|
|
Posted by Smarty on 06/07/07 06:19
I would want to be sure of a several things based on the correctly computed
loads:
First, can the phases be arbitrarily loaded to total 20 KVA? If so, the
total amperage available of 83.33 amps (20 KVA / 240 volts) would allow you
(as stated) to draw 29 / 30 amps as you plan without problems. If, however,
the individual phases are limited to 1/3rd of the current to each phase, you
will have a problem in 2 of the 3 phases with blown fuses / circuit
breakers, or worse.
Second, I would ***VERY CAREFULLY*** establish that your estimated load of
73 amps total is 'worst-case', since you are within about 12% of the claimed
generator capacity. You are not leaving yourself much margin in the event
that either your estimate is a bit optimistic for the load, or, more
significantly, that the generator manufacturer is giving an honest,
sustainable output.
Many generators have little "gotcha" clauses in which other factors such as
ambient temperature, humidity, altitude / air quality, etc. derate the
claimed output, in some cases severely. Moreover, even if none of the cited
exceptions occur, the generator may never meet 88% of the claimed maximum
output, in which case you will have to turn off lights, only make coffee at
certain times, etc.
Finally..........since your video production rests on frequency stability of
your power source, I would want to be damn sure that your video gear,
cameras, monitors, etc. all have good and stable 50 Hz sync ***IRRESPECTIVE
OF GENERATOR FLUCTUATIONS*****
Some generators actually do "AC TO AC conversion" by creating a DV rectified
source, and then chopping it, to avoid the inevitable dependency of rotating
mechanical generators on maintaining totally stable RPM. You do not want
your 50 Hz reference to fluctuate as the generator encounters changing loads
such as when lights are switched on / off.
Smarty
"Bernie Dwyer" <b_duibhirz@yahooz.comz.auz> wrote in message
news:46679C76.6B5C1C52@yahooz.comz.auz...
> Hi - are there any sparkies (electricians) here?
>
> I'm shooting some rainforest scenes in a couple of weeks and I will need
> suitable lighting.
>
> I've worked out the loads and want to confirm that I'm hiring a suitable
> 3-phase generator. Here's the details:
>
> All voltages are Australian, i.e. 240VAC, 50Hz. All calculations rounded
> up for a safety margin.
>
> Phase 1: unit/makeup. Small lights, airbrush compressors, hot water jug,
> etc. Total 14 amps
>
> Phase 2: lights on set, total 29 amps
>
> Phase 3: lights on set, camera power, field monitor, smoke machine, etc.
> Total 30 amps
>
> By my calculations, this comes to 17.52 KW of mostly resistive load, so
> no power factor to worry about.
>
> I can get a 20KVa generator for a reasonable price, and this would seem
> to fit the bill. 17.52 KW shouldn't stress a 20KVa generator. I want to
> leave a bit of a reserve. The next one up is a 60KVa generator, and it
> costs a lot more.
>
> Any opinions?
>
> (duh, this is the interweb, there'll be opinions, count on it:-)
>
> --
>
> Bernie Dwyer
> There are no 'z' in my address
Navigation:
[Reply to this message]
|