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flashman
01-11-2007, 10:38 AM
Morinig gentlemen, I was trying find some info on some capacitor accidents or near misses. We have some lineman that don't think or unaware of the dangers of capacitors in a trouble or regular linework situation. If anyone has had any insights or stories I would appreciate all. Thanks. flashman.

CPOPE
01-11-2007, 06:49 PM
What does OSHA say

1910.269(w)(1)
"Capacitors." The following additional requirements apply to work on capacitors and on lines connected to capacitors.

Note: See paragraphs (m) and (n) of this section for requirements pertaining to the deenergizing and grounding of capacitor installations.

1910.269(w)(1)(i)
Before employees work on capacitors, the capacitors shall be disconnected from energized sources and, after a wait of at least 5 minutes from the time of disconnection, short-circuited.

1910.269(w)(1)(ii)
Before the units are handled, each unit in series-parallel capacitor banks shall be short-circuited between all terminals and the capacitor case or its rack. If the cases of capacitors are on ungrounded substation racks, the racks shall be bonded to ground.

1910.269(w)(1)(iii)
Any line to which capacitors are connected shall be short-circuited before it is considered deenergized.

http://www.usace.army.mil/publications/armytm/tm5-684/chap13.pdf

Stick-it
01-13-2007, 09:01 PM
Use a load break tool to open them up

dbrown20
01-14-2007, 10:02 AM
Flashman, come to think of it they did have a pretty bad one in the AEP system back in the summer. Serviceman closed in a capacitor from a small service bucket with one of those short extendo sticks and the capacitor blew up and severely burned him. I think he has made a full recovery by now but we saw a picture of his bucket and it was pretty badly burned also. If you're in the AEP system you probably read of this. It happened in Texas.

Saw a guy get the crap knocked out of him once by a capacitor that wasn't discharged.

I don't recall if the former was from a fixed bank or not. dbrown20

scammy
01-15-2007, 11:23 PM
we consider compasitors the mostdangerous piece of equiptment we have ,,they not only store volts but also amps

BigClive
01-16-2007, 03:44 AM
we consider compasitors the mostdangerous piece of equiptment we have ,,they not only store volts but also amps

Or to be more technical. They store a "charge". The voltage will depend entirely on the charge in them. The amps bit is their devastating ability to dump their entire charge in one blinding bang with much more force than a source with higher impedance like a line.

Worse still is the fact that their construction is basically a coil of alternate layers of insulator and conductor, often with an electrolyte or oil in between. The large conductor area, thin insulation and the enclosed nature means that a common failure mode is an internal short with violently explosive results. Not so great if you just closed it in.

Most caps have some form of discharge system fitted in the form of a suitably rated resistor to trickle discharge them when not powered, but these are not reliable and often fail. You should always assume that a capacitor is charged and use a suitable high impedance device to shunt it and discharge the stored energy in a controlled manner.

Incidentally, the charge on a cap on an AC application will be directly connected to the exact point it is disconnected. If you pulled one of it's leads at the mains zero crossing point (where the sine wave changes polarity) then the charge on the capacitor could be zero. If however you pulled it at the peak then it could be fully charged. The chances of you pulling it at zero charge, particularly fast enough to avoid an arc is almost zero.

If however the cap is in parallel with a functional transformers primary, then that should discharge the cap.

wstxpwr
01-16-2007, 04:50 PM
dbrown, you got it right. I don't know about up there but we are now required to test them before closing in on them. If there even slightly out of range we are required to at least pull the jumpers and tag it as bad. And then we are required to contact dispatch and have them log it in the abnormal database. That was the problem in Abilene this particular cap tested bad at some point but not taken out of service for some reason. When the service man went to close his seasonal banks he did not know this one was bad. So now we test before we close, we close them from the ground if possible and we don't do it without a qualified observer. Sure make you respect them.

scammy
01-16-2007, 09:34 PM
thanks clive you are correct with the word (charge),,,cap bank or capasitors alone should be respected and aproached with open eyes,, did see the results of one that had exploded,,,way more powerfull than a grenade,,compares more to a claymore mine

dbrown20
01-19-2007, 07:16 PM
dbrown, you got it right. I don't know about up there but we are now required to test them before closing in on them. If there even slightly out of range we are required to at least pull the jumpers and tag it as bad. And then we are required to contact dispatch and have them log it in the abnormal database. That was the problem in Abilene this particular cap tested bad at some point but not taken out of service for some reason. When the service man went to close his seasonal banks he did not know this one was bad. So now we test before we close, we close them from the ground if possible and we don't do it without a qualified observer. Sure make you respect them.

