sizing fire pumps generators

[Mefi01]

Hello everyone,

can someone give me a firm answer on the way in which generators feeding fire pumps can be sized ? is this carried out with respect to the inrush current or the nominal bearing in mind the first is 3times the latter ( start Delta starting)?

 

[waross]

It depends.
How many pumps?
What HP?
For motor starting, a rule of thumb is the generator available capacity in KVA must be three times the motor running rating in KVA.
Or, just use current. eg: base load on the generator is 75 AMPs, the motor rated current is 50 Amps;
Generator capacity should be at least 3 x 50 Amps plus 75 Amps = 225 Amps.

However, if you must justify your calculations, go the the Caterpillar site and find and use their free generator sizing software. The software will allow you to change the default voltage starting dip if you so desire.

The sizing soft ware is based on a more conservative voltage dip then will be seen when using the three times rule of thumb and so will recommend a larger set.
Using the three times rule will be using information obtained free from the internet.
Using Caterpillar's sizing software will cover your ASSets.
Note that the last version of the sizing software that I used allowed my to tweak the voltage target dip and determine the voltage dip that would be seen using the three times rule.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

By the way, the power output of a diesel engine is proportional to the specific gravity of the fuel.
For critical service you may consider oversizing the set so that full power will be available in the event that you inadvertently receive a load of light fuel. In some areas the fuel supplied in the winter may be as much as 10% lighter than summer fuel.
I have seen instances of a major gen-set engine manufacturer publishing performance figures based on heavier than normal fuel.


Bill
--------------------
"Why not the best?"
Jimmy Carter