# Re: Harmonic filter for better power quality

Home Electrical Engineering Forum General Discussion Harmonic filter for better power quality Re: Harmonic filter for better power quality

#11633
Alen Matanovic
Participant

Thank You for brief help..

In meanwhile I've found the way to calculate needed values for capacitor and inductor (needed by programe) and I've got some new “printsreens” to share:

impendance caracteristics @ bus – 3

and reduction of THDi to some 7% at PCC:

Still, I want to ask something more,, what does this voltage presents, and how to determin it's value,, and I mean on the Voltage that is required by Programme as You can see at my first post in fllter data picture? I've set aprox. voltage level of 430V (because main is 400V) just to perform calculation,, and it seemed to work, but I'm looking to find formula for it's precise calculation..

Also, I'm able to change my loads specifications because they are not strictly set,, so if I change from kVA@pf – to – kW and kVAr,, nothing changes, from my perspective of problem,, because if I just “add” those kVArs I'm not sure if I'm geting proper value for my capacitor bank.. Lets say, for example, if my linear load is set as: 100 kW and 20 kVAr, and orher three, ASD 40 kW and 5 kVAr, Fluo. lighting 25 kW and 5 kVAr,, and PC center 30 kW and 5 kVAr,, simple problem is how should I properly add those to gain value for reactive power request by my loads.. I asume that linear load would have “ohmic” character, ASD drive “inductive”,, and Fluo and PCs “capacitive” character,, so simple adding (20+5+5+5=35 kVAr) is definatelly questionable,, more proper way would be “phazor” addition.. but interesting fact is that if I set my filters capacitor bank to 0.035 MVAr it provides better THDi atteunation than it's if I set it to phazor value 20,616 kVAr,, I supose that programe is not able to differ those differences.. Once knowing this “voltage” and “capacitance” it's simple to calculate “inductance” using Thompsons relation..

The only information provided by programmes “manual” and “help” is:

Filter Data:

•  Resistor:  Resistance of resistor of the filter in ohms.

•  Inductor: Real and imaginary impedances (ohmic resistance and inductive reactance) at system frequency in ohms.

•  Capacitor Bank (1 and 2):  The reactive power of capacitors for the system frequency in MVARs at the voltage level specified in kilovolts

… which doesn't helps me very much..

Here are also the links for my calculation of those filters, as well as “reverse” calculation (that's the way I found to calculate my filters) of filters that are provided in example in the users guide of this book (I'm going to apologize again, now for two reasons, first is those materials are not in English, since I'm from adriatic region, but You can see/look only at calculations…. other reason for apologize is “messy” pdfs because my scanner just got broken, so I was using my camera)..

primjer iz knjige” would be “example from the book” and “računanje filtera” would be my filter calculation..

example form the book (please notice that “2.filter” and “3.filter” are notch 5th and 7th filters respectively….. how come is Xc value different for both filters and it's close to 20 MVAr set by the load?……. there You can also see those voltages like 120 kV that are set “in decimal”):