GE IS200EGDMH1AGG Exciter Ground Detector Module

The IS200EGDMH1AGG is a high‑performance exciter ground detector module manufactured by GE Industrial Systems as part of the EX2100™ excitation control series. This module is specifically engineered to detect ground faults in the field circuit of synchronous generators. It continuously monitors the leakage resistance between any point in the generator field circuit (on either the AC or DC side) and ground, providing a critical safety and protection function for the excitation system.

The IS200EGDMH1AGG mounts directly into the Exciter Power Backplane (EPBP) rack and features a double‑slot, double‑height (6U) Eurocard form factor. In a simplex excitation system, a single EGDM is used; in a redundant system, three modules operate together, configured as Controller (C), Master 1 (M1), and Master 2 (M2), to ensure high availability and continuous ground detection even during module replacement or maintenance.

This module works in conjunction with the EXAM attenuator module, which is housed in the High Voltage Module inside the Auxiliary Panel. The EXAM module senses the voltage across a precision ground sense resistor and sends the signal to the EGDM(s) via a nine‑conductor cable. The IS200EGDMH1AGG processes this signal and communicates with the exciter control system over fiber‑optic links, enabling real‑time measurement of field ground resistance. This capability is essential for preventing damage to the generator field winding and avoiding costly unplanned outages.

The suffix AGG indicates a specific revision and factory configuration that maintains full backward compatibility with all EX2100 control systems while incorporating the latest design enhancements. The module contains no user‑adjustable settings, making it highly reliable and easy to replace. It is designed to meet rigorous industrial standards for safety, electromagnetic compatibility, and environmental performance.

Functional Description

The IS200EGDMH1AGG is the core component of the ground detection function in the EX2100 excitation control system. Its primary purpose is to measure the resistance between the generator field circuit and ground. A low resistance reading indicates a ground fault, which can lead to serious damage if not addressed promptly.

In a redundant configuration, three EGDM modules are assigned roles as Controller (C), Master 1 (M1), and Master 2 (M2). The role of each module is determined by a set of program pins on the P2 backplane connector. The DSPX (Digital Signal Processor) board in the controller rack decides which master provides the drive signal to the sense resistor in the EXAM attenuator module. This decision is communicated over the EISB (Exciter Internal Serial Bus) to the C module via a fiber‑optic link. Upon receiving this information, the C module either energises or de‑energises a relay in the EXAM module (depending on whether M2 or M1 is the active master). Simultaneously, a differential signal is sent to M1 and M2 indicating the chosen master. This signal enables the signal generator on the active master and selects the test command source on each module.

The active master receives an oscillator signal from the DSPX over a fiber‑optic link. It converts this signal into a positive or negative 50‑volt square wave. This square wave is sent by cable to the EXAM module and applied to one end of the ground sense resistor. The resulting voltage drop across the sense resistor is proportional to the field circuit resistance to ground. The signal conditioner inside the IS200EGDMH1AGG receives an attenuated (10:1) differential signal from the sense resistor. It amplifies this signal with a unity‑gain differential amplifier that has a high common‑mode rejection ratio (CMRR), then converts the amplified signal into a frequency using a voltage‑controlled oscillator (VCO). The VCO drives a fiber‑optic transmitter that sends the frequency signal to the control system for processing.

The signal conditioner circuitry is powered by an isolated power supply to maintain personnel and equipment safety, given the high common‑mode voltage present at the sense resistor. The module also includes a test feature: the signal conditioner can measure the power amplifier output level by grounding the bridge side of the attenuated sense resistor on command from the control section.

The C module also generates a test command at each transition of the oscillator signal. This test command produces a non‑retriggerable 250‑ms test signal on each module (M1, M2, and C) to verify proper operation. The test command transitions must be separated by more than 250 ms for a new test signal to be generated.

Power Supply and Signal Generation

The power supply section of the IS200EGDMH1AGG receives 24 V dc from the appropriate EPSM (Exciter Power Supply Module) through the EPBP backplane. An internal DC‑DC converter generates the following voltages:

• ±65 V dc (non‑isolated) – supplies the power amplifier in the signal generator section.

• +5 V dc (isolated) – powers logic circuits and the fiber‑optic transmitter.

• ±15 V dc (isolated) – powers the signal conditioning circuits (differential amplifier and VCO).

The power amplifier output is a voltage source with an output impedance of less than 1.0 Ω. It produces a ±50 V square wave, current‑limited to approximately 80 mA. During normal operation, the period of this square wave is 5 seconds. During test operation, the period reduces to 400 ms to allow more rapid verification.

Hardware Characteristics

Physical Form Factor

• Size : Double‑slot, double‑height (6U) – occupies two adjacent slots in the EPBP rack.

• Mounting : Horizontal insertion into the backplane via edge connectors.

• Front Panel : Provides two fiber‑optic connectors, three green LED indicators, captive screws with ejector tabs, and the board designation label.

