mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Which is a better option for the primary of a power transformer?
Delta vs Wye primary
- Thread starter mbrooke
- Start date
- Status
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
General question .... general answer .....
Delta primary is best
Delta primary is best
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Delta is good. If the secondary is delta, you must either use s delta primary or leave the center point of the wye floating
Otherwise high circulating neutral currents can result.
Otherwise high circulating neutral currents can result.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
What are the pros and cons for each type in your debate?
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Be sure that if any of these MV XFMRs are being paralleled on the secondary, that you make those units the same (both delta or both Wye primary), due to the phase shift differences.
It depends on how the transformer will be protected on the primary and secondary, which is related to the physical size of the system on both sides, i.e. the lengths of cable or lines, and the level of reliability required. In general, delta primary and wye secondary is preferred for industrial and commercial applications. In utility applications it varies. Some utilities use wye-wye transformers with appropriate protection schemes and they can achieve acceptable reliability if the line impedances are high enough relative to the transformer impedances. In cases where the line impedances are less significant it may be difficult to economically coordinate the ground fault protection, so delta wye transformers are used to create separate "ground fault islands", which allows lower cost ground protection to be employed without sacrificing clearing times. Generally when we see wye-wye transformers in commercial or industrial occupancies it is difficult or extremely expensive to coordinate the protective devices and maintain acceptable clearing times to avoid literally burning the equipment down in case of a fault.
As with all generalizations, exceptions to the above do exist. For a conclusive answer, have a power systems engineer prepare cost estimates to protect a system with each type of transformer, ensuring that equal levels of reliability and equipment protection are provided in each system. Then compare the costs of the two options and you can select the lowest cost option for the particular situation.
As with all generalizations, exceptions to the above do exist. For a conclusive answer, have a power systems engineer prepare cost estimates to protect a system with each type of transformer, ensuring that equal levels of reliability and equipment protection are provided in each system. Then compare the costs of the two options and you can select the lowest cost option for the particular situation.
That's true, however ferroresonance is only a problem with single pole tripping devices (i.e. fuses) on the delta winding. If a 3 phase tripping device (breaker, recloser, etc.) is used with a delta primary ferroresonance is not a concern. Even if we're not concerned with ferroresonance, if we want to use fuses for primary protection think about the fuse response to a ground fault. Depending on the location in the winding, a fuse may not see a ground fault on a delta winding or it may have a slow response. A wye primary will allow the fuses to operate faster resulting in less damage to the transformer and faster clearing, meaning a shorter voltage sag for other custoemrs on the line.
All of that being said, any medium to large industrial service should have a delta wye transformer to segregate utility ground protection from plant ground protection, and it should be equipped with a 3 phase primary tripping device to better protect the transformer.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
Thanks! I was actually concerned about Ferroresonance as one of the possible problems. Ive heard that a grounded wye primary will cause inductive heating if one fuse blew? How many leg cores do I need to eliminate that issue?
Bugman1400
Senior Member
- Location
- Charlotte, NC
You can have resonance on either primary or secondary with either g-wye or delta on either side. As with most cases with resonance, it depends on the LC tuning of the circuit and the things that excite it. For example, I've seen resonance on a g-wye distribution side because a large customer used arc furnaces in their steam plant. The distribution circuit had an LC frequency that the arc furnace excited and this caused substation breaker to fail twice before we figured out what was going on. We couldn't change the arc furnace so, we had to change the LC circuit. This is typically done by adding TRV capacitors at the breaker. In theory, you can have up to 2.0 pu voltage peak during resonance. Typically, resonance will not be a problem when there is adequate loading.
The general reason using delta on primary and g-wye on distribution secondary is isolation of zero sequence fault current from the primary. Another reason is phasing on the distribution side. Another reason is that g-wye primary becomes a source of zero sequence fault current when you have a ground fault on the primary. This can confuse the relays as to the direction of the fault and delay breaker tripping or result in in-correct breaker tripping.
The general reason using delta on primary and g-wye on distribution secondary is isolation of zero sequence fault current from the primary. Another reason is phasing on the distribution side. Another reason is that g-wye primary becomes a source of zero sequence fault current when you have a ground fault on the primary. This can confuse the relays as to the direction of the fault and delay breaker tripping or result in in-correct breaker tripping.
- Status