The Problems Associated with Embedded Power Generation

The rate of the development of energy sources that are alternatives to hydrocarbons is happening at a greater pace than any other time before; this is mainly because of the environmental reasons i.e. the limitation of carbon dioxide emissions and for the longer-term sustainability of energy supplies. The role played by such alternative energy sources is not without significant effects as we shall learn in the next section.

In most cases, small generating plants and renewable power stations are connected to low voltage distribution networks and not high voltage transmission grids. Embedded power generators can cause problems to the network operator such as:

• System stability problems when a significant proportion of system demand is supplied by randomly intermittent generators, especially at light load. Small generators with low inertia do not provide the same buffering capacity as larger plant under the power swing conditions associated with system disturbances. If a generating plant fails, it is typically disconnected from the network to maintain system stability despite increased demand from the remaining generating sources. Only once the disconnected plant is running in a synchronized way can it be reconnected to the grid.
• Voltage control and quality problems when generators embedded within the distribution network start/stop generating. This can cause other network users to suffer voltage fluctuations, dips and steps outside of the statutory limits and inject unwanted harmonics into the voltage waveform. The remedy requires much more active operation of low-voltage tap-changers on transformers.
• Frequency control problems, many new form of generation don’t provide the expected response to low frequency, exposing users to more severe and frequent excursions in system frequency.
• Large scale renewable sources such as offshore wind and wave power are likely to be located remote from load centers. Development of these energy sources requires significant investment in reinforcing and expanding the transmission grid.
• The traditional network infrastructure causes additional difficulties in the sitting of new generators. Distribution networks are generally designed and operated in radial configurations and are not designed to accommodate active sources of energy. Embedded generation adds to local fault levels and thus, sooner or later leads to the need for larger switchgear as well as the redesign of the protective systems.

With appropriate engineering redesign and investment, some of these problems can be overcome; nonetheless the costs of reinforcing the existing distribution network, upgrading control and protection systems, switchgear, transformers and reactive plant to provide for substantial embedded generation have to be factored in. Hence, there is a technical limit to the development of renewable energy supplies if the output is geared solely to direct connection to the electricity supply system.

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