The stronger the magnetic field created, the stronger the electrical power produced. The strength of the magnetic field is adjusted by controlling the current to the rotor. Three phase electrical energy is created by three separate wire windings in the stator.
A source is required to create excitation before it can be self-sustained from the generator. Outputs include annunciation, alarms, meters, and a full range of data for the distributed control system.
A power bus is required to feed the exciter current to each end of the rotor coil. Field breakers are used to protect both the AC and DC sides of the generator. Power rectifiers convert AC power to DC power. Cooling systems maintain operating temperatures required for reliable operations.
Field discharge system is required to remove the energy from the rotor while the mechanical power source is slowing down. The field flashing equipment is used to generate the initial electromagnetic field until the generator creates enough voltage to self-excite and sustain the mechanical to electrical power conversion. Redundant bridge configurations are common. In case multiple bridges are present, the excitation system will perform current equalization to balance the bridge outputs.
The converter interface consists of all intermediary devices between the controller and power rectifier. It converts the control signal to firing pulses and isolates the control electronics from the power section. On excitation systems manufactured by Reivax, diagnostics tools for monitoring the power rectifier are provided on the HMI.
The status of fans, fuses, and semiconductor temperatures can be checked in real-time, as shown below. This screen demonstrates normal bridge operation.
All 6 thyristors are conducting normally. Current is equally balanced between the 3 branches. In this screen, the HMI is indicating a problem with fan A. There is also an indication of a fuse problem with thyristor 5. The measured current through this thyristor has dropped to zero, indicating that there is no conduction.
The PPT is a 3-phase step-down power transformer used in static excitation systems. Its purpose is to step down incoming AC voltages from the synchronous machine to a level that can be supplied to the power rectifier. The main purpose of the field breaker is to interrupt the excitation and serve as an isolation point for performing maintenance and troubleshooting.
Both AC and DC solutions are common. The field breaker can be installed either directly in the field circuit, or between the secondary of the excitation transformer and the rectifier of the system. In the latter case, the breaker is often called an AC contactor instead. The field flashing circuit is used in the start-up process, when the magnetic flux in the generator is too low. The field of the synchronous machine is temporarily connected in parallel to an external DC supply, such as a station battery, until the synchronous machine develops enough terminal voltage such that the excitation becomes self-sustaining.
Afterwards, the field flashing is interrupted. The crowbar is a safety feature designed to protect the excitation system and field winding from external surges, generator pole displacement, etc.
If you would like to discuss these features with a qualified engineer to better understand the advantages, please call our toll free number REIVAX. Please fill out this form to be able to receive a quote within 24h.
Support Request a Quote rna reivax. For synchronous motors, it is responsible for maintaining a constant power factor. A sample diagram of the full control loop is shown below:. The most common limiters and their functions are given below:. Typically, the following physical operating limits are represented: Rotor thermal limit Turbine limit Practical stability limit Pole slip limit In addition, the following limiters are typically represented: Over Excitation Limiter OEL Under Excitation Limiter UEL Excitation systems manufactured by Reivax include a dynamic capability curve that can be used to monitor operating conditions in real-time.
A single-line diagram of an AC rotating exciter is shown below. A single-line diagram of a DC rotating exciter is shown below.
Enter your text here. As the generator is rotated, the stator supplies input voltage to the AVR. In addition the AVR has sensors that monitor the output of the stator. The current is induced onto the stator for load output. The biggest drawback to this system is the AVR is impacted by the load the generator is powering. When the load increases the voltage begins to decrease and the AVR must provide more current to the exciter to support the demand.
This pushes the AVR to its limits.
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