From: John De Armond
Newsgroups: alt.energy.homepower
Subject: Re: Problems with Standby generator (240V 15Kva)
Date: Sat, 10 Jun 2006 23:58:15 -0400
Message-ID: <k94n82571nemvnjv7c117fv9t7jrv6brnd@4ax.com>

This can be a devilishly difficult problem to solve and sometimes it
just isn't possible with a given generator.

It's probably not the governor or else you'd hear the change in noise
in the engine.  One of two broad areas - the voltage regulator board
is oscillating or the regulator is interacting with the load to cause
hunting.  The later is the most difficult situation.

An oscillating regulator can be caused by too much loop gain or
improper phase compensation.  Better regulators
(commercial/industrial) have adjustments for both.  Some higher end
digital units can even tune themselves.  Look for pots on the board
labeled something like "gain", "phase compensation", "lead/lag", etc.
If the regulator includes a PID loop, you might find pots labeled
"rate", "reset", "integral", "derivative" or something similar.  These
may be pots that are on the board itself and hidden from the outside
by the case or covers.  If there is only a simple voltage adjustment
then either the regulator does not have such sophistication or the
values are fixed.

A very reactive (inductive or capacitive) load that results in low
power factor can profoundly confuse simple regulators and even more
sophisticated regulators that aren't adjusted for the conditions. This
interaction cause the regulation to hunt or oscillate.

Common examples of low PF loads are compact fluorescent lamps, some
conventional fluorescent lamps.  Cheaply made and/or lightly loaded
motors.  Some microwave ovens.  A lightly loaded step-up or -down
power transformer.  Even a long (the definition of which can vary
widely) line between the genny and load can exacerbate the problem.

I'm just kinda shooting in the dark here since I don't have any
technical information nor data to work with.  You might try
disconnecting loads, preferably substituting back pure resistive
(heating) loads to maintain the same load on the generator, to see if
any cause the hunting to change.

BTW, the optical tach won't respond rapidly enough to let you see
governor hunting.  You'll need a stroboscope for that.  The Strobotach
is the top-of-the-line luxury version but cheaper ones are available.
Perhaps you could rent or borrow one.

(just in case you don't know how it works.) A stroboscope apparently
freezes the motion of the rotating object with its short duration,
repetitive flashes.  Since the stroboscope flashes at a constant rate,
any momentary change in speed of the object being strobed will cause
its image to jitter back and forth or rotate back and forth.  Very
easy to spot.

John


On Sun, 11 Jun 2006 01:58:16 GMT, Rod Out Back
<someone@IHATESPAM.BIGPOND.COM> wrote:

>Folks,
>
>I wondered if anyone might be able to point me in the right direction
>here...
>
>I live in outback Australia.  Electricity grid power is 240v 50Hz. We
>have a (2nd-hand) 15Kva (Single Phase) standby generator which kicks
>into gear if the grid power fails. It runs until the power control
>unit detects grid power, and then switches back over to grid power
>after the grid has been on for a set amount of time(currently 10
>minutes).  At this point, the genset shuts down.
>
>Genset is a 2cyl Lister/Petter diesel motor driving a McCaul brushless
>alternator. Unit is rated for 15Kva, and I understand the previous
>owner was a telecommunication company; using the genset to maintain a
>battery bank in a large telephone exchange.
>
>Problem:  While the genset is running, we have a very noticeable
>flicker in the lights.  The flicker varies in intensity, and seems to
>be related to the load the alternator is under.
>If I put about a 5-7 kilowatt load on the alternator, the flicker
>nearly dissappears. I am wondering if the alternator has been adjusted
>to suit a constant, heavy load in it's previous life, and that the
>light loading is causing me the flicker.
>
>Possible causes as I see it:
>
>Engine speed.  This one is easy to fix, and I suppose the easiest to
>check.  I do have an optical tachometer here, which can tell me if it
>is running at 1500rpm.  However, I note that the last time I checked
>power to the house when the genset was running, it was pretty close to
>the correct voltage(I think it was 248 volts with light load).
>However, it makes me wonder if the engine revs are set a little to
>high?? Or would a too low setting cause the same?
>
>Alternator control board.  I can get another unit if this one is
>flakey, but there is an adjustment on the board to adjust output (cant
>remember exact adjustment), and I wonder if this has been adjusted for
>a constant heavy load. I wondered if the light/intermediate loading
>from the house is causing me grief.
>
>Unfortunately, I dont have a local genset whizz that I can call, and I
>expect I will have to resolve this one myself.
>
>Apologies if this is posted to the wrong group, but I wondered if
>anyone had encountered similar problems with standby generators.
>
>Any thoughts or suggestions gratefully accepted.
>
>
>Cheers,
>
>Rod.....Out Back