A steam generator can be called a motor

What is meant by full load, part load and zero load?

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  • What are full load, part load and no load?


As Full load is the term used to describe the operation of a machine to generate kinetic energy with maximum power. When it comes to power generation, these are mostly internal combustion engines in the form of piston engines or turbines - however, an electric motor can also be operated at full load; Vehicles are colloquially referred to as full throttle. If the engine or turbine is operated with less than full power, they will run in Partial load. Zero load means that the engine is not producing any power - i.e. it is switched off or idling or is disengaged, but in any case does not give off any kinetic energy to the gearbox, generators, etc.

Farewell to the full load paradigm in power generation?

For decades, the power system only knew one thing: full power generation, running the power generation systems "on the line". Conventional power plants, especially nuclear reactors, are designed precisely for this mode of operation. However, not only on the 20th anniversary of the Renewable Energy Sources Act (EEG) it can be stated that these times in the electricity system are definitely over due to the volatile feed-in from sun and wind.

Power generation systems need to change today flexible With "air" in the generation output, adjust both upwards and downwards to the load status in the network, which in turn is increasingly characterized by the volatile feed-in of wind power and photovoltaics. A power generation plant of any type that you economic optimum only reached at full load, can no longer work optimally in this power system. Due to the great importance of renewable energies in the electricity system, we are clearly moving in the direction of one part-load-based Power generation system, where full load can neither represent the optimum nor the measure of all things. Following this idea, it seems to be necessary to shift the technical and economic optimum of the power-generating units more and more from full-load operation to part-load operation - which is possible by adapting the design and parameterization.

Influence of the load status on efficiency in CHP units

The load condition of a CHP does not match its Efficiency equate. This depends heavily on the type of engine and the operating conditions. The decisive factor here is the correlation between capacity utilization, speed, the size and type of engine and the operating temperature. Today's motors usually achieve high degrees of efficiency with a high load close to full load, but this can lead to greater wear. Partial load and idling often have poorer efficiencies in today's engines, because the fuel consumption is higher in relation to the energy generated - but there is less wear. The optimal operating condition in the field of tension between performance, wear and consumption must be determined individually for each engine and each turbine. This can be read from the power, torque and other optimum curves, which depict the load conditions on the test bench.

At the same time, however, it also plays rotation speed an important role. If it is too high for the required output, the efficiency is also reduced. Anyone who has ever tried to drive a car at 50 km / h in first gear knows the phenomenon - with a lot of noise, high wear and disproportionate consumption, the engine is definitely not working in the optimal range due to the disproportion between speed and gear. The size of the motor also plays a decisive role in terms of efficiency. With larger engines there is less power loss. The ratio of volume and surface area of ​​the combustion chamber ensures lower heat losses, so that operation is more efficient. In addition, the larger dimensions ensure less friction losses. The rule of thumb “more cubic capacity in relation to power equals longer service life” is still justified today, as these engines have less compression and can therefore work with lower working pressures.

As far as the different degrees of efficiency are concerned, so wise Gasoline engines Efficiencies of 35-40 percent while Diesel engines can have up to 50 percent. Ship engines, on the other hand, have efficiencies of up to 55 percent. Furthermore, the degrees of efficiency also differ according to the type of application. While CHPs have their best efficiency close to full load at high torque, the best efficiency for car engines is in the partial load range. With the increasing demands on the Flexibility of power generation systems with CHP units However, many engine manufacturers are also starting to optimize their CHPs not only for the “near full load range”, but also for the partial load range. Today's CHP units in the biogas industry usually work as positive-ignition engines with spark plugs and, like vehicle engines, can be optimized for certain load conditions.

However, these engine-related aspects do not yet provide any information about how lucrative the operation of a CHP unit is in the various operating modes. This depends on whether that CHP is operated according to the price of electricityhow big the spreads are on the electricity market, whether there are other revenue opportunities such as the provision of control power (and what the prices are on this market) or whether there are also heat supply obligations. Other aspects that determine how lucrative operation is, for example, the requirements, how often a CHP unit changes its load, how well and quickly the engine can react to load changes and how high any maintenance costs can be due to increased or reduced wear. With today's engine technology, unlike in the past, a significantly higher number of starts and stops as well as load changes can be achieved with reasonable wear than in the past.

Full load, part load and the optimum of efficiency

Turbines in large power plants are, just like CHP engines, heat and power machines - only on a much larger scale, without pistons and via a detour: They are not operated directly with the fuel, but with steam from a steam generator, which produces water under the Converts the energy supply of the fuel (coal, oil, gas, fuel rods) into high-pressure steam. The power of the turbine is controlled by the Steam throughput regulated; the steam flows onto the turbine blades and sets them in rotation. Power plant turbines can also run at full load, part load and zero load - however, the efficiency also changes with the steam throughput. Because the steam turbine, just like the CHP combustion engine, has a clearly defined one Optimum performance.

This optimum, which does not have to correspond to the full technically possible performance of the turbine, is the full-load optimum of the power generation plant. All load states below and above are at the expense of the efficiency and are expressed in increased consumption of fuel and / or higher wear. For example, nuclear reactors can also be operated with an output of 105 or 110 percent - but outside of warships under combat conditions, this is neither recommended nor usual. The problem of the optimum efficiency also illustrates why the flexible adaptation of the turbine output to different network conditions in old large power plants is rather unpopular - it is at the expense of economic efficiency and is therefore often only used in the course of on-site modernizations realized. Renewable energies, on the other hand, where full load - with the exception of bioenergy and pumped storage power plants - is more of a theoretical value, have a clear advantage here: Changes in load conditions due to changing weather conditions do not affect the efficiency, but are partly conceptual, partly inherent characteristics, for example in photovoltaics and wind power.

Full load hour

The term Full load hour is a unit of measurement, with which one indicates the degree of utilization of a system. Since systems usually do not run at full load all year round, but sometimes only work in partial load operation or are switched off for maintenance, the work carried out over the entire year is stated in full load hours.

The maximum number of full load hours per year is 8760 hours (365 days with 24 hours each). Full load hours vary depending on the type of system, weather conditions of the respective year or system-specific restrictions.

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