DG set rating calculation

for squirrel cage motors kva (g) = 0.42 x a x motor kw where a = 7 for dol starters, 2.5 for star delta starters, 3 to 4.5 for auto-transformer or invertor starters, 1.5 for slip-ring motors with resistance starters for slip ring motors with high starting power factor kva (g) = 1.12 x motor kw For multiple motor starting assume biggest is to be started first. eg 3 motors m1,m2,m3 whose size increase relative to there numerical value, then kva (g) = kva m1(running) + kva m2 (running) + (X x 0.42 x kw m3

What should be the value of X given in the formula for multiple motor starting ?

What should be the value of X given in the formula for multiple motor starting ?

what is the factor 0.42 ? can u clarify?

I forgot to mention previously that the figures I have given are based on 20 to 25% volt drop which should be ok for most switchgear coils but may be noticable on lighting installations and computers

A rule of thumb is to limit the motors that start simultaneously to .5 hp per kW of generator capacity. So if it is a 200 kW generator, no more than 100 HP of motors can be started simultaneously (or 75 kW). In general a 40% drop in voltage will drop out a motor starter.

Marathon Electric has a great "FREE" genset cd-rom catalog that has an excelent genset sizing software program in excel included.

The sizing program takes into account NEMA rating of the motor, voltage, Hz, type of starting and if you're doing multiple motor starting or sequence starting.

I've found this program excellent over the years in sizing gensets in the rental market for customer's motor starting jobs, including sizing for very large motors using multiple paralleled gensets to get the desired skva.

How can calculate the capacity of a Dg set required if various loads including motors are given? Specify the ratings required for various satrting methods of motors, like DOL , Star Delta and Auto Transformer.

for 71.00 KW how to calculate DG capacity

Dear Mr.Pradeep,

Several times, this topic is discussed. Pl. search in this Forum, you will get several replies.

Pl. refer the link below.

http://cr4.globalspec.com/search/sitesearch?do=show&sort=textmatchrank&srch=selection%20of%20capacity%20for%20DG%20set&srchobjs=t%2Cc&fs=12&order=asc

DHAYANANDHAN.S

Dear Mr.Pradeep,

In addition to my Posting No.13, above,with a link detail, pl.refer the following link which gives more details.

https://app.box.com/s/6205bfbb7766fbb51890

This link is retrieved from my archives. I think this answers your quiery.

DHAYANANDHAN.S