kva calculation of load to spec generator

[DCjr]

Greetings,
My customer has asked me to calculate the size of generator needed to power equipment in remote location. I have a generator specialist who will actually make the final calculation based on the nature of the load and starting sequence and match it to a gen-set. My task is to get the required loads and details on to a spread sheet and forward it to the gen guy. I have reviewed my reference books as well as the internet including several post on this forum and am still not clear.
The system will be 120/208 WYE. Grounded neutral. They are hoping for apx. 75KVA gen set.

VxAx1.73/1000, amps came from NEC 430.250
Watrer pump @ 25HP 3ph 208V.=26.92KVA
Water pump @ 7.5HP 3ph 208V.=8.711KVA
Water pump @ 10 HP 3ph 208V.=11.0.8KVA
hyd pump @ 7.5 hp 3PH 208v=8.71KVA

1ph 120v=???
2 BATTERY CHARGERS@120 V 2.4 KVA= 4.8KVA
1 BATTERY CHARGER@ 120 V 1.2 KVA = 1.2 KVA
70 LED LIGHT FIXTURES @ 120 V 19 W= 1.33 KVA

The equipment list is not final, what I need to know if you would be so kind, is if my 3 phase calc is accurate, and on the 120V loads do I tally the KVA up and make one fat total or do I balance the loads between phases, take the sum of the highest leg x 1.73? Or take the sum of the highest leg and X 3?

Also the generator specialist will take into the calculation the start up currents.

Regards,
Dick Carlton

 

[wsbeih]

Greetings,
My customer has asked me to calculate the size of generator needed to power equipment in remote location. I have a generator specialist who will actually make the final calculation based on the nature of the load and starting sequence and match it to a gen-set. My task is to get the required loads and details on to a spread sheet and forward it to the gen guy. I have reviewed my reference books as well as the internet including several post on this forum and am still not clear.
The system will be 120/208 WYE. Grounded neutral. They are hoping for apx. 75KVA gen set.

VxAx1.73/1000, amps came from NEC 430.250
Watrer pump @ 25HP 3ph 208V.=26.92KVA
Water pump @ 7.5HP 3ph 208V.=8.711KVA
Water pump @ 10 HP 3ph 208V.=11.0.8KVA
hyd pump @ 7.5 hp 3PH 208v=8.71KVA

1ph 120v=???
2 BATTERY CHARGERS@120 V 2.4 KVA= 4.8KVA
1 BATTERY CHARGER@ 120 V 1.2 KVA = 1.2 KVA
70 LED LIGHT FIXTURES @ 120 V 19 W= 1.33 KVA

The equipment list is not final, what I need to know if you would be so kind, is if my 3 phase calc is accurate, and on the 120V loads do I tally the KVA up and make one fat total or do I balance the loads between phases, take the sum of the highest leg x 1.73? Or take the sum of the highest leg and X 3?

Also the generator specialist will take into the calculation the start up currents.

Regards,
Dick Carlton

I suggest you use available genset sizing software like Specsizer , caterpillar specsizer.cat.com
It is free. Just register, and create your project.

You are right regarding the starting inrush currents. In order to get with 75KVA, I expect that you'll end up having multi step to start your loads.

 

[DCjr]

wsbeih,
thanks for your response, I have downloaded the application you have recommended. It looks very thorough. I will try it, however I hoped to have some guidance on the fundamentals of the penciled calculation.
DCjr