Load management

Power plant management is ecologically and economically sound use of existing power plants and planning any required new power plants.

The design of the power plant capacity and distribution networks must always be under the consideration of peak demand.

  • 4.1 Control of service provision
  • 4.2 Dynamic characteristics of thermal power plants
  • 4.3 Control of energy Bezuges
  • 4.4 neighboring networks
  • 5.1 Management predictable fluctuations
  • 5.2 Management not predictable fluctuations
  • 6.1 correlations in the system turbine / generator
  • 6.2 Overload
  • 6.3 underload
  • 6.4 Measures
  • 9.1 Reference Books
  • 9.2 Technical Papers and Technical Articles


In an electrical distribution network as much electrical energy must be fed constantly, as is currently required by the consumers. ( See also Rule power ( mains ) ). Minor discrepancies lead to a change of the mains frequency and the supply voltage, larger may cause large-scale power outages.

Large quantities of electrical energy can be saved only by lossy conversion into other forms of energy. To cover peak load electrical energy is therefore in pumped storage power plants or compressed air storage power plants converted into other forms of energy and cached. Since the storage of electrical energy is uneconomical in large quantities and should only be used for the peak demand, certain power plant capacity must at all times be ready to meet this peak load.

The main task of power plant management is to keep delivery and purchase of electric energy in balance. In the past, power plant management contributed to a few exceptions, only the output side ( equal to the supply side). There are efforts (see end of article) to control also increases the demand side in the near future.


In order to guarantee the balance must

  • Be estimated in advance, will be at what time provide as much energy
  • Can react to unforeseen increase or decrease in consumption,
  • Able to respond to problems in the power grid, at power plants and consumers.

For this one needs

  • A wide range of power plant, which can meet different tasks and optimally operate cost-effectively,
  • Measurement and control devices that receive the current state in the power grid, can intervene and can generate statistics about the power consumption,
  • Regulated relations with neighboring networks to fall back in case of emergency on the reserves of these networks can.

Fluctuations in demand and production

Predictable fluctuations

Due to customers' habits such as food preparation at certain times, the use of electric lighting, and production processes of the industry, fluctuations in the electricity consumption which will result in the statistics. These statistics can be used to predict the energy consumption.

The energy demand is not only dependent on the time of day but also on the day of the week (weekday / weekend), holiday, holidays, seasons, outside temperatures, wind speeds, bad weather, economic data, sales forecasts, etc. The more specific you can capture the dependencies of power consumption, the more accurate forecasts for the energy requirements can be incorporated into the power plant management. The same is true for the producers.

With fluctuating energy supply (especially of wind -dependent wind power and solar photovoltaic dependent ) is predicted to supply power for short and medium-term periods on forecasting systems ( see, eg wind power prediction and forecast solar power ).

Unpredictable fluctuations

Customer behavior can vary considerably at certain times of the forecast, for example, special events or the weather. The power plant management must respond to this relatively short notice. Besides, it can also cause failures in power plants in the electricity grid and large consumers, need to respond instantly to the. On the generation side, the discontinuous feed, for example, wind farms must be compensated.

Load control

Control of service provision

Power plants are divided into three categories based on their performance and rate of change of its operating costs per kilowatt hour:

  • Base load: power plants are operated as base-load plants, provide affordable energy available, or have a low rate of power change. They will operate the unit around the clock with almost full power. The performance of baseload plants must be easily governed not necessarily. River power plants are preferably used to generate base load. With them, a very good performance control with high load gradient is possible since no complex procedural process is preceded as in thermal power plants. This ability, although it qualifies as peak load power plants, but you would at a throttling energy, in the form of water flowing past, give it away. The same applies to other power plants where the energy is volatile. ( Wind, geothermal and photovoltaic power plants)
  • Lignite-fired power plants can be controlled by 3% per minute and must be operated with at least 40 % of the maximum power.
  • Nuclear power plants can be controlled per minute to 3.8 to 5.2 % and must be operated at least 50-60 % of the maximum power. By using the minimum load of condenser heat dissipation, the minimum performance drops to 0%.
  • Coal-fired power plants can be controlled per minute by 4% and must be operated with at least 38 % of the maximum power. They are also used in the medium load range.
  • Geothermal power plants can also be covered by the constant energy available to supply base load.
  • Peak load power stations are operated as peak-load power plants, any change in performance must be able to follow in the network and thus have a very high dynamic range. Peak load power plants only a few hours per day are usually used, to the absolute peak consumption and unplanned fluctuations in power consumption, especially in case of failures of other power plants. As peak load power plants, especially gas turbine power plants and pumped storage power plants are used because they can react extremely quickly. Nuclear power plants, which are operated with at least 80 % of their rated power, could contribute to peak load in the range of 80 % to 100 % of their performance.
  • Power supply: This includes all power plants for the reduction is mandatory, ie, those that are operated by third parties according to their own criteria and can not be controlled by the network operators. These include external power plants in the industry who are not integrated into the line regulation, and heat-controlled cogeneration plants, wind turbines, solar panels and other uncontrolled regenerative energy sources. From the network behavior, these power plants are more in electricity consumers with the opposite sign. There are also remote-controlled CHP plant associations and wind farms that do not fall into this category.

