diesel generator AVR setting question 1

[tonylazyz]

I am in the process of changing AVRs on three matching, paralleling 200kW diesel generators on a ship. The new AVRs have an additional option the original AVR did not have. On the original AVR the LAM (load acceptance module) reduces active load to offset decreased engine speed due to load. On the new AVR I have the option to select between active load and frequency to control response to load. My question is under what conditions would one choose one option over the other. Below are the relevant sections from the old and new manual. The generators in question are Leroy Somer 400VAC/50Hz driven by Cat C9 turbo-diesel engines.

Original AVR (R488)
"on application of a load, the rotation speed of the gen set decreases. When it passes below the preset frequency threshold, the LAM causes the voltage to drop by approx 13% and consequently the amount of active load applied is reduced by approx 25% until the speed reaches its rated value again."

New AVR (R450)
"on application of a load, the rotation speed of the gen set decreases. When it passes below the preset frequency threshold, the LAM causes the voltage to drop proportionately to the frequency (LAM1) or to the active power (LAM2) depending on the rotating switch position. This reduces the active load scale applied until the speed returns to its rated value."

Thanks

 

[catserveng]

Use the frequency option if you want it to respond like the other units. You will likely have to make some additional adjustments to get the rolloff frequency the same as the other units with the different AVR.

On some of these AVR's the rolloff Hz of the LAM was fixed by the rated Hz settings, I don't have a manual handy but you may find you will have to adjust the rolloff Hz of the other two older AVR's to match the new AVR.

Most units that size that use that AVR don't parallel, so LS wasn't real worried about making sure they would play nice with other AVR's, at in my experience.

Hope that helps, MikeL.

 

[crshears]

Hey tonylazyz, the Electric Motors & Generators Engineering forum would have been a better fit for your question...good thing so many of us monitor both that forum & this one.

Just sayin'...



CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

The frequency option is also called UFRO, Under Frequency Roll Off.
Many AVRs with the UFRO option are jumper selectable between 50 Hz and 60 Hz.
The frequency doesn't have to drop very much before some motors and transformers go into magnetic saturation.
I much prefer the action of UFRO to handle motor and transformer loads during intervals of reduced frequency.
UFRO typically becomes active when the frequency drops 3 Hz below the nominal frequency. It reduces the voltage in proportion to the frequency drop. Thus a safe V/Hz ratio is maintained to avoid saturating motors and generators.

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

 

[tonylazyz]

Thanks all and thanks CRShears, I'll check out Elect Motors & Generators