GE IS200EDCFG1A Exciter dc Feedback Board

The IS200EDCFG1A is an Exciter DC Feedback Board designed by General Electric (GE) for its EX2100™ Excitation Control System. This board is primarily used to measure the field voltage and field current at the SCR bridge and transmit these signals via a high-speed fiber-optic link to the EISB board in the control panel. Fiber-optic communication provides both voltage isolation between the two boards and high immunity to electrical noise.

The core function of the IS200EDCFG1A board is to convert high-voltage, high-current signals from the power side into low-level signals usable by the control side through isolation and conversion. It receives voltage and current signals from the SCR bridge, amplifies them differentially, feeds them into a Voltage Controlled Oscillator (VCO) to convert them to frequency signals, and then sends them via fiber-optic transmitters to the EISB board for excitation regulation and protection by the control system.

The board designs flexibility for different application scenarios:

• Voltage Measurement: Provides seven voltage range selection jumpers to accommodate different PPT voltage levels from 140 V to 1300 V (later versions support 1400 V).

• Current Measurement: Measures field current via a DC shunt, with a maximum input signal of 500 mV.

• Fiber-Optic Communication: Supports two types of fiber optics, allowing selection based on transmission distance: Plastic Optical Fiber (POF) up to 10 m, or Hard Clad Silica (HCS) fiber up to 90 m. The minimum bending radius is 1.5 inches.

The board features one green LED indicator (PSOK) to indicate power supply status. The board is powered by an external ±24 V dc supply, and internal regulators generate +15 V dc, -15 V dc, and +5 V dc for the various circuits.

The IS200EDCFG1A board includes the following main interfaces and components:

• J16 Connector: +24 V dc power input

• P1 Connector: Field current shunt signal input

• E1 Stab-on Connector: Field voltage input (SCR bridge negative)

• CF OF Fiber-Optic Connector: Field current feedback pulse output

• VF OF Fiber-Optic Connector: Field voltage feedback pulse output

• JP1-JP6, JP9-JP10: Voltage range selection jumpers

• JP7, JP8: Fiber type selection jumpers

• PSOK LED: Green power status indicator

  
  

II. Main Functions

The primary functions of the IS200EDCFG1A include, but are not limited to, the following:

1. Field Voltage Measurement

The IS200EDCFG1A board measures the voltage between the SCR bridge negative terminal and the positive terminal of the current shunt. By selecting different resistor combinations via jumpers, the bridge voltage can be scaled down to suit different PPT voltage levels. The scaled signal is input to a differential amplifier. The amplifier's output voltage (-5 V to +5 V) controls a Voltage Controlled Oscillator (VCO), generating a frequency signal proportional to the voltage, which is sent to the EISB via fiber optics.

2. Field Current Measurement

Field current is measured across a DC shunt at the SCR bridge, generating a low-level signal with a maximum value of 500 mV across the shunt. This signal is input to a differential amplifier. The amplifier's output voltage (-5 V to +5 V) controls a VCO, generating a frequency signal proportional to the current, which is sent to the EISB via fiber optics.

3. Fiber-Optic Communication

The board uses two fiber-optic connectors (CF OF and VF OF) to send current and voltage feedback pulses, respectively. Fiber-optic communication offers the following advantages:

• High-Voltage Isolation: Complete electrical isolation between the power side and the control side, ensuring personnel safety.

• Noise Immunity: Fiber optics are immune to electromagnetic interference, ensuring high signal transmission quality.

• Long-Distance Transmission: Transmission distances up to 10 m or 90 m depending on the fiber type selected.

4. Power Supply

The IS200EDCFG1A board is powered by an external ±24 V dc supply, input via the J16 connector. Three onboard voltage regulators generate:

• +15 V dc: Powers analog circuits.

• -15 V dc: Powers analog circuits.

• +5 V dc: Powers digital circuits.

The green LED indicator PSOK is driven by the ±15 V outputs and lights up when the power supply is operating normally.

5. Flexible Configuration

The board features multiple jumpers for configuration based on site-specific conditions:

• Voltage Range Selection: Jumpers JP1-JP6 and JP9-JP10 select the PPT voltage level. Only one jumper can be inserted at any time.

• Fiber Type Selection: JP7 (current feedback) and JP8 (voltage feedback) are set independently to select Plastic Optical Fiber (POF) or Hard Clad Silica (HCS) fiber.

