The last couple post are suggesting that maybe these Cap banks were not engineered correctly? These banks are made by General Electric and were probably installed late 70's early 80's. I have no idea how long they broken or when they failed. The one thing I do know is that we have over 40 locations with these same exact cap banks all installed during the same time. There are 6 locations that are still operating correctly. All the faulted non operating locations share the same signs of failing the same way. The resistor is fried, internal fuse blown along with two of the three main overcurrent protection fuses, but all Caps within bank test ok.
Failed Capacitor/resistors
- Thread starter raiderUM
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By no means am I an expert on capacitors, I think that is very apparent. I am here to ask stupid questions so I can learn from you guys not be misleading, my apologies. I do not know the resistor wattage rating. It looks to me like the resistor got really hot, its discolored and very brittle. The resistor in the picture broke in half when I tried to remove it. I have not yet found a failed capacitor when checking with my meter.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
120710-2353 EDT
raiderUM:
In an earlier post I provided you with approximation dimensions of various wattage resistors.
I just do not believe the resistor failures are in any way the cause of the fuses blowing.
We do need to know if these are 2 W resistors.
Where are you located?
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raiderUM:
In an earlier post I provided you with approximation dimensions of various wattage resistors.
I just do not believe the resistor failures are in any way the cause of the fuses blowing.
We do need to know if these are 2 W resistors.
Where are you located?
.
Can you think of any changes in the load that may have cause an increase PF issue? It's just strange that you took out a resistor.
I would be concerned that the voltage spiked increasing the voltage across the resistor and fried the resistor. The fuse frying may be a symptom of a problem, the fuse blowing may have been to protect the capacitor.
I would be concerned that the voltage spiked increasing the voltage across the resistor and fried the resistor. The fuse frying may be a symptom of a problem, the fuse blowing may have been to protect the capacitor.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
I am thinking the ambient temperature may have contributed to the resistors demise. We do not know that the resistor had failed electrically, only that is was being cooked. It failed mechanically when removed.
T
T.M.Haja Sahib
Guest
The internal fuse in a capacitor could blow, only when one or more of its capacitor elements are shorted. So when this happened, it might have affected the voltage distribution across the terminals of the capacitor, where the resistor was connected. The capacitor where the resistor failed might have experienced higher voltage than the rating of the resistor, which might have consequently failed causing the main fuse to operate. This may be ascertained by checking the capacitance of the capacitor, where the resistor failed. It would have a lower capacitance than the name plate value!
I know that the load has changed greatly over the last 40 years. Most of these Cap banks are way to over sized at each location. One location I have Two 250Kvar banks, so 500kvar total, I only need 100Kvar to correct PF to unity at peak time. So maybe the load change over the years has contributed to this?
Yes, I have checked all of them. Each one is rated at 40.2 uf and they all tested "good".
I had a 150Kvar bank at the Rec Center. There was a bad resistor on one of the three 50kvar banks. I tried to turn the bank back on after I replaced the main fuses in the disconnect. The sound that followed was incredibly load and nerve racking. It sounded like something was arching out, so I immediately turn the main disconnect off... changed my pants:blink: and removed the bad 50 kvar bank. This left me with only 100kvar at this location but everything worked fine after removal of the bank with the bad resistor in it.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
120711-1014 EDT
raiderUM:
You are not local enough for me to look at your resistor.
An overheated small resistor exploding would not be a really large sound or long in duration. I ran an experiment once on a 100 ohm 1/4 W resistor in series with an 18 V Transorb transient limiter. This series combination was connected across 120 VAC resulting in a loud pop, and no damage to the Transorb. The resistor was destroyed as expected. Peak power to the resistor could have been as high as about ((120-18)*1.4)2/100 = 208 W. The purpose of the experiment was to see if the Transorb in this combination was an effective protector of a semiconductor input circuit. Note: in this case a resistor is a less expensive fuse than a fuse.
I will bring home the IR temperature meter and get an estimate of the surface temperature of a 2 W carbon comp at 2 W.
For a replacement you could use two 91 k 2 W 5% resistors in series. This will greatly increase the lifetime of the bleeder. Or a 100 k in series with 82 k, or two 82 k in series.
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raiderUM:
You are not local enough for me to look at your resistor.
