×
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

Advantages of Parallel TX Operation

Advantages of Parallel TX Operation

Advantages of Parallel TX Operation

(OP)
In considering operating a double ended substation (2 x 100% rated TX) with the tie breaker closed, one of the obvious considerations are fault levels.  However, another consideration is reliability relating to "survivability" for the process in this mode.  For common faults, such as a fault on the tie breaker, you could conceivably lose both transformers.  However, for high side TX faults, you may be able to isolate the transformers automatically without a process upset (transients notwithstanding).  On the other hand, if you operate with the tie breaker open, you minimize exposure to common faults, but risk losing the process where the TX is taken out of service.  Is anyone aware of a step by step evaluation of why you may want to operate in one mode vs the other?

Thanks in advance.

Ken Almon

RE: Advantages of Parallel TX Operation

The selection of mode of operation (ie tie cb closed or open)in such a case is mearly a question of choice.
You have assessed the pros and cons so no need to go into that.
From a survey aspect however, it may be noted that in a majority of the double ended system arrangement the tie breaker is normally open with a fast auto close control in the event of a fault free loss of any one of the Tx incomer.

RE: Advantages of Parallel TX Operation

Agreed.  Generally you'd want the tie normally open.  However, if you'd take a large loss on interruption of power, but can't quite justify a UPS system, then a normally closed tie might make sense.

RE: Advantages of Parallel TX Operation

KenAlmon,

For 'tie breaker closed'mode operation I feel Partial differential protection shall be provided for each of the bus sections for prompt isolation of faulty section without affecting the power supplies to the healthy bus section.

The partial differential protection is provided in each of the transformer incomers like OC / EF protection. The difference lies in that instead of incomer CT alone connected to the protection, it is parallel combination of incomer and bus tie CTs that is connected to the partial differential protection. The settings and coordination is done similar to normal incomer OC /EF protection.

Another advantage with this scheme is that there is no separate OC/EF protection provided for the bus tie and thus one step is avoided in protection coordination.

RE: Advantages of Parallel TX Operation

(OP)
Thanks for your comments.

rraghunath - Yes, partial diff is in the cards for the scheme, if we do decide to go with the ties NC, we will use partial diff.

Busbar - I have the 1990 version of the standard and while discussing reliability with regards to a tie breaker on a secondary selective scheme, they define a "failure" as having an outage greater than 5 seconds.  I am afraid application of that definition exceeds (greatly) our definition.  As a result, the formulae relating to reliability cannot be used with any accuracy.  Thanks anyway for the link.

I am not sure there is anymore to be discussed on this subject; almost knew the answer before writing...

Ken

RE: Advantages of Parallel TX Operation


Good point about the IEEE text, Ken.  Five seconds is spitting in the face of sub-cycle power continuity, I guess.  
  

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