Power Factor Correction

[Fulthrotl]

Industrial situation, gravel quarry.

4 conveyors, interlinked, staged starting,
biggest load first, to prevent largest inrush from being
stacked on top of running loads.

480V. 3Ph. Wye

Running Amps Starting Amps

A phase 217 364
B phase 219 364
C phase 217 361

Total KW 65
Total KVA 182
PF .355
THD .9%

largest motors (two 50 hp driving common shaft)
are on soft start, rest are across the line contactors.

service cycle is 40 hours continuous, once per month.
a number of starts and stops during that 40 hours,
but uninterrupted to the largest extent possible.
power factor right at 40% for all separate loads, as well.

i'm wondering if power factor correction might be warranted
here? my thought would be to correct it at the service with
a cap that would be switched off when the conveyors were
not in use, to prevent overcorrection.

is this even worth bothering about?

 

[GoldDigger]

i'm wondering if power factor correction might be warranted
here? my thought would be to correct it at the service with
a cap that would be switched off when the conveyors were
not in use, to prevent overcorrection.

is this even worth bothering about?

1. Does customer pay POCO a low PF penalty?
2. Is the voltage drop on the service and feeder wiring great enough to worry about?
3. If there is a long run of wire from service to largest motor, consider putting some of the cap bank at/near the motor.
4. Do you think that putting caps on the motor side of the starter would cause too much stress on contacts?

 

[mivey]

Your pf penalty around here might be around $600/year around here so you have to look at the install cost of the capacitors.

Normally, the losses can make it worth locating near the load, especially if you are a long way from the meter point. Consider that you might drop the load by something like 100 amps, the line loss can add up. The catch with your load is that it only runs 5.5% of the time so the accumulated energy loss is probably not a huge factor if you are reasonably close to the meter.

With that, POCO pf penalty is probably going to be the key deciding factor.

 

[Fulthrotl]

Your pf penalty around here might be around $600/year around here so you have to look at the install cost of the capacitors.

Normally, the losses can make it worth locating near the load, especially if you are a long way from the meter point. Consider that you might drop the load by something like 100 amps, the line loss can add up. The catch with your load is that it only runs 5.5% of the time so the accumulated energy loss is probably not a huge factor if you are reasonably close to the meter.

With that, POCO pf penalty is probably going to be the key deciding factor.

thanks for that SWAG... that means it's a non starter.

i contacted the people operating the facility, and they have never
received an electric bill since the service was turned on a year and
a half ago, so they aren't all that interested in reducing the bill lower.

:huh:

 

[mivey]

and they have neverreceived an electric bill since the service was turned on a year and a half ago

Holy missing meters Batman!

 

[Fulthrotl]

Your pf penalty around here might be around $600/year around here so you have to look at the install cost of the capacitors.

Normally, the losses can make it worth locating near the load, especially if you are a long way from the meter point. Consider that you might drop the load by something like 100 amps, the line loss can add up. The catch with your load is that it only runs 5.5% of the time so the accumulated energy loss is probably not a huge factor if you are reasonably close to the meter.

With that, POCO pf penalty is probably going to be the key deciding factor.

the biggest load is the farthest away.....

100 hp. on parallel 500 mcm aluminum, 650' away.

 

[Ingenieur]

That pf is very low
what are the motor pf ratings?

Ph ang 70 deg
var ~ 170 lagging

to get to pf 0.85
you need 130 var
a good bit for the KW load

 

[Jraef]

Power factor correction caps and soft starters can be a tricky combination. One false move and the SCRs can short in the soft starters. I always recommend upping the PFC caps on a separate contactor that ONLY closes after the soft starter goes into bypass.

But again, no point in doing it at all if nobody cares.

 

[Besoeker]

Power factor correction caps and soft starters can be a tricky combination. One false move and the SCRs can short in the soft starters. I always recommend upping the PFC caps on a separate contactor that ONLY closes after the soft starter goes into bypass.

I agree. PFC and soft starters are poor bedfellows. The fast switching edges....
But we always had the PFC on a separate contactor - if you don't disconnect it some motors self excite.

But again, no point in doing it at all if nobody cares.

I agree with that too. And the minimal running hours also make it of debatable merit.

 

[Ingenieur]

What is the total connected HP?
number of motors
HP each
thanks

something is amiss
45 kw is 60 hp
you stated 1 motor alone is 100?
and 2 x 50

most motors in that range have a pf of 0.80 even when 50% loaded

 

[mivey]

the biggest load is the farthest away.....

100 hp. on parallel 500 mcm aluminum, 650' away.

So you might save $25-$50 per year on reduced losses for that load if you locate correction at the load rather than at meter. A typical large commercial load would run maybe 56% of the time and might save $250-$500 per year.

