×
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

5 MVA Generator

5 MVA Generator

5 MVA Generator

(OP)
Customer has a 5MVA Generator operating in island mode, and the question is what would be the biggest motor we could connect to this GEN considering a typical IEC 6Kv motor with starting current ratio of 6.5 times flc.Efficiency 95% and power factor 0.90, and a starting voltage of 80%

RE: 5 MVA Generator

The maximum rated motor that the generator can start will depend on many factors.

What is the base load?
What is the generator AVR droop characteristic?
Since you mention 650% starting current, I assume that you are only considering DOL start, if you use other means of starting, you will be able to start higher rated motors also.


Anand Sekhar

RE: 5 MVA Generator

(5MVA minus base load)/3
respectfully

RE: 5 MVA Generator

Hello Magneticted,

This formula could help: Motor HP x(KVA/HP) x (1000/Motor voltage)= LRA.

Taking account the Generator most be cappable to deliver all LRA Then the Gen Amps = LRA.

LRA= 5000 KVA /1.73 x (0.8 x 6) KV = 601 Amps. Is/Im = 6.5 then Im = 601/6.5 = 92 Amps where Is = Istarting= LRA  and
Im= I motor.

Motor KW = 1.73 x Vm x Im x PF x Eff = 871 KW

If you have a generator capable to whistand a instantaneus over load of 300 % then the new Gen KVA= 15000 and the new LRA = 1803 the new  Im = 277 Amps and the new  Motor KW = 2465.

You most take account the  Gen Set characteristics in order to know if is possible a 300% overload and it`s lasting time.

Regards

Petronila    

     
  

RE: 5 MVA Generator

Possibly up to around 5000hp depending on the starting method.

From what I've seen, most generators can support around 200% current for something like 10 seconds. So, for a full voltage start, Waross pretty much has it. Generator MVA x 2 / 6 or generator MVA divided by 3 meaning the motor could be about 1600kW. For reduced voltage start you can start a motor up to around MVA / 2 so the motor could be around 2500kW.

With a VFD you could get maybe get up to around a 4000kW motor or so. You have to take the efficiency of the motor and the VFD off the generator capacity. The motor and VFD together might be around 80% to 85% efficient.

Of course, this is all theoretical and it really depends on the complete system so it needs to be studied in detail.

RE: 5 MVA Generator

And the base load.  And how much dip your motor starter can tolerate before chattering the whole thing into oblivion.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

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