Network integration of wind power - Wind Power Integration: Connection and System Operational Aspects - page 110

continue generating during n-1 or n-m-T conditions. The above debate suggests the
arguments to be significantly less strong for wind generators. Tidal stream gen-
erators, for example, might be treated more like traditional generation because they
will be predictable and hence relied upon in dispatch. Thus if probabilistic analysis
based on real wind farm performance shows that wind farms can be relied upon to a
degree, the case for reinforcement is strengthened. If the critical outage could be
communicated to a wind farm controller then the wind farm output could be cur-
tailed to manage the network problem, hence averting the time delay of several
years and the cost penalty of main system development. The approach has been
termed 'Connect and Manage'. Whilst the cost of backbone investment is spread
over the life of the asset for customers, there are also other elements which increase
and are added to the utility's tariff bill to users, e.g. depreciation, operation and
maintenance, and these should be approximately proportional to the size of the
asset bill. This issue is not trivial. In Northern Ireland the plan is to almost double
the size of the transmission system. In the rest of Ireland considerable new 400 kV
circuits are required. In GB there is a plan to avoid onshore transmission between
Scotland and the Southern part of the island using a subsea network. In Germany
and other parts of Europe there are large EHV AC and HVDC plans to transport
large quantities of wind power long distances. Almost certainly each of these
developments will bring utilities into lengthy debate with objectors and create long
achievement delays.
Network planners would probably insist that the curtailment or special pro-
tection scheme (SPS) meets the reliability standards of protection, since the con-
sequences of failure might be system overload and widespread outage.
Two complications then arise:

the embedded generation system input may come from a group of wind farms,
in different ownership

●

there may be several different combinations of system contingencies which
give rise to the need for constraint; the amount of constraint needed may vary
with system loading, other generation patterns and which contingency outage
causes the problem

●

Management of the problem is therefore complex, involving wide area security
constrained re-dispatch with a secondary objective of cost or equity management. In
a market system, wind farms might pre-bid for constraints, but the system provider
should not compensate parties with non-firm connections, since in accepting a
connection agreement they agreed to a disconnectable network connection until the
backbone network can be reinforced. The economic settlement would be internal
within the affected group of wind farms. Market dispatch and settlement systems
need a level of sophistication to accurately dispatch and reward under 'connect and
manage' systems. It might be different if the utility were to decide never to build out
the investment because it is cheaper to compensate the generators. In those cir-
cumstances there may be a case to pay compensation for the constraints rather than
the greater cost of additional circuits. The cost of an SPS, the associated protection
standard communications and financial settlement system may be excessive.