DG-sizing

what is DG

"DG" appears to signify "Diesel Generator". If so, these calculations look correct, but one must insure that the 2000 kVA rating by the manufacturer is continuous duty, not standby duty. Otherwise, there is a further derating factor. Furthermore, most manufacturers have a derating factor for cases where the load PF is greater than 0.8 that may need to be taken in to account.

NEMA MG 1, Article 33.3.3 requires that the generator overloading shall be

- 10% for at least 2 hours out of any consecutive 24 hours of operation

- 50% for at least 30 sec

If it is NEMA standard generator, it should be able to withstand 50% load for at least 30 sec.

- MS

thanks a lot sir,i got , what i had expected.

(1) Since soft starter is used, check for derating due to harmonics on DG set rating. Check extent of harmonics (or input power factor) of the soft starter and apply corrected data in DG sizing for the largest motor load.

(2) Check for voltage drop at DG terminals/soft starter input terminals during largest motor starting.

sir please clarify about the "rating of the largest motor in Kva..."

As much as I know, that at the time of starting, the Power Factor of Induction Motor is around 2 to 3. Say 2.5

So, The RLMT should be = RLM*2.5/(PF*H)= (426*2.5)/(.25*.9)(For Soft Starter)

that is equal to= 4733.33 kva

Sir, Please do reply...