×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Switching transformer neutral to earth link ?

Switching transformer neutral to earth link ?

Switching transformer neutral to earth link ?

(OP)
Hi,
I have a 33kV distribution system with three bus bars and two bus couplers (oeprating normally closed). Each bus bar is supplied from a transformer and in normal operation the three transformers operate in paralllel.
The client specifies the NER to limit earth fault current to 400A.
Th earth fault curent limitation can have then 3 values (400, 800 and 1200A) depending on how many transformers are paralleled.
Is there any advantage in implementing an NER switching logic in order to have one NER in service at any given time with a fixed 400A limitation ?
Otherwise is there an issue with protecting the system with these multiple earthing points ?
(the syetm may be less sensitive since the earth fault current may spilt between the three NERs?)
Thanks  
 

RE: Switching transformer neutral to earth link ?

Switches fail, ungrounded systems are far worse than impedance grounded systems, therefore no switching.  Shouldn't be that difficult to work with the differing fault currents, just let the relays know how many transformers and torque control different elements based on known maximum fault current.

RE: Switching transformer neutral to earth link ?

Can you consider connecting all three transformers to a transformer neutral bus and then grounding the neutral bus through a single NGR?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Switching transformer neutral to earth link ?

That could work too, good one Bill.

RE: Switching transformer neutral to earth link ?

Hi.
It's a big problem!!!
Last week we config and check two such systems with NER switching, in one case it was must, second case like to your case, but with 2 transformers.
It's work now, but I don't like this solution.
Are it will be auto switch or manual?

Second, I think possible work with 3 NER in parallel, but design biggest size of NER and add REF ( 87N) functionality.
In additional set protection for minimum ground fault level. With newer relays possible coordinate with current 100A or less.

Bill, IMHO, your option is good one, but have some problem with maintanance and one fail point ( only one NER in the system)

Best Regards.
Slava
 

RE: Switching transformer neutral to earth link ?

(OP)
If switch option is selected it will be automatic through a control system.
But I start thinking like Bill and David that this is not the good option.
The problem is that this switchgear will supply an industrial plant, but will also supply an overhead line.
There is a compromise to find between:
- A too low NER value with problems of capacitive currents for insulated lines and imepedant faults on the overhead line
- too high a fault current, which is detrimnetal to thermal withstand of equipment.
I think I will be going with 600A for one NER with one transformer on line (and a maximum of 3 x 600A when the three transformers are paralleled)
Thanks       

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources