Y-Y transformer bank with LV grounding resistor
Y-Y transformer bank with LV grounding resistor
(OP)
We are looking at installing a three phase transformer bank made out of 3 single phase oil filled transformers rated 167kVA each, to feed an small industrial load. The HV is a 4 wire system 24940GrdY14400V
The LV neutral will be connected to ground via an NGR
If we choose a Y-Y connection, I understand that the primary should not be solidly grounded? Is it correct? and if so, why can it not be solidly grounded?
Would we be better off by using a Delta-Y connection? (suppression of harmonics)
Thanks!
The LV neutral will be connected to ground via an NGR
If we choose a Y-Y connection, I understand that the primary should not be solidly grounded? Is it correct? and if so, why can it not be solidly grounded?
Would we be better off by using a Delta-Y connection? (suppression of harmonics)
Thanks!






RE: Y-Y transformer bank with LV grounding resistor
RE: Y-Y transformer bank with LV grounding resistor
RE: Y-Y transformer bank with LV grounding resistor
If your HV is a 3 wire sistem and you are sure that remote source of your high voltage is solidly grounded, you can use a Delta-Y connection.
RE: Y-Y transformer bank with LV grounding resistor
Grounding the wye point of a transformer bank fed from an ungrounded delta will not accomplish much as there is no return path back to the delta source. It may cause interesting issues with the utilities protection schemes.
The voltages that you give imply a four wire system so you should be safe with a wye:wye transformer bank, but remember, "grounding" the primary wye point means connecting it to the system neutral, NOT just driving a ground rod or connecting it to your grounding grid.
Bill
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"Why not the best?"
Jimmy Carter
RE: Y-Y transformer bank with LV grounding resistor
I am not understand.You mean that there is not fault to ground at LV- starGround because of the MV-delta?
RE: Y-Y transformer bank with LV grounding resistor
Thanks for the answer! the medium voltage system feeding the bank of 3 - 167kVA is a solidly multigrounded 24.9kV.
So for this appliaction (ie a NGR in the LV) the H0 must be solidly grounded (as Waross indicates, tied to the system ground).
The LV X0 must then be an insulated bushing and will be connected to ground via the Neutral Grounding Resistance.
Besides blocking the triplens, is there any advantage in using a Delta-GrdY connection instead of staying with a GrdY-GrdY bank? (the LV GrdY being in both cases grounded via a low impedance Grounding resistor)
Thanks again!
RE: Y-Y transformer bank with LV grounding resistor
In this instance the ffont has indicated that the primary supply is a four wire system with a multiple grounded system neutral conductor. My comments concerning a floating primary wye point do not apply on ffont's system.
One of the big advantages of a wye primary in some areas may be availability of transformers. If the local practice is to connect individual transformers line to neutral you may find that there is a good selection of 14,400 Volt transformers available on the suppliers shelf while 24,940 Volt transformers are a special order which have to be located and shipped into your area.
In a delta:wye transformer or bank, secondary line to neutral loads or faults become line to line loads or faults on the primary.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Y-Y transformer bank with LV grounding resistor
Then in case the primary of wye-wye transformer is fed from an isolated 3 wire system, by providing a neutral grounding transformer at sending end, will the problems listed by you be solved?
Can you comment on odlanor's response of 6th. I find some contradictions.
RE: Y-Y transformer bank with LV grounding resistor
RE: Y-Y transformer bank with LV grounding resistor
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Y-Y transformer bank with LV grounding resistor
RE: Y-Y transformer bank with LV grounding resistor