The excitation system is responsible for supplying direct current for the synchronous machine field windings.

    • For synchronous generators, it is responsible for maintaining a constant terminal voltage.
    • For synchronous motors, it is responsible for maintaining a constant power factor.

Beside regulator function, excitation system also work as a Limiter – Limit the synchronous machine to work within the boundary & capacity.

In addition, the modern excitation system equip with the Power System Stabilizer (PSS) function,  to dampen the electromechanical oscillations arisen from the power system or the unit itself.  Often according to the IEEE 421.5 model.

RTX Excitation System 

Through our collaboration with Reivax, we are proud to offer the state-of-art RTX excitation system and voltage regulator for full range of power generator

RTX excitation system provide the high performance solutions with advanced control features in an easy-to-install platform.

This cutting-edge solution for Excitation System/Automatic voltage regulator (AVR) is perfect for customers that seek an exceptional cost-benefit ratio solution.  Key differentiators of RTX System are:

Compact platforms to easily replace aging systems.
Exceptional PSS and AVR performance

Reliable operation for all types of synchronous machines
Flexible installation and integration solutions

Economical solutions with quick delivery and easy

Rich Experience in Excitation System

Since 1991, Reivax designed and produced the excitation control. Till today, more than 2000 system are installed.


      • Hydroelectric
      • Thermal – Gas & Coal fired
      • Diesel generator


Experience in replacing many excitation system AVR, i.e. ABB Unitrol P/M,  Siemens Thyripol, Simadyn D, Basler SSE, GEC-Alsthom, Toshiba Analog AVR, and many more.

Type of Excitation System 

Brushless Excitation System (in-direct excitation) 

The brushless excitation is common used in many small to medium size generator.  There’s no carbon brush, commutator or slip ring to the generator.  Instead replace to Permanent magnet exciter and 3-phase main exciter with the silicon diode rectifier.

The excitation control DC output of voltage regulator will feed to the non-moving field winding of main exciter.  The voltage regulator will regulate the field current of main exciter depending upon the excitation power requirement/generator voltage.

    • Typical Application:  Diesel genset, Gas/Steam turbine Generator, Mini Hydro
    • Excitation Current output:  10 ~ 100 A
    • Voltage Regulator/AVR Compact module design

Static excitation system (SES)  Direct excitation:

In static excitation systems, the power rectifier directly supplies the field winding of the synchronous machine. There is no pilot exciter.

A static excitation system is terminal-feed (also called bus-feed) when the supply is taken from the machine itself through a power potential transformer (PPT). The primary of the PPT is connected to the stator of the machine and the secondary supplies power to the rectifier.

Static excitation systems are not inherently self-exciting, so they require an external supply to jump-start the excitation process and build up sufficient magnetic flux. This process is called field flashing.

    • Application: steam turbine generator, gas turbine generator,  or hydroelectric turbine.
    • Excitation Current output:  200A – 10,000A


In the static excitation system, it is a complete system for control, power conversion, and protection.  Its modular design with key components:

    • Excitation AVR Control,
    • Power Driver,
    • Pre-excitation circuit
    • Excitation breaker 41 AC/DC type,
    • Discharge  circuit.
    • Excitation Transformer

Main Control Functions of Excitation System 

Regulator – Terminal voltage and reactive power control. Excitation systems use closed-loop or feedback control to regulate the machine’s output.

Limiters – Limit the synchronous machine to work within the boundary

      • Overexcitation limiter
      • Stator current limiter
      • Volts/hertz limiter
      • Underexcitation limiter
      • Minimum excitation limiter

Protections – Protection the machine, excitation system and auxiliary from damage.

    • Volts/hertz protection (24)
    • Terminal undervoltage protection (27)
    • Terminal overvoltage protection (59)
    • Reverse power protection (32)
    • Loss of field protection (40/32Q)
    • Field overvoltage protection (59F)
    • Stator overcurrent protection (50/51)
    • Field overcurrent protection (76F)
    • Minimum field current protection (37F)
    • Overfrequency (81O)
    • Underfrequency (81U)

Power System Stabilizer (PSS) – Damping of electromechanical oscillations arisen from the power system or the unit itself.

Increase the Reliablility and Availability

In order to provide the high reliability of the system, and to minimise the single point of failure, the excitation system can build with redundancy design.

In this design, one the control, I/O module, bridge, fan is on standby mode. It can activate in millisecond time, enhance the reliability.

    • Redundant Voltage regulator Controller
    • Redundant I/O module
    • Redundant thyristor bridges
    • Redundant cooling fans for each thyristor bridge.
    • On-line maintenance can be performed on control & thyristor bridge

Visualisation & Remote Monitoring Access

The RTX comes with the human-machine interface offers the user all the options in a friendly environment and withgreat interactivity  for operation, testing and maintenance. Graphics:

    • Main – Overview
    • Operation
    • Generator Capacity Curve Monitoring
    • Alarm (Sequence of event, 1ms time sampling)
    • Data trending

Remote Communication Capability

Many of the digital control is capable for remote communication with most DCS, HMI and SCADA. RTX control equips with communication capabilities:

    • Modbus TCP 
    • Modbus RTU
    • DNP3.0
    • IEC 60870-5-104/101
    • IEC 61850 – MMS