What is an Excitation System?
The function of an Excitation System is to supply DC voltage to the synchronous machine (generator, motor, or condenser) rotor winding (field), providing the machine’s excitation current. Without excitation current, the machine operates without a field, and consequently, no voltage is generated (induced) in the stator windings (only a reduced voltage will appear at the generator terminals, induced by the machine’s remanent magnetism).
Furthermore, the Excitation System is also essential in controlling the voltage generated by the machine, since varying the field voltage also varies the terminal voltage.
The main components of a modern Excitation System are: voltage regulator, power converter (rectifier), excitation transformer, field breaker, field flashing, and field overvoltage protection (crowbar).
Excitation System – RTX
RTX POWER is an Excitation System for generators, motors and synchronous condensers.
A modular, single-platform solution, it serves synchronous machines with nominal currents from 10 A to 7,000 A.
Main control and protection functions incorporated into RTX POWER: Digital Voltage Regulator (AVR), Field Current Regulator (FCR), Reactive Power Control (VAR), Power Factor Control (PF), Dynamic Limiters (OEL, UEL, SCL, MEL, VHL), Power System Stabilizer (PSS), and Synchronizer.
RELIABILITY AND ROBUSTNESS THROUGH DESIGN
The REIVAX panel design separates the RTX POWER main controller from the heat-emitting power section, preventing the electronic components from being unnecessarily exposed to heat. The electronic circuitry is protected from the heat in a dedicated enclosure or section within the cubicle.
The REIVAX design philosophy is to oversize each system by 20-30% compared to the nominal operating requirements to increase the excitation system life cycle.
FLEXIBLE REDUNDANCY OPTIONS
Depending on budget constraints and physical space limitations, REIVAX offers the most competitive solution. A selection of redundancy options is offered for control channels, I/O interfaces, thyristor bridges, power supplies, and fans.
FLEXIBLE RECTIFIER CONFIGURATIONS
Customers can select the configuration that best suits their needs. Current sharing between two (2) or more thyristor bridges or a hot standby configuration with two (2) thyristor bridges.
ARCHITECTURE
CONTROL
The CPX06 is a REIVAX programmable controller, based on an x86 CPU, developed for use in excitation systems, digital governors, and automation systems. It features a communication and time synchronization interface. The CPX06 also serves as the input, output, and control module and can be interfaced via a CANopen protocol or Ethernet communication. The control signal is sent to other devices through the CANopen interface and PWM outputs.
A complete enable and failover interface ensures high reliability of the CPX06, which can operate in both single-channel and redundant topologies.
POWER
The TTM01 is a digital controller used in excitation systems to trigger and monitor a thyristor bridge. It integrates with CPX06 controllers via the CANopen network, monitoring the temperature and conduction current of each thyristor, as well as the status of the bridge’s fuses and fans. Based on the control signal sent by the CPX06 and the measured synchronization voltages, it calculates the number of independent pulses to control the three-phase thyristor bridge. The generated pulses are isolated and amplified, then sent to each thyristor in the rectifier bridge.
The TTM01 allows bridge triggering for four-quadrant operation through a configuration that informs whether the controlled bridge operates with positive or negative current.
Additionally, REIVAX offers its own power drive hardware:
DRV01 – Nominal output current: 20A
Chopper-type power drive with DC output, suitable for use as a power interface in voltage regulators for generators and synchronous motors. It features internal measurements, and the analog outputs are isolated from each other, eliminating the need for external sensors.
DRV04
Retificador de tensão trifásico baseado em tiristores para aplicações em reguladores de tensão. O drive processa energia para excitação de máquinas síncronas e recebe um sinal de referência tipo PWM (Modulação por Largura de Pulso) do regulador, proporcional ao ângulo de disparo. Contém todos os sensores necessários para controle de tensão, medindo as principais grandezas envolvidas e dispensa o uso de sensores externos para fechar as malhas de controle do regulador. Corrente nominal de saída, de acordo com a versão escolhida: 75 A, 200 A ou 400 A.
EXCITATION SYSTEM TOPOLOGY
Different types of excitation systems have emerged over the years and have undergone significant technological evolution.
The two most common applications are met with RTX POWER, depending on the machine being controlled.
RTX POWER for Static Exciter
This system consists of a large-capacity power converter that supplies voltage and current directly to the machine’s field winding.
Its main advantages include very fast (almost instantaneous) response time and simplified maintenance, as it has no rotating parts.
This type of excitation is the most widely used today, primarily due to its very fast response time, which generally contributes to improving the stability of the electrical system.
Many older designs, which used a rotating exciter as the excitation system, have been converted to static excitation systems by disconnecting or even removing the rotating exciter.
RTX POWER for Rotating Exciter
A system consisting of a small-capacity power converter that supplies voltage and current to an alternating current machine (AC exciter), which amplifies these signals and, after passing through a rectifier (diode bridge), injects them into the synchronous machine field winding.
This diode bridge can be static (stationary) and require brushes to send the current to the generator field, or the diodes can be rotating, requiring no brushes (a system known as brushless).
Its advantage is that it requires low-capacity components (power converter, field flashing, transformer, and breaker). Brushless systems, lacking brushes, prevent potential sparking.
Its disadvantages include slow response time and exciter maintenance.
FEATURES
THYRISTOR BRIDGE DIAGNOSTICS
The RTX POWER excitation system combines advanced instrumentation and an intuitive user interface to quickly identify maintenance needs.
The thyristor bridge extraction system (on demand) allows easy access to thyristors and fuses.
OSCILOGRAPHY AND SOE
Coordination with other plant events is easily accomplished by synchronizing the RTX POWER with an IRIG-B, NTP, or PTP signal, and utilizing the REIVAX recorder high-frequency sampling capabilities (less than 1 ms).
A signals recorder special feature includes eight (8) triggers for pre- and post-event recording, allowing customers to visualize the system behavior after an event (alarm or trip).
COMMISSIONING AND TESTING
Testing is significantly facilitated by the RTX POWER’s intuitive interface, featuring a transfer function graphical representation according to IEEE 421.5, a built-in step response tool, oscillography, and the ability to change control loop and limiter parameters, all in one place.
Power System Stabilizer (PSS) testing is easily performed using the software’s built-in frequency response tool, without any additional external instrumentation.
Reduce commissioning time and achieve early commercial operation, whether you perform the commissioning yourself or enlist the help of a REIVAX professional!
BUILT-IN SYNCHRONIZER
The grid synchronization function is essential in any generator or synchronous motor. In this process, the machine’s voltage, frequency, and phase angle are adjusted to ensure smooth closing of the circuit breaker (52).
RTX POWER has this function built into the hardware of the powerful CPX06 controller.
Synchronization configuration parameters are easily accessible via the graphical HMI.
ROTATING DIODES MONITORING
In RTX POWER for brushless rotating exciter, the rotating diodes are typically monitored to detect whether one of the diodes is open or short-circuited.
If one or more diodes is open, the RTX POWER will signal an alarm. If one or more diodes are short-circuited, the RTX POWER will signal a trip.
This functionality was implemented on the same hardware and software platform as the powerful CPX06 controller. Fault configuration parameters are easily accessible through the graphical HMI.
COMMUNICATION INTERFACES
The RTX POWER communicates with the SCADA system easily via IEC 61850 GOOSE/MMS, DNP3.0, IEC 104/101, or Modbus TCP/IP protocols.
Consult REIVAX for other protocols.
