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Excitation systems can reduce maintenance in biomass-fuelled plants


There are nearly 5000 active biomass power plants generating a total of over 83 GW of electricity worldwide, with 1000 more expected to be in operation by 2033, according to German market intelligence firm ecoprog. Biomass power plants use organic feedstock such as wood pellets, agricultural residues and forestry waste as fuel to generate high pressure steam to drive a turbine and synchronous generator.


These plants can operate as standalone power plants or in industrial cogeneration systems but can face several challenges that directly impact their operational efficiency and reliability. Fluctuations in fuel, moisture content and energy density can affect combustion efficiency, leading to voltage and frequency fluctuations that jeopardise power supply stability. In addition, biomass combustion generates significant ash build-up, residues and corrosive gases that can degrade equipment, increasing maintenance costs and reducing operational lifespan.


Excitation specialist Excitation & Engineering Services contend that brushless excitation systems help biomass plants maintain stable voltage, reduce maintenance needs, and ensure reliable grid compliance.


Excitation systems


Excitation systems can be crucial in addressing these challenges, by regulating generator voltage and providing reactive power support. They supply DC power to the generator field windings, creating a magnetic field in the rotor that induces AC in the stator. When instability occurs, such as fluctuating fuel quality, the system rapidly adjusts the DC to maintain stable output.


Biofuel power station


A well-designed excitation system precisely controls the generator voltage, rapidly adjusting to load fluctuations. It can handle sudden shifts without triggering instability and normally includes features such as fault detection and quick corrective actions. This ensures compliance with regulations like the UK’s Grid Code and the Connection and Use of System Code (CUSC) while minimising downtime and reducing maintenance needs in challenging conditions.


These regulations require generators to keep voltages within strict limits and provide reactive power to stabilise the grid, particularly during fluctuations in demand or network disturbances.


Performance


By stabilising the generator’s voltage and supporting reactive power, a well-maintained excitation system ensures consistent performance through regular servicing, calibration and testing. This reduces the impact of combustion instability, helping prolong the plant’s operational life and minimise downtime.


Biomass plants, typically smaller than traditional power stations, have unique design and maintenance demands, for which brushless excitation systems are particularly suitable.


An engineer inspecting the excitation system


Compared to static excitation systems, which rely on additional components such as brushes and external rectifiers, brushless excitation systems are more compact. Their smaller size allows direct integration


38 | June 2025| www.modernpowersystems.com


into the generator eliminating, the need for bulky external enclosures. With fewer moving parts and minimal maintenance, they are said to offer improved reliability and reduced operational costs, ideal for smaller decentralised applications.


The role of brushless excitation systems


In such systems, a rotating exciter mounted directly on the generator shaft generates an AC voltage to be rectified and supplied to the field windings. This design removes the need for brushes and commutators, components that are prone to wear and gathering carbon dust – common issues in static systems, they can lead to reduced reliability.


Brushless systems can offer fast voltage regulation, essential for smaller plants that must adjust to load fluctuations quickly. Their compact, self-contained design makes them ideal for decentralised biomass stations where space and consistency are critical. EES provides bespoke brushless excitation system designs to enhance reliability and provide low-maintenance benefits crucial for biomass plants in a rapidly growing and diversifying energy sector. The robust design, able to tackle fuel variability and ensure grid compliance, can help ensure that plants improve performance and extend operational life, while reducing the frequency of downtime.


For more information visit www. excitationengineering.co.uk/consultancy


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