×
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

GENERATOR EARTH FAULT PROTECTION

GENERATOR EARTH FAULT PROTECTION

GENERATOR EARTH FAULT PROTECTION

(OP)
I have 2 x 1MW 6.6kv diesel generators (paralleled), connected to the delta winding of a 6.6/11kv step-up transformer. A grounding (zig-zag) transformer is also connected here, with grounding via a resistor. There is no earth-fault ct at this neutral-point, and access is very difficult.
The generator neutrals are not connected.
Regarding earth-fault protection, can I use core-balance type toroids (ct) around the 3 phases at each generator, as I already have earth-fault relays fitted on each generator ? Would this give adequate earth-fault protection ?   

RE: GENERATOR EARTH FAULT PROTECTION

  There are several ways to detect earth faults (for protection). All of them are based on current fault detection performed by two different procedures:
  a) Meassuring current (or voltage)on grounding resistor path.
  b) Meassuring zero sequence current either by the sum of the three line currents at secondary side of meassurement CT's or by a core-balance type toroids (ct) around the 3 phases at each generator as you propose.
   Proceure a) is the most common and simple way to do that, since grounding resistor path current is exactly the fault current.
   Procedure b) is also eassy to improve, since the 3 meassurement CT perform, generally, their secondary windings arranged in star connection whith one common wire (return path) and three active wires. The return wire current amounts three times  the current fault value(referred to CT's secondary, of course). Regarding your proposal, core-balance type toroids (ct) around the 3 phases at each generator is quite valid but normally used for low power installations or, as in your case, when no other alternative does exist.
   Hoping help you.

Julian

RE: GENERATOR EARTH FAULT PROTECTION

CTs installed on each generator circuit, as you describe, will give sensitive protection for the individual generators.  There needs to be earth fault protection for the earthing transformer and earthing resistor as well, unless both are continuosly rated for full earth fault current.
This would protect the earthing transformer/resistor combination against earth faults on the 6.6 kv busbar or uncleared faults on the generator circuits.  If you can't access the earthing lead of the resistor or the connection between the resistor and the transformer to install a CT, then you would probably need to install a toroidal CT on the earthing transformer phase leads in the switchgear.

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! Already a Member? Login


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close