Delta wye transfomer during a grounded phase
Delta wye transfomer during a grounded phase
(OP)
What happens when one or two phases fault to the MGN (multi grounded neutral) of a distribution system with the effected phase fuse blowing (but still grounded) while feeding a delta wye transformer? Will any inductive tank heating take place? Will a 3 limb vs 5 limb core make a difference?
Basically I am entertaining the idea of using a delta wye padmount instead of a conventional 5 limb wye grounded wye grounded, however I am unsure if certain fault scenarios create special protection concerns. Both the over head feeder and underground riser are protected via fuses, so single phasing and shorted phasing is a concern.
Basically I am entertaining the idea of using a delta wye padmount instead of a conventional 5 limb wye grounded wye grounded, however I am unsure if certain fault scenarios create special protection concerns. Both the over head feeder and underground riser are protected via fuses, so single phasing and shorted phasing is a concern.






RE: Delta wye transfomer during a grounded phase
Assume you lose A phase on the primary due to the open fuse. The delta will actually collapse. A-B and A-C will add up to B-C voltage. I don't think the ground fault matters at this point other than causing the fuse to blow. Result on secondary is two phase to neutral voltages at half value and the other one at rated voltage.
RE: Delta wye transfomer during a grounded phase
You'll have some trade offs going to delta wye ground wye ground. Your phase voltages will be impacted by unbalanced load. Delta wye ground I think is preferable in industrial systems due to the loads being mostly 3 phase (motors) and balanced and it segregates the grounding and providing a ground source.
RE: Delta wye transfomer during a grounded phase
Also my worry is not just an open fuse, but that phase back feeding (shorted) into the MGN before line crews show up. As long as the transformer itself does not become damaged I am content.
And- for those who know about ferrorsaonance. As long as the transformer remains under about 15-20% load, the resonant condition will be dampened out?
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
http://s000.tinyupload.com/index.php?file_id=30823...
This link works. Just don't click on the bait. The zip file downloads when you click on the file name.
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
There will be no zero-sequence current, even though there is current from ØB to the MGN (it is all pos- and neg-sequence).
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
Line to line quantities on the delta would never be affected by zero sequence because zero sequence doesn't produce a voltage differential across each winding.
The thing when I looked over your calculations that I had never thought of before is that the type of load I think could dictate what happens on the secondary of the transformer. The load that you used in your calcs was 100 A load in phase with the voltage on each of the phases, a constant current load, probably single phase. Zero sequence current on the secondary is generated by the change in angle of the secondary voltages and zero sequence current is produced due to the currents not adding up to zero. If you had just a passive load, I don't think you would have seen any zero sequence currents on the secondary because the secondary voltages with just positive and negative voltages would have only produced positive and negative sequence currents. I suppose you might see something similar with constant power loads. I suppose this isn't profound or anything but I guess the type of load you have could determine if you should care what is happening on the high side in respect to tank heating.
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
http://www.geindustrial.com/publibrary/checkout/Wh...–The Why of the Wyes: The behavior of transformer Y connections. All these incorporated in the IEEE Standard C57.105-1978(R2008) Transformer Connections in 3 phase distribution systems.
RE: Delta wye transfomer during a grounded phase
I am looking at this wrong. The zero sequence voltage at the transformer secondary due to the load would be zero because it is grounded. It can't be anything but zero. The load is generating the zero sequence voltage due to how it interacting with the voltage imbalance. I find it curious that the secondary voltage consisting of just positive and negative components could cause zero sequence currents to flow but I don't think that has anything to do with tank heating. I don't think the loads can impact your problem.
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
In case of wind farm transformers, please check the core construction. If it is 4 or 5 limbed, stabilizing delta will be required to bring down the zero sequence impedance. With a 3 limbed core it may not be necessary.
RE: Delta wye transfomer during a grounded phase
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Delta wye transfomer during a grounded phase
In so far I'd like to thank everyone for the replies. :) I've learned a lot in this thread and still am.
RE: Delta wye transfomer during a grounded phase
The secondary voltage depends only on the primary winding voltages. I have neglected any voltage drop in the transformer winding from load current. There is no zero-sequence secondary voltage because VAB + VBC + VCA= 0. There can be zero-sequence secondary current regardless of the secondary voltage. Consider if there is only load connected from one secondary phase to neutral. The zero-sequence current would be 1/3 of the load current.
RE: Delta wye transfomer during a grounded phase
Wouldn't you just include some grounding impedance if you were worried about back feeding fault current?
RE: Delta wye transfomer during a grounded phase
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
In fact in wye, I would be concerned about back feeding load heating the winding itself from being fully shorted out. I have never though about this, but it now just ran through my mind.
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
I think the confusion is due to what you think V0 is. V0 is the same magnitude and angle on all three phases. Whatever is on the third leg that is unconnected will be come mix of zero, negative, and positive sequence flux. The zero sequence flux by definition will be the same in each leg and it can't return through the open or faulted phased leg. So, there will be flux that passes in the third leg but it won't be just the zero sequence flux. The voltage on phase A can be zero, but that is due to all the sequence components adding up to zero for that phase. It is just like how a single line to ground fault has I1=I0=I2 but current is only present on one of those phases. The sequence components in the unfaulted phases add to zero so you have what you expected, only current in the faulted phase.
RE: Delta wye transfomer during a grounded phase
There are problems with a wye/delta connection when the wye neutral is connected.
This may be mitigated by floating the neutral.
Back feeding will be primarily from motor contributions that do not have a neutral connection so the wye/delta issues will be mitigated.
As to secondary voltages during a fault.
With one phase open the two windings connected to the open phase will be in series across line voltage. The voltage division will be determined by the loads on the individual transformers.
With one phase faulted to ground on an ungrounded system the result will be the same.
With one phase faulted to the neutral, the voltages across the windings connected to the faulted phase will drop from line to line to line to neutral voltage.
The phase angles will shift. With B phase faulted the winding at A-B will become A-N and the winding at B-C will become N-C.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
https://www.ieee.li/pdf/viewgraphs/basic_distribut...
RE: Delta wye transfomer during a grounded phase
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Delta wye transfomer during a grounded phase
RE: Delta wye transfomer during a grounded phase
A delta fed from a wye with the neutral connected has the ability to transfer power from one or two phases to the third phase.
The phase windings in a grounded wye are independent of each other, unless the phantom delta is present.
Bill
--------------------
"Why not the best?"
Jimmy Carter