That's correct, it's a 57.0 - 60.5 Hz operating window.
http://www.heco.com/portal/site/heco/menuitem.508576f78baa14340b4c0610c510b1ca/?vgnextoid=12a290a2decab110VgnVCM1000005c011bacRCRD&cpsextcurrchannel=1#bk6
According to that website, the requirement only applied to systems
interconnected after 2011/12/23 (maybe someone was trying to be poetic
by having this change take effect at the winter solstice) so this would
only be encouraged for legacy systems. I'll leave it to a HI-based
installer to comment on how easy it is to actually upgrade inverters to
this wider window. I'd guess you have to order directly from the
inverter manufacturer to get these settings pre-configured.
When the grid has excess loads and not enough generation, the frequency
drops. Similarly, excess generation causes the frequency to increase. By
opening the inverter window on the low end, this keeps all that PV
generation online when the grid needs as much power as it can summon.
The inverter window remains a maximum of 60.5Hz since the utility can
just dial back their own generation-- excess generation is much easier
to solve than excess load.
In the continental US, grid operators can usually rely on nearby
resources (natural gas-powered peaker plants, for example) to help
provide additional power when it's needed in an area. This makes
frequency problems pretty rare for us. Unfortunately for Hawaii, the
nearest backup generator is a few thousand miles away. Puerto Rico has
similar requirements for the same reasons. I believe that next week the
IEEE 1547 committee will finalize what exactly these windows will be in
the new edition.
Dave
On 2013/2/4 18:44, Mark Frye wrote:
Folks,
I was told that because the HI grid has poor frequency control,
grid-tied inverters have to have their low frequency limit set to 57 Hz
so they can ride out the worst low frequency events.
I find it hard to believe that this has been done for every single
inverter installed in HI.
But, what do I know.
Can anyone shed some light on this?
Thanks,
Mark Frye
Berkeley Solar Electric Systems
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