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power factor - round 2

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Posted by philkryder at gmail on March 21, 2013, 3:57 am
 
A couple years back some folks in this group helped me to use a KillaWatt  
device to deterimine powerfactor on some "lighly loaded" ac motors.


Time has passed.

I installed corrective capacitance based on my spreadsheed and formulas pro
vided by others in the group. Thanks for all the help.

More Time passed.

What we learned recently is that though the AVERAGE powerfactor is "low" -  
.5 or less sometimes,
there are SPECIAL PEAK LOAD EVENTS that may last for a few seconds (less th
an 5) every minute or two.


Coincident with those peak load events, control circuits in the same "neigh
borhood" - i.e. cicuit need to fire control solenoids for hydraulic control
s. The motor is a half-horse 120v 60 cycle that drives a hydraulic pump. On
 average - 95% of the time - there is no load - but, when there is a a sole
noid opens a valve to a hydralic motor and then, other solenoids open valve
s to hydraulic cylinders...

You can guess where this is going.


When the load is applied voltage drops from 120 nominal to 106 or so. Solen
oids fail to fire. Power factor changes dramatically.

So, given that my KillaWatt only does averages, we rented a Fluke meter tha
t records mins and maxes within each one-minute interval.

I'm inclined to re-tune the capacitors based on highest power Factor  seen  
over an entire 10 hour shift, rather than the average seen by the Killawatt
 while I happen to be looking.

Any other suggested actions?

Also, "what happens" with a corrected circuit at a 98% power factor when th
e load increases and the motor's power factor rises from .5 to .85 causing  
the circuit to be "over corrected"

thanks in advance.
Phil








Posted by g on March 21, 2013, 4:12 pm
 
On 20/03/2013 20:57, philkryder at gmail wrote:


or less sometimes,

lots of inductive loads, 0.5 _is_ rather lousy


5) every minute or two.

what is a SPECIAL peak load event???

"neighborhood" - i.e. cicuit need to fire
  control solenoids for hydraulic controls. The motor is a half-horse  
120v 60 cycle that drives a hydraulic pump.
On average - 95% of the time - there is no load - but, when there is a a  
solenoid opens a valve to a hydralic motor
and then, other solenoids open valves to hydraulic cylinders...

Solenoids fail to fire.

Provide more information re how long the voltage stays low.

If the voltage drops that much to a constant low 106 volts, then the  
supply to the motor is dangerously under-dimensioned. Update the supply  
to a larger cable and fuse. If you are talking about a short time  
interval (less than 1 seconds) for the voltage drop then that is normal  
due to the momentary high start current of the motor. The voltage should  
come up to close to nominal after the motor runs at rated speed. But  
since you are stating that the solenoids fail to fire, it indicates that  
the voltage is too low over the time the motor runs...

//g


Posted by mike on March 21, 2013, 5:41 pm
 On 3/20/2013 8:57 PM, philkryder at gmail wrote:

device to deterimine powerfactor on some "lighly loaded" ac motors.

provided by others in the group. Thanks for all the help.

or less sometimes,

5) every minute or two.

"neighborhood" - i.e. cicuit need to fire control solenoids for hydraulic
controls. The motor is a half-horse 120v 60 cycle that drives a hydraulic pump.
On average - 95% of the time - there is no load - but, when there is a a
solenoid opens a valve to a hydralic motor and then, other solenoids open valves
to hydraulic cylinders...


Solenoids fail to fire. Power factor changes dramatically.

records mins and maxes within each one-minute interval.

over an entire 10 hour shift, rather than the average seen by the Killawatt
while I happen to be looking.


load increases and the motor's power factor rises from .5 to .85 causing the
circuit to be "over corrected"


Your objective is unclear.
When you get the power bill, are you billed for volt-amps or watts?
If it ain't broke, don't fix it.

The KillAwatt is limited to 2kw or so.  Anything that can be measured  
with that
is IRRELEVANT.

When there's no load, the power factor is IRRELEVANT.

If you are billed for volt-amps or you just want to be a "good citizen",
You want to provide power factor correction at EACH point of load under
normal conditions for that load.

Judging from your statements, your problem is RESISTANCE in the wiring
or motors severely overloaded...or both.

Don't think it makes a lot of sense to try to power correct a transient
load at turn-on unless you switch it in ONLY during turn-on.

A 120V solenoid shouldn't fail to energize at 106V.  I expect  your
transient goes much lower than that.

You need a storage oscilloscope and a current/voltage probe to determine the
transient conditions that you experience.

Think the end result will be bigger wiring.



Posted by Jim Wilkins on March 21, 2013, 8:20 pm
 
http://www.nationalgridus.com/niagaramohawk/non_html/eff_elec-demand.pdf  

jsw






Posted by j on March 21, 2013, 10:25 pm
 On 3/20/2013 11:57 PM, philkryder at gmail wrote:

Overcompensating will lead to current leading voltage, and when your  
motor loads that is what will happen. I don't see this as bringing any  
happiness to the assorted solenoids et all.

You have a small motor, power factor correction at idle has no real  
benefit as the savings are minor. If you really want a better PF for  
some altruistic reason, then you will need to switch out the  
compensation when demand goes up.

My recommendation is to just remove the capacitors.



device to deterimine powerfactor on some "lighly loaded" ac motors.

provided by others in the group. Thanks for all the help.

or less sometimes,

5) every minute or two.

"neighborhood" - i.e. cicuit need to fire control solenoids for hydraulic
controls. The motor is a half-horse 120v 60 cycle that drives a hydraulic pump.
On average - 95% of the time - there is no load - but, when there is a a
solenoid opens a valve to a hydralic motor and then, other solenoids open valves
to hydraulic cylinders...


Solenoids fail to fire. Power factor changes dramatically.

records mins and maxes within each one-minute interval.

over an entire 10 hour shift, rather than the average seen by the Killawatt
while I happen to be looking.


load increases and the motor's power factor rises from .5 to .85 causing the
circuit to be "over corrected"



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