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Boots 211
12-24-2010, 12:11 AM
I am a electrician, the other morning a nursing home I work at called with complaints of electrical problems through out facility. I checked incoming voltage and found 114/116/117 pahse to n. 200v ph/ph. The system is a 120/208 wye. Outside a noticed a fuse hanging on the 3ph capacitor bank on pole. I beleive the primary voltage is 12kv. My question is if one of the capacitor was off would that affect the voltage causing a low voltage problem in complex? I need a quick lesson on capacitors.

wtdoor67
12-24-2010, 09:15 AM
When checked at the meter point you were allowed 5% increase or decrease over the nominal voltage. So for 120/208 you would be allowed 114/198 for your low reading and of course 126/ 228 for your highest reading. Anything below or above these readings would be considered outside the norm.

However spot checking doesn't always result in good readings because at the moment you checked it things might have been okay. Your readings sound within the limits to me.

Ask the power co. to set a recording volt meter for a few days readings and then you can look at the charts and tell if there's a problem. Also check other locations on the same transformer if possible or other close by locations.

One fuse blown on a nearby cap bank will sometimes cause imbalance. Also check further down stream on the customers wiring and compare to the incoming readings.

T-Man
12-24-2010, 09:35 AM
That cap bank with the blown fuse could be the problem depending what part of the day you checked. If there are a lot of industrial customers in the area and they are up and running they will cause a drop in voltage due to the induction they are crearting, If the bank comes in with all three phases the capacitance will compensate and bring the voltage and the wattage in line.
Sometimes when one fuse is down on a bank, the company elects to open all three phases via the kyles below the fuses and make repairs when they can get a crew there later (Not good to operate a bank with out gang switching) so the bank you were looking at may be off line and not helping the voltage problem.
Is there voltage problems with neighboring customers? There could be a problem at the station feeding this aera on the tap changer which can cause low volts for customers but more customers would be afffected.
I think the suggestion of getting the power company involved can give you some help.

Trbl639
12-24-2010, 12:23 PM
When checked at the meter point you were allowed 5% increase or decrease over the nominal voltage. So for 120/208 you would be allowed 114/198 for your low reading and of course 126/ 228 for your highest reading. Anything below or above these readings would be considered outside the norm.

However spot checking doesn't always result in good readings because at the moment you checked it things might have been okay. Your readings sound within the limits to me.

Ask the power co. to set a recording volt meter for a few days readings and then you can look at the charts and tell if there's a problem. Also check other locations on the same transformer if possible or other close by locations.

One fuse blown on a nearby cap bank will sometimes cause imbalance. Also check further down stream on the customers wiring and compare to the incoming readings.


That cap bank with the blown fuse could be the problem depending what part of the day you checked. If there are a lot of industrial customers in the area and they are up and running they will cause a drop in voltage due to the induction they are crearting, If the bank comes in with all three phases the capacitance will compensate and bring the voltage and the wattage in line.
Sometimes when one fuse is down on a bank, the company elects to open all three phases via the kyles below the fuses and make repairs when they can get a crew there later (Not good to operate a bank with out gang switching) so the bank you were looking at may be off line and not helping the voltage problem.
Is there voltage problems with neighboring customers? There could be a problem at the station feeding this aera on the tap changer which can cause low volts for customers but more customers would be afffected.
I think the suggestion of getting the power company involved can give you some help.

Give the local power company a call and like Door said, get em to put a Recording Vmeter on there........and as T-man mentioned, the cap bank might be off-line, the local T-man will know and can usually get things straightened out for ya.......

Boots 211
12-24-2010, 07:35 PM
Penelec was called and trouble man responded he did tell maintance man that one capacitor was bad, but left other two still plugged in, Electrical equipment did come out and install a recroding meter as you all suggested, i guess it will record for a week. i was more curious about the capacitor with one being off if that would efect the other two phases?

wtdoor67
12-24-2010, 09:31 PM
I have read, capacitors will only have effect up to their point of installation. This would mean to me that anything further downstream would not be effected.

Also the phase to ground readings you report do not indicate an imbalance bad enough to worry about.

I was told once how to figure imbalance but I forget. I think you average the readings and then figure from the average. Or you can ask Swamprat, I'm sure he has a handle on it.

robob24
12-25-2010, 01:21 AM
I dont have any power experience so I am not trying to sound like I know something so dont bash.
As the maintenance guy, I had a building in a metro area with similar problems. Random power issues for about 2 months.
One morning I found the problem, on the pole behind the building one of the old CU jumpers had broken right at the split bolt. It was a little breezy that morning and still dark enough to see it arc. It was only moving about 1/2", just enough. The trouble guy that showed up looked at me kinda funny when I pointed it out. Old habit, always lookin up.

