I have an industrial customer that is expierencing short power blips on their entire system. They happen a couple times a week for less then a second, but that is enough to shut down their process. I assume that it is related to the utility company, and will pursue that avenue, but in looking at the power factor, it is between .75 and .80. Is there any way that a poor power factor can cause internal problems like this? Luckly the utility company doesn't penalize for poor power factor. Any thoughts?
Power Factor
- Thread starter shockin
- Start date
- Status
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Most likely the "blips" are grid switches going on in the utility, not really much you can do about that other than plan accordingly. One plan is to look at critical systems and implement what is called a "P.O.R.T." protocol (Power Outage Ride Through). It involves using control systems with power loss backup devices such as small UPS's or capacitors (on the control circuits) so that contactors don't drop out for 1 or 2 seconds. But these sorts of things can cause as many problems as they solve if used without care. So investigate what really needs to be kept running and why, then start looking for strategies.
Improving your power factor may have other benefits, but is not likely related to the problems you are seeing.
Improving your power factor may have other benefits, but is not likely related to the problems you are seeing.
charlie
Senior Member
- Location
- Indianapolis
I assure you that the serving electric utility does charge for poor power factor in the case of an industrial customer. We only charge for power factors of less than 85%. That sounds good until you realize that we will give you a credit for a PF better than 85%.shockin said:
If you look at the bill, it may be hidden like showing kW and then changing to kVA somewhere in the bill (I have seen that done and just about missed seeing it). There is a vast difference between kW and kVA an I have seen bills where a charge is made for kVA and it sort of just changes in the bill. BTW, they will also be hit for a demand charge (trust me). :wink:
charlie said:
It may be possible that the penalty is there, but the bill is pretty basic. Just two lines and a total. This is a very small local municipal utility company and this is one of only two industrial customers they serve. I wouldn't be surprised if they don't panalize for it.
The reason the "blips" kill this company is they have probably 100 CNC machines running plus numerous other pieces of equipment. When they loose power (even for .5 seconds) in the middle of a program, the machines crash. The overall load averages 1400 amps @ 480 I don't believe there is much I can do to help them ride out the blips. Any thoughts?
charlie
Senior Member
- Location
- Indianapolis
Yes, follow Jraef's advice. Finding out what the scope of the problem is and then designing an installation that will mitigate the problem will work. You will probably need the help of an engineering company to nail everything down unless you have the expertise to do this yourself.shockin said:
wirenut1980
Senior Member
- Location
- Plainfield, IN
The CNC machines are sag sensitive. I bet a nickel that the problem is with the controls dropping out on voltage sags. A cheap thing to try is to ether feed the 120 V controls through a UPS, or replace the control transformer with a constant voltage transformer (CVT), and size it for twice the load. Do that on one machine and see if that machine rides through when the others stop.
- Location
- Illinois
- Occupation
- retired electrician
wirenut1980
Senior Member
- Location
- Plainfield, IN
don_resqcapt19 said:
I am not talking about ride-through for the whole machine, just for the controls. I suspect these are the components that are sag sensitive. A 1 KVA or 2 KVA CVT per machine or a UPS sized for the control load is all that would be needed. I would try this on one machine and see if it works.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
A perfect application for ride through flywheel technology. Batteries or anything related that uses them is not good for this type of application, as each time the batteries take a hit (blip) they life is degraded.
drbond24
Senior Member
- Location
- Barboursville, West Virginia
shockin said:
That was happening to us last year quite a bit. We complained to the POCO about it and it actually got better. They claimed that they trimmed the trees away from the power lines, but whatever they did worked.
For the most part there is nothing you can do about it unless you want to spend a great deal of money. You could check out http://www.omniverter.com/. We had them in here to give us a sales pitch. They were quite impressive, but management wouldn't spend the money for it.
These are excellent ideas. The "brains" of the machine only need disturbance ride-through, and not the "muscle".
BUT, first of all define exactly what is happening. It could be internal or external causes. Once the events are quantified and time-stamped, you can find the root of the disturbance, then you can make your next logical move (either fix the problem, or, deal with the problem).
There are many power quality meters out there. I like to get the utility involved, often they will apply their metering at no or little cost to help out. Also, there are inexpensive monitoring and notification devices (e.g. "I-Sense" monitor > $1K installed), which will record the event and send out an email, page, etc. Then, you pinpoint (hopefully) the cause. Internal shorts on large motors / heaters can sag an entire facility, as can CB switching on the grid.
BUT, first of all define exactly what is happening. It could be internal or external causes. Once the events are quantified and time-stamped, you can find the root of the disturbance, then you can make your next logical move (either fix the problem, or, deal with the problem).
There are many power quality meters out there. I like to get the utility involved, often they will apply their metering at no or little cost to help out. Also, there are inexpensive monitoring and notification devices (e.g. "I-Sense" monitor > $1K installed), which will record the event and send out an email, page, etc. Then, you pinpoint (hopefully) the cause. Internal shorts on large motors / heaters can sag an entire facility, as can CB switching on the grid.
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