Those with a blown fuse are always left for the line crews to test where I work. The service people never try them. If they are not within normal range then we change them if there's one handy or disconnect them. If there several in the bank then it may be evened up and then closed in and the bad one replaced later. dbrown20

NU Limey
01-20-2007, 06:05 PM
Cap. maintainence is a big pain. When working on them you have to make sure after you deenergize they are shorted out, we usually use a piece of wire in a shot gun grounding the bushing to a ground for about 10 sec. There are testers on the market to check them, depending on your line voltage and kvar. We don`t have too many issues at 5 and 12kv. When we get to 34.5, that a different ballgame, we have alot of 1800 and 2400 kvar banks. A while ago our company retrofitted these and others with oil switches. After burning up a couple loadbreak tool trying to open cutouts, things got a re-look. Load break tools alone are not designed for bigger banks. There are various that have to be looked at first, proximity to other cap banks, conductor size,etc. Most of our oil switched banks are timed controlled from the ground to allow the person to get out of harms way in case something wrong. last year I watched an oil switch launch after the fuse was thrown in and the switch was in the open position. We all give these things alot of respect and never turn your back on them!!

CenterPointEX
01-20-2007, 06:50 PM
.......Here in Houston they have oil switches and chicken switches to operate the oil switches. A chicken switch is a toggle switch mounted in a meter base at the bottem of the pole. We attache a twenty five foot piece of string to the toggle and operate it from that far away. Down here in high humidity conditions the conductivity of the air plays a part in the violence of arc explosions.

.... That being said here is my linemanease on the functioning of a Capacitor. The problem Caps try to correct mainly is pressure. The further you get away from the source and the greater the resistance, the lower the voltage and higher the amperage gets. Same as if you were at the far end of water line. The further away, the lower the water pressure. So the Cap bank functions not unlike a water tower. The water is pumped up to the top and the weight of the water prouduces a great pressure. Electrons flowing down the wire then run into the Cap where they spread out on big thin cookie sheets of copper stacked up and seperated by semi conductor.
So electrons are stored on these cookie sheets like water in the tower. If you ground the load side of Cap bank you get a massive expunge of electrons to ground. Same as if you punched a hole in the bottem of the water tower. If a water tower fails the result is catastrophic.

That reminds me of a story... Once several trucks were summoned to a location that fed a huge heavily loaded industerial complex where they were complaining of flucuating voltage... We were out there with four of thier engineers. When I pulled the chicken switch to put the bank online the oil switches started opening and closing rapidly. All the Lineman headed for the hills like a flash of lightning. When I looked over my shoulder I saw one of the engineers with a blank look on his face watching me run. The other three were looking up mesmorized by the noise the bank was making. When they realized their prediciment they all bolted at the same time into each other and fell in a pile... they got up and started to run again when all hell broke loose... again they all lay in a pile... The circuit locked out and no one was hurt... It was mean, but I could not contain myself laughing at the pile of engineers laying on the ground clawing for air and trying to figure out which way was up... the look on thier face at zero hour was priceless...:)

dbrown20
01-20-2007, 08:20 PM
The newer ones here also have the "chicken switches". They have a time delay however that gives you about 30 seconds to move away after you activate the switch. dbrown20

BigClive
01-20-2007, 10:43 PM
.... That being said here is my linemanease on the functioning of a Capacitor. The problem Caps try to correct mainly is pressure. The further you get away from the source and the greater the resistance, the lower the voltage and higher the amperage gets. Same as if you were at the far end of water line. The further away, the lower the water pressure. So the Cap bank functions not unlike a water tower. The water is pumped up to the top and the weight of the water prouduces a great pressure. Electrons flowing down the wire then run into the Cap where they spread out on big thin cookie sheets of copper stacked up and seperated by semi conductor.
So electrons are stored on these cookie sheets like water in the tower. If you ground the load side of Cap bank you get a massive expunge of electrons to ground. Same as if you punched a hole in the bottem of the water tower. If a water tower fails the result is catastrophic.


That's more like a description of a reservoir capacitor in a DC system. It doesn't work for an AC system since the cap is alternately charging and discharging as the polarity of the supply changes at 50/60Hz.

