The IS200EPCTG1A is an Exciter PT/CT Interface Board designed by General Electric (GE) for its EX2100™ Excitation Control System. This board is the standard version within the EPCT series, primarily used to isolate and condition field generator Potential Transformer (PT) and Current Transformer (CT) signals before transmitting them to the control system, providing precise generator voltage and current feedback signals for the voltage regulator.
The IS200EPCTG1A board features two sets of three-phase voltage transformer input channels and two sets of current transformer input channels (supporting either 1 A or 5 A current levels). Output signals from all isolation transformers are sent via cables to the EMIO board in the control rack. Additionally, the board provides one non-isolated analog input channel, configurable as ±10 V voltage input or 4-20 mA current input, for connecting other field signals.
In a Simplex control system, signals are sent to the EMIO board in the M1 controller via the J305 connector. In a Redundant control system, signals are distributed to the EMIO boards in the M1, M2, and C controllers via three connectors J305, J308, and J315, achieving redundant measurement.
The IS200EPCTG1A board designs reliability and safety for field applications:
Voltage Inputs are fuse-protected, with cable lengths up to 1000 feet (#12 AWG wire).
Current Inputs use non-pluggable terminal blocks (TB2, TB3) to prevent dangerous high voltages from CT open circuits.
Isolation Transformers provide electrical isolation, ensuring control side safety.
Test Points offer 12 voltage test points (TP1-TP12) for convenient on-site commissioning and troubleshooting.
Isolation Switches, allow safe board replacement under energized conditions.
The board includes two three-phase voltage isolation transformers (T1, T2), four current isolation transformers (T3-T6), one removable 24-terminal voltage input terminal block (TB1), two non-removable 4-terminal current input terminal blocks (TB2, TB3), three 25-pin Sub-D output connectors (J305, J308, J315), one analog input type selection jumper (JP1), and 12 test points. The board design meets industrial-grade standards and is suitable for critical measurement applications in power plant excitation systems.
II. Main Functions
The primary functions of the IS200EPCTG1A include, but are not limited to, the following:
1. Generator Voltage Measurement
The IS200EPCTG1A board receives three-phase voltage signals from the customer's potential transformers via the TB1 terminal block. Voltage inputs are nominally 115 V rms (50/60 Hz), and each input is fuse-protected. Two isolation transformers on the board convert the input voltages to low-level signals for three-phase open delta voltage measurement. For a 115 V rms input, the secondary output is 1.533 V rms. The measured signals are sent to the EMIO board via connectors J305, J308, and J315.
2. Generator Current Measurement
The IS200EPCTG1A board receives two current signals from current transformers via terminal blocks TB2 (Phase A) and TB3 (Phase C). Each CT provides 0-1 A rms and 0-5 A rms windings, but only one is connected to the EPCT board. Cable length can be up to 1000 feet, and wire gauge up to #10 AWG. Current isolation transformers isolate the input current and convert it to low-voltage signals sent to the EMIO board via connectors.
Important Safety Design: Terminal blocks TB2 and TB3 are non-removable to prevent accidental opening of CT circuits under load, which would create dangerous high voltages.
3. Analog Input
The IS200EPCTG1A board provides one non-isolated analog input channel, configurable via jumper JP1 for two types:
This input channel can be used for other field signals such as temperature, pressure, or position. Cable length can be up to 300 meters, with a maximum two-way cable resistance of 15 ohms. The analog input signal is simultaneously distributed to all three controllers via connectors J305, J308, and J315.
4. Signal Isolation and Distribution
All voltage and current measurement signals are electrically isolated via isolation transformers, ensuring control side safety. The isolated signals are output through three 25-pin Sub-D connectors (J305, J308, J315):
J305: Connects to the EMIO board in the M1 controller.
J308: Connects to the EMIO board in the M2 controller.
J315: Connects to the EMIO board in the C controller.
In simplex systems, only J305 is used. In redundant systems, all three connectors are used, providing redundant distribution of measurement signals.
5. Test Points
The IS200EPCTG1A board features 12 test points (TP1-TP12) located to the right of the transformers for on-site commissioning and troubleshooting:
TP1-TP4: PT1 secondary voltage signals (AB, BC)
TP5-TP8: PT2 secondary voltage signals (AB, BC)
TP9-TP10: CT Phase A secondary current signals
TP11-TP12: CT Phase C secondary current signals
These test points can be measured using an oscilloscope or multimeter, but care should be taken not to ground them through the measuring device.
