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M R SrinivasParticipant
Hy Rudy,
It is quite clear that the presence of harmonic will increase the kWh consumption in the network.
The excess energy consumption is due to the following:
a) Losses in the conductors/switchgears due to Skin effect.
b) Losses in transformers / reactors (Iron core) due to increased:
– Magnetostriction (Sound loss – you can hear more humming noise when harmonic is more).
– Core loss.
c) Higher energy consumption in Rotating machines such as Induction motors, Generators due to Negative torque induced in the rotor winding when Negative sequence harmonic are present.
Other stray losses..
The problem is in quantifying or making the losses tangible. To do that it is important to have detailed analysis of each of the equipment in the network, which may be very tedious job.
In most of the cases, even if we quantify the losses, and if we install any harmonic filtering solution such as passive or active filters, the loss saved due to reduction of harmonic and internal losses in the filters may be almost equal.
Best regards,
M R SrinivasParticipantThe kVA of AHF is as you rightly pointed out = Losses + VxI.
But, the point is, what ever the harmonic current injected by AHF is used to cancel out the harmonic current from Nonlinear loads (VFDs, DC Drives, Furnace, UPS, Etc). Hence as seen from system side, the net current will be the vector difference of Load harmonics and Active filter harmonic current.
It is like Capacitor connected to motor.
The capacitor will draw leading current & the motor will draw lagging current. The Capacitor current & motor inductive current will cancel out vectorially, and as seen from the source side the effective current will reduce, and hence the kVA will be less.
Active Filter topology is similar to above.
M R SrinivasParticipantYes, have received two documents, its quit exhaustive, will go through and reply shortly.
M R SrinivasParticipantYes, please send data available with you, it will help us to design suitable solution.
M R SrinivasParticipant@guest said:
hello jim…im an electrical eng student…
i’m studyingthe cause of the overheating of equipment at a factory in the philippines.
Do we just divide the total current capacity of the LVSG by 2 to determine the model of the AFH to be installed… can u explain why.Current THD = Phase A = 972.5 x 26.9% = 261.60 Amperes
Phase B = 1051.3 x 25.1% = 263.87 Amperes
Phase C = 1001.2 x 26.2% = 262.31 AmperesMinimum Required AHF Capacity = Max. Current THD = 264 Amperes
Recommended AHF Capacity = 300 AmperesRecommended Total AHF Capacity for LVSG1A = 600 Amperes
Sir can you tell me why the recommended total capacity is 600 A…
Can you give me a good reference how active harmonic filters work… I cant understand how AHF produce the opposite needed current… where does the current came from. From other source? Is it better than a passive filter?
I need help from people who are knowledgeable in this topic.. help me. Thanks
I have more data… just tell me if the above is insufficient.
Hy Francis,
This is M R Srinivas, am replying on behalf of Jim Johnson (as we work in same organization).
First of all, the harmonic current in each phase is below 300Amps, hence 300Amps AHF will be okay. As 300A, AHF can generate 300A of harmonic current in each phase.
However, I understand that the LVSG is divided into two, does it mean you have two LVSG, and in each LVSG the harmonic current is about 260Amps/phase ? please clarify.
Yes, the busbar/cables/circuit breakers will over heat due to skin effect. Rotating machines such as Induction motors & Alternators will consume more power or fuel for a given load due to negative sequence harmonics.
The passive filter if designed properly will work, but there are many limitation of passive filters.
Please share us your email ID, will email few PPT’s that explains the effects of harmonics.
Best regards,
M R SrinivasParticipant@guest said:
Hallo jimwe are connected with maintenance of electrical distribution system in india. As u know our std frequency is 50 Hz. systen rated voltage by sypply agency is 11 KV . we installed 250 KVA 11/.433 KV transformer at our site. our Max demand is approx 210 KVA. and type of loads are lighting Mechanical laundry, traing workshops with lathe etc. We are facing problem of low pf. while checking the parameters LT voltage is 460 volts . An old power factor corrector 115 KVAR is in system but not working. How can we increase our Pf to unity or 0.99 lag. are harmonic filters also essential?
Hy Smita,
The Power Factor at the 11kV Grid meter is an ratio of kWH to kVAr….i.e. the PF what is indicated in the electricity bill from Utility department is kWH/kVAH.
So, to improve the power factor close to 0.99, we need to maintain the ratio of kWH to kVAH almost equal, this is possible only by using Automatic Switched Capacitors using microprocessor based PF Regulator.
For a Max Demand of 210kVA, you need about 100kVAr, APFC panel and 1no.5kVAr capacitor unit. The 5kVAr capacitor unit should be connected at the secondary side of transformer permanently to provide reactive power for Transformer magnetizing circuit. But, make sure the capacitor voltage is 480V.
Filter are not necessary.
Hope above answers your question.
M R Srinivas
M R SrinivasParticipantHy,
The AHF (Active Harmonic Filter) will have a loss of approx. 40 to 50Watts per Amps.
Fot 50A, AHF the loss will be approx. 2kW to 2.5kW.
Yes, by adding AHF the kWH consumption will increase in the system, but the main reason for adding AHF if to improve the quality of power. The AHF is always promoted as Power Quality improving equipment and not as energy saving device.
Having said that, there are lot more benefits of filtering harmonic. In many cases where Induction motors are used in the network having higher harmonic levels, the AHF will reduce the energy consumption in motors due to reduced negative sequence harmonic.
Hope above answers your query.
Best regards,

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