I think the primary function of capacitor banks is power factor correction for large transformer arrays where the inductive lag between voltage and current is compensated for by the capacitors leading power factor. This saves on wire and transformer size from the source.

CenterPointEX
01-21-2007, 03:20 AM
Yes the purpose of a Cap is to correct the power factor, but who knows what the hell that means? Yes polarity flops... Yes the electrons spread out on the copper sheets in the Cap... Yes when you raise the voltage you lower the amperage which is heat, because there is less heat you can use smaller wire and xfmr. The water tower analogy is just a method to put a mental handle on the magic that is electricity. I mean who the "F" can see an electron. We can see the effect of it the Shat , but they is invisible... Freakin Magic if you will. Tomorrow I will attempt Linemanease definition of Power Factor, Inductive and Capacitive loads. I would be interested in your non-Tech description of Power Factor and or Capacitors B.C.

BigClive
01-21-2007, 08:12 AM
Easiest description of power factor is to explain that when driving an inductive load like a trasnsformer the voltage and current go out of phase with each other like two sinewaves side by side. In a transformer this is caused by the back EMF from inducing a magnetic field in the large core and then it's collapse as the sinewave goes down again and the polarity changes. Because capacitors have the opposite effect this cancels out the lag and brings the voltage and current into sync again. The difference between the voltage and current waveforms increases the perceived load and poses a burden on the supply system. This is why large buildings are sometimes monitored for bad power factor and charged accordingly to encourage them to apply local correction.

On appliances and equipment you'll see power factor described as a cos phi value where phi is like an "O" with a slash through it. Perfect power factor is one worst power factor is theoretically zero. Typical values for a tranformer might be about 0.6.

To be honest, your average Joe lineman doesn't really need to know any of this. All they need to know is basic electrics, nuts, bolts and wires. It's the engineers job to monitor power factor and apply protection if required. I'm what you might call an old-school spark who did my apprenticeship at a time when you got taught EVERYTHING! Generation, transmission, distribution, sub distribution, building wiring, control wiring, electronics, older technology, motor control.... The works. It comes in useful from time to time.

CenterPointEX
01-21-2007, 08:51 AM
They also taught us electrical theory. You said a mouthful there... and I understand what you said. Now break it down into english... Explain all that in laymens terms that an eighth grader could understand.

You, I , L.A., and Hemmingray are some sick puppies all of us here this time of day...

Hemingray Insulators
01-21-2007, 09:31 AM
well i'm here cuz church don't start till 11 CP.

Hemingray Insulators
01-21-2007, 10:34 AM
they do have a bible study b4 church, but most of the youth group is gone on winter retreat, so theres no bible study b4 church today for the teens. well, i'm off to church now.

BigClive
01-21-2007, 04:56 PM
To be honest, it's hard to break power factor down into simple language. to understand it completely you need to know the electrical characteristics of inductors and capacitors in an AC application.

It;s easiest to say that if you removed the parallel power factor correction capacitor from the traditional fluorescent light fitting in your kitchen it would make the meter turn faster.

Of course, maybe I'm just too much of a tech head. Your turn to make power factor easy CP.

CenterPointEX
01-21-2007, 09:14 PM
To be honest, it's hard to break power factor down into simple language. Si, Whey... Es Que lo dice antes... That being said... Power factor... matching the truck with the load. Volts times amps equals watts.
Volts times amps equals watts. Watts are a measure of energy or power.

In plumbing terms, the volume of water times the pressure it is under will determine its power. The higher the pressure the lower the volume of water or smaller size water pipe you need to do the work... for instance...

...Lets say you had a pressurized water pipe shooting water at a water wheel turning a motor. If the pressure is low the water dropping on the wheel woul turn it but not at its designed speed. If the pressure was too high it would damage the water wheel. When some one flushes a toilet, the pressure at your shower head drops for a second. If you had a large holding tank inline before the shower head the flushed toilet would not affect the pressure at the shower head. In the same way when a heavy load is suddenly put on a power line the voltage/pressure drops. A Cap bank inline near that load would reduce the pressure drop in the same way the holding tank affects the drop at the shower head. Thats why they put capacitors in AC units... for start up purposes. Ever notice how sometimes when your AC kicks the lights dim for a flash then come back up.



