Hi Bill,
Can you explain why the 6kVA rule on split phase systems?
I mean why 6?
thanks,
jay
peltz power
On Aug 8, 2008, at 8:48 PM, Bill Brooks wrote:
Jeff and Ryan,
The 6kVA value comes from the California Rule 21 that I worked on.
It only
applies to split-phase 240V systems (6kVA on 120V). There is no
specific
limit for imbalance on a 3-phase service.
A basic rule for single phase generation on a 3=phase service is to
rotate
among the phases in a balanced manner. This means the largest
imbalance
possible right now is 7kVA because of the SMA SB7000US. There is a
single-phase SatCon that is 30kVA, but it would be silly to buy a
single-phase Satcon when the major on 3-phase units.
The best way to place the imbalanced single-phase generators on the
service
is to test the current on all three phases and put the inverter(s)
on the
most heavily loaded phase(s). This reduces the site imbalance by
reducing
the imbalance on the serving transformer (lowering current on the most
heavily loaded phases). It is common for 3-phase services to have
imbalances
of 10 kVA or more, so single-phase inverters can reduce the problem
rather
than make it worse.
Make any sense?
Bill.
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