Delta vs Wye.

Hello all,
This is not my area of expertise, and I would like to hear your comments, not just what the theory says.
What are the pros and cons of using Delta or Wye to power an industrial plant?

Thank you!

If you have any loads that need a neutral (think lighting), then you need a wye.

With a delta you end up with usually, one of the phases grounded, so you must remember to only install 2 of 3 fuses and the 3rd phase gets a bus bar.

Here we have a wye sevice, but the neutral hasn't been carried anywhere past the MDP, since the lighting loads are off it.

Can you say that this is a good summary of their pros and cons?

The WYE power system generally offers neutral grounding giving the user a dual voltage system which is ground fault protected and the neutral reference many drive systems required for operation. The phase voltages are balanced to ground level unless the neutral is not hooked up and/or disconnected. If the neutral is not connected the system can no longer be used as a dual voltage power system. This could result in phase voltages becoming unstable. Transient voltages can cause severe damage to the insulation systems of all the equipment connected to it. WYE power systems cannot and do not filter out the harmonic noise caused by the controls and drives they are powering.

The DELTA power system is generally not grounded with an intentional ground connection at the power transformer level so the ground current level is very low with the first ground fault. It can operate smoothly with one phase solidly grounded. It is a natural harmonic filter and can feed surge current when necessary with less line voltage fluctuations. The DELTA power system design has been the workhorse of the industry for years, but it also has its draw backs: Phase voltages can become unbalanced to ground for many reasons, there is no neutral reference required by some drive manufacturers, and the second ground causes a phase-to-phase fault through ground. Transient voltage events cause high voltage stress on the insulation systems of all of the equipment.

you would get better results if you posted your qustion on an electrical website. i also belong to www.mikeholt.com - an electrical forum.

regards,
james

James Mcquade said:

you would get better results if you posted your qustion on an electrical website. i also belong to www.mikeholt.com - an electrical forum.

regards,
james

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Thank you for the tip! But, could you say your comments so we can close this thread?

Elcan said:

Can you say that this is a good summary of their pros and cons?

The WYE power system generally offers neutral grounding giving the user a dual voltage system which is ground fault protected and the neutral reference many drive systems required for operation. The phase voltages are balanced to ground level unless the neutral is not hooked up and/or disconnected. If the neutral is not connected the system can no longer be used as a dual voltage power system. This could result in phase voltages becoming unstable. Transient voltages can cause severe damage to the insulation systems of all the equipment connected to it. WYE power systems cannot and do not filter out the harmonic noise caused by the controls and drives they are powering.

The DELTA power system is generally not grounded with an intentional ground connection at the power transformer level so the ground current level is very low with the first ground fault. It can operate smoothly with one phase solidly grounded. It is a natural harmonic filter and can feed surge current when necessary with less line voltage fluctuations. The DELTA power system design has been the workhorse of the industry for years, but it also has its draw backs: Phase voltages can become unbalanced to ground for many reasons, there is no neutral reference required by some drive manufacturers, and the second ground causes a phase-to-phase fault through ground. Transient voltage events cause high voltage stress on the insulation systems of all of the equipment.

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I would say this is a good 100 word or less summary of wye vs delta. You do not make any mention of what your industry is and this is the importaant part I think.

KNOW THY LOAD

Then figure out how to supply it.

Dan Bentler

leitmotif said:

I would say this is a good 100 word or less summary of wye vs delta.

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Thank you for your comment!

You do not make any mention of what your industry is and this is the importaant part I think.

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My question is in general. I heard about a plant (a sloughterhouse) that was configured as delta and they wanted to change to wye with ground, and that made me think about this topic.

Elcan,

its been too long for me to give the pros and cons.

i'll try

the y system can give you dual voltages.
it can also give you 3 phase , neutral and ground depending
on your plant requirements.
it can also give you a wild leg system in which 2 of the 3 phases line to ground will give 120 volts, the other phase will give 240 volts (if you go with 240 volts).

the delta system does not give you dual voltages unless you use a setp up/down transformer.

like i said, its been too long.
each has its own merits, pros and cons.

the key is what will your plant be doing, loads, power factor,
start / stop currents, and a host of other questions.

i mentioned the site because thats what they do and
you will get a lot of insight.

regards,
james

Thank you, James!

All of the above comments deal with the operational aspects of delta vs. wye distribution but ignore the safety aspects.

The wye system is, by my estimation a far safer system than delta. First, the voltages (assuming the center of the wye is grounded) are entirely predictable---480V phase to phase and 277V phase to ground. With floating delta, while you will have 480V phase to phase, there is no control over phase to ground voltages. One leg could and often is accidently grounded so it will be zero volts to ground but the other two phases will be forced to 480V to ground. Or, worse, the whole network can be taken to a very high voltage to ground. I've seen 4160/480V transformers with defective or leaking insulation which produce 480V phase to phase but have the whole secondary network floating at 4160V to ground. Your maintenance people have 1000V cat IV meters but unknowingly are being exposed to much higher lethal voltages. I've seen floating networks in automotive plants floating 800VDC above ground. That, too, is not what your maintenance people are equipt to handle. And there is NO WARNING that these voltages are present!