  
  

III. System Applications

1. Application in EX2100 Excitation Control System

The IS200EDCFG1A is a critical feedback board for measuring field voltage and current within the EX2100 Excitation Control System. Its roles within the system include:

• Field Voltage Feedback: Measures the field voltage output from the SCR bridge and transmits the voltage signal via fiber optics to the EISB board for closed-loop voltage control by the Automatic Voltage Regulator (AVR).

• Field Current Feedback: Measures the field current output from the SCR bridge and transmits the current signal via fiber optics to the EISB board for field current limiting, protection, and monitoring.

• Electrical Isolation: Provides complete electrical isolation between the power side and the control side via fiber-optic communication, ensuring the safety of low-voltage control circuits.

• Signal Conditioning: Converts high-voltage, high-current signals into low-level signals suitable for control circuit processing, with linearization.

2. Redundant Configuration

In systems requiring high reliability, three IS200EDCFG1A boards can be installed for redundancy. The excitation system can continue to operate even if one board fails. However, it is important to note that due to the high voltages involved, online replacement of a failed board is not supported, even in a redundant configuration. System power must be turned off for replacement.

3. Typical Application Scenarios

• Voltage and current feedback for synchronous generator excitation systems

• Voltage regulators for steam turbine generators

• Power units for hydro turbine generator excitation

• Excitation systems for gas turbines

• Upgrades and retrofits for industrial excitation systems

  
  

IV. Detailed Interface Description

1. Power Connector J16

J16 is a 2-pin connector for external ±24 V dc power input:

2. Current Input Connector P1

P1 is a 4-pin connector (2 pins used) for connecting the field current shunt:

3. Voltage Input Connector E1

E1 is a stab-on connector for field voltage input:

4. Fiber-Optic Connectors

5. Power Indicator

V. Jumper Configuration

The IS200EDCFG1A board has 10 jumpers for configuring the voltage range and fiber type.

1. Voltage Range Selection Jumpers (JP1-JP6, JP9-JP10)

These jumpers select the PPT voltage level of the SCR bridge. Only one jumper can be inserted at any time. Select the corresponding jumper based on the actual system voltage:

Important: Only one voltage range jumper can be inserted at a time. Inserting multiple jumpers simultaneously will cause measurement errors.

2. Fiber Type Selection Jumpers (JP7, JP8)

These two jumpers select the fiber type for current feedback and voltage feedback, respectively, and can be set independently:

Note: The minimum bending radius for these cables is 1.5 inches. Avoid excessive bending during installation.

VI. Installation and Replacement

1. Mounting Location

The IS200EDCFG1A board is mounted inside the auxiliary cabinet of the EX2100 excitation system, secured in top and bottom slides. During installation, pay attention to:

• Ensure the board is inserted in the correct orientation.

• Push lock pins must be fully engaged to prevent the board from loosening.

• Fiber-optic cables should avoid excessive bending, maintaining the minimum bend radius.

2. Replacement Procedure

Important Safety Warnings:

• The EDCF board involves high voltages and does NOT support online replacement. Even in redundant systems, power to the excitation system must be turned off before replacement.

• Before replacing the board, follow the complete de-energizing procedures outlined in the Installation and Startup Guide (GEH-6631). Adhere to all local Lock-out/Tag-out practices. Allow time for capacitors to discharge.

• Use safety test equipment designed for high voltages to confirm circuits are de-energized before touching them.

• Adhere to ESD (Electrostatic Discharge) precautions when handling the board. Wear a grounding strap and store the board in anti-static bags.

Replacement Steps:

1. Verify Power Off: Ensure the panel containing the EDCF board is completely de-energized.

2. Open Cabinet Door: Open the auxiliary cabinet door. Using high-voltage test equipment, verify that circuits are de-energized.

3. Label Cables: Verify all cables are correctly labeled according to the markings on the board for easy reconnection.

4. Disconnect Cables:

• Grasp each side of the stab-on connector that joins with board terminal E1 and gently pull it loose.

• Disconnect connectors P1 and J16.

• Disconnect fiber-optic connectors CF OF and VF OF.

5. Unlock Board: Unlock the push lock pins holding the EDCF board in the top and bottom slides.

6. Remove Old Board: Slide the old board out of the slides and remove it.

7. Inspect New Board: Verify that the jumpers JP1 through JP10 on the new EDCF board are in the same positions as the original board.

8. Install New Board: Orient the new board in the same direction, slide it into the slides, push it fully in, and lock the push lock pins.

9. Reconnect Cables: Reconnect all cables and fiber-optic connectors as labeled, ensuring they are properly seated.

10. Restore Power: Close the auxiliary cabinet door, restore power to the excitation system following procedures, and test operation.