×
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

Charging current

Charging current

Charging current

(OP)
Hi,

I`m looking for guidelines on how to measure the capacitive charging current on a 400 V 3500 kVA system.The intention is to limit the ground fault current close to the capacitive charging current.

Thanks.

Grundig

RE: Charging current

After checking that the system is free of grounds, ground one phase and measure the current with an ammeter to estimate the capacitive current to ground. Measure phase currents with no load on the system to estimate combined phase to phase and phase to ground charging currents. How will you discriminate a ground fault from capacitive charging current if they are similar values? The charging current may change as motors and motor feeders are connected and disconnected. Depending on the type of cable, the  ratio of phase to phase and phase to ground charging current may change. You may want to consider a higher current limit for your system.  

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

RE: Charging current

What location is this for? LV systems in most (all?) of Western Europe are required to be solidly earthed, and what you are proposing sounds like a high impedance earth of some form.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Charging current

(OP)
Thanks all for the prompt replies. The intention of using high impedance grounding is to limit the magnitude of fault current to a safe value.

Grundig

RE: Charging current

You are correct vennivivi- in general the minimum neutral-grounding-resistor let-through current should be equal to, or larger than the system charging-current.  The document linked below contains detailed information about the selection of a neutral-grounding resistor.

Ground-Fault Detection, Charging Current, and Neutral-Grounding Resistor Selection

Typically, charging current will be 0.5 A per 1000 kVA on low-voltage systems, and 1.0 A per 1000 kVA on medium-voltage systems.  Consequently, 5-A, 15-A, and 25-A grounding resistors are common.

---
Cory Anderson
http://startco.ca/

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