Dynamic characteristics of thermal power plants

The power output of power plants can not be changed quickly. Depending on the design are certain limits to be observed.

  • The performance of lignite power plants can be changed by about 3% of the rated power per minute. Of coal power plants by about 4% The power can be changed between 40 % and 100 %. The start- after stability and the subsequent minimum operating time are both over two hours.
  • Gas turbine power plants achieve change speeds up to 20 % of rated power per minute and therefore are particularly well suited to cover rapid load fluctuations. They are also characterized by very short start-up of minutes. The power can be changed between 20% and 100 %. Therefore, this type is very suitable for peak load power plants.
  • In nuclear power plants must be distinguished: Pressurized water reactors achieve change speeds up to 2% of the rated power per minute. The power can be changed between 20% and 100 %.
  • In BWRs, the minimum power is 60 % of rated power, but the rate of change is twice as high at 4% per minute.

Control of the energy Bezuges

A load control is achieved within certain limits, by the control of consumption, through:

  • Ripple control systems: this way, consumers can be turned on or off ( consumables) according to the requirements of the power generation business. This is primarily used for industrial Größtverbraucher such as aluminum and electric steel plants. For a certain advantage within the electricity price can be reduced or increased by the electric utility, the power consumption of these industries. This is also used for night storage heaters. These can be loaded when there is otherwise no consumer for the instantaneous power plant capacity. As a result, even at night creates a certain level of load on the power grid, and the proportion of base load power plants such as nuclear power plants to increase the power plant. According to the Association of Electrical lies the potential for load shifting half in energy-intensive companies and half in private households, trade and commerce, and services. Load management can offset demand and reduce the cost of energy change significantly.
  • Storage power plants: pumped storage power plants, for example, can always, if there is no consumer finds for the instantaneous power plant output, merge into the pumping operation to pump water to a higher ground storage tanks. They are mainly operated at night in order to utilize the baseload plants better. They are also used for short-term support of the frequency with load and generation variations. The problem is the very high cost of the plants and the binding to the appropriate geographical conditions.

Neighboring networks

In addition, parallel networks can be involved in the management of the power grid to obtain base-load, mid-load or peak-load current or supply. In case of malfunction neighboring networks can help to stabilize the frequency of the overall network by providing or removing power to a greater extent. In Europe, the UCTE is responsible for coordinating the operation and expansion of the interconnected European grid.

Management of electricity demand

Management predictable fluctuations

Due to the forecast of the demand for electricity and the predictions for the non-controllable power supplies (mainly photovoltaic and wind energy) for generating one days transition plan for all participating power plants is created. The distribution of the expected daily output at basic, intermediate and peak load power plants takes place one hand on the technical possibilities, but on the other hand so that the cost of electricity to be kept as low as possible.

Management is not predictable fluctuations

If unforeseen fluctuations in electricity demand, so is the control of the power plant capacity (not renewable generating capacity. , Wind and photovoltaics can only turn down is why such power plants require so-called shadow power plants) tried to respond to these fluctuations. When amendments in relation to the forecasts, a slow, through adjustments to the " roadmaps" for the medium-load power plants can intercept the changes. If the additional changes quickly, may have to step in peak-load power plants in order to respond quickly to the changes.

When outages of power plants high power needs to be replaced in a very short time. Then, fast-reacting power plant types, such as pumped storage power stations enabled. At the same performance increases are requested in slightly slower reacting gas power plants and medium-load power plants and possibly also ramped up an additional power plant of the so-called hot spare. In parallel to the ramp-up of capacity in the medium-load power stations and replacement power plant, the power is reduced in the peak load power plants.

In case of failure of a major consumer control of the network must run the other way around: Shutting down the performance of medium-load power plants. Since this does not work immediately, quickly substitute consumers must be switched on (eg pumped storage power plants) or possibly active peak load power plants will be shut down quickly. The equivalent loads can be switched off when the medium load power plants have reduced their performance.

Effects on the grid frequency

Correlations in the system turbine / generator

The mechanical power, which has to provide a turbine power plant, in order to maintain a constant rotational speed of the synchronous generator, is dependent on the active electric load of consumers are connected. The required torque and the rotational speed of the turbine are proportional to the product of torque and rotational speed (revolutions per second).

