I recently purchased 2 little voltmeters they look like the sort that would go in a control or instrument panel they are connected with just 2 wires which provide the operating supply ( they light up green and red) however the green one states it will work between 20and 500 volts and the red one between 60 and 480 volts. When they are both on the green one indicates normally around 241 volts the red one shows 235 volts why the discrepancy I know it's not much but makes you wonder if one of them is lying. Secondly I've noticed that the green one tracks voltage changes faster than the red one and that a few times the green one jumps down to 238 then up to 241 multiple times while the red one stays the same and I think can see a slight flicker in my filament lamps when this is happening incidentally both meters are connected to the same plug a 2 pin 5 amp one
The problem with 3F is that shifted by 1/3 of a cycle it looks the same on all 3 phases, so with identical loads on all phases the neutral currents do not cancel, causing odd effects at star-delta transformers.
Indeed I've seen neutrals specced to be 3x the size of the lines, in IT data centres and so forth (Not that I've ever done any wiring in such places, just I follow such things with interest) effectively making it 3 single phase circuits. Because of harmonics. I imagine with our rapidly evolving power usage this is of serious concern to DNO's and such like?
Even back in the late 80s when I was training at a large university on the maintenance dept, there were issues with harmonics around the computing services floor (back then it was a single floor of the maths building) I recall being told to hold on to the 95mm2 singles feeding the busbar trunking and asked if i thought that heat was normal
The problem with 3F is that shifted by 1/3 of a cycle it looks the same on all 3 phases, so with identical loads on all phases the neutral currents do not cancel, causing odd effects at star-delta transformers.
Indeed I've seen neutrals specced to be 3x the size of the lines, in IT data centres and so forth (Not that I've ever done any wiring in such places, just I follow such things with interest) effectively making it 3 single phase circuits. Because of harmonics. I imagine with our rapidly evolving power usage this is of serious concern to DNO's and such like?
Even back in the late 80s when I was training at a large university on the maintenance dept, there were issues with harmonics around the computing services floor (back then it was a single floor of the maths building) I recall being told to hold on to the 95mm2 singles feeding the busbar trunking and asked if i thought that heat was normal
