Re: How can I switch 220V~ at a fast rate without a relay?

From your question it looks like you want to switch 220 VAC with low 
distortion and that you want to preserve the sinusoidal waveform.  To 
preserve the sinusoidal waveform you must switch on or off *only* at the 
beginning of each sine wave cycle, which would be 50 Hz (20 millisecond) 
for the mains in Europe, and I'm going to assume that this is what you mean 
by 'switch very often'.  

To do this you need a suitable relay *and* what is called a zero-crossing 
detector.  This detector monitors the input sine wave and puts out a pulse 
when and only when the input voltage is close to zero volts.  You use this 
pulse to switch the relay on or off.  Then we need the relay.  What you 
want is really a solid state relay--it is the only type fast enough to 
switch at 50 Hz--and a relay based on MOS power transistors will ensure low 
distortion.  Digi-Key (www.digikey.com) lists a number of such relays, and 
some of them have the 'zero-crossing' provision built in, so you can take 
care of everything with one part.  The listed prices run from US$5 to 
US$15, and the switching times are all below 2 milliseconds, which should 
easily meet your distortion requirements.  Just a couple of things:

1.  You want to use an opto-isolated relay for safety.  This uses infrared 
light from a built in LED to turn on the transistors.
2.  When working with 220 V~, remember that the peak-to-peak voltage is 622 
V to which you must add a tolerance.  DO NOT USE A RELAY RATED AT LESS THAN 
800 VOLTS!!!!
3.  WHEN WORKING WITH SUCH HIGH VOLTAGES, USE **EXTREME** CAUTION!!!!!!

Good luck!