Hi I had alook at the posts on lost neutral, but my question is not covered. Here we go, can someone provide me with composite waveforms for a split phase system with the neutral in place along with the waveform when the neutral is open.Please see link.(http://www.allaboutcircuits.com/vol_2/chpt_10/1.html),

 

the voltage waveform present on the neutral will depend on the load(s)

 

the voltage waveform present on the neutral will depend on the load(s)

You can assume any load, but let's say it is balanced. What I am looking for is this . You have 2- 120volts relative to the neutral, and 240 volts across lines 1 and 2 .Looking at say 2 cycles of the 240 volts How does 2 cycles of the waveforms for the 2 -120 volts superimpose on the waveform of the240 volts.Or if not superimposed drawn side by side THE neutral line is the minus side for the top half and the plus side for the bottom half, but can we draw the 2 --120 volts waveforms with their own zero reference line. This is a curiosity of mine and would be glad for ideas.

 

The individual voltage drops across the two series loads will add up to 240V.

If the loads are identical each load has 120V across it.

Depending upon where you take a (single ended) reference point for a simultaneous two channel measurement you will get various waveform results. For a fully floating system there are really only three cases - with the reference at the common connection of the loads or at either side of the 240V source. If you have access to a circuit simulation program you could easily satisfy yourself as to the various combinations possible.

Alternatively if you used an oscilloscope with two true differential input channels you could correctly place the probes across the loads and satisfy yourself that

1. For identical loads their voltages were of equal magnitude and in phase and algebraically sum to 240V.
2. For different loads their algebraic summation will still be 240V but their individual magnitudes (& possibly phase - with reactive loads) will be different.

 

Sorry - I forgot there are two AC sources involved. So there will be more than three (single ended) measurement configurations possible depending on where one places a reference node. I guess that makes four if one includes the common connection point for the two 120V sources.

 

This is a PSIM model which shows some of the possibilities regarding measurement "schemes".

 

Hi TNK, thanks for your interest and effort. I do not have a simulation program. If I may say, if there was an any one to provide a solution , it would have been you . I really appreciate your contibution to the forum, and read possibly all your posts. Thanks again.