An overheated small resistor exploding would not be a really large sound or long in duration. I ran an experiment once on a 100 ohm 1/4 W resistor in series with an 18 V Transorb transient limiter. This series combination was connected across 120 VAC resulting in a loud pop, and no damage to the Transorb. The resistor was destroyed as expected. Peak power to the resistor could have been as high as about ((120-18)*1.4)2/100 = 208 W. The purpose of the experiment was to see if the Transorb in this combination was an effective protector of a semiconductor input circuit. Note: in this case a resistor is a less expensive fuse than a fuse.
I will bring home the IR temperature meter and get an estimate of the surface temperature of a 2 W carbon comp at 2 W.
For a replacement you could use two 91 k 2 W 5% resistors in series. This will greatly increase the lifetime of the bleeder. Or a 100 k in series with 82 k, or two 82 k in series.
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gar,
I just spoke with the electronic guy, he confirmed that it is 180K resistor and it is 2W Carbon Comp. He suggested replacing resistors with 180K but 5W, as this would help dissipate the heat better. He said this happens all the time, as the resistor gets hot it becomes more brittle and then it fails.
I just spoke with the electronic guy, he confirmed that it is 180K resistor and it is 2W Carbon Comp. He suggested replacing resistors with 180K but 5W, as this would help dissipate the heat better. He said this happens all the time, as the resistor gets hot it becomes more brittle and then it fails.
I voted for that also in my post #18.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
120711-1228 EDT
raiderUM:
You can get an Ohmite 150 k 15 W metal oxide 2" x 1/2". Does not look like Ohmite makes 2 W carbon comps any more. Actually I think Allen-Bradley made Ohmite carbon comps.
You are unlikely to fine wire wound high resistance power resistors. Some Ohmites went to 100 k. If you are searching you probably want to use the words metal film or metal oxide.
The resistance value is not critical other than how it affects --- discharge time, wasted power, and the resistor power rating. Voltage capability is function of over the surface breakdown, or surface leakage.
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raiderUM:
You can get an Ohmite 150 k 15 W metal oxide 2" x 1/2". Does not look like Ohmite makes 2 W carbon comps any more. Actually I think Allen-Bradley made Ohmite carbon comps.
You are unlikely to fine wire wound high resistance power resistors. Some Ohmites went to 100 k. If you are searching you probably want to use the words metal film or metal oxide.
The resistance value is not critical other than how it affects --- discharge time, wasted power, and the resistor power rating. Voltage capability is function of over the surface breakdown, or surface leakage.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
120711-1302 EDT
I have just run a temperature test on a 2 W carbon comp.
Room air temp 70 F. IR generally reads about this on various objects.
A 15 ohm 2 W Ohmite carbon comp is supported horizontally in free space by two small clip leads. DC voltage and current measured to determine power input to the resistor. Power from an adjustable HP regulated supply.
2 W 190 F or a rise of 120 F.
1.25 W 150 F for a rise of 80 F.
80/120 = 0.67
1.25/2 = 0.63
Reasonably close check. One does not expect this to be linear, but I might expect the lower temperature to be higher. My IR measurement has potential for substantial error.
.
I have just run a temperature test on a 2 W carbon comp.
Room air temp 70 F. IR generally reads about this on various objects.
A 15 ohm 2 W Ohmite carbon comp is supported horizontally in free space by two small clip leads. DC voltage and current measured to determine power input to the resistor. Power from an adjustable HP regulated supply.
2 W 190 F or a rise of 120 F.
1.25 W 150 F for a rise of 80 F.
80/120 = 0.67
1.25/2 = 0.63
Reasonably close check. One does not expect this to be linear, but I might expect the lower temperature to be higher. My IR measurement has potential for substantial error.
.
T
T.M.Haja Sahib
Guest
The 100 A internal fuse would be inside the can of the capacitor and I want to know how you came to know it was blown.
The blown fuse is not internal to the capacitor.
See post #10.
You can quite clearly see the striker pin protruding from the lower fuse.
Most of us would take that as a pretty good visual clue as to the status of the fuse.
Wouldn't you?
T
T.M.Haja Sahib
Guest
The OP mentioned 600A main fuse and 100A internal fuse. Only one blown fuse is shown. Where is the other blown fuse?
How would that be possible if the capacitors had blown internal fuses?
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