MI-Lineman
12-25-2010, 09:46 AM
Any ideas when it started? Yeah your barely in range but I see too many hands just blame it on the customers equipment? Hard to trouble shoot from a desk (unless you're a stupavisor!:D) but if the voltage comin in is low could be a load issue? We get that here a lot! Could be fixed at regs on line or at sub? Maybe there's added load and a good ol fashioned re-conductor could take care of it! Nah! Just add more boosters!:rolleyes: Hopefully if it's on their side and if more customers on the line are complainin they'll check the primary voltage? Seen a lot of hands add spurs and cans or upgrade'em to only finally check the primary voltage after when it doesn't help and it's too low to begin with!:rolleyes:

What the Penelec guy say about the voltage on his side? You said comin in but where? In you equipment or at the srvc? They add any load at the business? Whats the symptoms? Blinkin lights? Equipment shuttin down or unable to fire up? Did ya check voltage while equipment firin up or runnin? You may have a worse voltage problem than that if ya got a lot of equipment firin up at the same time? That's what the recorder is for! Wait and find out what they say and let us know?

Just so you know if ya run into this again and the co. seems to be takin too long (like what happens here too much?) the Flukes (I don't know what you use?) have a voltage recordin setting on them! They only record the lowest and the highest in I think a 99 hour period but it gives ya a good idea?

Good luck and BTW we get a $55 service charge for the help!:D Just Kiddin!

CPOPE
12-25-2010, 11:09 AM
I have read, capacitors will only have effect up to their point of installation. This would mean to me that anything further downstream would not be effected.

Also the phase to ground readings you report do not indicate an imbalance bad enough to worry about.

I was told once how to figure imbalance but I forget. I think you average the readings and then figure from the average.

They(capaciators) correct power factor up to their point of application from source to load. Create a voltage rise because of this so are also helpful in voltage regulation.

ELI the ICE man. E or Voltage Leads Current for an Inductive Circuit. I or Current in a Capacitive Circuit Leads E Voltage. Fi-ng beautiful thing is unity PF power factor.

This capacitor may have oil or vacuum switchers and should have a cell phone modem radio to be smart grid capable. Power Factor correction by installing and switching capacitors to correct or bring back to unity cosine of the angle between voltage and current = 1 Watts=KVA x PF The more you monitor and correct power factor the more you reduce system losses...... Nice

You calculate imbalance by summing Phase current vectors magnitude and angle. Normally I1=I2=I3 should be actively corrected and balanced in an efficient system as near to zero as you can get it. Neutral current only gets about as good as 20% to 33 percent of phase current. Thus you can install a 1/3 reduced neutral because it only carries the imbalance.

Or you can ask Swamprat, I'm know he has a handle on it.

Merry Christmas Brothers, Even the narrow back electrician asking the dumb linemen questions.

burnitup
01-21-2011, 12:27 AM
Armchair thought, cust voltage pretty balanced and all low about same amount, I would look towards circuit problem.Might be the cap but with only one door open would expect a little wilder voltage differential, maybe station caps offline?

T-Man
01-21-2011, 07:05 AM
Armchair thought, cust voltage pretty balanced and all low about same amount, I would look towards circuit problem.Might be the cap but with only one door open would expect a little wilder voltage differential, maybe station caps offline?

burnitup=Yikes what a handle for this trade site. . .LOL But I agree, it looks like a three phase problem explained like that. Either the whole bank is out of service, the feeder field three phase regulator is on the fritz, or maybe as stated the auto tapchanger is not working. (sometimes when the regulation is set for switching the tap changer is taken off auto and forgotten to be restored. . .this could be as simple as finding that.) Great line of thought Burnitup

T

muddy
03-25-2011, 09:00 PM
check hot leg or neutral its loose somewhere or broke

Trojan
04-07-2011, 10:40 PM
A blown fuse on a capacitor bank could cause the current and voltages to be out of phase as they relate to other phases ( A & B phase fuse closed and capacitor cells in service=in phase current and voltage making for a good power factor but C phase open= current and voltage out of phase making for a bad power factor).Sensitive equipment (especially medical or computer driven stuff) will see this and not operate so as to avoid damage.

burnitup
04-12-2011, 01:42 AM
T-MAN the name Burnitup came from the fact that I like to cook low and slow on my smoker,but it is kinda of scary to think of it that way,and about the cap I am not the smartest guy in the world but generally when I see a cap with a blown fuse or tap I have some pretty crazy voltages, but you never know and thats what makes being a troubleman great,it's the thrill of the hunt.

Trojan
04-16-2011, 05:51 PM
You're right about the crazy voltages. I forgot to say phase to phase voltage needs a test. The phase to neut may be within limits, but if a phase is out at the cap and everything is out of sync, the Phase to phase may show it.

CLUTCH
06-03-2011, 11:02 PM
If it's a switched bank loosing one phase may cause the contol to open the oil switches and take the bank off line.Our controls do that when reading a high neutral current which loosing a phase will cause. If it's a fixed bank the remaining energized caps will still be pumpin'.

HIVOLTS
06-16-2011, 07:02 AM
Most fused banks don't have oil switches too. One blown fuse will cause you trouble, no doubt. The effect of a capacitor bank on the line is like throwing a pebble in a pond. it ripples out in all directions but the further you get from the point of impact the less effect it has. Far enough out and you need another bank.