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Lowering or Reducing Phase to Earth Fault Current

Lowering or Reducing Phase to Earth Fault Current

Lowering or Reducing Phase to Earth Fault Current

(OP)
Dear All Sifoos,

My distribution system is 33/11kV and using NER to limit the earth fault current,
for 30MVA, the earth fault current = 1600A , by using 4 Ohms resistor,
for 15MVA, the earth fault current = 800A , by using 8 Ohms resistor.

Q1. What will happen if we try to limit the earth fault current, let say below 100A.
Q2. And how to achieve that?
Q3. What is the implications or effects?
Q4. Is there any other utility in this world practically limit their earth fault current below 100A.

Thanks.

 

RE: Lowering or Reducing Phase to Earth Fault Current

Izn't simple issue.
For the industry application, it's possible and good solution.
For the distribution, I think  it's possible with compensated grounding only ( via Petersen coil).
You have take in account a protection issue too, with small current, maybe you will need use directional earth fault protection. Or via reactor grounding.

Best Regards.
Slava

See attached:
http://tesla.selinc.com/techpprs/6123.pdf.

RE: Lowering or Reducing Phase to Earth Fault Current

(OP)
Thanks..slavag..
Actually,i'm doing a pilot project with a utility company.
any suggestion would help..

thanks again!!!

RE: Lowering or Reducing Phase to Earth Fault Current

Refer to IEEE Green Book for recommendations for grounding.

RE: Lowering or Reducing Phase to Earth Fault Current

You have to ask yourself why these values and what is your design criteria. If your transformers feed fused systems then will there be enough current to blow the fuse on a single phase earthfault... 100A is a little low methinks for this.

RE: Lowering or Reducing Phase to Earth Fault Current

(OP)
Well,now i understand the concept.

Is there any reference project which is to transform low resistance grounding system to high resistance grounding system.
 
Anybody write about it? What is the implication? Result?


I don't think there any issue on the tx fuse. In my country, we are using 11/0.4kV TX Dyn11 with max rating of 1000kVA, and using RMU with the fuse located at 11kV side. By the way HRC is use for protecting the TX, isn't it?
 
Thanks  

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