Author Archives: Suryanarayanan G

Dr InPhase Edu Series – An Exercise in Reactive Power Calculation

Doctor_Character-04-1Good day every body, Today on our Edu Series we will focus on some practical knowledge related to Reactive Power calculation.  Calculating your reactive power is critical as it can help make sure that your design is reliable and you get a reliable power factor output.

Consider an electrical network with the details below,

Demand = 2500kVA; Initial PF1 = 0.76; Desired PF2=0.97.

The reactive power required to achieve the desired PF (0.97), is calculated as below:

We know that

Where φ is the angle between voltage and current vectors.

From the above,

Now here arises the doubt. We say, the above method of calculation is flawed. There is a fundamental electrical engineering mistake. Before you go on any further, we would like you to think and comment in the comments section below if you find the flaw. Because once you scroll down, you are likely to lose your unique perspective on the above. Therefore, please comment and proceed for the answer below. This can help knowledge sharing with numerous angles / perceptions. Thanks in advance for that.


The mistake is in Point ②. We have considered the same kVA for ① where the pf is 0.76, and② where the pf is 0.97. When actually, it is Real Power or kW which remains constant. Load remains unchanged, which in other words translates into constant kW and NOT constant kVA.  The same is shown in the diagram below:

From the above diagram, we know now the ‘kvar’ required to improve the system from PF1 to PF2 (i.e, 0.76 to 0.97) is,

Applying Pythagoras theorem for the above diagram,


Which implies, [kvar1 = kW × tan φ1] and [kvar2 = kW × tan φ2]. Substituting these in equation ④,

In terms of power factors,

This is a generic formula to calculate the reactive power demand when the present power factor and the desired power factor are known. The same formula reduces to the following for desired power factor being Unity.

Where φ is the power factor angle.

We sincerely hope that this exercise helps you in calculating reactive power demand with more clarity.

Do you have a Challenging Power Factor Correction or Compensation issue, no matter how dynamic your load or reactive power is we can find the right solution for you. Get in touch with us today.

This article was originally published in

The author Mr. Hasan Mydin is part of the “Advanced Power Quality Solutions” department at InPhase. He is a self-confessed Power Quality enthusiast with more than a decade’s experience solving power quality problems across India and even abroad. To know more about him, check out  his LinkedIn Profile.

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

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.

Active Harmonic Filter – Working Principle

Doctor_Character-71The quest for human existence boils down to solving problems around us in the process to making the world a better place. What is generally observed is that a new problem pops up every time we think we have a solved a longstanding issue. This is a perpetual cycle, probably even necessary for our existence. Nevertheless, the big problems of our times in the Power Quality domain are power factor, harmonics and unbalance. The  many reasons for poor power quality can be attributed to the types of loads in use. More complex loads lead to more power problems.

Many solutions have been proposed for power quality problems. But there is one that stands out – the IGBT based voltage source converter, popularly known as Active Harmonic Filter. This article is an attempt to convey just how much the Active Harmonic Filter is capable of and how it makes it all possible. In simple terms we have set foot to explain the working principle of Active Harmonic Filter Shortly the Active Filter. 

The ever increasing load complexity

At first, consider the load to be purely resistive; a simple incandescent lamp maybe, just to make things more “real” (pun intended). In such a case, only real power will be drawn from the grid. Just when things are going smooth, we decide to connect an induction motor at the load end. But, the induction motor requires an excitation current in the field coils for its desired operation. Hence, drawing pure real current from the grid is no more sufficient. Therefore, in addition to the real power, a new component, namely reactive power is drawn from the grid.

As our next step in this experiment, we introduce a new “problem” in our setup. We deliberately rearrange our loads such that they are not balanced, i.e. the current drawn in the three individual phases are not equal. In technical terms we call this phenomenon, load unbalance. Just for representation, it is shown as if unbalance is a new component being drawn from the grid. In reality, however, unbalance is a “phenomenon” and not a “component”. The idea of this representation will be disclosed in the following lines.

