underfrequency settings

[electrofelon]

I keep going through this with one of the utilities around here. Can someone explain this or did the wording of this get befuddled somewhere along the line? So standard frequncy range is typically 59.3-60.5 HZ. This is what pretty much all inverters default to and what is stated in the New York State Standardiazed interconnection agreement. The NYS SIR does also say however:

....If deemed necessary due to abnormal system conditions the utility may request that the generator operate at frequency ranges below 59.3 Hz in coordination with the load shedding schemes of the utility system.

This utility is saying regarding the underfrequency setting "the maximum acceptable setting is 57Hz at .5 seconds." I think what they mean is "the maximum deviation from nominal is -3 HZ" or "the minimum underrequency setting is 57 HZ" or do you think that really want it to stay online until you get below 57 HZ?:?

 

[ron]

I'm not sure, but if the grid sways to 57hz, bad things are happening.
Unless this is some islanded small grid system, the US "GRID" better not be swaying that much or the "stuff" is in and around the fan blades and we have big trouble.

 

[electrofelon]

I'm not sure, but if the grid sways to 57hz, bad things are happening.
Unless this is some islanded small grid system, the US "GRID" better not be swaying that much or the "stuff" is in and around the fan blades and we have big trouble.

Yeah, and the way it is worded, they have NO MINIMUM, so my inverter can still be operating at say 20 HZ. I can't believe that is what they intend.

 

[Hv&Lv]

Your interpretation is correct. When I set up a relay for solar I set the UF pickup at 59.7 and the OF at 60.25
and it’s 57 for 30 cycles... so it’s a fast dip and trip

 

[electrofelon]

I heard back from the utility and this is what they said,

Our company has a generic requirement for all interconnecting generation setting their frequency at a maximum acceptable setting 57 Hz at 0.5 seconds. This is because we must comply with NPCC PRC-006, Under frequency Load Shedding Program, which is designed to require that generation interconnected to our distribution system rides through small system disturbances and helps us to avoid shedding load in certain circumstances. This lower frequency setting will also help in avoiding your generator from tripping off line under the normal UL 1741 frequency settings.



This must be set to a maximum of 57 Hz in order to proceed with Final Acceptance.

It still seems odd they care about small PV systems riding out sags in frequency. Also doesn't seem to make sense that there is no MINIMUM required.

 

[Hv&Lv]

I heard back from the utility and this is what they said,



It still seems odd they care about small PV systems riding out sags in frequency. Also doesn't seem to make sense that there is no MINIMUM required.

A few years ago the thinking was to drop the solar if there is a fault or a blip in the grid.
with so much solar now dropping all of it at once if there is a small blip in the system would cause cascading outages.
the thinking now is to let the solar farms stay on During a fault condition and let the reclosers do their job.
same way with UF. Dropping that much generation at one time could have terrible effects on the grid.
we have raised our trip settings on the solar now so they don’t drop out during an outage.
now I have them monitored on a 32 relay

 

[wwhitney]

I think you can safely assume that in both cases where they say "maximum" they mean (maximum magnitude negative deviation from 60 Hz), i.e. minimum to a mathematician.

Cheers, Wayne

 

[ggunn]

A few years ago the thinking was to drop the solar if there is a fault or a blip in the grid.
with so much solar now dropping all of it at once if there is a small blip in the system would cause cascading outages.
the thinking now is to let the solar farms stay on During a fault condition and let the reclosers do their job.
same way with UF. Dropping that much generation at one time could have terrible effects on the grid.
we have raised our trip settings on the solar now so they don’t drop out during an outage.
now I have them monitored on a 32 relay

Large commercial/utility scale systems already do that.

 

[electrofelon]

A few years ago the thinking was to drop the solar if there is a fault or a blip in the grid.
with so much solar now dropping all of it at once if there is a small blip in the system would cause cascading outages.
the thinking now is to let the solar farms stay on During a fault condition and let the reclosers do their job.
same way with UF. Dropping that much generation at one time could have terrible effects on the grid.
we have raised our trip settings on the solar now so they don’t drop out during an outage.
now I have them monitored on a 32 relay

So by "raised our trip settings" you mean "lower our trip settings"?:dunce:. Yeah what Wayne said, it's confusing.

So I get what you are saying about lowering the underfrequency trip setting to keep solar on longer, but don't you want a range so the solar ultimately kicks off if something really bad is happening? My POCO is saying I can have no underfrequency trip at all - that is logically what it means if you don't have a minimum.

 

[Hv&Lv]

So by "raised our trip settings" you mean "lower our trip settings"?:dunce:. Yeah what Wayne said, it's confusing.

So I get what you are saying about lowering the underfrequency trip setting to keep solar on longer, but don't you want a range so the solar ultimately kicks off if something really bad is happening? My POCO is saying I can have no underfrequency trip at all - that is logically what it means if you don't have a minimum.

I raised the pickup from 200 amps to 320 and went from a 50 to a 51 for tripping to reduce some nuisance tripping when a fuse operated and the solar farm was feeding the fault.

so I mean raised the settings, not lowering anything..

 

[Hv&Lv]

Large commercial/utility scale systems already do that.

??
yeah, we didn’t do it yesterday...
been like that a couple of years now.

 

[electrofelon]

I raised the pickup from 200 amps to 320 and went from a 50 to a 51 for tripping to reduce some nuisance tripping when a fuse operated and the solar farm was feeding the fault.

so I mean raised the settings, not lowering anything..

What does "went from a 50 to a 51" mean?

 

[Hv&Lv]

ANSI relay numbers...
50 is instantaneous. The pickup is what it is.
51 is time Overcurrent. The pickup asserts and times according to the time delay and the curve assigned