Environmental Engineering Reference
In assessing maximum reaction time, voltage problems require rapid response,
whereas thermal time constraints are likely to give a few minutes response time.
Voltage problems can, however, be addressed by dynamic reactive power devices
positioned strategically, whereas thermal issues must be addressed either by SPSs
or main network development, which may be prevented or delayed by permission
issues (as above). SPS can be used as a temporary measure while awaiting new-
build permissions. In the economic sense, the cost of the SPS is a hedge against
main project delay.
The above discussion relates solely to alternatives to network development to
accommodate wind generation. The presence of traditional reliable generation at a
load centre defrays load serving network expenditure. This is definitely not the case
for wind generation unless coupled with some form of firmness, e.g. diesel generator
backup or direct-acting demand side management. Nonetheless, arguments about
whether to carry out load-related developments or allow load shedding can be
influenced by the presence of wind generation. Suppose a combination of traditional
generation outage and network outage is estimated at once in 40 years. Then the
presence of wind might mean that only when wind generation falls below, say,
60 MW is load shedding required. This is estimated to be 1/3 of the period of high
load, so the risk moves to 1 in 120 years, making the development project less viable.
The recent proposed change to the UK Security and Quality of Supply Stan-
dard (SQSS) for the transmission system includes the expected values of embedded
generation given in Table 4.2. At the time of writing the UK load serving standard
P2/6, which will consider the value of embedded generation in load serving
security, is also due for review.
There is a further issue in making network investment decisions - energy
balance. Again there is much complexity in assessment. Two examples illustrate
Maximum effective contribution of embedded large power stations to
demand group importing capacity (% of LCN)
Note : Persistence represents the minimum time for which an intermittent generation source is expected
to be capable of continuously generating for it to be considered to contribute to securing the group