Why are Power Grids so Large?

As to why they chose 60 cycles over 50 I have no clue

I believe it goes back to Tesla and the early days of a.c. Tesla, worked out (for the equipment of the time) that the most efficient arrangement was 3-phases, 60Hz and around 220V. The Americans adopted the 60Hz but but kept the 110-ish volts of their existing d.c. system (which probably was safe to touch - even today we regard up to 120V d.c. as ELV) - while Europe adopted the 220V bit but for some reason preferred 50Hz.


One theory I rather liked was that 220/240V was adopted in regions that drank tea, 110V in areas that preferred coffee. The logic being that you need 2-3kW to boil a reasonable sized kettle to make a pot of tea but practical sized domestic plugs & sockets can only carry 10 to 16A - hence 220-ish volts in tea areas (i.e. British and Dutch influence). Coffee percolators could manage on less power so that 110V was sufficient - e.g. in the US.


   - Andy.

Generally you leave the fuel in the reactor, and raise or lower control rods in between the fuel to alter the rate of reaction, and therefore the vigour of steam production.

It is the economics of keeping the plant running without an income from sales that makes it worth running land based reactors at full power.

It is quite possible, but very wasteful to keep a reactor in the tickover state with the fuel in almost indefinitely.
The MOD has a large no of redundant submarines in that state.

The UK formerly used many different frequencies including 12 cycles, 15, 16.67, 25, 33.3, 40, 50, 60 and 100 cycles, and others. The Weir report recommended a new standard of 50 cycles, based on this being the highest frequency already in widespread use. Higher frequency supplies existed but were never popular. 50 cycles was also considered to be the lowest frequency suitable for domestic lighting. At less than 50 cycles lamp flicker becomes obtrusive especially on low power lamps.

The lower frequency supplies were primarily for electric power, not for lighting. Factories with a low frequency power supply tended to either use gas lighting, or a separate DC supply for lighting. Another option was 6 volt vehicle headlight lamps worked from transformers, these tended not to flicker due to the very thick filaments.


IIRC Lynmouth had a 100 cycle supply until 1952 when the local power station was destroyed by the great flood.

Well we can of course shut down our nuclear reactors, but it is much easier to wind the gas up and down. If we ever are over supplied by nuclear power then you will see it being modulated.


On the question of frequencies, low ones allow thicker and more lossy laminations on motors and so on, and that makes traction easier to make.

Higher frequencies make transformers lighter, and lamps less flickery. (much below 50Hz, flicker becomes really noticeable on thin filaments that have not much mass.)

The weight  of transformers ironworks thing is the reason behind 400Hz on 'planes.


Both 50 and 60 Hz are both near the fairly slowly changing optimum / compromise for lighting and motors, given the steels and bearing speeds of the 1920s when it was all being hammered out for various national grids..

Great replies- thanks :)