The torque which has to supply a turbine with a generator set, in this case depends on the current from which is withdrawn from the generator, and therefore on the electric power is taken from the generator. Due to the current draw an opposing torque is generated in the generator.

Are mechanical power supply to the turbine and electrical generator in the power take-off in equilibrium, the torque of the turbine of the same size as that produced by the generator "counter " torque. The turbine-generator ( turbine and generator) runs with constant speed.


The generator is then withdrawn an additional power, this means that the current in the alternator is increasing. This in turn causes an increased generated "counter " of the torque generator. Can not be offset by a simultaneous increase in power to the turbine side of this torque, the entire mechanical system generator / turbine is braked by the difference of the torques. The difference between the supply of mechanical power and electric power of removed the rotational energy of the mechanical system is then taken from the generator / turbine.

We now come to a new equilibrium at a lower speed on: The case against reduced induction increases the current drawn from the mains. Is required for the same mechanical power more torque, so this can only be provided at a lower speed. That is, electrical overload in the network leads to lower frequency, if not,. Eg more gas supply to the gas and steam turbine, the power is increased The lower speed turn leads to a lower voltage in the generator is induced, so that this reduces also on the electrical side, the extracted power.

Under load

In the opposite case, when less electric power is decreased, is provided as mechanical, reduces the lower side, the decrease in current on the "counter " torque in the generator set and the system generator / turbine is accelerated. The performance difference is converted into additional rotational energy, if it does not reduce the fuel or steam supply to the turbine. Finally, there is a new equilibrium in which this lower torque is delivered at a higher speed. That is, electric lower load in the network leading to over-frequency, if it is not throttled, for example, the flow of energy.

Similarly, a higher voltage in the generator is induced by a higher rotational speed which causes an undesirable under certain circumstances higher performance electrical loads. Therefore, the applied mechanical power must be constantly regulated according to the electrical load for all turbine types.


The task of the power plant management is to identify network overload or underload network in time. For this purpose also serves the very accurate measurement of the line frequency. Even with minimal deviations of a few thousandths of the mains frequency measures be taken to the so- discovered compensate for over-or under load in the network. A deviation of the grid frequency by more than 2 % already triggers drastic measures to stabilize the grid, such as load shedding in power plants ( underload ) or in the power supply ( in case of overload ). With a deviation of the grid frequency by more than 5 % from the nominal value, the network is no longer operated stably, power plants turn to protecting the systems automatically.


The so-called Intelligent the electricity grid ( smart grid) is expected to change the power plant management and greatly reduce its importance. In the future it will be increasingly possible to control the demand from certain consumers ( see Research Project E -Energy BMWi ).

For example, you can remotely control night storage heaters via mobile networks on and off during peak demand occurs. Also you can temporarily remotely Cogeneration and off ( including among some mini- cogeneration plants ).

In addition, you want using electricity meter affect (eg with remote reading ) the demand behavior of the connected electricity customers.

Cold reserve

Power plant preservation can be performed at power plants, which are not used for an indefinite period, but will be operated again later called these power plants also cold reserve. Since the current prices on the European power exchanges in 2008, 2009 and 2010 were relatively low, there was little reason to reactivate conserved power plants.

Since many nuclear power plants in this revision and addition from March 2011 more old nuclear power plants were shut down because of the nuclear moratorium, only a few nuclear power plants were in May 2011 on the network. This may be a reason to reactivate conserved power plants.


Reference Books

  • Prof. Dr. Günter Springer, expertise Electrical 18.Auflage 1989 publishing - Europe - ISBN 3-8085-3018-9 Teaching Aids
  • Ing Rene Flosdorff / Dr. Günther Hilgarth, Electrical Distribution, BG Teubner Verlag, Stuttgart, ISBN 3-519-36411-5
  • A. Senner, expertise Electrical Engineering 4th Edition 1965 Publisher - Europe - teaching resources
  • Ing Wilfried knee / Ing Klaus Schierack, Electrical System technology - power plants, grids, switchgear, protection devices, Carl Hanser Verlag, Munich / Vienna, ISBN 3-446-15712-3
  • Electrical test book 1970 Publisher - Europe - teaching resources

Technical Papers and Technical Articles

  • Module power distribution, DEXA MCP
  • Walter Castor, fundamentals of electrical power supply, HAAG Library, HAAG Electronic Measuring Instruments GmbH, Waldbrunn
  • Gary Marshall, Power Quality Application Guide: reliability, reliability and redundancy, German Copper Institute Leonardo Power Quality Initiative
  • Prof. Dr. Ing Kathrin Lehmann, Electrical Power Engineering, Lausitz University
  • Fred Prillawitz / Manfred Krüger, system perturbations by major disruptions, University of Rostock
  • Ing Tobias Braun Berger, Fundamentals of electrical engineering, TU - Braunschweig