ABB UNITOL 6000 excitation system

Manual mode (MAN): Excitation current regulator based on PI filter. As a backup mode, the excitation current can be manually maintained when the PT signal is lost.

Compensation and limitation: including active/reactive current droop compensation, as well as a series of limiter circuits to ensure that the generator operates within safe limits:

Maximum/minimum excitation current limit

Maximum stator current limit based on cooling medium temperature

P/Q under excitation limit

Volt/Hertz (V/Hz) limit

Independent limiter in manual mode

Additional controls: power factor/reactive load control, and power system stabilizer (PSS).

2. Protection and monitoring

All monitoring and protection functions can be freely configured at three action levels:

Only issue an alarm signal: reminding the operation and maintenance personnel of the abnormality, but the unit continues to operate.

Switching to redundant channel: When the main channel fails, it automatically switches to the backup controller or converter to achieve disturbance free switching.

Immediate excitation trip: In case of serious faults such as overcurrent and demagnetization, immediately demagnetize to protect the generator rotor and stator.

The main available protection functions include overcurrent protection (instantaneous/inverse time limit), volt/hertz protection, demagnetization protection, rotor temperature monitoring, thyristor conduction monitoring, and actual value monitoring. This layered protection mechanism allows engineers to make the most reasonable response strategy based on equipment importance and fault severity.

3. Data and event recording

The internal event recorder of the system can process and store up to 2000 events with real-time timestamps. The data logger is pre configured with the function of collecting a large number of measurement values and internal signals, and automatically triggers when a fault occurs, greatly facilitating fault diagnosis and continuous improvement. In addition, a freely configurable high-speed recorder is provided for compliance testing or power grid event analysis.

4. Power System Stabilizer (PSS)

PSS is a key function for improving the dynamic stability of the power grid. It dampens power oscillations between the generator and the transmission system by modulating excitation. The UNITOL 6000 offers multiple advanced PSS options:

PSS 2A/2B/2C: Compliant with IEEE 421.5-2016 standard.

PSS 4B/4C: also compliant with IEEE standards, using different compensation structures.

Adaptive PSS (APSS): Developed by ABB Switzerland, it can dynamically optimize PSS parameters based on current grid conditions, maximize availability in weak grid environments, and avoid tripping caused by insufficient damping.

For the compliance audit of power grid companies, selecting and verifying appropriate PSS models is a key step in grid connected power generation projects.

Hardware Platform and Power Converter: Physical Bearer of High Performance Computing

The UNITOL 6000 is based on ABB's AC 800PEC high-performance processor platform. This platform is an extension of the ABB 800xA control system, designed specifically to meet the high-speed requirements of power electronic control.

1. Control unit (AC 800PEC)

The core advantage of AC 800PEC lies in its extremely high processing speed:

Fast I/O: The typical cycle time for analog and digital process I/O is 400 microseconds.

Integration of closed-loop and logic: High speed closed-loop control and conventional process logic can be implemented in the same controller.

Low speed I/O: Typical cycle time is 10 milliseconds, used for non critical signals.

Fast Logic: Programmable logic used for converter pulse control and fiber optic communication, with a cycle time as low as 25 nanoseconds.

This means that whether it is fast voltage regulation response or complex trigger pulse generation, AC 800PEC can be completed on a unified hardware platform, simplifying the system architecture and improving reliability.

2. Power Converter Series

The converter is selected based on the system's requirements for maximum excitation current and voltage. To meet high availability requirements, up to three redundant channels can be configured, and online maintenance functions can be optionally selected. The main converter series include:

D1 to D5 series:

The maximum voltage of single-phase or three-phase AC power supply is 1080 V.

The rated power frequency is 50 to 480 Hz (16 2/3 Hz can be customized).

Cooling fan noise ≤ 70 dB (A).

Compact fully integrated converter and control unit with integrated service panel.

UNL14300 series (for X-power):

The AC power supply voltage can reach up to 1500 V.

The high insulation test voltage can reach up to 7.5 kV.

Active current sharing control ensures that the current of each bridge arm is balanced during parallel operation.

Optional: Redundant fans that can be replaced during operation, drawer style design to support online safety maintenance and functional testing.

In engineering practice, the choice between D series or UNL series depends on the excitation voltage level of the generator, insulation requirements, and whether hot swapping maintenance is required. For example, for high-voltage excitation circuits or critical units that require online maintainability, UNL14300 is a more suitable choice.