×
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

I am aware of several switchgear manufacturers that have developed, an

I am aware of several switchgear manufacturers that have developed, an

I am aware of several switchgear manufacturers that have developed, an

(OP)
I am aware of several switchgear manufacturers that have developed, and are marketing, mechanical "zero-volt closing" capacitor switches. they claim that this eliminates transients when energizing capacitors. These switches energize capacitors on the zero-volt crossing of the line voltage.

My question is:

How will these switches react to energizing capacitors that have residual voltage on them from "zero-current" switch openings, which is a natural occurence?

It is my understanding that zero-volt closing is only practical when energizing completely de-energized capacitors.

RE: I am aware of several switchgear manufacturers that have developed, an

I may be wrong, but I believe the discharge resistor does the trick. It is not uncommon for modern capacitors to have these resistors in parallel to the cap. When the cap is disconnected, the residual energy on the capacitor can discharge progressiveley through the impedance of the resistor. Most power factor bank controllers manage this by preventing a disconnected cap from being reconnected within a certain time limit (a couple of minutes say), to enable the capacitor to discharge itself completely (or sufficiently). These controllers memorise the switching history of the capacitor, and even measure how efficient it is, and if it doesn't compensate as it should, it can actually warn you that the bank is faulty ...

Otherwise you are right, the residual energy could create some voltage transients. That is why it is so important to verify that those resistors are connected, or even better, built into the capacitor.

Hope this was helpful !

RE: I am aware of several switchgear manufacturers that have developed, an

(OP)
Thanks bfuchs. This has been very valuable information to me. I should probably get hold of someone at a local electrical utility and observe capacitor switching first hand. thanks again.

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