What are the main benefits between DELTA and WYE systems...?

[Nooshzad]

What are the main benefits between DELTA and WYE systems...?

 

[DanDel]

Benefits to who or what? To the manufacturer of equipment connected wye or delta? To the owners of such equipment? To the Utility? To the electrician or engineer?
Usually, design specs call for wye or delta.
Wye will provide a neutral, and delta won't.
Wye winding insulation can be rated lower tahn delta winding insulatuon for the same applied voltage.

 

[Nooshzad]

DanDel-

As you've mentioned, I like to know the benefits to mfg. of equipment, end-user of equipment, Utilit company. Also, you mentioned that no Neutral line for Delta, then what about the center tap from Delta to get 120V (line to center)...?

thanks

 

[Heydave]

The 120 volt circuit is a Wye connection.
Delta does not send any power through a neutral no matter what the load imbalance is between the legs. That requires a wye circuit.
Much of the electrical noise found on telephone lines etc. comes from the current flowing through neutral from wye circuits. I have seen this voltage as high as 110 volts between neighborhoods. Since telephone pairs are insulated at the customer end but referenced to ground at the central office, this results in 110 volts common mode to ground! In one case I worked with, a telephone worker was killed when the voltage to ground was 180 volts because of neutral voltage drop.
When a neutral carrying high currents is cut, the result is often fires and occasionally deaths. When an unbalanced wye feed has its neutral back to the source, or between legs, cut, the underloaded leg will go overvoltage and the overloaded leg will go undervoltage. Either case will destroy equipment. From a safety standpoint, 3 phase delta is safer and cheaper to deliver than 3 phase wye but we do not live in a three phase world. We have both 3 phase and single phase thus we have wye circuits to deliver the single phase power.

 

[busbar]

One reference is Franklin & Franklin, J&P Transformer Book, Butterworths. Tradesoffs are numerous, and out of the scope of this forum to detail. Some self-study will be necessary.

 

[Nooshzad]

thanks for everyone's input...I think as "busbar" suggested, I need to some self studing to better educate myself. I wonder if there is a good and simple to follow book out there...?

thanks again to everyone.

 

[davidbeach]

The 120V circuit off of a 240V delta with a center tap IS NOT a Wye connection. It is 120V phase to "neutral", available from two of the phases to neutral. The third phase is the "wild leg" and operates at 208V phase to neutral. This neutral is not centered between all of the phases as it is in a wye system, and this is one of the reasons that there has never been a definition of "Neutral" included in the NEC, nobody has written one that includes everything used as a neutral while excluding everything that is not used as a neutral.

 

[mta0303]

Is this common to use a large capacity (50 to 60 MVA) step down transformer with on load automatic voltage regulator (+/-)15% for the auxiliaries of a power plant instead of simple on load tap changer?
What is the impact on cost, if such transformer is used?

An expert advised is requested please.

mta0303

 

[peebee]

As previously requested, you need to be a bit more specific about the type of device in question.

If transformers: at least one winding of most transformers is usually specified as delta to trap zero-sequence currents, including 3rd-harmonic currents. The zero-sequence currents end up circulating within the transformer (hence the name "circulating currents&quot rather than being imposed on the primary transformer supply.