×
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

sizing of transformer

sizing of transformer

sizing of transformer

(OP)
I have 9 110V ac to 5kv transformers, these are energised for 1 second periods every 60 seconds. I also have 3 110Vac panel mount octal type relays powered on continuously.

How do I size the transformer required to step down the supply from 230 to 110, & size the fuse required.

Thanks

RE: sizing of transformer

To find the KVA of the stepdown transformer, multiply the kva of the 5kv transformer by 9 and add the KVA used by the relays. Use one transformer.
Each 5kv transformer primary should be fused. Use a fuse rated for the continous primary current of the 5kv transformer. This will protect the transformer. If it is necessary to protect the load, more information is required.
Use one fuse for the three relays. Fuse the relays for 3 or 4 times the current the relays actually draw.
The preceding is based on the assumption that the 5kv transformers are small since they have a 110 volt primary. Thus it will cost less to oversize the stepdown transformer rather than having an optimum design.
Also if it is likely that the 5kv load will have frequent short circuits, use circuit breakers rather than fuses.
5kv IS DEADLY. HAVE A QUALIFIED PERSON REVIEW YOUR DESIGN.

RE: sizing of transformer

Also watch the contact ratings of your power relays on the 110 volt side. These need a minimum rating to handle transformer inrush current. You then need to go 3 times larger than this so that the power relays will last 10 times longer. In your application this amount of oversizing will give you VERY reasonable life. Otherwise, you could be replacing the relays once every 3 months.

Mike Cole, mc5w@earthlink.net

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