Security of supply
Jersey Electricity satisfies around a third of the Island’s energy requirements. Ensuring security of supply is one of our core objectives. To achieve this, we focus heavily on ensuring our infrastructure is securely designed and well maintained as well as on putting in place plans to restore power when equipment does fail.
Our track record
Like many power utilities, we measure our success at achieving supply security by monitoring the average Customer Minutes Lost (CMLs) experienced during the year. This is the total length of time supplies were interrupted during a year for each customer, on average. In general terms, since we installed our second interconnector between Jersey and France in 2000, our network has delivered power into homes at a reliability level of around three to five times that of the UK mainland. This is a considerable achievement given the limited scale of the Jersey network and the limited levels of ‘connectivity’ that the Island enjoys when compared with other UK cities and regions of a comparable scale.
Until 2012, we imported over 90% of Jersey’s electricity from low carbon sources in France through two undersea supply cables (interconnectors), the remainder coming from local generation at La Collette Power Station, two smaller generation units at Queen’s Road and the States-owned Energy from Waste Plant. The loss of our first, older interconnector in June 2012 resulted in a temporary increase in on-Island generation until our third interconnector, Normandie 3, was installed and operational in 2014.
Principles around security of supply
Operating a relatively small, isolated network, such as Jersey’s, with a combination of submarine interconnection and local embedded generation calls for a unique and complex approach to security of supply. Though we base our standards on those of the UK Energy Networks Association (ENA), we have adapted them to recognise the special island conditions in which we operate.
Like the UK, we have one standard at the higher voltages, with another at the lower voltages. In short, we operate one standard, ‘adapted N-1 design standard’ for our submarine cables and generating assets (above 11kV) and another, the 'N design standard’ for parts of the network operating at the lower 415V.
Put simply, the N-1 standard means that the network is designed to accommodate the loss of the largest single component in the system should it fail. The N standard is a lower standard where no such redundancy is designed into the system with reliance instead on a fast response time to affect a repair.
During 2013, the States of Jersey, using a third party consultant, reviewed energy security in the Island and endorsed our security of supply standard and our investment activity to comply with this security standard going forward.
How we manage security of supply
No matter how resilient a public power network is, it is impossible to provide an absolute guarantee of electricity supplies 100% of the time. No public utility will do this. Electrical components do fail from time to time. And even if provision is made to cover such events, there is always a finite time required to switch systems and assets to cover the loss.
For Jersey Electricity to even attempt to provide 100% supply reliability, the Company would have to invest in considerable additional infrastructure in the form of duplicate generation, transmission and distribution assets. Given that demand for electricity varies significant throughout the day and also from season to season, these assets would be heavily under-utilised given that they would only be used in the rare times there are power system and/or component failures. This would be extremely expensive and would result in considerably higher, unaffordable tariffs.
That all said, we make every effort to minimise any interruption through prevention and response.
- Prevention: by designing, operating and maintaining the network to minimise interruptions and installing quality components in critical systems that are well tested and robustly designed
- Response: by developing operating procedures to restore supplies, when they have failed, safely, efficiently and swiftly.
Security Supply Standards define how we meet these twin challenges. There are four basic aspects of which the cornerstone is the N-1 design standard
N-1 Design Standard
The ENA specifies restoration times at different voltage and asset levels within the network. For example, networks operated at 11kV and above are built and maintained to an ‘N-1 design standard’. This means the network is designed to cope with the loss of its largest component (which would require a repair) without a loss of on-going supply.
It must be noted that N-1 does not guarantee uninterrupted supplies as the restoration process may require switching of circuits and there is often a finite time needed for switching, particularly when this is done manually.
Switching circuits to ‘bypass’ the fault is more desirable than immediately having to repair a circuit, because repairs often take longer and are more uncertain of achieving a speedy, successful outcome.
We work to an ‘adapted N-1 design standard’ for our generation and import activities as our submarine cables and generators are designed in a system together.
Adapted n-1 supply security standard provided by operating submarine cables and generators together
1. Loss of submarine cable,plus generator Meet all load in the event of a simultaneous loss of:
- Largest import cable
- One diesel set
- One GT
2. 48-hour Meet 75% of peak load in event of loss of all import capacity
- Assuming no simultaneous loss of any on-Island plant
3. 1-in-8 Meet all load in the event of a 1-in-8 winter peak demand
4. No co-incidence Do not plan to meet the load should we experience any joint occurrence of the above events
1. Loss of submarine cable, plus generator
The system is designed to meet all the load in the event of a simultaneous loss of the largest importation cable, plus a diesel generator as well as a gas turbine generator. We manage this by using the temporary loading capabilities of any remaining submarine cable/s left in service if one failed. The loss of the failed cable is then covered over the longer term by on-Island standby generation, which is started up, synchronised and switched in. Furthermore, we can also meet demand with the additional coincident loss of our largest diesel generator together with the largest gas turbine.
2. 48-hour Standard
The system is designed to meet 75% of peak demand (95% cover over annual energy load curve) over the very short term in the event that all importation capacity was lost. This standard allows the French transmission operator RTE to affect its own French network restoration in the event that all supplies from France are lost. Note that beyond the 48-hour period, Jersey Electricity has enough of its own generation capacity to meet the Island’s full demand as the Company has sufficient time to start its slower start generators.
3. 1-in-8 winter peak demand
The demand for electricity, like any energy, is highly dependent on how cold it is. Some winters are harsher than others and therefore demand for electric power is considerably higher in some winters than others. We have designed the system to cope with a 1-in-8 winter.
4. No coincidence of above items 1 to 4
Finally, our design standards aim to allow us to continue to supply customers in the event that either 1 or 2 or 3 of the above happen but not in cases where more than one of those situations is happening at the same time.
For parts of the network operating at 415V, including our 415V/11kV substations, we work to an ‘N design standard’. This is typical of a network utility where a lower standard of reliability is accepted because a loss at this voltage level typically only affects a much smaller number of customers. Simply put, unlike N-1, this means we need to affect a repair before supplies are restored.
What can businesses, public sector organisations, emergency services and individuals do to mitigate loss of supply?
Jersey Electricity is unable to provide specific advice on mitigation as this substantially depends on how electricity is used in the organisation or at home, and the value or importance of the activity or process being protected.
We recommend that all organisations of all sizes systematically conduct their own risk and business continuity assessments of all processes to ascertain the consequences of a loss of electrical supply, taking into account Jersey Electricity’s Security of Supply Standards. These might include an assessment of alternative ways of maintaining operational capability as well as an assessment of the duration over which the organisation needs to maintain supplies and the capacity of those supplies that will be needed pending provision of alternative arrangements.
Possible solutions may involve use of alternative business service providers on or off Island, in-house standby generation or uninterrupted power supplies. These should be carefully designed and sized to cover current and future the business needs and should be subject to regular reviews to assess whether any changes in their business warrant changes to their backup facilities.
Staff should be trained in the operation of backup equipment and regular planned preventative maintenance as well as repair arrangements put in place. All business continuity plans should be regularly tested. In addition, we would recommend considering the fuel supply chain including delivery and replenishment arrangements and the size of fuel storage needed to ensure that appropriate cover is in place.