how long do power factor capacitors last??

[.]

I have a service that has some really old capacitors on the 480V line
and some that are not so old, probably 10-15 yrs. They are different
manufaturers but identical application. The newer ones have failed and
are shorting out. The old ones are hanging on just fine.
Does anyone know what average lifespan of this type a capacitor in an
industrial environment such as a mine could be expected. This of
course would be with normal use and no huge transients etc.

Chris


To send me e-mail remove the sevens
from my address.

Chrisd

 

[John Gilmer]

Yes, per NEC 460-6.

Re: dischange resistors.

How are these sized? IOW: is there a requirement that a fully charged cap
will drop to, say, 10% within a certain time.

Otherwise, why not ship low voltage caps with say, .5 meg, resistors. They
could take 600 volts and draw less than a Watt.

EMWTK

 

[Ben Miller]

How are these sized? IOW: is there a requirement that a fully charged cap
will drop to, say, 10% within a certain time.

Otherwise, why not ship low voltage caps with say, .5 meg, resistors. They
could take 600 volts and draw less than a Watt.

From the 2002 NEC:

460.6 Discharge of Stored Energy.
Capacitors shall be provided with a means of discharging stored energy.
(A) Time of Discharge. The residual voltage of a capacitor shall be reduced
to 50 volts, nominal, or less within 1 minute after the capacitor is
disconnected from the source of supply.
(B) Means of Discharge. The discharge circuit shall be either permanently
connected to the terminals of the capacitor or capacitor bank or provided
with automatic means of connecting it to the terminals of the capacitor bank
on removal of voltage from the line. Manual means of switching or connecting
the discharge circuit shall not be used.

Ben Miller

 

[Dave M.]

Using a capacitor to propagate moderate to high power is nonsense, unless
savings due to power factor correction far outweighs the maintenance costs
of the banks and the reliability problem.

Dave M.

 

[bushbadee]

We were building a 400 Hz inverter for the SR71 and the output was tuned
with capacitors.
These capacitors had to work at 71 degrees C and 100,000 feet altitude.
We were running a bank of Metalized Mylar capacitors.
The test were run in a back lab where we had the equipment to produce the
vacuum of 100,000 feet altitude and it was, luckily break time.
When we heard loud explosions coming from that lab.
Luckily no one was in the lab.
When we went back into it we found that the caps had exploded and sent
shrapnel all over the place.
When the shrapnel from the first cap in the bank (There were about 15 caps
in it) hit the next one it went off and so on down the line.

Yes Caps can go off quite violently.

 

[Don Kelly]

We were building a 400 Hz inverter for the SR71 and the output was tuned
with capacitors.
These capacitors had to work at 71 degrees C and 100,000 feet altitude.
We were running a bank of Metalized Mylar capacitors.
The test were run in a back lab where we had the equipment to produce the
vacuum of 100,000 feet altitude and it was, luckily break time.
When we heard loud explosions coming from that lab.
Luckily no one was in the lab.
When we went back into it we found that the caps had exploded and sent
shrapnel all over the place.
When the shrapnel from the first cap in the bank (There were about 15 caps
in it) hit the next one it went off and so on down the line.

Yes Caps can go off quite violently.

Altogether different service demands and capacitor design. Bang is still
possible

 

[sammmm]

as a reliance electric service engineer, i was urging a group of steel
company electricians to
always close the cabinet door when energising the cabinet on early solid
state inverters.
as we closed the door and closed the 'big switch' one went off and
christened the cabinet
insides. it was a great demonstration!
sammmmm

 

[.]

Would 10 years in a non harmonic industrial environment be reasonable?
600V 100KVAR is typical ratings

I have a service that has some really old capacitors on the 480V line
and some that are not so old, probably 10-15 yrs. They are different
manufaturers but identical application. The newer ones have failed and
are shorting out. The old ones are hanging on just fine.
Does anyone know what average lifespan of this type a capacitor in an
industrial environment such as a mine could be expected. This of
course would be with normal use and no huge transients etc.

Chris


To send me e-mail remove the sevens
from my address.

Chrisd

To send me e-mail remove the sevens
from my address.

Chrisd

 

[sammmm]

i've not seen any caps that were bad. (in ordinary P-F correction use)
i've applied and also checked quite a few.
i understand that there are fuses internally in many.
we had some caps in 180 Hz tripler setups go but they were in
steel ingot induction furnaces and were water-cooled.
if the P-F gets too close to a leading situation the current will go
haywire.
i'm not engineer enough to get deep in the theory.
good luck, sam

 

[.]

I have some in a plant that I think suffered some large voltage swings
in the supply line when a neutral opened and teh ground wasnt good
enough to take care of it. They are 100Kvar 600V ABB units that
eventually failed, some quite violently.

I just assumed that they had been damaged by poor power quality and
replaced them. There are no harmonics anywhere in the system.

Now I have the same type of ABB units except they are 480V 60 Kvar
failing in another plant. I do not know the power history of that
installation and thats why I wonder if these are a short lived
solution (10 yrs) or is there a better way to go. The ABB ones have
many small cells inside and the replacements Commonweath Sprague have
10Kvar cans inside. Hopefully they will last longer.

i've not seen any caps that were bad. (in ordinary P-F correction use)
i've applied and also checked quite a few.
i understand that there are fuses internally in many.
we had some caps in 180 Hz tripler setups go but they were in
steel ingot induction furnaces and were water-cooled.
if the P-F gets too close to a leading situation the current will go
haywire.
i'm not engineer enough to get deep in the theory.
good luck, sam

To send me e-mail remove the sevens
from my address.

Chrisd

 

[Jimmie]

Would 10 years in a non harmonic industrial environment be reasonable?
600V 100KVAR is typical ratings







To send me e-mail remove the sevens
from my address.

Chrisd

Our enviromental crew decided it was time to change the ones in our 20 year
old UPS, never had a problem with them since installation. A few went bad
right after installation. They decided to do a complete change out based on
age. For a period of about a year we had 1 or 2 caps fail per month then
level off after that to no failures for a year. Prior to the change out
there had been no failures beyound the first year of the installation. Think
they should have left them alone.

 

[operator jay]

Would 10 years in a non harmonic industrial environment be reasonable?
600V 100KVAR is typical ratings







To send me e-mail remove the sevens
from my address.

Chrisd

In a benign environment power capacitors should last 20 years. This can be
shortened by many things including heat, dielectric degradation, physical
damage, etc.

Can you tell me about the different types of caps (such as name/type and
model) and describe the nature of their failure? I would avoid self-healing
capacitors, especially in an industrial environment. They can fail on
overvoltage transients that break down a section of the dielectric but fail
to vaproize the corresponding section of the metal layer (i.e. the capacitor
fails to self-heal). The result is an internal arc which burns away the
dielectric and releases gasses which burn. I understand acetylene can be
formed and will shoot out any hole or rupture in the can in a gout of flame.
I have seen failed dry self-healing caps which, by appearance, would support
this.

Sometimes capacitors are applied and everything works out fine. On the
other hand, if you continue experiencing problems, you may be wise to speak
to a consultant. They can examine your specific applications to see if
there are any concerns that need to be addressed. They can recommend
capacitor types and ratings, reactor types, control requirements, the whole
works. Sorry for the cop out, but there can be so much involved with
capacitors.

j