Thank you for your post.
The main problem here is that you wish to measure 3 phases. All of the oscilloscopes that we do are 2 channel and would thus not enable you to monitor 3 phases. You could use 2 scopes but they would need to be on seperate computers.
What you would need is a high voltage, isolating, differential probe. The size of this would depend on the size of the voltage you are looking at. If it is normal mains electricity of 240V then you could use our X10/X100 voltage probe which would fulfill your needs.
You would need a probe for all channels.
There is then a couple of ways you can go about monitoring. You could set the scope up with a trigger and infinate persistance so that any spikes would be drawn on the screen and would not disappear. This would enable you to see the quality of the electrical signal but could not tell you when these spikes happened.
The other way of going about it would be to set the trigger level slightly higher than the voltage level. This way if any spike came in it would see it and trigger on it. You could then set it to save on trigger and it would save each indivdual waveform of every time this happened. The only problem with this could be that if you are looking for positive spikes, it would not record any negative spikes.
As for which scope you would need, I would suggest the ADC-212/3 would be a good choice as this is also used in automotive diagnostics which looks at spikes and small signal changes.
Hope this helps