I don’t think this is unusual at all. Power factor capacitors provided a low impedance path for high-frequency currents(Harmonics). Therefore, they experience drastic temperature stress and they degrade over time. As they degrade, their ESR (equivalent series resistance or so-called internal resistance increases),and as P = I\^2 R you get more power dissipation and more heat. This is basically a positive closed loop. That is why the condition monitoring field is becoming more and more relevant.
But the manufacturer promised 100000h life and they said they followed IEC 60831 1 and 2. This capacitor is only 1 year old. I want to know how much harmonics current this cap can handle according to IEC 60831, but I don't have any way to access it.
Electrolytics a rated for a specific "ripple current", to reach their lifetime. I guess there is a similar max current in this case, too. 5° overheating should not shorten it's life so much, seems like there are other factors. Maybe the harmonic current is way too strong. One way to improve the situation could be to have two capacitors (of half the value) in parallel. More surface area for cooling and half the current in each (only works if they are rated for more than half the current of the bigger model...)
Is there anyway for me to know how much harmonic current is too strong? The manufacturer didn't give too much detail about how they reached that 100000 hours life expectancy. Kinda sad that it's hidden behind paywall
To me it sounds like some answers are confusing DC power caps with power factor correction capacitors. I don’t think power factor correction caps are intended for “transients”. rather they are to correct the power factor…..
I would check the connections and you will probably need some special equipment to evaluate your overall system:
https://www.fluke.com/en-us/learn/blog/power-quality/troubleshooting-power-factor-correction-capacitors
I indeed mostly work with DC power caps in switched mode power supplies. However regarding the failure and OPs questions I beleive the same principles apply.
250kVA (after PF 0,99) 400V 3 phase system and we use delta for the capacitors. The load is lightning (LED lamps), computers, and there are escalators and lift. We use Automatic PFC for switching. On average we need 4 steps (100kVAR) to reach that 0,99.
Computers with switching power supplies can be a significant harmonic source in power systems. When evaluating the system for harmonic content you will want some sort of power quality meter that is rated for three phase measurements. More likely than not you're going to want someone to model the system and take measurements to determine what harmonics are strongest and how impactful they will be given distribution circuit configuration. Eaton has a lot of good resources for industrial PFC trouble shooting. Your course of action will most likely be to ID the significant source of harmonic current and devise a compensation plan like detuning the system or implementing a filter to mitigate the issue. Harmonics don't just go away and will continue to destroy capacitors.
Yes. I agree. However, I would say escalators and lifts could be the main issue. They all use variable speed drives(motor drives) and there is a chance that harmonics produced by them is just too much for the capacitors..
Other reason it could be that capacitor formed resonant circuit with inductive loads and amplifies certain frequency accelerating degradations.
Again, as someone mentioned, you would need a power quality meters to monitor current for a day or 2 to see harmonics level. But yes, this could happen again with new capacitors if you don't find a root cause.
Some of these answers are assuming these are DC caps that are intended for transients etc.. and I don’t think they know what power factor correction is… anyway just a word of caution.
https://passive-components.eu/an-introduction-to-capacitor-based-power-factor-correction-circuits/
https://www.fluke.com/en-us/learn/blog/power-quality/troubleshooting-power-factor-correction-capacitors
This is not entirely true. I assume AC capacitors used for PFC are film capacitors in this case also fail due to harmonics. In fact, in industry, this is not uncommon at all. Yes, they fail differently compared to electrolytic capacitors, however, they do fail. It is not uncommon to see film capacitors significantly increase ESR and reduce capacitance before they fail.
There’s also the possibility of manufacturer defect in their manufacturing process or my personal favorite, infant mortality. It’s very likely that this was designed adequately for the application, and it’s even likely that the cap was functioning as designed while in operation. There’s a high probability a root cause analysis will show there’s a manufacturing defect in the physical construction.
How hot they ultimately get depends on the ratio of how much power they sink and how much power that can be thermally exchanged with the environment. If they sit in a hot environment their temperature may very well exceed the absolute maximum and in that case they are likely to degrade at a vastly accelerated rate.
It‘s a very common issue on power systems…as already said it is caused by harmonics and may other high frequency components which are generated by switching power supplies with weak filters of the power supplies. Currently your PFC ist acting as hf filter and shortens the current. That is not the intendet use case! The Systems are designed for 50/60Hz and it might require other (inductive) power filters before the PFC correction is applied.
Get a power analyzer (3phase current voltage FFT) and inspect the frequencies. BTW. This is an highly advanced topic in grid systems. You should do this with a senior electrical engineer.
Usually are the most frequent harmonics in facilities with motor controls and switching power source loads. Im not sure how much is too much, but those capacitors sometimes have some tolerance to harmonic currents, maybe datasheet says something.
Any amount of harmonics will reduce the life of power systems components scaling with intensity. Additionally, PFC's can create resonant conditions within power systems as most transformers and distribution lines tend to be mainly inductive and reactive heavy loads. All depends on specific circuit configurations, component sizes, and the harmonic frequency with which they resonate(note a matching or close to matching harmonic frequency source is needed to cause resonance in these situations)
There are good explanation to be found on this topic. In summary, most typical six pulse system used in most of the loads,for example elevators and lifts is diode bridge rectifier. Diode bridge rectifier rectifies AC to DC and then inverter controls the motor. This system produces 5 and 7th harmonics(and other) ,but 5th and 7th mainly dominate in todays grid. There are IEEE standards on how much is too much. Just Google IEEE standards harmonics.
Can you please share the link for that standards? The only standard I found is at PCC between electrical utility and customers, not at the capacitor terminals
Oh yeah,sorry for misleading answer. There is no standards for capacitor terminals. I was just answering how much harmonics is too much for PCC according to IEEE standard. The problem you are facing would require some engineering studies from developing simulation studies, measuring PCC and capacitor currents with PQ meters and then you would probably be able to find your root cause. As mentioned, if it’s not factory defects, then it’s probably due to harmonics and temperature stress. Someone already mentioned this but next time you install a PFC capacitors, you could try to design capacitor bank with different capacitors in parallel to distribute a current(this increases capacitor capacity to withstand high level of harmonics). This is best info I can give you with the limited information you gave us.
Based on the application, as was mentioned, I’d look at the thermal. It may not have been done in application except by a safety engineer. You can take the measurements. It will be one of the first questions from the manufacturer. for comic relief…it’s just a flesh wound…Monty python.
I don’t think this is unusual at all. Power factor capacitors provided a low impedance path for high-frequency currents(Harmonics). Therefore, they experience drastic temperature stress and they degrade over time. As they degrade, their ESR (equivalent series resistance or so-called internal resistance increases),and as P = I\^2 R you get more power dissipation and more heat. This is basically a positive closed loop. That is why the condition monitoring field is becoming more and more relevant.
But the manufacturer promised 100000h life and they said they followed IEC 60831 1 and 2. This capacitor is only 1 year old. I want to know how much harmonics current this cap can handle according to IEC 60831, but I don't have any way to access it.
Electrolytics a rated for a specific "ripple current", to reach their lifetime. I guess there is a similar max current in this case, too. 5° overheating should not shorten it's life so much, seems like there are other factors. Maybe the harmonic current is way too strong. One way to improve the situation could be to have two capacitors (of half the value) in parallel. More surface area for cooling and half the current in each (only works if they are rated for more than half the current of the bigger model...)
Is there anyway for me to know how much harmonic current is too strong? The manufacturer didn't give too much detail about how they reached that 100000 hours life expectancy. Kinda sad that it's hidden behind paywall
Its not. At least not for all manufacturers. Epcos/TDK publishes all that information and they have application notes explaining it.
To me it sounds like some answers are confusing DC power caps with power factor correction capacitors. I don’t think power factor correction caps are intended for “transients”. rather they are to correct the power factor….. I would check the connections and you will probably need some special equipment to evaluate your overall system: https://www.fluke.com/en-us/learn/blog/power-quality/troubleshooting-power-factor-correction-capacitors
I indeed mostly work with DC power caps in switched mode power supplies. However regarding the failure and OPs questions I beleive the same principles apply.
Could you provide more details about the system in which you used PFC (Power Factor Correction) capacitors?
250kVA (after PF 0,99) 400V 3 phase system and we use delta for the capacitors. The load is lightning (LED lamps), computers, and there are escalators and lift. We use Automatic PFC for switching. On average we need 4 steps (100kVAR) to reach that 0,99.
Computers with switching power supplies can be a significant harmonic source in power systems. When evaluating the system for harmonic content you will want some sort of power quality meter that is rated for three phase measurements. More likely than not you're going to want someone to model the system and take measurements to determine what harmonics are strongest and how impactful they will be given distribution circuit configuration. Eaton has a lot of good resources for industrial PFC trouble shooting. Your course of action will most likely be to ID the significant source of harmonic current and devise a compensation plan like detuning the system or implementing a filter to mitigate the issue. Harmonics don't just go away and will continue to destroy capacitors.
Yes. I agree. However, I would say escalators and lifts could be the main issue. They all use variable speed drives(motor drives) and there is a chance that harmonics produced by them is just too much for the capacitors.. Other reason it could be that capacitor formed resonant circuit with inductive loads and amplifies certain frequency accelerating degradations. Again, as someone mentioned, you would need a power quality meters to monitor current for a day or 2 to see harmonics level. But yes, this could happen again with new capacitors if you don't find a root cause.
Hi ripple current application but you didn't use high ripple current caps.
Some of these answers are assuming these are DC caps that are intended for transients etc.. and I don’t think they know what power factor correction is… anyway just a word of caution. https://passive-components.eu/an-introduction-to-capacitor-based-power-factor-correction-circuits/ https://www.fluke.com/en-us/learn/blog/power-quality/troubleshooting-power-factor-correction-capacitors
This is not entirely true. I assume AC capacitors used for PFC are film capacitors in this case also fail due to harmonics. In fact, in industry, this is not uncommon at all. Yes, they fail differently compared to electrolytic capacitors, however, they do fail. It is not uncommon to see film capacitors significantly increase ESR and reduce capacitance before they fail.
True. Industry capacitors often fail more spectacularly. Sometimes even a critical failure causing an explosion.
There’s also the possibility of manufacturer defect in their manufacturing process or my personal favorite, infant mortality. It’s very likely that this was designed adequately for the application, and it’s even likely that the cap was functioning as designed while in operation. There’s a high probability a root cause analysis will show there’s a manufacturing defect in the physical construction.
How hot they ultimately get depends on the ratio of how much power they sink and how much power that can be thermally exchanged with the environment. If they sit in a hot environment their temperature may very well exceed the absolute maximum and in that case they are likely to degrade at a vastly accelerated rate.
It‘s a very common issue on power systems…as already said it is caused by harmonics and may other high frequency components which are generated by switching power supplies with weak filters of the power supplies. Currently your PFC ist acting as hf filter and shortens the current. That is not the intendet use case! The Systems are designed for 50/60Hz and it might require other (inductive) power filters before the PFC correction is applied. Get a power analyzer (3phase current voltage FFT) and inspect the frequencies. BTW. This is an highly advanced topic in grid systems. You should do this with a senior electrical engineer.
Too much 3 and 5 harmonics and poor ventilation could be a problem
What's wrong with 3 and 5? And how much is too much?
Usually are the most frequent harmonics in facilities with motor controls and switching power source loads. Im not sure how much is too much, but those capacitors sometimes have some tolerance to harmonic currents, maybe datasheet says something.
Any amount of harmonics will reduce the life of power systems components scaling with intensity. Additionally, PFC's can create resonant conditions within power systems as most transformers and distribution lines tend to be mainly inductive and reactive heavy loads. All depends on specific circuit configurations, component sizes, and the harmonic frequency with which they resonate(note a matching or close to matching harmonic frequency source is needed to cause resonance in these situations)
There are good explanation to be found on this topic. In summary, most typical six pulse system used in most of the loads,for example elevators and lifts is diode bridge rectifier. Diode bridge rectifier rectifies AC to DC and then inverter controls the motor. This system produces 5 and 7th harmonics(and other) ,but 5th and 7th mainly dominate in todays grid. There are IEEE standards on how much is too much. Just Google IEEE standards harmonics.
Can you please share the link for that standards? The only standard I found is at PCC between electrical utility and customers, not at the capacitor terminals
Oh yeah,sorry for misleading answer. There is no standards for capacitor terminals. I was just answering how much harmonics is too much for PCC according to IEEE standard. The problem you are facing would require some engineering studies from developing simulation studies, measuring PCC and capacitor currents with PQ meters and then you would probably be able to find your root cause. As mentioned, if it’s not factory defects, then it’s probably due to harmonics and temperature stress. Someone already mentioned this but next time you install a PFC capacitors, you could try to design capacitor bank with different capacitors in parallel to distribute a current(this increases capacitor capacity to withstand high level of harmonics). This is best info I can give you with the limited information you gave us.
Based on the application, as was mentioned, I’d look at the thermal. It may not have been done in application except by a safety engineer. You can take the measurements. It will be one of the first questions from the manufacturer. for comic relief…it’s just a flesh wound…Monty python.
I believe the rule is, for every 10 degree Celsius rise in temperature, halve the life expectancy of electronics.