Posted on: 7th May 2012

It’s finals season, so you may not be able to get your experiments done at JET. Not because the scientists neglect their duties and sneak off to watch the football, but because JET is not allowed to run.

JET’s peak power demand is over one percent of the UK supply – albeit for very short periods – so the supply from the grid is limited to 575 megawatts, and JET’s two flywheels are used to top up if necessary. But at some times, JET is not allowed to take any power from the grid at all.

This happens when there are other major energy consuming events – such as halftime in a major football final, or in the ad-breaks in a popular TV show – times at which millions of people will switch on the kettle or go to the toilet, which creates an electrical load on the water pumping system. In fact JET power supply engineers are in regular contact with the grid, who advise every day the times at which pulses should be avoided – for example the fifteen to twenty minutes around sunset when lots of people turn on their lights. The engineers also monitor the frequency of the electricity supplied by the grid throughout the day: if the frequency falls much below the regulation 50 Hz they know the grid is under load and so they will recommend to the Engineer In Charge that pulses not be run.

There are also times when there is an unexpected load on the grid, on these occasions the grid operators can abort a JET pulse themselves. At the beginning of every JET pulse countdown, an alarm sounds in the UK national grid control room, giving the operators thirty seconds to decide whether there is enough capacity. If not, they can inhibit the pulse – a signal comes back to the JET computer system, which prevents the pulse from going ahead.

At these times, when no pulses can be run, the scientists just might sneak off to watch the football. But more likely, they will get back to their office and start planning the next experiment!