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Lifespan of HT Capacitor Bank

01/31/2020 4:16 AM

We have procured HT capacitor bank 800 KVAr 10 years back but it is never connected in the circuit.This is aluminium capacitor bank.I want to know whether we can use this now in the circuit or not. I want to know whether the life of capacitor bank will be affected since we have not connected it for 10 years after purchasing the battery bank.Kindly advise me at this juncture,I can connect and use this capacitor bank or since for 10 years,it is not connected in circuit,it may spoil.Please advise me.Thanks.

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#1

Re: LIFE SPAN OF HT CAPACITOR BANK

01/31/2020 4:32 AM

These sorts of questions need to be asked of the equipment supplier.

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#2

Re: LIFE SPAN OF HT CAPACITOR BANK

01/31/2020 5:33 AM

Depends on the storage conditions....Do they still look like new? If so I would power them up in a controlled environment if possible and check operation....

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#3

Re: LIFE SPAN OF HT CAPACITOR BANK

01/31/2020 5:40 AM

If it is visually looks alright - no leaks, damage etc. I don't see any problem is using the capacitor bank.

Electrical equipment including capacitor bank is designed for a life of 25 years when operated under prescribed conditions.

Since the bank has been in stores all these 10 years, run standard tests like capacitance and dielectric loss measurement just to confirm the healthiness before energising.

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#4

Re: LIFE SPAN OF HT CAPACITOR BANK

01/31/2020 6:18 AM

Capacitors do have a shelf life. While the shelf life is longer than the operational lifetime it will also degrade with warmer temperatures. Contact the original manufacturer. If you can locate a batch number on the capacitor this with the manufacturer's help may tell you how old are your capacitors.

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#8
In reply to #4

Re: LIFE SPAN OF HT CAPACITOR BANK

02/02/2020 12:31 AM

Capacitors as described by the OP easily have a 25 year operational life. The protection will take out a failed unit with a small voltage bump. If you have an entire failed bank, then you may see a voltage dip severe enough to trip off nearby inverter drives or disturb electronic circuit operation temporarily.

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#5

Re: LIFE SPAN OF HT CAPACITOR BANK

01/31/2020 7:14 AM

...and there is much to be gained by receiving the supplier's technical representative at site for a check on the equipment before energising.

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#6

Re: Lifespan of HT Capacitor Bank

01/31/2020 5:32 PM

If they are electrolytic capacitors, there is about a 1-2 year shelf life if they are left in a de-energized state, because the oxides on the films will dissolve back into the electrolyte and the first time you energize them, they can short circuit and explode! Electrolytic capacitors must be put through a “re-forming” procedure in which low voltage /current limited power is applied to the capacitors and slowly increased over a long period of time, as in days, until you reach the working voltage. You can do a search on “capacitor re-forming procedure” to get ideas on how to do this.

And/or as PWSlack said, contact the mfr for assistance...

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#7
In reply to #6

Re: Lifespan of HT Capacitor Bank

02/01/2020 11:18 AM

Cool, GA!

I never heard about re-forming aluminum capacitors. The method posted at Rockwell Automation identifies a gradual increase of 50VDC steps. For most of my capacitor experiences the first step would exceed the capacitor voltage which explains why I've not heard about this.

A word of caution, the energy stored in a capacitor increases with the voltage squared.

W=0.5*C*V^2

This can easily become a dangerous if not lethal amount of stored energy.

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#11
In reply to #6

Re: Lifespan of HT Capacitor Bank

02/02/2020 11:41 PM

You are right JRaef.

I too read it some time back.

Thanks for reminding me.

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#9

Re: Lifespan of HT Capacitor Bank

02/02/2020 9:51 PM

Operational life is based on them being energized once in a while, even once per year. If sitting unpowered fir 10 years, operational life means nothing.

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#10
In reply to #9

Re: Lifespan of HT Capacitor Bank

02/02/2020 10:40 PM

(High Tension) Power factor capacitors are not electrolytic, they work being subjected to line frequency when energized. The storage life of these units is longer than the operational life.

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#12

Re: Lifespan of HT Capacitor Bank

05/08/2020 6:13 AM

Hi nsrinivas,

You have not mentioned the type of HT capacitor since electolytic capacitors deteriorate fast if unused for for long time/

How ever open the following links and you may find some help.

https://www.dfrsolutions.com/hubfs/Resources/services/Long-Term-Storage-of-Al-E-Capacitors.pdf

https://digital.library.unt.edu/ark:/67531/metadc3104/m2/1/high_res_d/thesis.pdf

https://www.electrical4u.com/testing-of-capacitor-bank/

https://www.edn.com/whats-the-maximum-idle-time-for-capacitors/

Pl. post the information whether the HT capacitor is used and what type od testing carried out and also post the details of testing so that CR4 mambers will come to know the outcome.

DHAYANANDHAN.S

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