Regulating temperature of mains connected heating element: Skipping mains half cycles

[treez]

Thanks yes, i appreciate that probability makes synchronisation most unlikely...but there is juts that chance...and what if it happened..?...disaster?

 

[Easy peasy]

Seriously unbalanced single phase loads can trip the pole fuse - due to DC in the transformer

Firing full cycles is OK - but needs a uP to make it better, e.g. skip 1, fire 3, skip1 , fire 4, skip 1, fire 3 ...

this gives you a better range of control than other methods ...

 

[treez]

Firing full cycles is OK - but needs a uP to make it better, e.g. skip 1, fire 3, skip1 , fire 4, skip 1, fire 3 ...

Thanks for confirming its OK when full 20ms cycles are skiped....It just seems bizarre that a power network could be delivering GigaWatts of power in this way (all skipping sync'd up) and not suffer any difficulty.

 

[Easy peasy]

short answer is that it's not ...

 

[treez]

Thanks,

I think what would worry us is that we may not manage to chop the mains current waveform exactly at its zero crossing every time…and in fact there could be some little “bits” of mains current chopped when it was just slightly above the zero cross, (negatively or positively) and overall, these “bits” of current, could result in an overall DC level in the supply system.

Maybe this is why mains cycle skipping regulation is not that common?

 

[FvM]

Cycle skipping is produced by many power controllers with zero crossing solid state relays, in so far it's quite common.

 

[Easy peasy]

SCR's do a pretty good job of turning off at near zero current with just a bit of reverse - and this is generally symmetric - so easy to control 100A of a 3 phase 230/400 100kW disti transformer with no issues - just need well thought out control electronics - and a good programmer who can count to whole numbers of 20mS periods ...