Slow/Fast dial

We went to a power station a couple of weeks ago. A lovely 1930s art deco one in south-west Scotland. The dial in the middle was one of the best things about it - it only goes Slow or Fast. Nothing more exact than that. In a power station when you'd think things need to be quite precise. The whole place was great and then we got to walk over a dam. I've written it all up on Nothing To See Here.

Just wanted to say I enjoyed seeing this 'ephemera-esque' item on your blog. The items I feature on dovetail nicely with this post. Very interesting. Nice work.

Geeky engineer-type here. Since you asked... ;-)

The slow-fast indicator (called a synchroscope) is used when bringing a turbine up to speed and preparing to connect it to the national grid. The turbine drives an alternator (the kind of generator that produces AC), and the faster the alternator spins, the higher the frequency of the power it produces. Before an alternator is connected to the national grid, it must be running exactly in step (not just generating the same frequency, but also at the same point of output)-- otherwise bad things happen. The synchroscope is what you use to determine this.

The synchroscope's needle actually spins round and round like a clock hand, anticlockwise if the alternator is running slow (that is, at less than the grid's 50 Hz frequency), clockwise if fast. The closer the frequency matches, the slower the needle turns. Finally, when the needle is just c-r-a-w-l-i-n-g, the operator waits for it to point straight up (indicating perfect synchronization), at which point he makes the connection.

The frequency meters (the ones labeled "Hz") give a pretty good idea of an alternator's speed, but its output must also be "in phase" to connect with the grid. The synchroscope indicates when all is correct, and it really IS quite precise.

Thank you for that Old Grouch. It sounds like a truly amazing machine. I'm sorry for being so flippant about it.

Apologies unnecessary... it IS amusing, even to those in the know ;-)

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