Power flows on the SHETL network for each of the seven years from 2006/07 to 2012/13 are illustrated in the following series of figures: Figure C.1.1 ; Figure C.1.2 ; Figure C.1.3 ; Figure C.1.4 ; Figure C.1.5 ; Figure C.1.6 ; and Figure C.1.7.
Power flows on the SPT network for each of the seven years from 2006/07 to 2012/13 are illustrated in the following series of figures: Figure C.2.1 ; Figure C.2.2 ; Figure C.2.3 ; Figure C.2.4 ; Figure C.2.5 ; Figure C.2.6 and Figure C.2.7.
Power flows on the NGET network for each of the seven years from 2006/07 to 2012/13 are illustrated in the following series of figures: C.3.1; Figure C.3.2 ; Figure C.3.3 ; Figure C.3.4 ; Figure C.3.5 ; Figure C.3.6 and Figure C.3.7.
While the complex power flow program used computes nodal voltage, phase angles and both real and reactive power flows on the system only the real (MW) power flows have been displayed on the figures, both for ease of presentation and for clarity.
The requirements placed on the transmission system depend on the size and geographical/ system location of generation and demand.
SYS Boundaries and SYS Study Zones introduced the 17 SYS boundaries which are used for the purpose of illustrating system performance, illustrating the need or otherwise for transmission system reinforcement and for describing opportunities. These boundaries encompass the 17 SYS Study Zones.
Table 7.2 and Table 7.3 summarise the Planned Transfers, under the SYS background, for each of the 17 SYS Study Zones and across each of the 17 SYS boundaries respectively. Please note that, the generation capacities used and, accordingly, the resultant level of planned transfer, relate to the expected contributory generation plant rather than the installed capacity. This is in line with the power flows illustrated by the series of figures in Appendix C.
In general terms, the disposition of demand and generation across the GB transmission system is such that much of the generation capacity is located in or towards the northern parts of the system while much of the demand is located in the southern parts of the system. As a consequence, the resultant power broadly flows from the northern parts to the southern parts of the system, particularly at times of the GB system peak.
The capacity of transmission contracted generation is set to rise by some 18.2GW over the period 2006/07 to 2012/13 (Table 3.5 refers). Amongst other things, Generation Disposition described the disposition of this future plant. In broad terms 5GW will be located in Scotland, 1.7GW in the north of England and the midlands with the remaining 11.5GW south of the midlands to south boundary. However, these figures do not include the prospective growth of embedded generation; particularly in wind farms. This receives some consideration in Embedded and Renewable Generation.
The year on year fluctuations in planned transfer, displayed in Table 7.2 and Table 7.3, are not only a function of changes in demand and installed generation disposition, but also of the changing contributory plant disposition. Generation Disposition reports that, the forecast disposition of contributory generation and ACS demand across the system is such that, against the SYS background, the high power transfers at times of peak demand from the, northern parts of the system to the southern parts, are expected to persist.
Under the 'SYS background' the export from Scotland into England (i.e. across Boundary 6) displays a more or less steady increase over the period. Most 'North to South' boundaries display a similar trend, which is partly a product of the northern location of much of contracted renewable energy developments. Small perturbations reflect the changing 'in merit' generating plant.
The import into the Southwest Peninsula is reduced over the period due to new generation scheduled to connect in that part of the network while the demand in London displays a steady growth resulting in a gradual increased London import over the period.
Figure 7.3 and Figure 7.4 illustrate the broad power flow pattern for 2006/07 and 2012/13 respectively. The capability of the GB transmission system to transport these levels of power transfer across system boundaries is the subject of Transmission System Capability. Amongst other things, that chapter explains that in considering boundary transfers and capabilities and the possible need for additional reinforcement it is important to take account of the requirements of the planning criteria in the Licence Standard. In particular, planning criteria relating to the main interconnected transmission system require that a margin for security (i.e. the interconnection allowance) should be allowed for.
Click to load a larger version of Figure7.3 image
Click to load a larger version of Figure7. 4 image
The outturn power flows at the peak of any year may differ from those given in Table 7.2 , Table 7.3, Figure 7.3 , Figure 7.4, and the series of figures included in Appendix C for a number of reasons. These include:
There are clearly a great many variables, which will influence the outturn power flow. However, whilst the power flows displayed in the various tables and figures of this chapter may not be experienced in practice, they are nevertheless indicative of the flows to be expected under the SYS background. Power flows, transmission capabilities and the possible need for further transmission reinforcement based on our current view of a more likely outturn than the SYS background are discussed in GB Transmission System Capability.
2006 Seven Year Statement