Second, 277VAC to ground does not usually conduct thru dust unless it is very wet or is otherwise conductive. 480VAC, on the other hand, ionizes dust easily. When that happens, you can have a properly locked out, tagged out machine with the 480V to ground conductors leaking current around the disconnect thru ionized dust causing the load side conductors to float up to 480V. I had this happen to me twenty years ago on a corner-grounded 480V floating delta system and I am lucky to have lived thru the experience. That's right, a locked out and tagged out machine with 480V on the load side conductors! This would not have happened if the machine had been fed with grounded-wye 480V.

Bottom line: I believe floating 480V networks should be unlawful to install due to the safety issues. If any of you are unfortunate enough to work in a facility with this kind of power distribution, please protect yourself by adding a four-legged ground wire to your tool kit. Whenever you lock out a machine, also attach one leg of the ground strap to ground and then the remaining three to each of the load-side conductors. Only then can you be sure they are safe. I know, its a bother; but it's your life.

And, as for new construction, please, no more floating networks.

I really appreciate your comments, Dick.

DickDV said:

All of the above comments deal with the operational aspects of delta vs. wye distribution but ignore the safety aspects.

The wye system is, by my estimation a far safer system than delta. First, the voltages (assuming the center of the wye is grounded) are entirely predictable---480V phase to phase and 277V phase to ground. With floating delta, while you will have 480V phase to phase, there is no control over phase to ground voltages. One leg could and often is accidently grounded so it will be zero volts to ground but the other two phases will be forced to 480V to ground. Or, worse, the whole network can be taken to a very high voltage to ground. I've seen 4160/480V transformers with defective or leaking insulation which produce 480V phase to phase but have the whole secondary network floating at 4160V to ground. Your maintenance people have 1000V cat IV meters but unknowingly are being exposed to much higher lethal voltages. I've seen floating networks in automotive plants floating 800VDC above ground. That, too, is not what your maintenance people are equipt to handle. And there is NO WARNING that these voltages are present!

Second, 277VAC to ground does not usually conduct thru dust unless it is very wet or is otherwise conductive. 480VAC, on the other hand, ionizes dust easily. When that happens, you can have a properly locked out, tagged out machine with the 480V to ground conductors leaking current around the disconnect thru ionized dust causing the load side conductors to float up to 480V. I had this happen to me twenty years ago on a corner-grounded 480V floating delta system and I am lucky to have lived thru the experience. That's right, a locked out and tagged out machine with 480V on the load side conductors! This would not have happened if the machine had been fed with grounded-wye 480V.

Bottom line: I believe floating 480V networks should be unlawful to install due to the safety issues. If any of you are unfortunate enough to work in a facility with this kind of power distribution, please protect yourself by adding a four-legged ground wire to your tool kit. Whenever you lock out a machine, also attach one leg of the ground strap to ground and then the remaining three to each of the load-side conductors. Only then can you be sure they are safe. I know, its a bother; but it's your life.

And, as for new construction, please, no more floating networks.

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How would you get a 800VDC reading? Wasthis meant to be 800VAC?

One advant of a Wye system is that many VFD Drives and Servos (particularly those coming in from Europe) can only run on a 480V Wye system. The Componenets used on the power circuit are only rated for ~400V line to ground. In a Wye system it is nearly impossible to get over 277V line to ground. On a Delta system if one line goes to ground (or near ground) the other legs can see voltages of ~480 Line to ground and then blow the filtering capacitors and other under rated components in those drives. This could effect any and all of those drives in your plant.

Even the newer AB drive have jumpers in them in regards to filtering capacitors. Basically you have to disable those components if you hook up the drive to a 480 wye system (this is default way they ship these drives). If you enable those components in a 480 wye and you have a ground fault you could blow the filtering capacitors of any drive that has those enabled.

No, Tim, I meant 800VDC. Since the network itself is floating with respect to ground, it could be ANY voltage to ground, AC or DC, high or low or zero. That's precisely where the hazard comes in.

And, yes, many drives will not tolerate floating or corner-grounded systems. AB goes to the extreme of removing all of their front end surge suppressors on ungrounded power leaving the drive essentially naked. Some others only need to disconnect their surge suppressors going to ground leaving the phase-to-phase protection in place. In addition, the output short circuit and ground fault protection has to be turned off to avoid all kinds of nuisance faults when the input power makes a sudden shift in ground reference. I will not commission any DC drive with unbalanced or ungrounded power. If the plant has only floating AC, a transformer is required. If you don't do that, the motor armature is being slammed back and forth 120 times per second with respect to voltage to ground and the line capacitance will destroy the brushes prematurely from arcing.

Just one other issue with ungrounded input power on AC drives: All of the drive output pulse noise that couples into ground thru stray lead capacitance has no way to get back into the power leads on an ungrounded system. As a result, these pulses will seek some other path to the AC power network. Maybe it will be thru that computer power supply, or the shielding on your sensitive instrumentation, or some other ugly and highly inconvenient place.

There are simply dozens of nasty issues that come up with floating or corner grounded power. Some are just nuisances like false drive faulting and some are far worse, like electricians electrocuted thru their supposedly safe CAT IV 1000V rated meters.

I don't mean to whine on this subject but if I can save just one life, it will be worth it.

DickDV said:

No, Tim, I meant 800VDC. Since the network itself is floating with respect to ground, it could be ANY voltage to ground, AC or DC, high or low or zero. That's precisely where the hazard comes in.

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I am sorry but I just am not able to understand how you would get 800 DDC from a floating AC system?

I am just a maintenance tech with years of mechanical experience but I have only been doing electrical a little over a year so I have a lot to learn even on basics.

This is a very intresting subject / post. I am just trying to understand it fully.