Tuesday, 19 June 2012

Power to the People

Jersey is running on back-up generators after a major power failure overnight. Chris Ambler, from Jersey Electricity, said connections with both submarine cables to France had been lost. He said engineers had been working to restore supplies and find the cause of the power cut.  Mr Ambler said some off peak electricity and heating supplies were disabled after the power cut which affected thousands of islanders at about 23:30 BST. "Supplies are rather tight in the island, we are bringing in more generation in order to fulfil that demand," he said. "What we are saying to customers is just as a precautionary measure just to give us a little bit more headroom we have taken the decision to disable some of the off peak tariffs and off peak heating." (1)

ISLANDERS were this morning being asked to use electricity wisely after a major power cut plunged Jersey into darkness overnight. The power cut, which was caused by faults in the two undersea cable links with France, happened at around 11 pm and lasted up to three hours for some customers. This morning all of Jersey's power was being generated in the Island at La Collette but some of the generators were not expected to be up to full power until later this afternoon. As a result Jersey Electricity suspended its off-peak water and heating supplies and asked Islanders to limit their non-essential use until supplies are at full capacity. (2)

It is fortunate that the Jersey Electricity Company has maintained a system capable of local power generation. What must be considered, however, is how much capacity this has, and the time that it takes to bring every part of it online. Clearly, at times, the short-term capacity balance between expected electricity supply and electricity use was strained while the slower systems came on line, and that's in June, where the use of electricity is not great.

In winter time, the demand would be considerably greater, and there might be a longer hiatus before being able to establish full supplies. Heating is important in winter. In cold weather, residential buildings quickly lose their heat after an outage in the heat supply.

When the outdoor temperature is close to -5C, it takes about 48 hours for the temperature in the average 1970s home to drop from 20C to 5C. Jersey does not have that often have that degree of cold weather, but near freezing conditions were experienced this year, and while the time would be longer for the temperature drop, it would still occur.

The last reports on the Jersey Electricity Website are a few years out of date, but there is a note in the 2009 report that:

The highest load in Jersey this year was 153.1MW in January 2009, just slightly less than our largest ever peak of 156.8MW, which occurred in December 2007.

This puts us more or less on a par with Gotland, which also imports power via a cable link - a recent report that:

The backup power capacity is excellent, and consists of gas turbines and diesel units. The capacity of the gas turbines equals the maximum load on the electricity network, 160 MW.

The Gotland site also notes that:

The availability of sustainable backup power is limited, but GEAB keeps enough fuel in stock for four days' backup power which is estimated to be more than enough with the world in its present state.

This brings me neatly to several questions about the current situation in Jersey:

1) What is the maximum load that the network can support from backup power?
2) Has this even been exceeded while on the French link, especially in winter?
3) How close are we to reaching the limit? The increasing population, of course, has an increasing energy requirement.
4) How many days can Jersey run on backup resources?

The Gotland linkage to the mainland of Sweden, by the way, uses what is known as a HVDC transmission due to the long distance (90 km) across the sea.  This is an acronym for "high-voltage, direct current" - it is an electric power transmission system which uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required by the cable capacitance.

It would be interesting to know if Jersey uses that, as the total distances of cables are not far off. On the technical side, if you have ever wondered exactly how the cables are laid down and protected etc, this report from ABB gives the details:

In 1998 ABB was awarded the Channel Islands Electricity Grid Project, which reinforces the power supply from France to Jersey and, for the first time, connects Guernsey to the European mainland grid. The submarine part of this project was completed in July 2000. The main components delivered for the project were:

- Submarine cables between France and Jersey and between Jersey and Guernsey (approx 70 km)
- Underground cables on Jersey and Guernsey
- GIS substations
- New transformers and reactors

The two submarine cables are of the same basic design, i.e. three-core, separate lead-sheathed, and with tripleextruded XLPE insulation. Each has a fiber optic cable with 24 fibers integrated in it for system communication and inter-tripping. The cables have double wire armor (ie, an inner layer of tensile armor and an outer, so-called rock armor) to protect them from damage that could be caused by tidal currents and fishing. The cables have a diameter of approximately 250 mm and weigh about 85 kg/m in air. Both cables were delivered by the factory in their full lengths . Because of the risks posed by fishing activities, the cables between Jersey and Guernsey and the fiber optic cables between Jersey and France were jetted into the seabed for extra protection.

Jersey is underway for a third link to France. As the JEC website mentions:

We continue to make progress with the third interconnector between Jersey and France, which we aim to bring into service in 2013. This cable is necessary for three reasons. Firstly, the first interconnector is now 25 years old and our specialist advisors suggest it is approaching the end of its life.

Secondly, there are widely predicted shortages in the availability of heavy fuel oil and the specialist ships needed for safe docking in the Channel Islands, which could reduce the dependability of almost half our standby generation facilities that use this fuel.

Thirdly, we are currently unable to supply the Island's full requirements with low carbon, imported electricity
from the competitive European markets during the winter peak.

The third point is somewhat worrying, and is rather ambiguous. Does it mean that the winter demands may exceed capacity?

Incidentally, Gotland has now an infrastructure which includes electricity from wind farms. They have developed what are called "smart grids" to balance the demands and loads. Here is some background:

During the past years, there has been a considerable increase in wind power production. It started in 1984 and reached 15 MW by 1994. Today there are 48 MW installed producing about 100 GWh. On the southern part of the island, where the peak load is only about 17 MW, there is approximately 37 MW of wind power installed. The infrastructure built for existing consumption cannot receive the increasing production. The system is presently used to its limits at full wind power production.

Wind power production does not conform to consumption. The network must be dimensioned to withstand the transmission of production when the load is low, i.e., about 25% of the peak load. The electrical system is built for existing distribution and not for large distributed generation .

Wind power production of this size results in considerable consumption of reactive power, which ought to be compensated in a reasonable way to retain voltage quality while minimizing net losses. Production varies randomly, which puts considerable demands on voltage regulation. For the successful expansion of wind power, the electrical system must be adjusted so that it can regulate and retain voltage quality in regard to reactive and active power, and other phenomena that that arise in an electrical system with wind power production.

With the call for Jersey to look at wind generation from offshore wind farms, it is helpful to note that Gotland has been developing Gotland HVDC Light technology to allow for the variations in power from wind. Jersey is unlikely ever to have the winds that Gotland does, and it is a much smaller Island, but there may still be techniques and technology available that we can appropriate to improve our electricity generation in the long term.

Links:
(1) http://www.bbc.co.uk/news/world-europe-jersey-18484552
(2) http://www.thisisjersey.com/news/2012/06/18/power-cut-prompts-appeal-to-islanders
(3) www05.abb.com/global/scot/scot271.nsf/veritydisplay/8e1e666b438c7dffc1256e46004609d8/$file/abb%20special%20report%2011_03.pdf
(4) /library.abb.com/GLOBAL/SCOT/scot221.nsf/VerityDisplay/0364E3861597E488C1256FDA004C8CA9/$File/ciredgot.pdf

1 comment:

James said...

The last reports on the Jersey Electricity Website are a few years out of date, but there is a note in the 2009 report that the highest load in Jersey this year was 153.1MW in January 2009, just slightly less than our largest ever peak of 156.8MW, which occurred in December 2007.

It's certainly gone higher since: see this. I'm fairly certain BBC Jersey have reported new peaks subsequently.