System Stability and Voltage Control in a Low Carbon Future
The decarbonisation challenge is driving changes in the fuel source, location and
characteristics of generation in the UK. It is expected that renewable and low carbon
generation levels will increase significantly and this will present three specific technical
challenges for the UK in maintaining demand-generation balancing:
• The displacement of traditional fossil-fuelled plant by wind generation will have the
effect of decreasing the system inertia meaning that in the event of the loss of a
large generator the system frequency drops faster. In addition, the ability of the
wind generation to respond to such a loss is less; as sources such as wind and PV
have little or no ability to increase their output to compensate;
• The new generation of nuclear stations are much larger at 1.8GW compared with
the current maximum size of 1.3GW. This means that, with all other things being
equal, a single loss would result in a much larger frequency deviation;
• The output of renewable sources such as wind and PV whilst consistent at the
national level varies considerably within a geographic region. This inconsistency
presents new voltage control challenges to both the UK's transmission and
distribution network operators, which would otherwise require expensive capital
investment to manage.
Economic Considerations
The purchase costs of balancing services, which was valued at £547 million for 2010/11
(Source: 2010/11 Procurement Guidelines Report, National Grid), is ultimately borne by
GB customers and is set to increase significantly as the UK moves to a low carbon
electricity system (Source: Operating the Electricity Transmission Networks in 2020,
June 2011, National Grid).
Low Carbon Considerations
The current approach to provide a balancing response is to use generators operating as
spinning reserve, which can automatically deliver power when required to manage a
frequency deviation. As the scale of response increases, the cost of generators
operating in this manner will become more expensive as well as constraining wind
output levels. As carbon prices can be expected to increase over time, this can also be
expected to have an economic impact.
Method
CLASS is proposing to test the provision of ancillary services by the innovative
management of the HV distribution network. A feasibility study, undertaken by The
University of Manchester and Parson Brinckerhoff, has proven the viability of the
concept. The equipment will be configured to deliver the service autonomously in
response to a system trigger or NGET could command the service via an interface (to be
developed) between NGET's and ENWL's control systems. Monitoring equipment will be
fitted in parts of the distribution networks and in selected customers' premises to
monitor the provision of the services. In conjunction with customer surveys we aim to
test the hypothesis that customers see no impact on the quality of service delivered.
Trials
CLASS proposes to demonstrate this Method on 80 primary networks, serving around
400 000 customers. The networks will be chosen to provide a UK representative