current in 3 phase cap's
current in 3 phase cap's
(OP)
i need some help calculating the current in a 3 phase cap bank
the circuit is 230 kv with a three phase reactor in series with a 3 phase cap. the reactor is on the source side of the cap
reactor size is 2700 kva 1500 amp 3.2 mh
cap size ia 384 mvar
thank you
the circuit is 230 kv with a three phase reactor in series with a 3 phase cap. the reactor is on the source side of the cap
reactor size is 2700 kva 1500 amp 3.2 mh
cap size ia 384 mvar
thank you






RE: current in 3 phase cap's
But your current will be slightly different due to the series reactors. If you need a precise value, you will need to compute the capacitive reactance (from voltage and current above) and then create an equivalent circuit and solve that.
RE: current in 3 phase cap's
RE: current in 3 phase cap's
very much
RE: current in 3 phase cap's
http://www.nepsi.com/
RE: current in 3 phase cap's
RE: current in 3 phase cap's
Your calculation of current is correct if the voltage at the capacitor terminals is exactly equal to the nameplate voltage rating of the capacitors. The cap bank is a constant impedance load. As the voltage changes, so does the current (and the kVARs vary as the square of the voltage.)
If rated voltage is applied to the input **series** reactor, there will be voltage across the reactor that has to be accounted for if an exact solution is desired.
RE: current in 3 phase cap's
Be patient, someone will probably do the calculations for you. I haven't done these calculations for so many years that I'm afraid I may make some silly mistake.
If this is an assembly, it's worth a call to the manufacturer to ask for their recomendations.
yours
RE: current in 3 phase cap's
RE: current in 3 phase cap's
RE: current in 3 phase cap's
current without reactor 964 amps
In comparison to other effects such as voltage change, harmonics and capacitor tolerance, the reactor does not affect current much.
However, do be aware to include the reactor for calculations on a voltage differential scheme. We have a 115 kV bank that can be either 45, 67 or 112 MVAR with a 5 mH reactor. When it is switched from one size to another the drop in current flow through the reactor will cause a lower the voltage measured across the midpoint of the capacitor bank. Going from memory, it seems like the voltage change is about 1/4th that of a blown fuse. Not enough to cause a misoperation by itself, but it does eat into the safety factor.
RE: current in 3 phase cap's
it has help a bunch.
there is another question that i have.
we have a 230 kv abb pmi typer circuit breaker.
the drawings show what appears to be an additional
bushing bolted alongside of the breaker bushing.
any information on what it really is?
RE: current in 3 phase cap's
I think u meant without reactor 972 Amps and 964 otherwise.
I think dropped voltage across reactor lowers the Mvar capacity of the bank.
THX
Patrick7: In absence of any other information i would think that could be a Surge Arrester. Please check the manual, that should surely have respective data
RE: current in 3 phase cap's
973A with reactor
964A without reactor.
It looks like the capacitor current and voltage both rise just under 1% due to the reactor. And, the others are right in that the reactor does create a trap at about the 10.2nd harmonic.
RE: current in 3 phase cap's
Please explain.
Thanks
RE: current in 3 phase cap's
The voltage seen by the capacitor is the phasor sum of the source voltage and the voltage drops across the circuit resistance and the circuit inductance. Change the inductance and the voltage across the capacitor will change.
RE: current in 3 phase cap's
RE: current in 3 phase cap's
thank you
RE: current in 3 phase cap's
The current is not infinite, but is limited by the resisance of the inductor and the impedance of the source.
As the reactor resistance is very low, the current will be very high to the point that it is limited by the impedance of the source. In many instances, you may be able to assume the reactor impedance is zero with no serious errors in calculating the current limiting by the source impedance.
A small inductor in an electronic circuit with a fairly high resistance will have a very finite current and the resistance must be included in the calculations.
yours
RE: current in 3 phase cap's
The capacitive reactance is a negative number, call it -jX.
The inductive reactance of a tuning or detuning reactor is a positive number, call it jY, with an impedance (absolute value) lower than -jX.
The capacitor and reactor are in series so they add together, -jX + jY = -jZ. This new -jZ is a smaller impedance than the capacitor impendance alone so the series L-C circuit will draw more current than the C circuit.
More current through the same -jX capacitor impedance means there must be more voltage across the capacitor.
I hope this makes sense.
RE: current in 3 phase cap's
Thanks
RE: current in 3 phase cap's
RE: current in 3 phase cap's
The reactor impedance is j*2*pi*60*3.2mH = j1.32 ohms
The series combination is -j138 + j1.32 = -j136.5 ohms
The new current is then 230kV/sqrt(3)/-j136.5 = 972 amps
RE: current in 3 phase cap's
XC=-j137.8·(60/f)
XL=j1.32·(f/60)
At f/60=10.1951
XC=-j13.46
XL=j13.46
series combination is 0 ohms
RE: current in 3 phase cap's
the numbers i am getting are as follows.
cap current w/o reactor = 384,000,000/(230,000*sqrt3)
which is 963.92amps
then the cap imp is
cap imp. = -j(230,000)(230,000)/384,000,000
which is -j137.76 ohms
then the reactor imp is
reac. imp = j 2*3.14159*60*3.2e-3 = 1.206 ohms
then the current through the series combination is
cap imp + reac. imp = -j137.76+j1.206
which is -j136.55 ohms
so the current would be
230,000/(1.73)(-j136.55) = 972.4 amps
then setting the cap and reactor imped equal to each other and solving for the freq. yields a resonant freq. of 641.26
or the 10.687 harmonic.
correct?
thank you all sooooo much
RE: current in 3 phase cap's
RE: current in 3 phase cap's
we have a 230 kv abb pmi typer circuit breaker.
the drawings show what appears to be an additional
bushing bolted alongside of the breaker bushing.
any information on what it really is?"
This is a capacitor. It helps the arc suppressing by by-passing the high frequency. If you have these connected on both breaker poles (assuming a Y-pole breaker), you will have some voltage flowing over open CB. Remember to open disconnectors before grounding.
RE: current in 3 phase cap's
First off here is a list of the current sizes that we have as min. diameter.
bus size min size of acsr
2 266.8
2.5 266.8
3 266.8
3.5 397.5
4 795
5 1431
6 1590
There are several questions that come up. Your professional opinions and career experiences will be of great help.
First, Do we have to use ACSR? Or will AAC work?
What about the newer conductors available ACCC?
Second, Are the above min. sizes ok? and what is the max.
size?
Third, Is the dampening characteristic of the conductor
within the bus a function of the size ie the cross
sectional area, or weight of the conductor or both?
Fourth, How long is the max bus length that does not
require dampening?
Thank you for all your input and help.
RE: current in 3 phase cap's
thank you
RE: current in 3 phase cap's
RE: current in 3 phase cap's
Any kowledge of how to calculate resistors applied in the LCR filter circuit on a damping network and what purpose it would serve.
RE: current in 3 phase cap's
RE: current in 3 phase cap's
RE: current in 3 phase cap's
RE: current in 3 phase cap's