Standby Generator performance 4

[petefla]

1000kVA, 800kW, Standby Genset.
Diesel, 8 cylinder, turbo charged engine. 1,500 rpm.
Wye configuration on alternator.
3 phase load well balanced.
What one step load acceptance should be possible, as a percentage of full load rating ?

 

[alehman]

It depends on what voltage dip and recovery time is tolerable to the load. A diesel in good condition will be able to handle a 0 to 100% of capacity step, but the voltage dip may be 50% and take a few seconds to recover.

 

[bigamp]

The step load depends on the nature of the load, the characteristics of your genset and the dip in voltage and frequency that you (and the connected equipment) are prepared to (or able to) tolerate.

Genset manufacturers are able to provide performance data that will help you determine what the effect of various size step loads will be. In particular, a family of graphs to determine voltage dip versus motor starting kVA. You should therefore consult the genset vendor if possible.

As a rough idea, if your load is motor load and your motors are able to operate without stalling at 80% terminal voltage then you could probably accept a generator voltage dip of 15% whilst starting your step load. The largest step load would be whatever would result in a generator voltage dip of 15%. From IEEE Std 141 (red book), approximately 450kVA step load will cause a 15% voltage dip on a 1000kVA generator.

Regards

 

[Generation]

Hi petefla,

Detailed explanation and guidelines for this subject is all described in manual "Electric Power Application".
You can download this .PDF file from website

http://www.beckwith-machinery.com/engtech.html

 

[PAFred]

The answer to this is fairly simple the bigger the engine the more power , thus the more load that can be picked up on a block load.

How ever that being stated in the real world you idealy want to be able to pick up the full load with an engine sized to be the equivilent in horsepower. But more often than not the engine due to priceing and bidding wars is sized very close if not just under what is really neaded.

The bottom line is that you want a system that will be loaded to about three quarters of full rated capacity and an engine size in horsepower that can pick that block load up.

Something to keep in mind that I've come across on more than one time, Sometimes a genrator is connected to an engine with a greater KW rating than the engine rgarding horsepower. This is done to statisfy a KVA rating on a spec rahter than just a KW rating. The reason that this is an important note is this, If you have a generator with a data tag stateing that it is say 750 kW and the engine was sized to carry only the needed resistive KW you could easily have a system that the engine itself is too small to pull the full 750 KW at resistive load but can at reactive load. In other words #1 make sure of the engine horsepower as built by the OEM and then calculate the capability of it in electrical power or KW. Else you could be trying to get more than is possible from the engine driving the system!

I have come accross this numerous times so know your engines and your calculations to verify what you can expect or should expect.

 

[Generation]

Sorry to say this PAFred, but this doesn't answer the question at all!
The question was what amount of load step can be performed AS A PERCENTAGE of the full load rating.
This is depending on several items, such as engine BMEP, whether the engine is turbo charged, moment of inertia, governor performance, generator AVR design, etc.

All of this is quite clear explained in the manual on the website as already mentioned by me on the 9th December 2002.

Differences in Engine versus Generator power rating is not always caused by bad intensions of the supplier, but is mainly done for one of the following reasons:

1) The same engine and generator power rating is not available a standard batch line product. In this case it's common use to size the generator bigger as the maximum engine power. This in order to prevent overloading of the generator.

2) Project requirements for overcapacity of the generator in order to reduce the temperature rise of the generator, (for example if the the maximum ambient temperature is high)