×
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

electromechanical relays

electromechanical relays

electromechanical relays

(OP)
I'm trying to understand the differnece in operation between a 50/51 and a 67...

I understand that the 67 is a directional device and will only operate if current is in the reverse direction.

My question...what happens to a 50/51 relay when current is in the "wrong" direction?

RE: electromechanical relays

A 50/51 relay is bidirectional. It will operate once the set threshold is reached without regards to current direction.

God bless!

RE: electromechanical relays

Suggestion: Reference:
IEEE Std 141-1993 (Red Book)
1.
67 is ac directional overcurrent relay. It functions on a desired value of ac overcurrent flowing in a predetermined direction.
2.
50 is instantaneous overcurrent relay that functions instantaneously on an excessive value of current in either direction.
3.
51 is ac time relay. It functions when the ac input current in either direction exceeds a predetermined value, and in which the input current and operating time are inversely related through a substantial portion of the performance range.

RE: electromechanical relays


Aside — often there are electrical systems where power may flow in either direction at a particular node, and you may want to have varied tripping for different directions.  Simply— busbars, cable, fuses, breakers and transformers do not care the direction of power flow.  Typically, they operate unaffected by direction.

A 67 device will have an additional pair of terminals for a voltage- or current-polarizing source to establish directional characteristics.  
  

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