PF Correction

[ptonsparky]

POCO called this morning with an odd situation at one of their customers.

The PF at this location is leading. Extremely. At a time when their load is very low. Add load and the PF goes down, 75 to 60 was his example.

My thought was they are switching caps in when they should be out and visa versa. Customer owned capacitors.

Any other thoughts?

 

[kwired]

POCO called this morning with an odd situation at one of their customers.

The PF at this location is leading. Extremely. At a time when their load is very low. Add load and the PF goes down, 75 to 60 was his example.

My thought was they are switching caps in when they should be out and visa versa. Customer owned capacitors.

Any other thoughts?

I've seen miswired capacitors on irrigation wells that are in the circuit all the time, that would give you a leading factor when the well isn't running.

 

[ptonsparky]

I've seen miswired capacitors on irrigation wells that are in the circuit all the time, that would give you a leading factor when the well isn't running.

So have I but normally the POCO doesnt complain about that free help.

 

[Phil Corso]

POCO called this morning with an odd situation at one of their customers.
The PF at this location is leading. Extremely. At a time when their load is very low. Add load and the PF goes down, 75 to 60 was his example.
My thought was they are switching caps in when they should be out and visa versa. Customer owned capacitors. Any other thoughts?

Depends, of course, on Load! Does POCO have any idea of nature, or magnitude, of their customer's load? Was this a one-time event? One example... inadvertent Cap switching using Dynamic VAr compensation?

Regards, Phl CoRSO

 

[Jraef]

To the PoCo, the effects of leading PF can be just as bad as lagging. Nothing is "free". Most likely you are right, caps are just hooked up permanently ("bulk correction") instead of only when the inductive load comes on (referred to as "At Load" correction). It happens a lot when people use Soft Starters, because the instructions tell them to NEVER connect PFC caps down stream of the Soft Starter. Responsible mfrs then go on to instruct them to put the PFC caps up stream, but controlled by a separate contactor that only closes AFTER the Soft Starter is done ramping. Cheap mfrs sometimes fail to mention this, or cheap customers fail to heed it and just connect the caps upstream, permanently connected. Happens more than it should...

It could also be that they have contactor control of the PFC caps, but the contactor is welded closed. People often don't know how to size PFC cap contactors and under size them. There are also special contactors with in-line current limiting resistors that should be used in bulk correction situations. If they didn't do that, the contacts can weld easily.

Also, the idea that "why would they complain about free power?" leads to people connecting them permanently too. Leading PF can cause over voltage and damage to other equipment, especially when the PoCo does grid switching for load balancing. We all focus on the fact that they want .95 lagging because that's where they start penalizing you, but they want .95 lagging OR LEADING. You just rarely see them penalize for excess leading because it should be rare.

 

[ptonsparky]

Depends, of course, on Load!

Does POCO have any idea of nature, or magnitude, of their customer's load?Yes, instrument metering is what they call it.

Was this a one-time event? No, or they would not be calling me for suggestions. Not sure why they do anyway.

One example... inadvertent Cap switching using Dynamic VAr compensation?:?

Regards, Phl CoRSO

ok

 

[ptonsparky]

To the PoCo, the effects of leading PF can be just as bad as lagging. Nothing is "free". Most likely you are right, caps are just hooked up permanently ("bulk correction") instead of only when the inductive load comes on (referred to as "At Load" correction). It happens a lot when people use Soft Starters, because the instructions tell them to NEVER connect PFC caps down stream of the Soft Starter. Responsible mfrs then go on to instruct them to put the PFC caps up stream, but controlled by a separate contactor that only closes AFTER the Soft Starter is done ramping. Cheap mfrs sometimes fail to mention this, or cheap customers fail to heed it and just connect the caps upstream, permanently connected. Happens more than it should...

It could also be that they have contactor control of the PFC caps, but the contactor is welded closed. People often don't know how to size PFC cap contactors and under size them. There are also special contactors with in-line current limiting resistors that should be used in bulk correction situations. If they didn't do that, the contacts can weld easily.

Also, the idea that "why would they complain about free power?" leads to people connecting them permanently too. Leading PF can cause over voltage and damage to other equipment, especially when the PoCo does grid switching for load balancing. We all focus on the fact that they want .95 lagging because that's where they start penalizing you, but they want .95 lagging OR LEADING. You just rarely see them penalize for excess leading because it should be rare.

I believe they said it was .6 leading at times. I can't grasp that. My education is certainly lacking.

 

[GoldDigger]

It is not likely to be the factor in this case, assuming that the customer is a large industrial customer with heavy motor loads, but capacitor input power supplies without PF correction will have both a high distortion power factor (high harmonics) and a noticable overall leading phase PF on the fundamental.
A commercial customer with lots of older switching power supplies and no motors to speak of could end up with a leading PF. Just not of the magnitude seen here.

