS200 – Innovation Series, 200‑class.

• EXAM – Functional acronym: Exciter Attenuation Module.

• G1 – Generation/version.

• A – Base designator.

• A – Modifier (e.g., component variation).

• B – Revision (indicates EXAM_B or later, including test relay).

Warranty and Order Placement

• Warranty replacements (within the warranty period): Contact GE Energy Post Sales Service (contact details omitted per request).

• Spare parts or non‑warranty orders: Contact your nearest GE Sales or Service Office. Provide:

  • Complete part number: IS200EXAMG1AAB

  • Exciter serial number

  • Exciter Material List (ML) number

Note: All digits and letters in the part number are significant. GE may substitute later compatible revisions, but backward compatibility is assured. The factory should be consulted for any special configuration requirements.

Diagnostics and Maintenance

The IS200EXAMG1AAB has no on‑board diagnostics. Its health is monitored by the EGDM or EAUX/ERAX boards. The control system (via ToolboxST) can detect:

• Open or shorted sense resistor paths

• Loss of ±50 V square‑wave injection

• Relay failure (select relay or test relay)

• Ground faults (through the measured leakage current)

Common checks:

• Ground detector fails to detect known ground – Verify that the EXAM jumpers are set correctly for the system’s PPT voltage. Check that the E1/E2 connections are tight and free of corrosion. Measure continuity of the sense resistors (Rx, Ry, Rz) – they should be within tolerance.

• No square‑wave injected – Ensure the J2 cable is properly seated and that the EGDM (or EAUX/ERAX) is powered and configured as master.

• Relay does not change state – Apply 24 V dc to the appropriate relay pins and listen for a click. If no click, the relay may be stuck.

• Intermittent ground detection – Check the shield ground connection at TB1; poor grounding can introduce noise.

No routine calibration or adjustment is required. The module should be kept clean and dry. Periodic visual inspection for damaged components, cracked resistors, or loose connections is recommended during scheduled maintenance.