III. System Applications
1. Application in EX2100 Excitation Control System
The IS200EPCTG1A is a critical interface board for acquiring generator voltage and current signals within the EX2100 Excitation Control System. Its roles within the system include:
Voltage Feedback: Isolates and conditions three-phase generator voltage signals, sending them to the EMIO board for the Automatic Voltage Regulator (AVR) to perform voltage regulation and reactive power control.
Current Feedback: Isolates generator current signals (typically phases A and C) and sends them to the control system for field current limiting, load monitoring, and protection.
Analog Input: Provides a general-purpose analog input channel for other process signals related to the excitation system, such as temperature, pressure, or position.
Redundant Signal Distribution: In redundant systems, simultaneously distributes measurement signals to three controllers (M1, M2, C), ensuring uninterrupted measurement signals even if one controller fails.
2. Typical Application Scenarios
Voltage and current measurement for synchronous generator excitation systems
Feedback for Automatic Voltage Regulators (AVR) in steam turbine generators
Excitation control for hydro turbine generators
Excitation systems for gas turbines
Excitation control for industrial synchronous motors
IV. Detailed Interface Description
1. TB1 Terminal Block (Voltage Inputs)
TB1 is a removable 24-terminal block for connecting two sets of three-phase voltage transformer signals and one analog input. Terminal assignments are as follows:
| TB1 Screw | Signal Description |
| 1 | Potential Transformer 1, Phase A (PT1_PHA) |
| 2 | Potential Transformer 1, Phase B (PT1_PHB) |
| 3 | Potential Transformer 1, Phase C (PT1_PHC) |
| 4 | Not Connected |
| 5 | Potential Transformer 2, Phase A (PT2_PHA) |
| 6 | Potential Transformer 2, Phase B (PT2_PHB) |
| 7 | Potential Transformer 2, Phase C (PT2_PHC) |
| 8-20 | Not Connected |
| 21 | Analog Input High (Ain H) |
| 22 | Not Connected |
| 23 | Analog Input Low (Ain L, Return) |
| 24 | Shield (SCOM) |
2. TB2 and TB3 Terminal Blocks (Current Inputs)
TB2 (Phase A) and TB3 (Phase C) are non-removable 4-terminal blocks to prevent CT open circuits:
| TB2 Screw | Signal Description | TB3 Screw | Signal Description |
| 1 | CT Phase A, 5 A High (Cur_Pha 5H) | 1 | CT Phase C, 5 A High (Cur_Pha 5H) |
| 2 | CT Phase A, 5 A Low (Cur_Pha 5L) | 2 | CT Phase C, 5 A Low (Cur_Pha 5L) |
| 3 | CT Phase A, 1 A High (Cur_Pha 1H) | 3 | CT Phase C, 1 A High (Cur_Pha 1H) |
| 4 | CT Phase A, 1 A Low (Cur_Pha 1L) | 4 | CT Phase C, 1 A Low (Cur_Pha 1L) |
Note: Only one of the 1 A or 5 A windings for each CT should be connected to the EPCT board; the other winding is left unused.
