Category Archives: Case Study

Active Harmonic Filter- Mitigation Of Harmonics in a Poor Power Quality Environment-Case Study

Doctor_Character-04-1 Hello Everybody today’s article is a case study from our beloved Advanced Power Quality Solutions team. They have very neatly narrated how they helped a Steel Rolling mill with a unique power quality problem to extract more business benefit by cutting down their power quality problems. Interesting read don’t miss it.

InPhase has come across many customers dealing with various Power Quality problems. Our strength lies in providing customized and unique solutions, keeping in mind the problems that the customer confronts. In this article we share our experience with one of our customer, their problems, losses, and solutions. This customer is one of the largest steel manufacturers in India. Their annual production is in Billions of Rupees, but their production began to fall and penalties from Electricity Board increased because of presence of harmonics in their plant. So they decided to install Active Harmonic Filter to mitigate harmonics in their plant.  Initially the company had gone with a well known brand of Active Harmonic Filter but the filters had miserably failed owing to the unique situation of the customer. Luckily the customer came to know about InPhase and  Our Active Filter  through a channel partner, and approached us. InPhase conducted a Power Quality Analysis and suggested a cost effective solution accordingly (which cost lesser than the initial solution that failed) despite the challenging problem. The problem faced by the customer is outlined here,

  • Harmonic currents were high, the THDi was between 17-20% which is higher than the IEEE 519-2014 norms.
  • High Voltage Notches were also present in the plant.
  • Presence of even order harmonics which is normally zero in other plants.
  • Hot rolling mill loads were highly fluctuating and load patterns were abnormal.
  • The voltage varied up to 470V which is an abnormal behaviour.

Here, the main challenge faced while giving solution was to suppress current harmonics or THDi to less than 8% in an environment with high voltage spikes and indefinitely fluctuating plant load condition.

SOLUTION PROVIDED BY INPHASE:  InPhase proposed 2 x 450 Amps, 415V Active Harmonic Filter (Model:IPC150-AHF-450-V415) with CAN-bus communication that acts as a single 900A system. Specially designed RC tank circuits were incorporated  to handle notches and rigorous algorithm for high fluctuating loads. This was the  most cost effective, as well as the technically correct method to handle the situation. The 2 number of AHFs were connected in BUS A & BUS B, as the load distributes in those buses. The whole system has been pictorially described in the diagram below.


The major loads used by the customer are electric pre-heating furnace and rolling mill that generates the maximum harmonic current leading to increased losses in transformer, overheating of cables and thus polluting the electric network. The LT loads distributed among the Bus A & B are connected by an ACB Bus Coupler (Normally Closed). AHF calculates harmonic current, reactive current and unbalance current present in the entire plant from the current signal received from the CTs of respective transformers through the summation CT. Based on the on the dominance of power quality issue (harmonic, power factor or unbalance current) at any instant the AHF system injects the respective compensation current. InPhase AHF can achieve high level of modularity of up to 32 Equipments in parallel. CAN bus communication is used to communicate between two Active Harmonic Filters and operate in parallel to inject up 900A of compensation current.


The graph indicates the harmonic currents of various orders (3rd to 13th) before and after installation of Active Harmonic Filter. The successful installation of 2 x 450A Active Harmonic Filter has reduced the THDi from 17% to 4-5%, well below than the limits mentioned in IEEE 514-2014. This solution has helped the customer not only to cut down penalties but also to reduce failure of sensitive equipments which are vulnerable to harmonics. Also, various production losses were averted. Overall, InPhase was able to solve a problem of harmonics in very poor power quality environment. This was another feather in InPhase‘s cap. We would be extremely happy to help customers who face such outrageous Power Quality problems because at InPhase we are happy to tackle power quality challenges for our customers.

Get in touch today.

Meet you again with a interesting article, until then bye from Dr.InPhase

Thank you!


Thanks for reading…if you have questions don’t forget to ask me. You could write to me to or call +919632421402

IInphaseLogo(300dpi) (1)nPhase Power is a Power Electronic Product company manufacturing products for Power Quality and Power Conversion. InPhase is manufacturer of Active Filter, Active Harmonic Filter, Solar Inverter. InPhase majors in power system design for power quality and conversion. Driven by a management that has a combined experience of over 60 years in power system and power electronics InPhase nurtures innovation and passion in this field.

InPhase Power Active Harmonic Filter and Load Unbalance Compensation – A Case Study

Doctor_Character-04-1Well Good day readers, Today I bring to you a very interesting case study of how InPhase helped one of our customers to achieve Unbalance compensation. I was very impressed with our team on the effort that they have given on this as they made the customers extremely delighted. I hope you all enjoy reading it as well.

The brief story

InPhase Active Harmonic Filters are an all-in-one package, capable of compensating for reactive currents, harmonic currents and unbalance currents, we claim. However, in most sites InPhase was tasked to compensate for reactive and harmonic currents alone. Then, came along a company. We will call it ‘ABC’. ABC approached us saying they had a problem of current unbalance, and that they were being threatened penalisation and disconnection of the supply by the Utility, for the same.