Looking at the leading PF of .6 reported by POCO, I could easily see that as being the result of unswitched PFC intended to compensate for a number of motors at a PF or .6-.7 lagging, since with the motors turned off the resistive component of the load will be much smaller than with them running, allowing a relatively small PFC bank to result in a much worse leading PF than the lagging PF they were intended to compensate for.

 

[kwired]

Metering set up correctly?

I had a new service I connected about mid July. Couple weeks later I was still working on that site and saw poco guy messing around in the new transformer one day and I asked him what was up, when they read meters they discovered it was connected wrong and was reverse metering.

Don't know enough about how meters register power factor or if they can get that wrong without other obvious problems.

 

[GeorgeB]

POCO called this morning with an odd situation at one of their customers.

The PF at this location is leading. Extremely. At a time when their load is very low. Add load and the PF goes down, 75 to 60 was his example.

My thought was they are switching caps in when they should be out and visa versa. Customer owned capacitors.

Any other thoughts?

Could they use a synchronous condenser and have control problems ... MAYBE a reversed command?

 

[ptonsparky]

Talked to the POCO engineer last week and he updated me on this.

Just a bit embarrassed, he admitted their tech was wrong, the customer was not having a leading PF.
On the plus side they discovered that the customer owned PFC system had most likely not worked since its install or shortly after. From what I gathered thru the conversation Upper Management ordered the PFC, local had no idea what it was for and consequently paid no attention to it.

You would think the installing contractor would have taken the time to see if it actually worked so I am hoping for the 'shortly after'.

 

[Jraef]

Talked to the POCO engineer last week and he updated me on this.

Just a bit embarrassed, he admitted their tech was wrong, the customer was not having a leading PF.
On the plus side they discovered that the customer owned PFC system had most likely not worked since its install or shortly after. From what I gathered thru the conversation Upper Management ordered the PFC, local had no idea what it was for and consequently paid no attention to it.

You would think the installing contractor would have taken the time to see if it actually worked so I am hoping for the 'shortly after'.

I've been down that road with an automatic PFC system. Utility requires it, customer orders it, I installed it, set it up, tested it in front of the utility, utility signed off on it, the customer disabled it the very next day. They didn't want to maintain it. I have never recommended APFC since then, I'm an advocate of "at-load" PFC; attach smaller caps to the load side of the starters on motors that contribute to the lagging PF so they are only on when the load it on.

 

[The Great Sarducci]

That's certainly one of the more unusual scenarios when it comes to power factor. I will say that I feel really bad for the customer when they get served the bill from the POCO (unless they fixed the problem immediately I suppose). I presume that this is most likely an industrial customer that you're talking about? They seem to be really the only category of customers that POCO ever shows much interest in when it comes to monitoring pf. But from what I understand, there's not too many things the utilities hate more than someone who is pulling a leading power factor on the grid. That's why I'd imagine so many pf-correction bank systems aim at lagging values slighly below unity (like 0.95-0.97), rather than aiming to close to unity, should they blow past the mark following the quick deenergizing of multiple inductive pieces of machinery. I could be wrong about my understandings about the whole 'leading pf frowned on more than a poor lagging pf'. But from what I remember learning; you start going leading, you can expect much higher power quality penalties.

 

[kwired]

I've been down that road with an automatic PFC system. Utility requires it, customer orders it, I installed it, set it up, tested it in front of the utility, utility signed off on it, the customer disabled it the very next day. They didn't want to maintain it. I have never recommended APFC since then, I'm an advocate of "at-load" PFC; attach smaller caps to the load side of the starters on motors that contribute to the lagging PF so they are only on when the load it on.

If utility requires correction, you would think they would be monitoring the power factor to make certain the correction has not failed, that would catch the disabling of it the next day. Maybe they don't catch it the next day but whenever they do analyze power factor measurements/recordings.:huh:

 

[kwired]

That's certainly one of the more unusual scenarios when it comes to power factor. I will say that I feel really bad for the customer when they get served the bill from the POCO (unless they fixed the problem immediately I suppose). I presume that this is most likely an industrial customer that you're talking about? They seem to be really the only category of customers that POCO ever shows much interest in when it comes to monitoring pf. But from what I understand, there's not too many things the utilities hate more than someone who is pulling a leading power factor on the grid. That's why I'd imagine so many pf-correction bank systems aim at lagging values slighly below unity (like 0.95-0.97), rather than aiming to close to unity, should they blow past the mark following the quick deenergizing of multiple inductive pieces of machinery. I could be wrong about my understandings about the whole 'leading pf frowned on more than a poor lagging pf'. But from what I remember learning; you start going leading, you can expect much higher power quality penalties.

Around here the rural POCO's now want PFC on 50+ HP motors. There is a lot of single load services with 50+ hp motors - they catch them easily if the PF is low (about .95 is their target). They won't care if a single load 100 hp service is leading by .10, it is actually going to help them out when it comes to correcting the power factor still existing on the system that they don't require to be corrected.

Now if you were a huge industrial plant with a lot of kvar of correction and left all your correction connected on a down day, they could have issues with that.