The chapter will start with the basic principles of electrical engineering. The discussion will lead naturally to the transformer, found in all wind farms as well as throughout power supply systems. We then consider alternating current (AC) systems, with particular emphasis on active and reactive power and the use of phasors. Power supply systems are then considered. The chapter will close with an introduction to AC power transmission.

This chapter examines the effect of wind generation on the transmission and distribution network to which it is connected. Topics include control of voltage and power flows, the quality of supply and the protection of plant and equipment. The principles underlying network development in the face of increasing wind generation are reviewed. The perspective is that of a network operator sympathetic to wind power development. It will be seen that wind power capacity may exceed strict technical limits, provided wind power operators are prepared to accept occasional energy curtailment. Achievement of this ideal balance will require enlightened negotiation between the two parties.

While considerable progress has been made in wind power forecasting in the last decade or so, in terms of better understanding of the processes involved and higher accuracy of the forecasts, there is still plenty of scope for improvement. Clearly forecasts for the wind power production of whole regions or supply areas are more accurate than forecasts for particular wind farms due to the smoothing effect of geographic dispersion of wind power capacity. However, with the trend towards large wind farms, and particularly large offshore wind farms, there is a growing requirement for accurate forecasts for individual wind farms. There are considerable differences in the accuracy that can be achieved for wind power forecasts for wind farms located in very complex terrain compared to open flat terrain. Current research on meso scale modelling aims to address this problem. The development of offshore wind power also presents difficult challenges for wind power forecasting. The uncertainty attached to a forecast is a key concern, particularly when looking to the participation of wind power in electricity markets. The area of ensemble forecasting shows potential for further progress. The other area of interest will be the integration of wind power forecasting tools into the energy management systems of TSOs.

Flexible alternating current transmission system (FACTS) devices are expensive, and it is necessary to ensure that their functionality is required before specifying them. They perform four basic functions, which can be combined in different devices: 1. Power transfer between electrically separated systems 2. Active power management 3. Reactive power management 4. Waveform quality management.Active power management devices (for example phase shifters, static synchronous series compensators and unified power flow controllers) that are less relevant to wind technology, either internally or in connection terms, will not be discussed here. Current source converters for high-voltage direct current (HVDC) are dealt with for completeness, although it is likely that most large wind farms would be connected by voltage source converter technology, and doubly fed induction generators (DFIGs) apply this technology in their rotor circuits. Synchronous connection by lines and cables makes two electrical systems behave as one. This clearly is inappropriate if the frequencies are different or one system has a stability or fault level problem that would be exacerbated by connection with another source. In these circumstances the systems may be maintained as separate entities through a converter/inverter DC path. In each of the other applications, traditional technology exists but performs its function slowly or within a narrow range. It is the need for rapid action in controlling active and reactive power and the need to manage a wide range of waveform distortion problems that requires the application of FACTS devices.