ABC had approached various other well-known names in the PQ industry, but none were prepared to propose a solution. And so, InPhase conducted a PQ Analysis at their site. The study results were appalling. Currents in the 3 phases read: 175A, 352A and 174A respectively.

InPhase proposed to install our beloved Active Harmonic Filter to mitigate this problem. ABC said “Go ahead, do anything. Just fix this problem for us.” And so, the InPhase Active Harmonic Filter was installed at the site.

Everybody, including us, held their breaths. “Will it work?” was the question in everyone’s minds. Then came the time, to find the answer. Annnnd Lo! The phase currents read: 52A, 50A and 51A.

Everyone’s apprehension about the InPhase Active Harmonic Filter had turned into awe. The Managing Director of ABC going to the extent of saying “Dr. InPhase has come down to save us like Lord Vishnu (Hindu god; Preserver of everything and everyone in the Universe).” Not only did the Active Harmonic Filter go on to mitigate the unbalance, it was also compensating for reactive and harmonic currents, all at the same time.

If ever there was a happy ending, this was it. 🙂

The technical explanation

Moving on to the technical side of the problem. The cause for current unbalance of such magnitude was the nature of load being 2-phase. The currents before compensation in R, Y and B phases were 175A, 352A and 174A respectively. You might notice how the current in Y-phase was double that of R and B phases. Excellent observation, that! Now, here is the explanation:


The above diagram shows a delta-star step-down transformer. The outer windings represent the primary of the transformer. The windings on the inner side represent the secondary. Notice that the load is connected to the secondary across two phases only i.e. R and B.

The load forces the current direction in the secondary windings as indicated by Ir and Ib. Since the phase r and b are connected in series, Ir= Ib.

Ir and Ib are secondary currents induced from primary currents IRY and IRB. Subsequently,
IRY = IRB = I. Note also, how the direction of secondary currents differ from their corresponding primary currents.

From Kirchoff’s current law, incoming current at node R must be I+I = 2I.

The outgoing currents from node Y and B are ‘I’ each. What is observed here is that one phase carries twice the amount of current than the other two individual phases. This explains the observed readings of 175A, 352A and 174A.

It is a known fact that current has three components viz. positive sequence, negative sequence and zero sequence. Since our incoming current is through a 3-ph 3-wire system, we can ignore the zero sequence component.

Also, let us recall that both positive and negative sequence components are “balanced”, individually. It is only when they combine, unbalance occurs in the load current.  Just to be on the same page, let us understand what a “balanced current” means. In a 3-ph system, is the current flowing in each phase is equal, the system is said to be balanced in simple terms.

The magnitude of unbalance is calculated in percentage.


The calculation for this case would go as follows:

IR=352A ; IY=175A ; IB=174A

The average current,


Maximum deviation from Iavg = 352-233.67 = 118.33A



As a consequence of NEMA Standard MG-1, acceptable limit on current unbalance is 10%. Clearly, the unbalance in this industry was far from acceptable.

Now that the cause and magnitude of the problem were known, the next step was to mitigate it. And, to meet this objective, InPhase Active Harmonic Filter was installed.

It should be noted that the initial current readings IR=352A, IY=175A, IB=174A are a combination of reactive currents, harmonic currents and unbalance currents. And because we are concentrating exclusively on unbalance, let us take an arbitrary example to understand the same.


In the above example, the incoming currents are 100A, 100A and 40A. The underlying assumption here is that these currents are purely unbalance currents and they have no reactive or harmonic component.

InPhase Active Harmonic Filter takes feedback from 3-ph CTs. This allows the Active Harmonic Filter to measure current flowing in each line. Subsequently, this input is processed by the main controller in the equipment. The Active Harmonic Filter being an AC-DC-AC converter, can absorb and pump current from the line to the load such that the incoming current from the metering point is balanced.

The controller is capable of calculating the positive sequence component and negative sequence component from this input. Once this is calculated, it is a simple case of pumping the counteractive current to the negative sequence component, so that all that remains is the positive sequence. Recollect that positive sequence current is balanced and thus consequently, the line current is also balanced.


The above diagram is a representation of the aforementioned compensation process. Note how the line currents are balanced (80A each) whereas the load currents (100A, 100A and 40A) remain unchanged.

This way, the customer is happy that his electrical system is healthy, and the Utility is happy that the consumer’s loads are balanced and the grid is stable. Lastly, Dr. InPhase is also happy that he made it all possible. 🙂

It is time now, for you to experience the InPhase Active Harmonic Filter. Get in touch with us, we’ll help you to get your Power Quality problems resolved.

Thank you!



Thanks for reading…if you have questions don’t forget to ask me. You could write to me to or call +919632421402

IInphaseLogo(300dpi) (1)nPhase Power is a Power Electronic Product company manufacturing products for Power Quality and Power Conversion. InPhase is manufacturer of Active Filter, Active Harmonic Filter, Solar Inverter. InPhase majors in power system design for power quality and conversion. Driven by a management that has a combined experience of over 60 years in power system and power electronics InPhase nurtures innovation and passion in this field.