up vote 2 down vote favorite

I am thinking of the issue that

the TEPCO electric transmission networks cannot be taken over by other electric companies because of frequency difference.

TEPCO is the electric company having the nuclear crisis.

Why cannot generators having different frequencies supply in the same transmission line?

Edit

I think most electric equipments can work at either 50 OR 60 Hz. So what is the problem?

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up vote 7 down vote accepted

Equipment designed to work with one frequency power will not necessarily work with another frequency.

  • Transformers designed to work with 60Hz will have lower ratings when working at 50Hz (Important for power distribution and individual devices)
  • The speed (RPM) of AC motors is tied directly to the power line frequency.
  • AC Wall clocks wouldn't work :)

The combination of 50Hz and 60Hz would cause generators to fight eachother

  • See the plot of both 50Hz and 60Hz superimposed from Wolfram
  • The blue plot shows the difference. Where the function is large, the generators are fighting eachother (Big Boom!)
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up vote 3 down vote

A voltage phase mismatch from one generator and the power grid would mean a voltage difference between the grid and the generator during different parts of the phase(s). This voltage difference means current would flow to/from the grid and the generator, causing resistive heating in the lines.

Also, I don't know all the mechanical and electrical consequences of trying to run a spinning turbine in reverse, but I don't think it would be good.

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  • 1
    These consequences would be fatal to at least the generator. All electrical grid components are always precisely synchronized (using phase detectors) before being connected together. – jpc Apr 14 '11 at 14:53
  • The generator and turbine assembly would rather break apart mechanically than run asychronously to the net. – starblue Apr 14 '11 at 17:06
up vote 3 down vote

All power line components should work fine at both 50 and 60Hz.

On the other hand the whole electrical grid has to be precisely synchronized so there is no easy way to suddenly connect several circuits together.

There is no difference between connecting:

  • two out-of-phase generators
  • 24V DC to 12V DC
  • a supply directly to the ground (a short circuit).
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up vote 2 down vote

It's a lot more than just the transformers. It's turbines, control systems, meters, loads...

TEPCO's sole generating source isn't Fukushima - there's additional nuclear in Niigata as well as fossil fuel generation. You can't mix frequencies unless the whole system is changed.

Also according to Wikipedia, there are several HVDC stations that interconnect between the 50Hz and 60Hz grids through an intermediary conversion to HVDC. Inefficient, sure, but at least there is some interconnection.

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  • +1 It makes sense. I just wait for other additional answers. – LaTeX Apr 14 '11 at 13:44
  • What would be the effect of mechanically connecting two squirrel-cage motors which had appropriately-different different numbers of windings (e.g. a 119:99 ratio)? My impression would be that the 60Hz motor would want to turn at 0.504 revs/sec while the 50Hz motor would want to turn 50.505 revs/sec. The net effect would be that the 50Hz motor would convert electrical power to mechanical energy, and the 60Hz motor would do the opposite. There would be some "slippage" of the fields in the cage, but I don't know how much energy that would represent. – supercat Apr 14 '11 at 22:45
up vote 2 down vote

Loads notwithstanding, if you just connect a 50Hz source and a 60Hz source together, they will alternate between being in-phase and out-of-phase 10 times per second. So half the time, things would be fine, but the other half the time, the sources would be trying to burn one another out. This might not be such a big deal except that when the sources can supple megawatts, there would definitely be smoke.

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