Correlation between generating capacity and motor rating for DOL start
Correlation between generating capacity and motor rating for DOL start
(OP)
We are planning a captive power generation of approximately 18 MW ( 3 x 6 MW gas engine driven generators). Can we go for a 1600 KW DOL start motor ? What is the correleation between the generator capacity and the maximum permissible rating of motor for DOL start ?Is there anything we can take care in the generator specification to ensure this ?





RE: Correlation between generating capacity and motor rating for DOL start
1. Starting current, highly reactive. This causes voltage dip. Mostly KVA loading.
2. Starting mechanical loading. This causes possible slowing or stalling of the prime mover. This is kW loading.
The old rule of thumb (Which correlates fairly well with more sophisticated sizing methods) is that generator capacity in KVA must be 3 times the motor KVA. If deep voltage dips may be allowed, the factor may be reduced to 2.5 times the motor KVA.
For a more accurate assessment of the voltage drop during motor starting, go to the Caterpillar site and search for the generator sizing software. This is often more conservative than the 3:1 rule of thumb.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Correlation between generating capacity and motor rating for DOL start
In general though, if you need to accelerate a 16MW motor from an 18MW generator capacity system, the only way that can possibly happen is by having a VFD of some sort on the motor, even if you do not need to vary the speed when running.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Correlation between generating capacity and motor rating for DOL start
RE: Correlation between generating capacity and motor rating for DOL start
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla
RE: Correlation between generating capacity and motor rating for DOL start
D-oh!
Hey, what's a decimal point between friends, eh?
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Correlation between generating capacity and motor rating for DOL start
Going by the '3 times KVA' rule , 6 MW generation capacity should be sufficient (not allowing for voltage drops)for starting the motor.However we are considering the option of soft starter.
RE: Correlation between generating capacity and motor rating for DOL start
You probably need a complete system view rather than just the generator/motor starting view.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Correlation between generating capacity and motor rating for DOL start
For generator sizing we should consider [KVA=KVA(runing)+(KVA)(lasest starting)] for various prosses conditions and chose the largest value.
A soulotion for large motor starting is capacitor bank usage.it improve reactive part of starting current .