How the National Grid tripped up

The UK National Grid’s vulnerability to unforeseen circumstances was no better demonstrated last Friday when millions of homes – mainly in London and the South East – were affected by a power cut.

Up until then, most of us in the United Kingdom thought that this sort of problem only occurred in other less well-developed nations, unless, of course, you are old enough to remember the blackouts of the 1970s.

So why did the outage occur?

Just as people were clocking off work and looking forward to the weekend, two power stations disconnected simultaneously, both of which were completely separate and coincidental incidents.

The gas-generated Little Bedford plant was the first to go down at 4.58pm and then Hornsea Windfarm in the North Sea followed two minutes later.

As renewable energy cannot be generated on demand (no-one has the ability to make the wind blow, after all), there was a shortfall of available power on the grid.

The National Grid runs at a frequency of 50Hz, and when supply falls and demand for energy remains high, the frequency drops, in this case to 48.9Hz.

Drops in frequency cause substantial infrastructure damage and to safeguard against this an automated system shuts down part of the grid to cut demand, which in turn increases frequency back up.

The big problem lies with the demand cutting process. If automated, why is it automated to shut down hospitals, like the one in Ipswich and key transport hubs such as Clapham Junction in South London?

A government investigation has now been launched into the incident, the first of its kind since 2008, and the National Grid must review and report to OFGEM.

One of the obvious conclusions to draw from this is that the power network has little resilience, especially when it goes wrong at 5pm on a Friday afternoon.