Im looking at a Technical Paper from Chromalox a heater manufacturer among other things. and there are two examples for three phase circuits one is an open delta and the other is an open wye configuration. Just looking at the diagrams They looks exactly the same to me two resistances(elements) wired in series then a line voltage(phase) to each point one on each end and the third to the middle inbetween the elements?? however it is stated that for the delta version loss of a phase or element would reduce wattage output by 33% and for the wye it would reduce the output by 50%. what am I missing? the only thing really different is where they are measuring the Line voltage VL on the Delta they measure from one line to the centertap basically, on the wye it is across both heater resistances. any clarity would help thank you.:?
What Is the Difference between an open delta and an open wye?
- Thread starter Clayton79
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What's the difference between an open wye and a closed wye?
They are using the example of just two heating elements connected to a three phase system. its the Chromalox technical paper I-37 http://www.chromalox.com/catalog/re...ory-Three-Phase-Equations-Wiring-Diagrams.pdf
kwired
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Can you post the document in question or a link to it?
I don't see how you can connect the same element wye vs delta and get the same power out of it - even if only a partial delta or wye configuration. To connect in what is likely an "open wye" you likely have two phases connected to each end and the neutral connected to the common point. Lose one phase you lose one element and half the total output. But say this is connected to 480/277 volts and each element is seeing only 277 volts.
Now connect same elements in same fashion but instead of connecting the neutral to the common point connect the third phase there. I would call that "open delta" connected. But you get 480 volts across each element. Lose either phase on the open end and you still lose half the output because you will have no current flow in half of the elements. Lose input from the common phase but maintain continuity between each element on the common end and you will reduce voltage across each element to 277 (assuming they are equal resistance). This is not going to reduce output by one third but won't be too far from one third. It should reduce total output to about 58% of original output.
I don't see how you can connect the same element wye vs delta and get the same power out of it - even if only a partial delta or wye configuration. To connect in what is likely an "open wye" you likely have two phases connected to each end and the neutral connected to the common point. Lose one phase you lose one element and half the total output. But say this is connected to 480/277 volts and each element is seeing only 277 volts.
Now connect same elements in same fashion but instead of connecting the neutral to the common point connect the third phase there. I would call that "open delta" connected. But you get 480 volts across each element. Lose either phase on the open end and you still lose half the output because you will have no current flow in half of the elements. Lose input from the common phase but maintain continuity between each element on the common end and you will reduce voltage across each element to 277 (assuming they are equal resistance). This is not going to reduce output by one third but won't be too far from one third. It should reduce total output to about 58% of original output.
kwired
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Thanks, you answered my request before it appeared
Read what it says carefully.
They are saying that open delta circuit has 1/3 less output than a full delta circuit, they are not talking about losing a phase to something already connected in open delta fashion.
Similar meaning about the wye connected elements. Losing one element of a three phase element setup that is wye connected is not the same as losing an input phase to an open wye setup.
Read what it says carefully.
They are saying that open delta circuit has 1/3 less output than a full delta circuit, they are not talking about losing a phase to something already connected in open delta fashion.
Similar meaning about the wye connected elements. Losing one element of a three phase element setup that is wye connected is not the same as losing an input phase to an open wye setup.
iceworm
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Slow poster - Adding to kwired's response.
In the case of the diagram they show for losing an element in the Wye configuration, there is no neutral, so the two remaining elements are in series across the line voltage. So the power drops to 1/2 of the circuit with three functioning elements.
ice
In the case of the diagram they show for losing an element in the Wye configuration, there is no neutral, so the two remaining elements are in series across the line voltage. So the power drops to 1/2 of the circuit with three functioning elements.
ice
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kwired
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One reason to have the delta and wye configurations is the same elements can be used for two voltages.
Connect in delta to use on a 240 volt system - you put 240 volts across each element.
Connect in wye to use on a 480 volt system - you put 277 volts across each element.
Resistance of elements remains constant, you are only changing applied voltage to each individual element.
Of course you will get a little less output from the 240 volt configuration, and even less if connected to 208 volts.
Connect in delta to use on a 240 volt system - you put 240 volts across each element.
Connect in wye to use on a 480 volt system - you put 277 volts across each element.
Resistance of elements remains constant, you are only changing applied voltage to each individual element.
Of course you will get a little less output from the 240 volt configuration, and even less if connected to 208 volts.
So in the open Y there is no line connected to the center point? correct that would be the difference, I keep thinking Im hooking all three phases(lines) of power up. onlyl in the Open delta would you have all three Phases hooked up. Thank you, that would make sense, I forgot about the neutral center tap basically. Does that sound correct?
iceworm
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QUOTE=Clayton79;1550295
So in the open Y there is no line connected to the center point?
Yes. In the diagram shown, there is no neutral connected to the wye point.
correct that would be the difference,
I keep thinking Im hooking all three phases(lines) of power up. onlyl in the Open delta would you have all three Phases hooked up.
In the broken wye, all three phases are connected. Howerer, one phase is connected to a burned out element. So it is the same effect as the phase not being connected
Thank you, that would make sense, I forgot about the neutral center tap basically. Does that sound correct?
Yes
ice
So in the open Y there is no line connected to the center point?
Yes. In the diagram shown, there is no neutral connected to the wye point.
correct that would be the difference,
I keep thinking Im hooking all three phases(lines) of power up. onlyl in the Open delta would you have all three Phases hooked up.
In the broken wye, all three phases are connected. Howerer, one phase is connected to a burned out element. So it is the same effect as the phase not being connected
Thank you, that would make sense, I forgot about the neutral center tap basically. Does that sound correct?
Yes
ice
kwired
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In the open wye, it will still work with a neutral connected to the center point, and would still continue to work at 50% output if one element is open or loses the input phase conductor. If no neutral is connected then any open circuit condition means 100% loss of output.
Actually I need to change that, as well as earlier mentioned information - if no neutral is connected to the open wye each element if equal resistance will see 240 volts across it if connected to a 480 source. If you connect the neutral you are ensuring there is 277 volts across each element and some current will flow on the neutral, but loss of one element still leaves you with the other one still operating at 277 volts.
Now take a full wye and each element is operating at 277 with or without the neutral connected. But lose input or continuity in one element and you revert to the open wye connection conditions, and what happens from there depends if you have a neutral connection or not.
Actually I need to change that, as well as earlier mentioned information - if no neutral is connected to the open wye each element if equal resistance will see 240 volts across it if connected to a 480 source. If you connect the neutral you are ensuring there is 277 volts across each element and some current will flow on the neutral, but loss of one element still leaves you with the other one still operating at 277 volts.
Now take a full wye and each element is operating at 277 with or without the neutral connected. But lose input or continuity in one element and you revert to the open wye connection conditions, and what happens from there depends if you have a neutral connection or not.
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iceworm
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