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hello jim,
i am very impressed with the knowledge that you shared with us in your blog.i hav never seen such a pool of information gathered at one place on power quality solution.your knowledge will prove to be highly benificial for my project i.e. power quality improvement at distribution station .could u plz mail me research paper based on it.my email id is: chavar05@gmail.com
thank you!didar singh said:
will kvar effects generation & transmission
hi I need some electrical project to do can you help me
Hi Jim,
I love the way you explain things im learning alot just by reading your blog. I have a question on Power quality optimization as a tool to Energy efficiency perhaps you can help. I come from a non electrical engineering background but have an electrical hardware shop and some familiarity with electrical engineering, i’m considering changing my entire business to providing Energy efficiency technologies in Kenya. LEDs, CFLs, Geyser control systems, light automation systems, Solar, electricity monitoring are easy enough to understand…what i’m having a problem with is 3 specific Power quality improvement technologies; whether they work as said, what are their disadvantages and what else i should know about them. Most of the Engineers ive consulted seem to have limited experience with these technologies perhaps you may have encountered them. They are…Voltage Optimization (PowerPerfector UK), Capacitor type eg. KVAR US, Wave propelling chip ie. (Sunglobalsaver) The manufacturers talk about several benefits including Actual KVA reduction 15%, Power factor improvement, Harmonics reduction, Surge protection, less equipment wear & tear. My question is….Do they work as said? are there any disadvantages to using them that the manufacturer doesnt state? What else should i know about them? would you recommend them?
Hi, Owen,
It is pretty amazing to watch ‘technologies’ emerge when the cost of electricity increases or something is done in the name of reduced green house gasses or….
The three companies you have referenced deal with passive components (inductors and/or PF capacitors). They assembly them in unique ways and are touted as ‘new’, ‘energy saving’, ‘harmonic filter’, and ‘transient protector’, to name a few points.
As near as I can tell the device that employs a series inductor and star-delta transformers provides load balancing and transient protection primarily. Since it is an inductor, it will cause lagging PF to get worse – that is draw more phase shifted current for worse PF. The amount of transient protection depends upon the actual inductive impedance it contains. [This will cause the I2R losses to increase as well. See below discussion.]
Benefits would be balanced voltage and current draw per phase for cooler AC motor operation. Is there a ‘big’ problem here? Might this offset the phase shift caused by the addition of the inductor? Might this cover the added I2R losses the inductors/transformers cause? Maybe – maybe not.
The inductor does act as a harmonic filter. It helps to decrease the harmonic current drawn from the utility, but not at the nonlinear device. The amount of the benfit depends upon the impedance rating of the inductor. Low impedance has little effect while larger impedances (3-7.5%) have good effects. No idea what is designed into this product.
The other two products are PF capacitors in a box. They either correct for poor displacement PF (lagging current) of add leading current to cause leading PF (when no lagging is required). There is no KW savings for the user. The KVA is reduced and the KVAR is normally reduced (if lagging loads are present). Neither action provides any benefit to the users utility bill. If a device could generate KW and replace the utility KW supply, then there would be a user benefit – think solar panels or wind turbines.
PF capacitors (alone) do not filter harmonic current. They will cause resonance if high levels of harmonic current are present. PF caps won’t help but could harm installations when harmonic producing loads are present (say above 15% of total loading). [Here’s an interesting thought: More and more of the loads in residential homes are energy saving devices = electronic loads = harmonic producing loads. What happens as more and more electronics are installed in homes and these capacitors are in place?]
The discussion regarding energy savings typically hinges on I2R (I squared R) losses. This is a real loss within the electrical network and does waste energy. BUT at the user level it is usually very small (under 2% potetnial). However to the utility the sum of all the savings can be large. This is true because the energy to provide the I2R losses at the customer delivery point must be generated at the generation facility and ‘pushed’ through the whole electrical network (HV, MV and LV + transformers, etc). This can be 3-4 times the actual I2R losses for the sum of the users savings at a PCC with the utility.
Today there is no economic benefit for users to limit I2R losses. The utility charges for the KW delivered and that makes up more than 98% of the KW needed for operating the facility. If the utilities got serious and offered an incentive to save the 2% I2R losses, then there would be cash back for users, albeit small.
I made a point above that more of the loads in homes are based upon electronics because they save real energy – KW. This savings far exceeds any benefits PF caps will provide for I2R losses. Utilities sometimes offer rebates for installing energy savings devices because they can reduce the quantity of future generations facilities. Rebates for heat pumps, high efficiency furnaces, the new washing machines (VFD driven), to name a few exist. Why? Because the really save energy.
