Readers may recall the story I posted about a major power cut in the North of Scotland last month and the speculation that the underlying cause was windfarms. This has officially been put down to a faulty relay, but today Euan Mearns notes a letter by an electrical engineer in a local newspaper which tells another story:
SIR, I was amazed to learn that a Scottish Hydro Electric transmission spokeswoman said “repairs are being carried out on the faulty relay” that allegedly caused the power cut on April 16 (“works to fend off blackouts”, P&J, May 10).
I have been an electrical engineer for over 40 years and have never heard of anyone “repairing” a hermetically sealed relay switch.
The relay switch operated perfectly on the windy night of April 16 when it detected a sudden surge of voltage and frequency that fell outside acceptable parameters.
A relay switch has two states: on and off. All of these relay switches operated perfectly on the night, independent of the relay switch at Knocknagael Substation which is, itself fed by at least two windfarms, Farr and Moy.
This was what is known as a “rolling blackout”. It is ludicrous to suggest that all lights went out all over the north at 8.30pm exactly. My area went out at 8.43pm when the blast of wind reached Novar windfarm and toggled the relay switch to off to protect its local circuit and so on up the coast.
Grid operators can switch windfarms on and off remotely – if there is a risk of too much wind generating too much “wrong time” low-grade electricity with what is known in the industry as “flicker”. The grid cannot handle more than 10% of flicker contaminated electricity at any given nanosecond and this limit was exceeded on the night.
The operators were caught on the hop. With no electricity, all the windfarms had to be isolated manually.
The spokeswoman goes on to say that they will be making changes to how the protective equipment operates. This is code for shutting down windfarms even earlier in windy conditions so that the operators get more and more constraint payments for not generating when the wind speed is just right.
Andrew H Mackay, Tain