×
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

Complex Issue..Need Expert Help

Complex Issue..Need Expert Help

Complex Issue..Need Expert Help

(OP)
The transformer size is 1600 KVA.With rated amps 2100 Amps...The breaker is 2500A 4P,drawout motorized acb with micrologic trip unit with O/L,S/C & E/F protection-100 KA/1sec,make:schneider elctric,Model:NW25 H2+Micrologic 6.0 A..The locked rotor starting time of pump is 10 sec as per motor data sheet..
I have the following loads connected to Panel:
1.Two chillers of max load current 1003 A.Their starting current is 969 as the 4 compressors in it have inbuilt star/delta starters and are started in sequence.(from data sheet of chiller)
2.Three pumps of FLA 81 and Locked Rotor Amps of 555,out of which only two will be working.
3.One lighting DB
4.One 5.5 KW AHU
5.One 20 KW heater(Intermittent Load)..

Max Current =1003+1003+81+81+12+20+30=2230..Which I hope the transformer & breaker can handle.
However problem arises when one pump fails.When one pump fails and next pump starts Locked rotor amps of 555A will come..
so total current=1003+1003+81+20+30+555=2692..This is a problem ryt even though this occurs only during starting.Can the breaker handlethis current without tripping?What about the transformer?

RE: Complex Issue..Need Expert Help

The way you calculated the total current will give you the worst case (maximum), not a real total current. You have to calculate total kWs and kvars and then calculate the total current.
Even with 2692A in total, micrologic will hardly trip, if it is adjusted to rated current of 2500A, but you have to check a tripping curve settings. Schneider provides "Curve Direct" software for that purpose. Transformer itself will handle it for sure, but you have to check MV protection settings.

RE: Complex Issue..Need Expert Help

... having in mind that MV protection of transformer, if properly selected, has to handle transformer inrush current, it can't be possible to trip at such light overcurrent

RE: Complex Issue..Need Expert Help

(OP)
I already downloaded curve direct..But Im not sure as to the conclusion from that.Y axis it has time in sec..and x-axis they have current..So I need to check the intersection of 2600 A and note how mucg time it can hold right? Can you check out n tell me?

RE: Complex Issue..Need Expert Help

Yes, that's the principle, but I can't do it for you, sorry. Even if I want to, I don't know the settings of your micrologic. Pay attention that this tripping curve is adjustable in inverse (overload) area.

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