Connectors

Table 1 – J2C Connector Pin Description (IS200EGDMH1AGG)

LED Indicators

Three green LEDs are located at the top of the front panel. They provide immediate visual status of the module:

Test Points

Ten test points are accessible on the board for advanced troubleshooting and verification. Their locations are clearly marked on the printed wiring board.

Installation and Replacement Procedures

Handling Precautions

• Static sensitivity – The IS200EGDMH1AGG contains static‑sensitive components. Always wear a grounding wrist strap and handle the board only 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.

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

Offline Replacement (De‑energised System)

Use this procedure when the entire excitation system is shut down.

1. De‑energise the control panel following the EX2100 Installation and Startup Guide (GEH‑6631).

2. Open the cabinet door and test for zero voltage on all relevant circuits.

3. Label and disconnect all cables from the EGDM:

   • Remove the two fiber‑optic snap‑in connectors (U201 and U305).

   • If the J2C cable is connected to the backplane (external to the board), label and disconnect it.

4. Remove the board from the rack:

   • Loosen the top and bottom captive screws near the ejector tabs (these screws are captive and should not be fully removed).

   • Raise both ejector tabs to unseat the board from the backplane connectors.

   • Using both hands, gently pull the board straight out.

5. Slide the replacement IS200EGDMH1AGG into the correct slot, ensuring alignment with the card guides.

6. Seat the board by pressing firmly on the top and bottom of the faceplate simultaneously with your thumbs until the ejector tabs begin to engage.

7. Lower the ejector tabs and tighten the top and bottom captive screws evenly to fully seat the board.

8. Reconnect the fiber‑optic cables and any other cables removed.

9. Close the cabinet door and restore power. Verify that the upper green LED illuminates.

Online Replacement (Redundant System Only)

In a redundant EX2100 system, a failed EGDM can be replaced while the exciter remains online. The remaining two modules continue to provide ground detection.

1. Open the cabinet door and identify the failed EGDM using its front‑panel LEDs and Toolbox diagnostics.

2. De‑energise only the section of the EPBP rack that contains the failed EGDM. This is done by switching off the corresponding output of the Exciter Power Distribution Module (EPDM). Verify that the EPDM section’s LED is off and that the EPSM indicators for that section are off.

3. Confirm that control has automatically transferred to the other master. The middle LED on the active master module will be illuminated.

4. Disconnect the two fiber‑optic cables from the failed EGDM.

5. Remove the board using the ejector tabs and captive screws as described in step 4 of the offline procedure.

6. Install the new IS200EGDMH1AGG in the same slot, following steps 5‑7 of the offline procedure.

7. Reconnect the fiber‑optic cables.

8. Re‑apply power to that section of the EPBP rack via the EPDM. Verify that the upper green LED on the new EGDM illuminates and that the middle LED (if configured as master) or appropriate status appears.

9. Close the cabinet door. The system should automatically re‑integrate the new module.

Diagnostics and Maintenance

The IS200EGDMH1AGG does not require routine calibration. However, periodic checks using the test points and LED status are recommended. The EX2100 control system (via ToolboxST) provides diagnostic alarms for ground faults, module failures, and configuration mismatches.

Common LED interpretations:

• Upper LED off : No 24 V dc power from backplane. Check EPSM, EPBP connections, and fuses.

• Middle LED off (in redundant system when expected to be on) : Module not selected as master – normal if another module is active. If no master LED is lit on any module, check the program pins on P2 and the DSPX configuration.

• Lower LED off when master should be driving : Signal generator not active. Check the fiber‑optic oscillator input (U201) and the internal ±65 V supplies.

• All LEDs off : Board may be unpowered or completely failed.

Common diagnostic alarms:

• Ground fault alarm : Field resistance below the configured threshold. Investigate the generator field circuit immediately.

• Hardware incompatibility fault : The EGDM’s ID chip does not match the expected type. Verify that the correct EGDM variant (AGG) is installed and that the control system configuration is up to date.

• Master conflict : More than one module is trying to drive the sense resistor. Check the program pin settings and the integrity of the C module’s relay control.

Ordering Information

When ordering the IS200EGDMH1AGG, use the complete part number exactly as shown. The part number follows GE’s convention:

• IS200 – Innovation Series, 200‑class.

• EGDM – Functional acronym: Exciter Ground Detector Module.

• H1 – Generation/version.

• A – Base designator.

• G – Modifier (indicates specific coating, component selection, or factory configuration).

• G – Revision or additional modifier.

Warranty and Order Placement

• Warranty replacements (within the warranty period): Contact GE Industrial Systems Product Service Engineering:
  GE Industrial Systems
  Product Service Engineering
  1501 Roanoke Blvd.
  Salem, VA 24153‑6492 USA
  Phone (US): +1 888 GEA SERV (888 434 7378)
  Phone (International): +1 540 378 3280
  Fax: +1 540 387 8606

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

  • Complete part number: IS200EGDMH1AGG

  • 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.