De-tuned Capacitor Bank – Economical Way to Mitigate Harmonics

Published On: Sep 19, 2017


With change in type of load used by electricity consumers in last one decade, generation of current harmonics has increased significantly. These current harmonics generated by consumers, not only have a negative impact on the consumers own electrical system but also impacts electricity distribution companies adversely. Higher levels of current harmonics in the system results in distorted voltage waveform that results in overall poor distribution grid power quality.

pManifold, National Support Network (NSN) partner of APQI recently interviewed Mr.Shaikh Shamsher Ali, an industry expert from Spike Power Technology, India to understand his uptake on ‘De-tuned Capacitor Bank – Economical Way to Mitigate Harmonics’. (The views here are personal, and not to be associated with any company in any forms.)

According to you, why good power quality is important for industries? What are the major issues of PQ affecting industries?
In today’s modern highly mechanised world power plays a very major role. Therefore, the quality of power is expected to be the best if one expects the best output from any machine or system. Modern machine and control systems are having so much electronics and semiconductors that make the current to flow in very uneven manner and the cumulative impact is distortion to the very sine wave itself. One of the major by-products of such distortion is harmonics. Depending upon the type of harmonics it can cause more current to flow through the circuit, generate more heat, cause component failure or burning of cables and lower power factor. Negative harmonics can also cause mechanical problem like breaking actions and increase in equipment vibration.

How significant is the effect of harmonics?
In today’s time harmonics has a very big significance in every machine and system. Impact of harmonics will depend upon whether it is odd or even harmonics and positive sequence or negative sequence harmonics. High % third harmonics will increase the neutral current which is equally dangerous for the maintenance team. Fifth harmonics is negative sequence harmonics which has additional mechanical impacts like breaking actions and increased equipment vibration level. Today every facility has light, AC, Battery charger, UPS and most likely VFD. These are common loads across all facilities and generate third, fifth and seventh harmonics. If these harmonics wave forms are superimposed (as shown in below diagram), on fundamental sine wave then the distortion of sine wave is so much that at 90 degree and 270 degree when the value is supposed to be the maximum, it comes down to zero or beyond in reality. It is like accelerating for 50Kms and applying full break and releasing on regular intervals like every 10 seconds. The vehicle will not move but jump on the road. That is what happens into the control circuit and machine when there are several harmonics current. Generated excessive heat causes components failure and burning of cables etc. Resonance is another by-products of harmonics and its effects will depend upon whether it is series resonance or parallel resonance.

What are the available harmonic mitigation techniques?
There can be many options to mitigate harmonics depending upon the root cause of the problem, severity of the impact and economic considerations. In general industry use reactor based passive de-tuned harmonic filter at the main distribution panel level in order to keep both the voltage and current harmonics within IEEE 519 level at the LT side. Reactor based tuned passive filter can be used to limit the harmonics at any specific machine level generating higher harmonics. These are the most cost effective options. If any facility has number of harmonics with higher % and needs to be mitigated then it is technically and commercially advisable to opt for active harmonics filter as one active harmonic filter can mitigate all the harmonics. Active and passive harmonics filter works in different principles. Specifically designed transformers can also be used to give overall protection against harmonics. There are other technologies available for applications like resistance welders and electric arc furnaces where harmonics mitigation and reactive power compensation requirements are different. Harmonics mitigation on HT side is usually done at the sub-station level with reactor based passive harmonics filter for HT applications.
How did the plant team select a technology that would be technically and economically feasible to mitigate harmonics?
Plant team had three options to overcome the harmonics problem and avoid harmonics penalty. Active filter was expensive and ruled out. Tuned passive filter was also expensive and needed more than one filter since number of prominent harmonics was more than one. De-tuned passive filter was the best option because we could use the existing APFC panel and converted the same by replacing higher voltage capacitors and adding suitably rated reactors. This was the most cost effective way to convert the existing capacitor panel into passive harmonics filter. Rating and steps configuration remained the same as before matching the load configuration and yet took very little down time (One day) to convert the system.
What were the key benefits achieved focusing on below points?
• Return on investment
• Payback
• Savings in O&M, reliability etc.

Converting any APFC system into passive harmonics filter is very cost effective and Return On Investment (ROI) is very attractive if the customer considers the expenditure as an investment. ROI and Payback (PB) will depend upon the number of hour operation per day as it will have direct impact on the savings. Our experience shows the PB ranging from few months to maximum one year in various industrial applications. In this particular case the PB was 4 months. Due to mitigation of harmonics there will be less stress on the system leading to less failure / fault leading to savings in corrective / repairing maintenance. There will also be positive impact on equipment life and performance leading to better reliability.
What do you think are the main barriers for industries to address PQ in more serious manner as compared to today’s attitude towards PQ challenges those are well known?
Harmonics is one topic that has least significance in under graduation course. Therefore, the engineers has very little knowledge and experience about harmonics. Industry people don’t understand the adverse impacts of harmonics as expertise are not available who can do systematic analysis and diagnosis of power quality. Fly-by-night operators create myths to make quick buck but in that process lot of bad experiences and bitterness is being created in the end user’s mind. Lack of any Indian standards on harmonics mitigation make the application more complicated. Creating awareness about the harmonics, its negative impacts and viable techno—commercial solutions is the need of the hour.
What message/recommendation would you to like to give to fellow industry professionals to improve PQ environment?
People engaged in power quality business should update their awareness and make it up to date. People need to come out of the mind set of putting the capacitors and reactors into a panel to mitigate harmonics. It is much more than that. It is a systematic, analytical approach that needs to be taken step by step when one needs to offer a workable and reliable harmonics mitigation solution of any operational facilities. Calibrated and most appropriate 3 phase harmonic analyser / power analyser should only be used by trained technicians / engineers to take the readings. Facilities power distribution system needs to be studied well and the operations should be well understood before doing any analysis / diagnosis for the root cause. If need be then repeat readings should also be taken to ascertain if there is any intermittent occurrence of any actions that generate harmonics. Harmonics mitigation solution must be tailor made and techno-commercially viable.
What are your experiences and views about APQI and its contribution to the development of PQ eco system in India?
APQI in partnership with FICCI is doing a good job organising seminars and knowledge sharing sessions on PQ on regular intervals in different cities across the country for last several years. It is a good initiative and needs to be extended to educational institutes along with industries. Persons at the helm of the operations are competent to drive it forward and I think Govt. support can make more visible impact towards harmonics mitigation and power quality improvement.

Sir, tell us about yourself.

Ex-Indian Naval Artificer, did my Marine Electrical Engineering from Indian Naval Academy and BEE certified Energy Manager and Energy Auditor. Worked in Marine, Oil & Gas and Utilities in India, UK and Middle East for 33 years in areas like O & M, Manufacturing, Projects Management and Facilities Management besides Energy Conservation. Regularly Groom professionals in team building and soft skills. Presently pursuing PhD in Energy Conservation from University of Petroleum and Energy Studies at Dehradun. Write articles and present technical papers in various industrial forums on energy conservation and power quality.

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