×
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

Grounding in IT-system

Grounding in IT-system

Grounding in IT-system

(OP)
Why is there, on an 230 V IT-system (isolated neutral) on a ship, 127 V between ground and phase when there is no connection between tranformers neutral and earth?
Is this because of the capacitive currents in the long cables?

Thanx
Harry F

RE: Grounding in IT-system

Yes.  Ungrounded systems are really grounded through the distributed capacitance of the system to ground, mostly from the cable capacitance.  In most systems, this capacitance is fairly balanced, so the voltage to ground ground from each phase is about equal.  If the capacitances are not equal, then the voltages to ground can be very unbalanced.

RE: Grounding in IT-system


Be well aware that on an ungrounded system (capacitance only ø-grd) transients may develop up to several times the ø-ø voltage, from intermittent ground faults and resonant effects.  
  

RE: Grounding in IT-system

some times high resistance earthing will be done for the detection of ground fauls in floating neutral systems. This can also result in the same observation.

RE: Grounding in IT-system


Correctly sized high-resistance grounding can be desirable for damping transient and resonant overvoltages that inevitably occur on the inherent ø-grd capacitance.  

Particles vary widely, but to get an idea of related problems experienced by some, read though Thread238-3370 and Thread238-6870.  We’re approaching 50 years of warnings on ungrounded LV distribution.
  

RE: Grounding in IT-system

In isolated neutral systems, the first ground fault is not detected. If a second ground fault occurs, think of the situation. It appears exactly like a ph-ph short circuit. therefore in any ungrounded systems an indication of three phase lamps along with leakage current sensing is highly desirable.

RE: Grounding in IT-system

Suggestion to fharry (Electrical) Oct 13, 2002 marked ///\\\
Why is there, on an 230 V IT-system (isolated neutral) on a ship, 127 V between ground and phase when there is no connection between tranformers neutral and earth?
///There just may be a fault, namely one line has become grounded.\\\
Is this because of the capacitive currents in the long cables?
///Alternately, yes.\\\

RE: Grounding in IT-system

Yes JBartos is correct. 127V is a considerable voltage and possibly a fault coult exist. We can think that capacitive currents as an alternative.

RE: Grounding in IT-system

jbartos,

if one line has become grounded, fharry would have measured 230V between the two other lines and ground, 127V could be caused by a grounded neutral.

fharry should check if the 127V he measures are able to supply some current (e.g. a small light bulb).If the volatge sgoes down in that case, its jsut capacitive coupling.

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