Capacitor Question
- Thread starter CIECO
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Here is all I know-
Capacitors in parallel is equal to the sum of their individual capacitances.
Capacitors in parallel give you something called the harmonic mien (sp?). I don't know what that means.
This is a bit of a long winded bump to see if anyone will chime in.
Capacitors in parallel is equal to the sum of their individual capacitances.
Capacitors in parallel give you something called the harmonic mien (sp?). I don't know what that means.
This is a bit of a long winded bump to see if anyone will chime in.
eHunter
Senior Member
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- North Texas & Georgia
Not exactly an easy straight forward question.
Measuring the capacitance accross any 2 phase connections will be measuring all 3 capacitors as serial and parallel capacitors due to the internal connections.
A 3 phase delta connected capacitor bank has 3 capacitors, usually connected in an equivalent series parallel arrangement.
Are you able to access both connections to an individual capacitor, or is a sealed unit?
Measuring between Phases A & B has cap A in parallel with caps B & C which are in series with each other.
Measuring between Phases A & C has cap B in parallel with caps A & C which are in series with each other.
Measuring between Phases B & C has cap C in parallel with caps A & B which are in series with each other.
Capacitance in series
.
Capacitance in parallel
.
Measuring the capacitance accross any 2 phase connections will be measuring all 3 capacitors as serial and parallel capacitors due to the internal connections.
A 3 phase delta connected capacitor bank has 3 capacitors, usually connected in an equivalent series parallel arrangement.
Are you able to access both connections to an individual capacitor, or is a sealed unit?
Measuring between Phases A & B has cap A in parallel with caps B & C which are in series with each other.
Measuring between Phases A & C has cap B in parallel with caps A & C which are in series with each other.
Measuring between Phases B & C has cap C in parallel with caps A & B which are in series with each other.
Capacitance in series
Capacitance in parallel
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You bumped, but I just wobbled a little.
A three phase capacitor for Power Factor correction will usually be specified by nominal voltage and kVar energy capability. But they can also be specified by capacitance. In the latter case, the number would be the value of each of the three identical capacitors in the three-terminal, three phase unit.
They are meant to be used in a delta configuration to correct the power factor of a three phase motor or transmission line, whether that three phase load is wired as wye or delta.
PS: The term "harmonic mean" is used to describe a form of average value that uses the same calculation as resistance values in parallel, only multiplied by the number of resistors or capacitors in parallel. If two capacitances are equal, their harmonic mean is the same as that common number.
If they are unequal, it is weighted in favor of the smaller value.
1/2 ohm and 1 ohm resistors have a numeric average of .75 ohms. And you could also call that their average resistance when put in series. 1/2 + 1 =1.5, 1.5/2 = .75. Two .75 ohm resistor in series will have the same resistance as the original two in series.
1/2 ohm and 1 ohm resistors in parallel have a total resistance of 1/(2/1 +1/1) = 1/3 ohm. And the harmonic mean value would be twice that, 2/3 ohm. That is the value of two equal resistors which when put in parallel have the same total resistance as the original two in parallel.)
Anyway, two capacitors in series have a capacitance which is 1/2 of the harmonic mean, just as two resistors in parallel have resistance which it twice the harmonic mean.
If you have a three phase delta capacitor, there is no way that you can connect all three capacitors in parallel unless the unit has six terminals. If it did, you would get 3 x 96, not 2 x 96. But since you have only three terminals, by putting two of them in parallel you short out the third one and the result is just 192.
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Measuring between Phases A & B has cap A in parallel with caps B & C which are in series with each other.
Measuring between Phases A & C has cap B in parallel with caps A & C which are in series with each other.
Measuring between Phases B & C has cap C in parallel with caps A & B which are in series with each other.
I do understand what you are saying.
What I have is 2 3 phase caps 96uf 25KVAR paralleled X 11Banks and dont have one reading alike and just wanted to know what the value should be. Is a 96uf 3 phase cap. 3 96uf caps connected in a delta or is it some kind of combined formula? If they are 3 96uf caps then I should read 144uf phase to phase and with them paralled it should be 288uf phase to phase.
Measuring between Phases A & C has cap B in parallel with caps A & C which are in series with each other.
Measuring between Phases B & C has cap C in parallel with caps A & B which are in series with each other.
I do understand what you are saying.
What I have is 2 3 phase caps 96uf 25KVAR paralleled X 11Banks and dont have one reading alike and just wanted to know what the value should be. Is a 96uf 3 phase cap. 3 96uf caps connected in a delta or is it some kind of combined formula? If they are 3 96uf caps then I should read 144uf phase to phase and with them paralled it should be 288uf phase to phase.
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eHunter
Senior Member
- Location
- North Texas & Georgia
Are they fused internally or externally?
You may have some blown protective fuses or possibly some bad caps.
The formula for calculating the measured capacitance:
Phase A-B = 1/(1/B + 1/C) + A
Phase A-C = 1/(1/A + 1/C) + B
Phase B-C = 1/(1/A + 1/B) + C
eHunter
Senior Member
- Location
- North Texas & Georgia
144uF is a good value for (3) 96uF caps in a 3 phase delta config.
eHunter
Senior Member
- Location
- North Texas & Georgia
What manufacturer and model number?
eHunter
Senior Member
- Location
- North Texas & Georgia
Each 2543PHRMA capacitor cell is marked "3 x 96 uF" with a delta symbol.
Yes, the 144uF is a good measured capacitance reading.
(1/(0.0104 + 0.0104)) + 96 = 144 uF
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eHunter
Senior Member
- Location
- North Texas & Georgia
Is it?
The result is accurate.
You and I know that 2 like sized caps in series simply half the capacitance of 1, but I am not sure that the OP understands or knows this tidbit.
I was simply following the formulas set forth in post #3.
The object and hope was that the OP would learn how to calculate total capacitance in any combination series parallel circuit with the formulas provided.
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That's fair enough.
Would the OP have known where the 0.0104 came from?
Perhaps the derivation of that ought to have been shown before it was used?
eHunter
Senior Member
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- North Texas & Georgia
Good question and an unknown at this time.
Agreed, the work product could and should have been more complete.
jumper
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- 3 Hr 2 Min from Winged Horses
Del-boy has to disagree a bit here Bes.
eHunter clearly defined his math/formula/methodology in an earlier post.
Which is easily used to understand:
IMO.
Del-boy has to disagree a bit here Bes.
eHunter clearly defined his math/formula/methodology in an earlier post.
Which is easily used to understand:
IMO.
Yes, the basic formulas are straightforward.
It was the jump to the (1/(0.0104 + 0.0104)) that I thought might have been shown with greater clarity had it been done in steps if the purpose was to educate.
Just my thoughts......
jumper
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- 3 Hr 2 Min from Winged Horses
Agreed.
(You and I know that 2 like sized caps in series simply half the capacitance of 1, but I am not sure that the OP understands or knows this tidbit.) Yes the OP does know this. And all the OP realy wanted was a interpretation of the name plate. But thank you for the rest of the info.
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