Some pretty wide assumptions on my part about parameters but would be a reasonable guess with the givens.


Add: assuming they were billing for the load in the first place.

 

[Ingenieur]

At least 200 hp connected (100 + 2 x 50)

100% 200 HP ~ 150 kw
your load is 45 kw
30% loaded (not including any other motor or non-motor loads!)

what is the pf of a motor loaded to 30%
edit: could be in the 0.40 range or lower

probably better off down sizing the motors if this isvwhat is dragging the pf down

 

[Fulthrotl]

At least 200 hp connected (100 + 2 x 50)

100% 200 HP ~ 150 kw
your load is 45 kw
30% loaded (not including any other motor or non-motor loads!)

what is the pf of a motor loaded to 30%
edit: could be in the 0.40 range or lower

probably better off down sizing the motors if this isvwhat is dragging the pf down

i didn't shinny up to get the nameplate info on these,
but here's the individual loads:

#1 (300')
24A. unloaded, 307 peak, 7.6kw, 18.7 kva, .4 pf

#2 (450')
56A. unloaded, 306 peak, 19.6kw, 47.3 kva, .4pf

#3 (450')
56A. unloaded, 279 peak, 18.9kw, 47.0 kva, .4pf

#4 (450')
99A. unloaded, 348 peak, 26.3kw, 83.3 kva, .308 pf

aggregate
219A. unloaded, 364 peak, 65kw, 182 kva, .355 pf

i was more looking at available capacity for running
additional conveyors. my main panel for this occupancy
is 1,200 amps, and it's backed up by a distribution section
that is 2,000 amps, lightly loaded.

then i got the power requirements of what they wanted to run...
they were looking at another 350 amps, they said.

right around 350 amps @ 15 KV. :jawdrop:

does the voltage matter? well, yeah, it does.
"we need a bigger boat".

 

[Ingenieur]

If you have over 200 HP but only 45 kw something is wrong
so the pf is with the motors unloaded?
that makes all the difference
you most likely have no pf issue when loaded

 

[Fulthrotl]

If you have over 200 HP but only 45 kw something is wrong
so the pf is with the motors unloaded?
that makes all the difference
you most likely have no pf issue when loaded

It's 65kw unloaded total, i'm guessing 30% more current when
running fully loaded... end of this month is the next scheduled
operating cycle. i'll see what happens when it's under full load.

thanks for the info....

 

[Ingenieur]

It's 65kw unloaded total, i'm guessing 30% more current when
running fully loaded... end of this month is the next scheduled
operating cycle. i'll see what happens when it's under full load.

thanks for the info....

should be 2-3 times more 'real' current when running
pf should go from 0.35 to 0.80
VA should go up a little but real power goes up to 150 range and reactive power goes down as a result of the pf improvement

 

[mivey]

i was more looking at available capacity for running
additional conveyors. my main panel for this occupancy
is 1,200 amps, and it's backed up by a distribution section
that is 2,000 amps, lightly loaded.

then i got the power requirements of what they wanted to run...
they were looking at another 350 amps, they said.

right around 350 amps @ 15 KV. :jawdrop:

does the voltage matter? well, yeah, it does.
"we need a bigger boat".

Another 9,000 kVA? Yeah, I don't think you will be tweaking that out of the excess in the existing 1,700 kVA switchgear.

 

[Ingenieur]

Another 9,000 kVA? Yeah, I don't think you will be tweaking that out of the excess in the existing 1,700 kVA switchgear.

current loads are 480
what is the service?
I assume the 1200 is 480
is the 2000 480 ?

why the switch from 480 to 15kv?
where would the 15kv come from?
utility or step-up?
from the utility that gives free service? As in no bills for over a year lol

 

[Fulthrotl]

why the switch from 480 to 15kv?
where would the 15kv come from?

it's shore power for a boat.
the boat needs 15 kv.
boat is 925' long.
payload of boat is 80,000 metric tons.

the 15kv would come from a new
peddler that would have to be ran
from poco substation.

i didn't have specs on the ship when i
went to look at power available.
i wanted to know what the draw on
the shore was before the question was
brought up.

then i saw the specs on the boat, and
just shrugged... well, that isn't gonna happen..... :dunce:

 

[gadfly56]

it's shore power for a boat.
the boat needs 15 kv.
boat is 925' long.
payload of boat is 80,000 metric tons.

the 15kv would come from a new
peddler that would have to be ran
from poco substation.

i didn't have specs on the ship when i
went to look at power available.
i wanted to know what the draw on
the shore was before the question was
brought up.

then i saw the specs on the boat, and
just shrugged... well, that isn't gonna happen..... :dunce:

Kinda like having a butterfly net and suddenly realizing you're tracking a tiger...hmy: