Emerson’s Matt Pizarchik presented Excitation Theory and Ovation Excitation Tips and Tricks at the 2024 Ovation Users Conference. Here is his presentation abstract.
Generator voltage regulators are typically supplied by the generator OEM. This presentation will provide a basic overview of how voltage regulators work no matter who the manufacturer is. Putting voltage regulator controllers on the Ovation network provides better troubleshooting capabilities and ease of use for plant engineers, technicians and operators. Examples of realtime troubleshooting and using Excitation software to test response for to deviation for troubleshooting and compliance purposes.
Matt opened by explaining generator excitation theory. A generator excitation control system controls the generator terminal voltage. Voltage (the yellow loop in the image) is proportional to the current flowing through the generator’s field windings. As you can see, the field windings are the magenta loop energized by the excitation control system.
Raising excitation means increasing terminal voltage and pushing reactive power or VARs out of the unit. Lowering excitation is the opposite, lowering terminal voltage and absorbing reactive power. Excitation must also increase with load, so your excitation will work hard to steady the voltage while the plant moves up and down on load. Altogether, your generator will be locked in at 60Hz of the grid, and the more torque provided by the force on the turbine blades pushes a greater amount of real power out to the bulk electric system.
The excitation system needs to supply DC to the generator field for a static machine or supply DC to the exciter field if we have a rotating system. So, at the most basic level, your excitation system converts AC power to (a very choppy) DC output waveform.
Three-phase AC comes in from the excitation source, and a special thyristor control board turns on the six thyristors in the circuit, allowing conduction to the DC output bus to be positively biased. The amount of DC voltage is controlled by how much AC waveforms are captured when the thyristors are turned on.
The Automatic Voltage Regulator (AVR) constantly compares the terminal voltage to the voltage set point. If the voltage falls below the setpoint, the system will raise excitation and raise it if it is above the setpoint. The AVR controls generator voltage and lets you change reactive power (MVAR). It does not control active power (MW) but can be tuned to mitigate grid disturbances.
The Power System Stabilizer (PSS) enables the AVR to modulate the voltage response to the fluctuations in active power. When off, the AVR responds quickly to a voltage disturbance, resulting in a ripple in active power (MW).
Combining the Ovation Excitation System (OES) with the Ovation DCS enables complete plantwide control from a single platform, including operator screens, engineering tools, historians, alarm management, system security, spare parts, and lifecycle management.
The OES offers a triggered event recorder, which automatically captures high-speed data immediately before and after an excitation system disturbance. This data is stored in the Ovation Process Historian (OPH), and the conditions for an event trigger are customizable. Redundancy is available at the excitation network and data, digital exciter controller (DEC) module instrumentation, and power equipment.
Visit the Ovation Excitation System section on Emerson.com for more information on this integrated approach to generator excitation.
The post Generator Excitation Tips and Tricks appeared first on the Emerson Automation Experts blog.