Power Factor Correction

[Sahib]

you most likely have no pf issue when loaded

Automatic power factor correction equipment, if installed, would take care of no load power factor also!

 

[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

they ran the boat yesterday.... unloading 2,700 tons of aggregate an hour.

no load, all conveyors running was 50.2 KVA, .29 PF
2,000 tons per hour was 121 KW .57 PF

still not great, but the load doubled the power factor... i
didn't get another set of readings at 2,700 tons per hour,
but the design specs for the system are 3,000 tons per hour,
so i'm guessing the PF probably moved closer to .80

operators are trying to figure out how much unused capacity
they can wring from the conveyors by going to VFD's and overdriving
the belts. i don't see any good coming from that, and a host of problems.

they don't need a faster belt, they need a wider belt, but that's their call.
running it faster throws the material farther, and misses hoppers, etc.
and faster is harder on idlers, and whatnot.

thanks to all of you for your feedback.

 

[Ingenieur]

they ran the boat yesterday.... unloading 2,700 tons of aggregate an hour.

no load, all conveyors running was 50.2 KVA, .29 PF
2,000 tons per hour was 121 KW .57 PF

still not great, but the load doubled the power factor... i
didn't get another set of readings at 2,700 tons per hour,
but the design specs for the system are 3,000 tons per hour,
so i'm guessing the PF probably moved closer to .80

operators are trying to figure out how much unused capacity
they can wring from the conveyors by going to VFD's and overdriving
the belts. i don't see any good coming from that, and a host of problems.

they don't need a faster belt, they need a wider belt, but that's their call.
running it faster throws the material farther, and misses hoppers, etc.
and faster is harder on idlers, and whatnot.

thanks to all of you for your feedback.

good info
so 67% loaded ~0.60, almost doubled
a number at 2700 or 3000 would tell you alot
this still tells me the motors are over sized, a common issue
3 options
1 do nothing since it costs you nothing
2 size some caps to raise it 0.90 with 2 stages
at 3000 stg 1 33% of total
at 2700 stg 2 67%
at 2000 stg 1 + 2
or whatever the numbers tell you, but you get the drift
3 measure each motor when loaded
replace the over-sized ones as they fail (or as PM or budget allows)

 

[kwired]

good info
so 67% loaded ~0.60, almost doubled
a number at 2700 or 3000 would tell you alot
this still tells me the motors are over sized, a common issue
3 options
1 do nothing since it costs you nothing
2 size some caps to raise it 0.90 with 2 stages
at 3000 stg 1 33% of total
at 2700 stg 2 67%
at 2000 stg 1 + 2
or whatever the numbers tell you, but you get the drift
3 measure each motor when loaded
replace the over-sized ones as they fail (or as PM or budget allows)

They are only oversized if the load never exceeds 67% and maybe even up to about 75%. Doesn't mean there may not be significant run time with minimal load, but if the demand reaches say 75% at times then the motor used is likely what is needed for those times.

 

[Jraef]

...

operators are trying to figure out how much unused capacity
they can wring from the conveyors by going to VFD's and overdriving
the belts. i don't see any good coming from that, and a host of problems.

Amen to that. People think that just because the VFD can make the motor go faster, it's oK to do. They don't understand that you can't make a motor capable of more load than it is rated for.

they don't need a faster belt, they need a wider belt, but that's their call.
running it faster throws the material farther, and misses hoppers, etc.
and faster is harder on idlers, and whatnot.

thanks to all of you for your feedback.

I think you are dead on with that thought. I have seen that before, flinging rock into the air out past the hopper... D'oh:slaphead:

 

[mivey]

I have seen that before, flinging rock into the air out past the hopper... D'oh:slaphead:

That's a feature not a flaw.

 

[Ingenieur]

They are only oversized if the load never exceeds 67% and maybe even up to about 75%. Doesn't mean there may not be significant run time with minimal load, but if the demand reaches say 75% at times then the motor used is likely what is needed for those times.

That is why I said measure it

Using his numbers:
assuming 100% is 165kw at 0.9 pf (200 hp x 746 / 0.9 eff)
no load 65kw
67% loading 120kw (2000/3000 tph)
2000 tph (67% loading) adds ~ 55kw
if linear another 1000 adds 28kw
total ~ 150kw or 150/165 ~ 90% loaded
not a bad operating point