08-12-2017 09:22 PM
This is an excellent reference for sizing starting batteries,
The Caterpillar A&I Guide for starting systems is here,
Unfortunately CAT didn't include battery sizing guidelines in the A&I Guide
08-12-2017 01:20 PM
08-12-2017 01:13 PM
08-12-2017 12:40 PM
So are you paralleing CAT units to the Volvo units?
In certain load conditions, paralleled units with different V/Hz (or UFRO) settings can swap load back and forth. Ideally you would want to be sure all units that parallel have the same knee frequency settings and same slope, otherwise when a transient occurs the response may not match and you end up with one unit hogging the VAR load as frequency drops. Doesn't always happen but have seen a number of cases where it does cause instability on multiple paralleled units when a larger transient occurs.
Volts per hertz and Under Frequency RollOff are essentially the same thing, when engine speed drops, the voltage will droop per teh settings to allow the unit to unload somewhat and allow for a faster recovery. The knee frequency is the point below nominal rated frequency where the drop in volts per hertz will begin, usually at least 0.2 Hz and in some cases as much as 1 Hz below nominal. The slope is the rate of voltage drop per hertz, in most CAT analog voltage regulators the slope is 8 volts per hertz (usually called single volts per hertz), with a jumper option to go to "double volts per hertz". Most of the digital regulators have a broad adjustment range for Volts/Hz. I'm not sure off the top of my head what the Volvo (Stamford?) regulators are setup for, but if you want your system to function as best as it can you really should make sure all the voltage regulator characteristics are setup as close as possible. This is VERY important if you are using droop or cross current compensation for VAR sharing, is less of an issue if you are using some kind of active VAR share controller. like a Woodward, DeepSea, or something similar (don't mean to leave anyone out but there are a number of good active real and reactive power sharing controllers out in the world these days).
I recently worked on a system that the user complained of intermittiant instability, a small power plant at a fairly large sand and gravel quarry with three generators that could operate in parallel, but didn't always. Each generator supplier stated that his unit worked "fine", but in certain combinations during load transients the voltage and frequency would get unstable and some times trip off some loads or a generator. All were operating on both speed and voltage droop. None of the units were setup the same, each would carry a load standalone up to its rating with no problem, two of the units were setup close enough that they would parallel but the VAR share was terrible, and the real power share wasn't so good either. The culprit was the larger unit that had no speed or voltage droop setup, that particular vendor and the customer kept saying it "was the best unit on site", well yeah, frequency and voltage always constant no matter what the load was, and oversized for most of the loads it was driving. We brought in a resistive/reactive load bank, set all speed droops at 2.5%, all voltage droops at 3%, and set all the V/Hz (UFRO's) so that the had as close as possible the same characterisitic, and all units paralleled with no reported issues after that. No single unit was the cause and at some point someone had claimed "harmonics" was the problem. It was just poor setup and integration, which I see many times a year. Hope that story helps some.
You have not provided very many details about how your units operate, what they parallel to or what kind of loads they are driving, how you are doing both real and reactive power sharing and why you think harmonics may be an issue.
More information on your part wil get you better answers.
08-12-2017 11:57 AM