..... If you take a truck and load it half full and send it from point A to point B, you have not maxamized the potential of that truck. Conversley if you over load the truck, the truck is stressed, overheats and generally it's bad for the truck. When the power factor is correct the truck is loaded to its designed capacity the benifit is maximized. If a factory is paying for fuel by the truck load and they are only getting half a load they are getting screwed. If you overload the truck the trucking company is getting screwed.

An amp meter measures the flow of electrons. A high volume of flow against resistance creates heat.


If you raise the voltage/electrical pressure you lower the amperage/volume of electrons. Conversely when you raise the amperage the voltage/pressure goes down. A heavy load slows the truck down. Raises the amperage lowering the voltage.

If you lower the voltage and the amps go up, to many amps will flow thru your light bulb, it will overheat and burn up the fillament. Conversley if the voltage/electrical pressure is too high, the force of the pressure will blow the fillament apart. The electrical pressure/voltage is somewhat akin to water pressure.

In the case of a light bulb electrons flow from the source thru the fillament to ground.

In the case of an electric motor, the energy is used to create an electrical magnet and it does not flow to ground. It takes a lot of magnetic force or load to get a motor spinning, once it is spinning it does not take as much to keep it spinning. This is called an inductive load because unlike the light bulb it does not take electrons to ground but rather uses them to create an induced or magnetic force. Much like when you try to put opposite poles of a magnet togather there is a force between them pushing them apart and conversely the opposite. Industrial motors are three phase meaning they have three electrical lines going to them creating three magnets. these magnets are place around a rotor or metal bar attached to a shaft. It works like the push and pull of magnets. One magnet pulls until the bar gets to it, at that point the polarity on the magnet changes from negative to posative. During that transition at some point it is at zero polarity. When it is at zero, the next magnet in line goes negative and pulls the bar towards it, the magnet it just came from is going posative at that point and pushing the bar away as opposite polls on a magnet do when you try to put them togather. So the bar attached to the shaft keeps turning being alternatively pushed and pulled by the magnets. The phases or lines go from negative to posative sixty times per second here in the united states. The three phases or lines do this ninty degrees apart. When they are in phase the magnets go from negative to posative at just the right time to keep the motor turning. If two of the phases were at the same polarity at the same time the bar would just get stuck between them and not spin. If one of the phases has a lot of light bulbs on it the amount of electrons available to exert the magnetic force would not be the same as the other two unloaded phases. Thus the need for for a water tower/capictor close by to hold a large quanity of electrons to be dumped when the magnet calls for them. The capicitors store pressure if you will so the the pressure is the same on all three phases.

Now it is not all quite as simple as or exactly as I explained it, but these concepts and analogys sort of help wrap the mind around an abstract concept.

Hemingray Insulators
01-21-2007, 09:50 PM
I think you did a pretty good job at explaining PF in simple terms.

CenterPointEX
01-21-2007, 10:06 PM
Thank you Mr. Hemingway...
Si, Whey... Es Que lo dice antes... That being said... Power factor... matching the truck with the load. Volts times amps equals watts.
Volts times amps equals watts. Watts are a measure of energy or power.

In plumbing terms, the volume of water times the pressure it is under will determine its power. The higher the pressure the lower the volume of water or smaller size water pipe you need to do the work... for instance...

...Lets say you had a pressurized water pipe shooting water at a water wheel turning a motor. If the pressure is low the water dropping on the wheel woul turn it but not at its designed speed. If the pressure was too high it would damage the water wheel. When some one flushes a toilet, the pressure at your shower head drops for a second. If you had a large holding tank inline before the shower head the flushed toilet would not affect the pressure at the shower head. In the same way when a heavy load is suddenly put on a power line the voltage/pressure drops. A Cap bank inline near that load would reduce the pressure drop in the same way the holding tank affects the drop at the shower head. Thats why they put capacitors in AC units... for start up purposes. Ever notice how sometimes when your AC kicks the lights dim for a flash then come back up.



..... If you take a truck and load it half full and send it from point A to point B, you have not maxamized the potential of that truck. Conversley if you over load the truck, the truck is stressed, overheats and generally it's bad for the truck. When the power factor is correct the truck is loaded to its designed capacity the benifit is maximized. If a factory is paying for fuel by the truck load and they are only getting half a load they are getting screwed. If you overload the truck the trucking company is getting screwed.

An amp meter measures the flow of electrons. A high volume of flow against resistance creates heat.


If you raise the voltage/electrical pressure you lower the amperage/volume of electrons. Conversely when you raise the amperage the voltage/pressure goes down. A heavy load slows the truck down. Raises the amperage lowering the voltage.

