How to calculate the starting of 185kW motor at 1100kW base load?

[mfadzil]

Hi,

To refer;
Emergency Diesel Engine Generator Package
1500kWe.

Can anyone tell me how to calculate the starting of 185kW motor at 1100kW base load?

And;

What data and formula do I need to calculate the engine capability for the frequency drop for the above loading?

Thank You.

 

[davidbeach]

The genset manufacturers provide software for this purpose. That software, either your own copy or used by the manufacturer, will provide a far more accurate answer than anyone can provide here.

 

[mfadzil]

Thanks for your suggestion.
However, is it possible to have a very simple calculations for that matter? I'm looking a calculation that can prove the correct engine has been selected for certain use.

 

[waross]

Step one,

Emergency Diesel Engine Generator Package
1500kWe.

Is this set rated as standby, prime, or continous? Does the rating allow overloads? (Typically 110% of rated load for 1 hour in 12)
A rule of thumb;
Allow 3 times the KVA rating of the set for motor starting on a gen set shared with other loads.
Guesstimate #1 185 kW = 205 KVA. (PF 0.9)
Guesstimate #2 1100kW base load = 1222 KVA. (PF 0.9)
Guesstimate #3 1500kWe gen set = 1875 KVA (PF 0.8)
1875 kVA - 1222 KVA = 653 KVA
205 KVA x 3 = 615 KVA
This should be acceptable.
Frequency dip: This will depend on the response characteristics of the governor and the ability of the motor to accept block loading. A naturally aspirated set will pick up a block load better than a turbo aspirated set. BUT I don't think that in this instance you should forgo the better fuel economy of a turbo aspirated set.
A Permanent Magnet Generator to supply the Automatic Voltage Regulator will give you better voltage stability when starting the motor. It is an extra that will be worth the extra money in this application.
Your motor (185 kWe) is 12.3% of the rating of the set. (1500 kWe) This is a fairly conservative block load.
The seat of my pants says that you can expect reasonable performance from this combination.
One last comment; A voltage dip is often more noticeable to other users than a frequency dip. The PMG will help here. You may get some chirping from small UPSs from frequency dip when the motor starts. Look for UPSs that are tolerant of small frequency excursions or you may have ongoing issues with the gen set apart from the motor starting issues.
But, check the web sites of the major gen set makers for sizing software.
By aware that 3% frequency droop from no load to full load is a common spec on a great many gen sets. (The UPSs must be able to live with this)

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