Neutral Grounding Resistors and Wye Wye Transformers
Neutral Grounding Resistors and Wye Wye Transformers
(OP)
I think I already know the answer to this, but I will ask anyway.
A substation with a 10MVA 138KV/4160V Delta Wye transformer feeds our facility. The power company is planning to install a neutral grounding resistor during our next shutdown.
Here is where my question comes in. The transformer feeds our 4160V switchgear in the plant. A feeder for a 300KVA 4160/480V Wye Wye transformer comes off this switchgear. The transformer has an internal bonding jumper that is connected to both XO connections and is grounded to the plant grounding system. Will the neutral being grounded on the primary side of the transformer effectively make our neutral grounding system useless if we experienced a line to ground fault on the 4160V system?
A substation with a 10MVA 138KV/4160V Delta Wye transformer feeds our facility. The power company is planning to install a neutral grounding resistor during our next shutdown.
Here is where my question comes in. The transformer feeds our 4160V switchgear in the plant. A feeder for a 300KVA 4160/480V Wye Wye transformer comes off this switchgear. The transformer has an internal bonding jumper that is connected to both XO connections and is grounded to the plant grounding system. Will the neutral being grounded on the primary side of the transformer effectively make our neutral grounding system useless if we experienced a line to ground fault on the 4160V system?






RE: Neutral Grounding Resistors and Wye Wye Transformers
RE: Neutral Grounding Resistors and Wye Wye Transformers
RE: Neutral Grounding Resistors and Wye Wye Transformers
138000-4160 4160-480
Xfmr Xfmr
X0------------------------------------X0
| neutral |
N |
G |
R |
| |
+-------------------------------------+
plant grounding system
RE: Neutral Grounding Resistors and Wye Wye Transformers
I agree with you.
thanks.
RE: Neutral Grounding Resistors and Wye Wye Transformers
RE: Neutral Grounding Resistors and Wye Wye Transformers
Rafiq Bulsara
http://www.srengineersct.com
RE: Neutral Grounding Resistors and Wye Wye Transformers
I have never considered the installation of a res. grd. wye to grd. wye. Seems like a connection I would want to avoid.
Alan
RE: Neutral Grounding Resistors and Wye Wye Transformers
Hi OdessaEE,
From the electric point of view, the NGR on the 480 WYE side will further limit the SLG fault; however I am not sure why you want to add a NGR on the 480 WYE as I believe the power company has already determined the maximum SLG fault to be limited.
The disadvantage here is that your plant will see the SLG fault flowing from the power company 4160V system because of the 300kVA transformer winding configuration WYE (HV/LV sides). Ideally, you should specify a 300kVA Tfrm, Delta/Star (WYE)so your plant(480V system)will be protected from SLG flowing from the power company transformer (10MVA, 138/4160V, Delta-WYE), providing there is not other WYE/WYE transformer in your plant.
This network configuration SLG fault can be easily viewed if you apply the positive (+), negative (-) and zero (0) sequence diagram on both transformers.
I hope this help.
RE: Neutral Grounding Resistors and Wye Wye Transformers
YES, OF course!
In the zero sequence circuit of YY transformer ZL is connected with ZH.
RE: Neutral Grounding Resistors and Wye Wye Transformers
1- a resistor will be installed at neutral of 138KV/4160V Delta Wye transformer1 where is the source.
2- 300KVA 4160/480V Wye Wye transformer2 has both neutral solid grounded.
3- trafo1 is interconnected with trafo2
4- You experienced a line to ground fault on the 4160V system between trafo1 and trafo2
Well, there will be zero sequence circulating in the 4160 V between neutrals of trafo1 and trafo2(currents up) and ground-fault point(current down).
If you include a resistance in the neutral of trafo1, you will reduce ground fault current level in the 4160 system.