Just as we might begin to think that things couldn’t get any worse, drives-based motor control system is introduced! This power electronic marvel starts functioning; and consequently introduces harmonics in our power system. Therefore at this point in time, our power system suffers from the following problems – low power factor, load unbalance and harmonics.

The solution

Now that all possible problems have arisen in the system, it is time to introduce the hero – the Active Filter. For the sake of representation, let us assume that the Active Filters kills the problems one-by-one. Starting with reactive power, it is seen that the reactive power being imported from the transformer is compensated by a counter-acting power from the Active Filter. In an alternate view, it can also be seen as if the reactive power requirement of the load is fed by the Active Filter. Unbalance in a system can be attributed to presence of negative sequence components and zero sequence components of currents.  Active filter is capable of eliminating the negative sequence and zero sequence components from the electrical system, as shown. Here is a case study on Unbalance Compensation if you want to learn more about it. Subsequently, on elimination of unbalance, harmonics is the only problem left to be solved in the system.

The Active Filter senses the current from the CTs connected within the plant. With this input, the controller present in the Active Filter catches the harmonic content and pumps the same current in anti-phase. In this manner the harmonics are cancelled out in the system.

We hope that this article answers, in brief, the million dollar question of “How exactly does an Active Filter work?” Thank you for reading and hope to see you soon with a new article!

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 and manufacturer of 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.


IEEMA the industrial association for Electrical Industries is very proactive in educating and creating awareness in the market. Today IEEMA has announced a very insightful workshop on  Power Quality and Reactive Power Compensation. Take a look at the agenda and get in touch today to be part of this excellent program. We will meet you there.


Reactive Power Management has become very important now-a-days because of introduction of power factor based tariff. Power Factor (PF) is crucial in all Electrical Power utilizing environments. A good understanding of Power Factor is essential for practicing Electrical Engineers and middle level managers as a good control of PF could lead to many advantages – energy saving, reduction of current loading, higher output from motor and generators, longer life for cables and equipment  – to mention a few. However, the equipment that is used to improve power factor interacts with network harmonics and brings down overall reliability. This workshop addresses such issues and gives solution to mitigate these problems.





14th October 2016, Friday

10:00 am to 5:00 pm

The Fern Citadel Hotel
No. 41, Seshadri Road,
Ananda Rao Circle, Bangalore – 560 009
Tel : +91 080 4240 2222

Key Benefits

  • Gives basic knowledge of fundamentals of Reactive Power Management
  • Can be applied directly to any installation and hence a boon for Engineers and others
  • Gives knowledge about Power Quality in general and Harmonic pollution in particular along with practical solution to mitigate them


  • Benefits of Power Factor Improvement
  • Evaluating PF from Electricity Bill
  • Methods of improving Power Factor
  • Automatic Power Factor Correction (APFC)
  • Issues in Power Quality
  • Power Factor Improvement of DG Sets
  • Harmonics – Causes, Measurement and Mitigation
  • Harmonics and effect of adding Capacitors in the System
  • Harmonic Filters and Active Compensation

Target Audience

Transmission and Distribution Operating Personnel, Engineers involved in Planning, Designing and Testing of Power Control Equipment and Engineers in charge of Electrical Maintenance, Engineers from Public / Private Sector Power Utilities.

However, anyone with enthusiasm and interest for Power Systems are most welcome to attend.



k-subramanianA  Masters Degree in Electrical Engineering and having an overall experience exceeding over 30 years in various fields such as Design, R&D, Production, Erection & Commissioning. Presently working as a freelancer in Bangalore. His current activities include promoting Electrical Power Quality awareness in the fields of Harmonics and Reactive Power Management. A regular faculty in PSTI (Min of Power), Bangalore, Larsen & Toubro Switchgear Training Centres, and conducted program on DRUM (Distribution Reforms, Upgradation and Modernization) organized by (Min of Power) Govt. of India and aided by Govt. of USA. Visiting faculty in various Engineering Colleges.

WorkShop Fees:
Members : 3000
Non Members: 3500

For Registration Contact:
Mobile : +91 99800 04982 (Seetharaman K)

Visit for more details!


Team InPhase will be hoping to meet you there! Cheers!

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.