The UNS 2882a-P, known as the Extended Gate Controller (EGC), is a critical component within the ABB UNITROL® 5000 excitation system. It primarily serves as a redundant controller, designed to maintain basic system functionality in the event of a failure in the main control boards. The EGC is essential in dual-channel systems (e.g., D5x series) and is also widely used in dual auto-channel configurations with a backup controller (e.g., Q5x series).
The EGC features a complete field current regulation function and an independent gate control unit. Its design philosophy ensures that the system can maintain the most critical protection and control functions even if primary devices like the COB or MUB fail, thereby significantly enhancing the reliability and fault tolerance of the entire excitation system.
2. Key Features & Functions
1. Redundant Controller Function
The EGC incorporates a fully functional field current regulator for manual control mode, capable of taking over system control if the main controller fails. This regulator has independent setpoint generation, feedback acquisition, and pulse output capabilities, ensuring stable system operation during emergencies.
2. Independent Gate Control Unit
Unlike the gate control unit in the COB, the EGC supports a wider frequency range, suitable for various power systems such as 16⅔ Hz, 50 Hz, and 60 Hz. This flexibility allows the UNITROL 5000 system to be applied in railway power supply and other specialized industrial frequency applications.
3. Protection and Monitoring Functions
The EGC integrates multiple protection functions, including:
Inverse Time Overcurrent Protection, compliant with ANSI 51.
Instantaneous Overcurrent Protection, compliant with ANSI 50.
DC Short-Circuit Detection and Limitation.
Frequency Measurement.
High-frequency firing pulse chain generation.
These functions ensure the system can respond quickly to critical faults even in backup mode.
4. Independent Power Supply
The EGC is powered by an independent 24 VDC source, separate from the COB or MUB power systems. This further enhances its survivability and operational independence during a main system failure.
3. Working Principle & System Integration
1. Control System Architecture
As a backup to the COB, the EGC features independent hardware and software design. It connects to devices like the COB and MUB via ribbon cables, receiving status signals from the main system. It can automatically or manually switch to backup mode upon detecting a main system failure.
2. Regulator Operating Principle
In backup mode, the EGC's current regulator employs a Proportional-Integral (PI) control structure. Its proportional gain (KCR) and time constant (TCR) can be adjusted in multiple steps via hardware switches. Users can select appropriate parameters based on actual system characteristics (e.g., field winding time constant, load characteristics) to ensure optimal regulation performance.
3. Firing Pulse Generation
The EGC's internal high-frequency pulse generator produces a 62 kHz firing pulse chain. These pulses are optically isolated and sent to the GDI for power amplification, ultimately driving the thyristor bridge. Its wide pulse phase control range supports both rectifier and inverter operating modes, making it suitable for four-quadrant operation systems.
4. Protection Logic and Action
The EGC's protection functions are completely independent of the COB. Its overcurrent protection is divided into two stages:
Protection actions can be configured for alarm or trip and feature adjustable time delays to prevent maloperation.
4. Device Configuration & Settings
1. Hardware Configuration Switches
The primary configuration of the EGC is performed via an 8-position DIL switch S450:
| Position | Parameter | OFF State | ON State |
|---|
| 1 | Rated Frequency | 50/60 Hz | 16⅔ Hz |
| 2 | Switch Type | AC Switch | DC Switch |
| 3 | Switch Control | FCB does not open | For OFF command |
| 4 | Twin Converter | NO | YES |
| 5 | System Switch D5<>A5 | D5 System | A5 System |
| 6 | KCR Range Switch | Range 1 (0.1~7.5) | Range 2 (0.1~17.8) |
| 7 | TCR Range Switch | Range 1 (10~80 ms) | Range 2 (0.1~0.38 s) |
| 8 | t(I>) Range Switch | Range 1 (8~15 s) | Range 2 (16~90 s) |
2. Protection Parameter Settings
The EGC provides several hexadecimal rotary switches for setting protection parameters:
Start-up Overcurrent Setpoint: 1.05 ~ 1.8 x rated value.
Instantaneous Overcurrent Setpoint: 1.8 ~ 4.8 x rated value.
Inverse Time Delay: Selectable between two time ranges.
Current Regulator Gain (KCR): Adjustable on a logarithmic scale.
Current Regulator Time Constant (TCR): Supports pure P-mode or PI-mode.
Initial Setpoint (Ref. init): Adjustable from 20% to 65%.
Rectifier and Inverter Angle Limits: αmax 125°~170°, αmin 10°~55°.
3. Fuse and Power Supply
The EGC is equipped with an onboard 2A slow-blow fuse F600 to protect its internal power circuit.
5. Application Scenarios & System Advantages
1. Suitable for High-Reliability Applications
Ideal for scenarios with extremely high reliability requirements, such as main excitation systems in power plants, large synchronous motor drives, and railway traction power supply.
2. Supports Multiple System Architectures
D5x Dual-Channel Systems: The EGC acts as the backup controller for the second channel.
Q5x Dual Auto-Channel + Backup Controller Systems: The EGC serves as the third layer of protection.
Single-Channel System + EGC Backup: Provides a cost-effective, highly reliable backup solution.
3. Flexible Frequency Adaptability
Supports various power system frequencies like 16⅔ Hz, 50 Hz, and 60 Hz, making it suitable for different power standards worldwide.