3. J305, J308, J315 Connectors
Three 25-pin Sub-D connectors transmit measurement signals to the EMIO board. Pin assignments for J305 (to M1) as an example:
| Pin | Nomenclature | Description |
| 1 | CUR_AL_M1 | Current Phase A Input Low – To M1 |
| 2 | CUR_AH_M1 | Current Phase A Input High – To M1 |
| 3 | CUR_CL_M1 | Current Phase C Input Low – To M1 |
| 4 | CUR_CH_M1 | Current Phase C Input High – To M1 |
| 5 | PT1A_N_M1 | Voltage Input 1 Phase A Negative – To M1 |
| 6 | PT1A_P_M1 | Voltage Input 1 Phase A Positive – To M1 |
| 7 | PT1B_N_M1 | Voltage Input 1 Phase B Negative – To M1 |
| 8-13 | — | Not Connected |
| 14 | AIN_P | Analog Input Positive |
| 15 | AIN_N | Analog Input Negative |
| 16 | PT2B_P_M1 | Voltage Input 2 Phase B Positive – To M1 |
| 17 | PT2B_N_M1 | Voltage Input 2 Phase B Negative – To M1 |
| 18 | PT2A_P_M1 | Voltage Input 2 Phase A Positive – To M1 |
| 19 | PT2A_N_M1 | Voltage Input 2 Phase A Negative – To M1 |
| 20 | PT1B_P_M1 | Voltage Input 1 Phase B Positive – To M1 |
| 21-25 | — | Not Connected |
4. Test Points
| Test Point | Description |
| TP1 | PT1 AB Voltage Signal High |
| TP2 | PT1 AB Voltage Signal Low |
| TP3 | PT1 BC Voltage Signal High |
| TP4 | PT1 BC Voltage Signal Low |
| TP5 | PT2 AB Voltage Signal High |
| TP6 | PT2 AB Voltage Signal Low |
| TP7 | PT2 BC Voltage Signal High |
| TP8 | PT2 BC Voltage Signal Low |
| TP9 | CT Phase A Current Signal High |
| TP10 | CT Phase A Current Signal Low |
| TP11 | CT Phase C Current Signal High |
| TP12 | CT Phase C Current Signal Low |
5. Jumper JP1
| Jumper Position | Description |
| V | ±10 V dc voltage input |
| MA | 4-20 mA current input |
V. Installation and Replacement
1. Mounting Location
The IS200EPCTG1A board is mounted inside the EX2100 exciter auxiliary cabinet, secured to a mounting plate with three screws. The board should be located for easy wiring and maintenance access, ensuring the distance to PTs and CTs does not exceed specified limits.
2. Offline Replacement Procedure (System De-energized)
Safety Warnings:
WARNING: To prevent electric shock, turn off power to the excitation system and follow the complete de-energizing procedures outlined in the User's Guide (GEH-6631). Adhere to all local Lock-out/Tag-out practices.
CAUTION: To prevent component damage caused by static electricity, treat all boards with static sensitive handling techniques. Wear a wrist grounding strap and store boards in anti-static bags.
SPECIAL WARNING: Before disconnecting CT wiring, the CT isolation switches MUST be opened first. Failure to do so will result in dangerously high voltages due to an open CT circuit.
Replacement Steps:
Verify Power Off: Ensure the excitation system is completely de-energized. Test circuits before opening the control cabinet door.
Open Isolation Switches: Open the PT and CT isolation switches. Test the PT and CT circuits to confirm zero voltage.
Label Cables: Verify all cables are correctly labeled according to the markings on the board for easy reconnection.
Disconnect Cables:
Loosen the two screws securing TB1 and remove the TB1 terminal block (leaving external wiring attached).
Disconnect wiring from TB2 and TB3.
Remove connectors J305, J308, and J315.
Remove Old Board: Remove the three screws holding the EPCT board and take out the old board.
Inspect New Board: Verify that the JP1 jumper setting on the new board matches the original board.
Install New Board: Orient the new board in the same position as the removed one, align with mounting holes, and secure with the three screws.
Reconnect Cables:
Reinstall TB1 terminal block and tighten its screws.
Reconnect wiring to TB2 and TB3.
Reconnect connectors J305, J308, and J315.
Restore Power: Close the PT and CT isolation switches. Close the cabinet door, restore power to the excitation system following procedures, and test operation.
3. Online Replacement Procedure (System Running)
A failed EPCT board can be replaced while the excitation system is running, provided the system is operating in manual regulator mode.
Risk Warning: During online replacement, controllers, power supplies, and terminal boards remain energized and active. Extreme caution must be taken to avoid touching other live parts or causing short circuits. The exciter MUST be switched to manual regulator mode before starting.
Replacement Steps:
Switch to Manual Mode: Switch the excitation system to manual regulator mode via the keypad.
Open Isolation Switches: Open the control cabinet door. Open the PT and CT isolation switches.
Verify De-energized: Test the PT and CT circuits to confirm zero voltage.
Disconnect Cables: Same as offline procedure.
Remove Old Board: Remove the two screws holding the EPCT board (note: the document specifies two screws here, which may differ from the three in the offline procedure; refer to the actual site configuration) and take out the old board.
Install New Board: Same as offline procedure.
Reconnect Cables: Same as offline procedure.
Close Isolation Switches: Close the PT and CT isolation switches. Verify input signals are present using the test points.
Return to Automatic Mode: Close the cabinet door. Switch the excitation system back to automatic regulator mode via the keypad.
