[RE-wrenches] Xslent?
Exeltech
exeltech at yahoo.com
Mon Jan 10 08:58:45 PST 2011
By the way, in answer to answer your original question, capacitors of proper value, when installed in a circuit containing inductive loads, are capable of allowing the circuit to attain a power factor of 1.0. As part of our Underwriter's Laboratories testing for our grid-tied inverters, a test fixture is used that's capable of both inductive and capacitive reactance (it's part of the anti-islanding tests). I've witnessed the power factor being adjusted from 0.7 leading and lagging to an absolute perfect 1.0000 (yes, four decimals). It's all done by varying the value of capacitance in the circuit. Thus, if one were to use lab-grade test equipment, and take the time needed to make such a precision adjustment, it's possible to achieve absolute unity in an inductive circuit by "tuning" it with a capacitive circuit.
Dan
--- On Mon, 1/10/11, North Texas Renewable Energy Inc <ntrei at 1scom.net> wrote:
From: North Texas Renewable Energy Inc <ntrei at 1scom.net>
Subject: Re: [RE-wrenches] Xslent?
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Date: Monday, January 10, 2011, 8:29 AM
How efficient is a
capacitor in offsetting the power factor error? 99.9%... ±2%...?
Jim
Duncan
-----Original Message-----
From:
re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org]On Behalf Of
Exeltech
Sent: Sunday, January 09, 2011 9:03 PM
To:
RE-wrenches
Subject: Re: [RE-wrenches] Xslent?
--- On Fri, 1/7/11, Peter Parrish
<peter.parrish at calsolareng.com> wrote:
> What ever
is done to reduce the reative power, it has to be done
> in real
time (with a fraction of 0.016 seconds, the 60 Hz
cycle).
> You can’t
wait until later in the evening to solve a problem
that
> is
occuring during the day.
Peter is absolutely correct. Power
factor correction MUST occur on a half-cycle by half-cycle basis, and at
the exact moment of power consumption by the reactive load.
Anything else won't be effective, and may in fact worsen the power
factor at a given point in the grid.
> Real time
compensation can be often done with capacitors alone
> or in
conjuction with some smart electronics. Remember that
for
> short
periods of time capacitors can store considerable
amounts
> of energy
and can smooth out these reactive currents.
Capacitors placed across a power line will store
energy for exactly one-half cycle. At that point, the polarity
reverses, the capacitor is discharged to to zero, then recharged to the
opposite polarity. This process repeats every cycle.
What
DOES take place is a phase shift (displacement) in the current flow
relative to the voltage waveform. Power factor correction is done
with capacitor banks (we see them in substations and on power poles) to
offset the power factor of the grid itself, which by its design is
inherently inductive due to long runs of wire. Very large motors
will have individual "tuning" capacitors installed to offset inductive
reactive current flow. These capacitors are disconnected whenever
the respective motor to which they're connected is not in use. On
occasion, excessive capacitance exists in a circuit that must be offset
by inductance, but this is rare.
Like Tom Cruise said in Top
Gun .. "It's complicated."
Dan
--- On
Fri, 1/7/11, Peter Parrish
<peter.parrish at calsolareng.com> wrote:
From:
Peter Parrish <peter.parrish at calsolareng.com>
Subject: Re:
[RE-wrenches] Xslent?
To: "'RE-wrenches'"
<re-wrenches at lists.re-wrenches.org>
Date: Friday, January 7,
2011, 5:39 PM
I know only a
little about Power Factor “charges”, but we can figure out some other
“engineering” issues.
Power Factor
is a measure of the amount of reactive (out-of-phase) power compared
to real (in-phase) power. It is somewhat complicated but the PF is
unity for 100% in phase and 0 for 100% out-of-phase power.
The important
thing to remember is that (while holding the real power constant) for
PFs less than unity there is in addition to the real power, and
“in-flow” of power and an “outflow” of power four times a cycle. One
might say, “Why do I care about reactive power? It flows in and out
with no net contribution over the long run!). True, but the in-flow
and out-flow represents higher currents on the lines and
more losses. Or it means that there have to be
oversized service conductors to avoid the extra losses. Even if the
losses are avoided, the higher currents can trip overcurrent
protection devices, and of course the utility company needs to supply
(and take back) the extra currents in real time.
