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AC causing PV inverter to cycle into wait mode

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AC causing PV inverter to cycle into wait mode old dirtbeard 09-01-2007
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Posted by old dirtbeard on September 1, 2007, 4:10 pm
Hi,

My 6 kW grid-tie photovoltaic system is going into wait mode when my five
ton AC cycles on. I have 200 amp service to the house, but these summer days
the line voltage will drop from 240 to 225. The inverter is an SMA 6000U
with a minimum grid tie operating voltage of 213 VAC. I think that when the
AC cycles on, it either momentarily depresses line voltage below 213, or it
just causes the line voltage to change too quickly for the inverter to
maintain the sync (either one of these conditions will cause the inverter to
"detach from the grid" and go into a wait mode monitoring the state of the
grid).

Questions:
- Maybe the line drop from the pole is undersized? (does not seem likely
given that Edison must have connected it to the 200 amp panel).
- How likely would the gauge of the line drop be the cause of this problem?
- Does anybody know what gauge a 75 foot 200 amp line drop ought to be?
- Has anybody had success in getting their utility to replace the line drop
with a larger gauge drop?
- Is there anyway to add something to the AC circuit so that it has a
"softer start" so it does not depress the line voltage so much?

This is a real pain as the AC cycles about every 20 minutes and causes the
array to go off-line for five or ten minutes each time. I am losing a great
deal of electrical production and I can't believe it is good for the
inverter, either.

thanks,

doug



Posted by Uncle Monster on September 1, 2007, 5:04 pm
old dirtbeard wrote:
> Hi,
>
> My 6 kW grid-tie photovoltaic system is going into wait mode when my five
> ton AC cycles on. I have 200 amp service to the house, but these summer days
> the line voltage will drop from 240 to 225. The inverter is an SMA 6000U
> with a minimum grid tie operating voltage of 213 VAC. I think that when the
> AC cycles on, it either momentarily depresses line voltage below 213, or it
> just causes the line voltage to change too quickly for the inverter to
> maintain the sync (either one of these conditions will cause the inverter to
> "detach from the grid" and go into a wait mode monitoring the state of the
> grid).
>
> Questions:
> - Maybe the line drop from the pole is undersized? (does not seem likely
> given that Edison must have connected it to the 200 amp panel).
> - How likely would the gauge of the line drop be the cause of this problem?
> - Does anybody know what gauge a 75 foot 200 amp line drop ought to be?
> - Has anybody had success in getting their utility to replace the line drop
> with a larger gauge drop?
> - Is there anyway to add something to the AC circuit so that it has a
> "softer start" so it does not depress the line voltage so much?
>
> This is a real pain as the AC cycles about every 20 minutes and causes the
> array to go off-line for five or ten minutes each time. I am losing a great
> deal of electrical production and I can't believe it is good for the
> inverter, either.
>
> thanks,
>
> doug
>

Your 5 ton AC unit will be fed by a 50 to 60 amp 240 vac
circuit. You must understand that the LRA (locked rotor
amps) for such a unit can be between 120 and 150 amps
and the RLA (run load amps) will be between 17 and 25 amps.
Your 6 kw power system only puts out around 25 amps
continuous current. I don't what the surge rating for your
inverter is but I can guess that it is not enough to start
a 5 ton AC unit thus it will drop out and wait for the
load to stabilize before kicking back in.

[8~{} Uncle Monster

Posted by Telstra on September 1, 2007, 5:39 pm
Can you give the MAKE and MODEL NO of the AC Unit

> Hi,
>
> My 6 kW grid-tie photovoltaic system is going into wait mode when my five
> ton AC cycles on. I have 200 amp service to the house, but these summer
> days the line voltage will drop from 240 to 225. The inverter is an SMA
> 6000U with a minimum grid tie operating voltage of 213 VAC. I think that
> when the AC cycles on, it either momentarily depresses line voltage below
> 213, or it just causes the line voltage to change too quickly for the
> inverter to maintain the sync (either one of these conditions will cause
> the inverter to "detach from the grid" and go into a wait mode monitoring
> the state of the grid).
>
> Questions:
> - Maybe the line drop from the pole is undersized? (does not seem likely
> given that Edison must have connected it to the 200 amp panel).
> - How likely would the gauge of the line drop be the cause of this
> problem?
> - Does anybody know what gauge a 75 foot 200 amp line drop ought to be?
> - Has anybody had success in getting their utility to replace the line
> drop with a larger gauge drop?
> - Is there anyway to add something to the AC circuit so that it has a
> "softer start" so it does not depress the line voltage so much?
>
> This is a real pain as the AC cycles about every 20 minutes and causes the
> array to go off-line for five or ten minutes each time. I am losing a
> great deal of electrical production and I can't believe it is good for the
> inverter, either.
>
> thanks,
>
> doug
>
>



Posted by old dirtbeard on September 1, 2007, 6:23 pm
Hi,

Yes, thank you, it is a Lennox HS26-060-2P.

The way this grid-tie system works is that during the daytime when the array
is producing more elecricity than the house is consuming, it sends the
"excess" current back to the grid and spins the meter backwards. During the
day if we need more elecricity than we can generate, it draws the shortfall
from the grid. At night the meter spins forward just like there was no PV
system.During the day, though, the inverter needs to "lock on" to the
fequency and voltage of the grid to invert the 380 VDC to 60 cycle, 240 VAC.
The inverter can tolerate a grid voltage range of 213 - 262 VAC and a
frequency range of only about 59-61 hz.

The panels do not need to fully drive the AC, but when the AC cycles on, it
either is dropping the line voltage below 213 VAC or is dropping the voltage
so quickly that the inverter loses it's sync on the line. I am thinking that
the line drop from the pole cannot supply the start-up volt-amps required by
the AC condenser.

Thanks for any help you can provide.

doug





Posted by Bob F on September 1, 2007, 8:42 pm

> Hi,
>
> Yes, thank you, it is a Lennox HS26-060-2P.
>
> The way this grid-tie system works is that during the daytime when the array
> is producing more elecricity than the house is consuming, it sends the
> "excess" current back to the grid and spins the meter backwards. During the
> day if we need more elecricity than we can generate, it draws the shortfall
> from the grid. At night the meter spins forward just like there was no PV
> system.During the day, though, the inverter needs to "lock on" to the fequency
> and voltage of the grid to invert the 380 VDC to 60 cycle, 240 VAC. The
> inverter can tolerate a grid voltage range of 213 - 262 VAC and a frequency
> range of only about 59-61 hz.
>
> The panels do not need to fully drive the AC, but when the AC cycles on, it
> either is dropping the line voltage below 213 VAC or is dropping the voltage
> so quickly that the inverter loses it's sync on the line. I am thinking that
> the line drop from the pole cannot supply the start-up volt-amps required by
> the AC condenser.
>
> Thanks for any help you can provide.
>

Have you talked with the manufacturer of the inverter?

Bob



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