Just to make another point, when utility bill savings are proclaimed, it is usually based upon the utility bill. How much of the utility bill is affected by the weather – not what the user does or doesn’t do? Is the weather for any period of this year equal to same period as last year (the usual basis of comparison)? Not very often. The variables also are was the heat or air conditioning turned on or off – for the same periods of time as last year? My point is that such compariosns are hard to do and typically are subject to many variables – which by the way the equipment suppliers from above use to their advantage when charges increase.
hi, we have a 2500kVA transformer 13.8kV/480 V system – supplying harmonic loads -2 x 300 kW-6 pulse variable frequency drive and motor at 480 Volts. The system also has one 30 kVA UPS. There is standby 1 x 1250 kVA generator also.
We propose to install harmonic filter however there is no isolator switch on main bus to connect, since UPS tripping is observed during operation of motors.
How to determine the size of active harmonic filter?
Please advice
Hi, govindraraj,
The absolute most accurate method is to perform a power analysis and create a computer model. The power analysis defines the entire electrical sysem from the utility to the loads. It is also very expensive and takes an fairly long time to complete.
Schneider Electric have developed an active harmonic filter selection tool that uses some approximations to short cut the above time and costs and provide an accurate solution. The tool includes guidelines and ‘best practices’ discussions to help you install the optimum equipment for best results in harmonic current elimination.
Using that tool and the information provided, yields the following provided the VFD and UPS have 3 to 5% impedance inductoance installed either on the mains (3-phase line reactor) or DC bus chokes. The TDD is calculated at 238 amps of rms harmonic current = 30.87% TDD. So, you need an active harmonic filter that is rated 1.2 x 238 = 286 amps.
Quick solution no cost invovled. But you need to be sure the inductors are present or a 300 amp active filter will not provide the beenfits expected.
Contact your local Schneider Electric representative for local assistance.
Rgerads and good luck,
Jim
Excellent!
Mr. Jim
My question is still unanswered… please guide me..awaiting your reply…..
Hi, Mahesh,
Sorry for the tardy reply.
The selection of a detuning frequency is 1) defined by the objective and 2) customary and usual practices within a country or region of geography or 3) philosophy of the designer.
The 189 Hz tuning represents a detuning to protect the PF capacitors used for power factor correction from 5th harmonic currents (for a 50 Hz electrical system). This tuning actually permits small amounts of 5th harmonic current to flow in the capacitors. The 5th harmonic frequency is at 250 Hz.
The detuning frequnecy defines the amount of 5th harmonic (in this case) current that will be permitted to enter the capacitors. Tuning at the 5th harmonic will result in resonance. So, tuning below the 5th harmonic is done to limit the 5th harmonic current flow and prevent resonance.
189 Hz tuning is at the 3.78th harmonic. This indicates that the resonant point for this PF cap bank is at this frequency. Since this frequency is not suppose to be present it is a safe frequency to prevent excessive 5th harmonic current flow into the capacitors and prevent resonance from occurring. This tuning permits the capacitors to provide power factor correction at the banks rating and survive in a 5th harmonic rich environment
By tuning closer to the 5th harmonic, more 5th harmonic current will flow into the capacitors and provide more 5th harmonic filtering. The capacitors must be increased in current capacity to handle the total higher current as 5th harmonic current flows into the capacitors.
The capacitor bank is considered a 5th harmonic filter when the tuning frequency is above the 4.7th harmonic order. At 4.8, about 80% of the 5th harmonic current is removed from the source system. At 4.9, about 90% of the 5th harmonic current is removed from the source system.
Simulations must be made to review the resonant frequencies that may occur due to adding capacitance into the electrical system. Source characteristics, transformer and cabling impedances, the type of loads installed – both linear and nonlinear – must be included in the simulation. Omission of any data could result in an undefined resonance frequency.
Our engineers typically use SKM Tools to model the system. I assume Matlab can do the job as well.
Something to keep in mind, as capacitors age the farad rating changes. This results in the frequency rating of the detuned circuit increasing. Thus a detuned capacity bank for some frequency below the 5th harmonic will actually over time ‘walk’ to the 5th harmonic frequency and resonate. So, regular maintenace must be performed to insure the capacitors are healthy and are not in danger of causing resonance.
Also, if any of the simulation variables (electrical system, transformers and cable impedance, loads, etc) change the simulation must be reviewed. It is possible to add one load and cause resonance.
Finally, different companies that provide detuned capacitor systems tune to different frequencies. Some of this is based upon their capacitor designs and some is based upon local customs or company philosophy. It is typical to see detuing for PF correction to levels between 3.8 and 4.3. 5th harmonic filters are typically tuned to 4.8 to 4.9. But any tuning can be achieved based upon the needs.
Obviously, tuning to perform 5th harmonic cancellation for the source system costs more than tuning at 3.8th order. The capacitors and inductors must be rated for the higher currents permitted at the higher tuning points.
Hope this helps,
Regards, Jim
Thank you a lot for sharing this with all people you actually recognise what you’re speaking approximately! Bookmarked. Kindly also talk over with my website =). We may have a hyperlink alternate agreement among us
Hallo jim
we 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?
i saw more maturity of the persons giving comments.
Imran Jalal
@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
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.
@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,
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