What ever is
done to reduce the reative power, it has to be done in real time (with
a fraction of 0.016 seconds, the 60 Hz cycle). You can’t wait until
later in the evening to solve a problem that is occuring during the
day.
Real time
compensation can be often done with capacitors alone or in conjuction
with some smart electronics. Remember that for short periods of time
capacitors can store considerable amounts of energy and can smooth out
these reactive currents.
I can well
imagine how an inverter can be designed to generate both real and
reactive power, and therfore an inverter can reduce the amount of
reactive power that needs to be supplied by the utility company – but
not when the sun isn’t shining. I suspect that these types of
inverters will have oversized output circuit wiring to handle the
reactive currents without adversely impacting their efficiency rating.
If I have
time this weekend, I will take a look at Apparent’s
website.
- Peter
Peter T.
Parrish, Ph.D., President
California Solar Engineering, Inc.
820
Cynthia Ave. , Los Angeles , CA 90065
CA Lic. 854779, NABCEP Cert.
031806-26
peter.parrish at calsolareng.com
Ph 323-258-8883, Mobile 323-839-6108, Fax
323-258-8885
From:
re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jamie
Johnson
Sent: Friday,
January 07, 2011 2:03 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Xslent?
It's an
interesting product for a niche market if it actually works as
they say (Disclaimer:I am not
claiming that it does), after speaking with an individual who
I believe is the VP of Production for Apparent (use to work
for EnPhase according to their
website), he claims that the product is currently installed at
the Google campus on a solar canopy for some of their EV
chargers (can anyone verify this?)
They have
several other beta installs as well, however the individual I
spoke to said they were only installing small systems at beta
test sites (where the Util co charges for VAR's using
separate meters like for EV charging) for now. No
pricing has been set for the inverters, and they are not available for
sale to installers yet.
Apparently
they claim the inverter can create/produce VAR's by taking 1
watt of power from the grid at night or from the solar output during
the day and turning it into approximately 9 VAR's to offset the
customers charges for VAR usage from the Grid. This is
where the KVAh production on
the graph before sunrise and after sunset comes
from.
I still
would need to see a third party head to head comparison test before I
believed it. Again niche market inverter for when the
utility co charges for VAR's.
Jamie
--------
Original Message --------
Subject: Re: [RE-wrenches] Xslent?
From: August Goers
<august at luminalt.com>
Date:
Fri, January 07, 2011 10:24 am
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Hi
All -
Thanks for the helpful info! We did a little more
research on our end and
I guess Apparent is the new brand name
for the Xslent product.
What
baffles me is the chart where they show that they're
producing power
before and after sunrise and sunset:
http://www.apparent.com/products/mgi.html
The
system must include batteries? Someone on their marketing team
is
really going to town...
Best,
August
-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org]
On Behalf Of jay peltz
Sent: Thursday, January
06, 2011 4:43 PM
To: RE-wrenches
Subject: Re: [RE-wrenches]
Xslent?
HI
Peter,
I agree with you that for now on residential it makes
no sense.
However for commercial that might have to pay extra for
PF issues, to have
the inverter adjust for this makes
sense.
Its the reason they( inverter companies ) are doing
it.
I"ve heard a better
more complete reason of course from Bill Brooks, who
maybe can
chime in.
sorry got away from me,
jay
peltz power
On Jan 6, 2011, at
2:34 PM, Peter Parrish wrote:
> I can't understand how any
inverter WOULDN'T deliver its power with the
> voltage and
current 100% IN PHASE.
>
> When the voltage and current
are not 100% in-phase that represents
reactive
> power.
Reactive power flows positive for a quarter of the AC cycle,
then
> negative for a quarter of a cycle, then positive and
then negative. The
net
> result over one AC cycle is ZERO
power delivered to the load.
>
> So reactive power is
worthless.
>
> Worse, it results in higher currents (and
voltages) for the same amount
of
> in-phase power, putting
additional stress on circuits.
>
> -
Peter
>
>
> Peter T. Parrish, Ph.D.,
President
> California Solar Engineering, Inc.
> 820
Cynthia Ave. , Los Angeles , CA 90065
> CA Lic. 854779, NABCEP Cert.
031806-26
> peter.parrish at calsolareng.com
>
Ph 323-258-8883, Mobile 323-839-6108, Fax
323-258-8885
>
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