If you lower the voltage and the amps go up, to many amps will flow thru your light bulb, it will overheat and burn up the fillament. Conversley if the voltage/electrical pressure is too high, the force of the pressure will blow the fillament apart. The electrical pressure/voltage is somewhat akin to water pressure.

In the case of a light bulb electrons flow from the source thru the fillament to ground.

In the case of an electric motor, the energy is used to create an electrical magnet and it does not flow to ground. It takes a lot of magnetic force or load to get a motor spinning, once it is spinning it does not take as much to keep it spinning. This is called an inductive load because unlike the light bulb it does not take electrons to ground but rather uses them to create an induced or magnetic force. Much like when you try to put opposite poles of a magnet togather there is a force between them pushing them apart and conversely the opposite. Industrial motors are three phase meaning they have three electrical lines going to them creating three magnets. these magnets are place around a rotor or metal bar attached to a shaft. It works like the push and pull of magnets. One magnet pulls until the bar gets to it, at that point the polarity on the magnet changes from negative to posative. During that transition at some point it is at zero polarity. When it is at zero, the next magnet in line goes negative and pulls the bar towards it, the magnet it just came from is going posative at that point and pushing the bar away as opposite polls on a magnet do when you try to put them togather. So the bar attached to the shaft keeps turning being alternatively pushed and pulled by the magnets. The phases or lines go from negative to posative sixty times per second here in the united states. The three phases or lines do this ninty degrees apart. When they are in phase the magnets go from negative to posative at just the right time to keep the motor turning. If two of the phases were at the same polarity at the same time the bar would just get stuck between them and not spin. If one of the phases has a lot of light bulbs on it the amount of electrons available to exert the magnetic force would not be the same as the other two unloaded phases. Thus the need for for a water tower/capictor close by to hold a large quanity of electrons to be dumped when the magnet calls for them. The capicitors store pressure if you will so the the pressure is the same on all three phases.

Now it is not all quite as simple as or exactly as I explained it, but these concepts and analogys sort of help wrap the mind around an abstract concept.

BigClive
01-22-2007, 05:18 PM
Sorry to be Mr ***** here, but that didn't actually explain power factor at all.

Volts times amps equals watts simply doesn;t work with transformers. In that case volts times amps equals volt/amps (VA KVA) which is an inductive equivalent.

The Capacitor in an air conditioning unit is either for power factor correction or as a motor capacitor, either supplying a phase shift for rotation at power up or continuously.

The storing energy in a capcitor until needed still harks back to DC applications. It's completely different from power factor.

Sorry if this is boring the pants off everyone else. You don't really need to know this much about PF anyway. Just stick the cap where they tell you. :)

Once Hems been to power school he can melt our brains with a more precisie definition of PF.

CenterPointEX
01-22-2007, 06:20 PM
BC, I did qualify it with a disclaimer at the end... Not quite as simple or exactly but kinda sorta...
.....Since you insist, in AC applications Watts is acutally, Volts times Amps times the Power Factor. The illustration of the optimumly loaded truck does come close to the explanation of power factor. If the sine waves of the voltage/pressure and Amps/rate of flow of electrons were in phase then the formula Volts times Amps equal Watts would hold true. Since they are not normally in phase, this is not the case. The maximum posative voltage/pressure does not coincide with the maximum amperage/flow of electrons. The truck/volt is not optimumly loaded with electrons/amps.
.... In a heavy industrial load the pressure/volt curve peaks and valleys get way ahead of the the Amp/electron-flow curve. Thus the Truck/Volt is not fully loaded with Amps/electons. In a heavy industrial situation the truck is usually about thirty five percent loaded. A good capicitor system can up that to around sixty sixty five percent.

....In a heavy insudtrial load the maximum pressure happens before the max flow of electrons happens. Because of the sheer volume of electrons being called for they move slower and can't keep up with the volt/pressure sine wave. Thus the need for the Caps/Water Tower type energy storer... Remember the pressure is going from a posative pressure to a negative pressure sixty times per second. The electon are alternatively flowing away from the source and back to the source.
......... In AC current the electrons dont flow in one direction like water in a water pipe, but vacilate back and forth. What is happening is the same as if you were flipping a horse shoe magnet back an forth alternativly creating a push pull force on the electrons. Pretty much that is exactly what is happening.