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Dr. InPhase Edu Series – How to use Krykard ALM-32/33/35 to carry out Power Quality Study

Hello Everybody. This is Dr. InPhase!!! In this dual part series I’ve already presented How to use Fluke 434-Series II for carry out Power Quality Study. In second part I’m going to walk through on How to use Krykard ALM-33/32/35 for carrying out Power Quality Study to record and analyze various Power Quality factors like Harmonics, Unbalance, Power Factor and so on.

KRYKARD ALM 32/33/35

  • To measure and record RMS voltage, current, power parameters in an electrical network.
  • To record the variations (power parameters) in the electrical network.


– Press to power up or power down the Krykard ALM-32/33/35 Analyser. The home screen shows RMS waveform for voltage and current.


  • In home screen Press Configuration Button
  • Select Date/Time in Configuration screen
  • Press Enter button
  • Make the changes in DATE & TIME by using Navigation keys & Press ENTER.
  • Press Return button after the changes are made.


  1. Measuring results belongs to different phases are presented with individual colors. Every region in the world having different sets of color code for the Phase sequences.
  2. Here we proceed with Indian region.
  3. The following steps are configuring the Phase Colors as well as Languages also.


  • Press Configuration button
  • In Configuration screen, each Function keys belongs to different language.
  • In this screen the selected Function key belongs to English language.
  • Krykard ALM-32/33/35 offers 26 regional languages along with English.


  • Press Configuration button and Select Display
  • Press 2nd Function key for the Colors option
  • In this screen, we can change the voltage, current color coding of Phase & Neutral as per the region by using of Navigation keys.
  • If we select 1st Function key, there will be an option for Brightness adjusting. Brightness can be adjusted as per the requirement using Navigation keys.

  • If we select 3rd Function key, an option for automatic Display shutdown. Select Never/Automatic as per the requirement.

  • If we select 4th Function key, an option for Night mode. Activate/Deactivate as per our requirement.


  1. Krykard ALM-32/33/35 has a several preprogrammed wiring setup of electrical system/equipment.
  2. Based on the system configuration like Three phase, Two Phase, Single Phase we can choose accordingly in the analyser also.
  3. The following steps are configuring the available wiring setup of Krykard ALM-32/33/35 for the electrical system which we want to analyse.

  • Press Configuration Button
  • Select Electrical Connection
  • Select the appropriate Configuration from the list of connections.
  • Available connections are- 3 Phase 3 Wire, 3 Phase 4 Wire, Single Phase 2 Wire, Split Phase 3 Wire.


  • Connection example shown in the above picture.
  • Analyser we could use to connect in HT side (like 11kV, 33kV), LT side (like 415V, 690V) by taking CT and PT reference from the Breaker panel (ex. VCB).
  • We can analyse the load in feeder wise as well as connecting the particular load also (like VFD, DC Drive, etc.)


  • This probe for connecting the PT reference side or PRIMARY side or Direct BUS BAR SIDE.

  • Press Configuration Button
  • Select Sensors and ratios and press Enter
  • Select the corresponding Function key for voltage (U)
    • 110V is common PT secondary voltage.
    • Select Ratio set-up and press Enter for Change PT ratio as per the Primary Voltage by using navigation keys.
    • Connecting in Live BUS BAR side PT ratio should be 3U 1/1
    • Example: Connecting in 33kV side VCB/Breaker side means PT ratio will be 0033.0k/0110.0
  • Press Enter after  the changes are made.
  • Press Return button after the changes.

  • This probe is for connecting in Measuring or Protection CT

  • The pictures show how to connect the probe in to the CT reference side.

  • Press Configuration Button
  • Select Sensors and ratios and press Enter
  • Select the corresponding Function key for current (A)
  • Select Ratio set-up 3A.
  • Press Enter after the changes are made (CT Ratio).
  • If we select Ratio set-up A1+A2+A3, for changing the CT ratio for individual phase.
  • For Neutral sensor, it is not available in ALM 33; By selecting 3 Phase 4 Wire configuration there will record Neutral Voltage & Current readings in virtual which we can by the display also.
  • Press Return button (Back to the previous screen)


  • This probe for connecting to the PRIMARY side or direct BUS BAR side.

  • Press Configuration Button
  • Select Sensors and ratios and press Enter
  • Select the corresponding Function key for current (A)
  • Select Ratio set-up 3A 1/1.
  • Set the ratio for 65A to 6500A. It can measure up to 1000A.
  • Press Return button (Back to the previous screen)

*After this above setup, the Analyser is ready for measurement.


  1. After doing the initial setup now the Krykard ALM-32/33/35 is ready for taking the measurements.
  2. The following steps are for checking the connection and then proceed to start the measurement.


* The figures below explained for the correct connection setup.

This is the first thing should check for the connection verification.

  • After the connection is made, Press Waveform display Mode key the above screen will appear.
  • Use Navigation keys to see Voltage (3U) or Current (3A) waveform.
  • Select corresponding Function keys to see THD, CF (Crest Factor) and all.
  • Select this function key for Vector view of Current & Voltage (Explained detailed in below)
    • The below two screens are vector view of Voltage and Current.
    • In 3 Phase 3 Wire configuration, the directions should be clockwise and order should be Red-Yellow-Blue (RYB).

  • In 3 Phase 4 Wire configuration, the directions should be clockwise & order should be Red-Yellow-Blue (RYB)

  • Compare the Amperes and with Analyser and the connected Breaker panel side or Load side.
    • Check the amperes in the Multifunctional meter or Ammeter of the Breaker panel.
    • If the Ampere is not matching with the load side check the CT ratio fixed. If it is wrong change it accordingly.
  • if amperes match check the Directions of vector as per the above diagrams.
    • If the directions are not proper check the CT Probe direction in the breaker panel.
  • Both Amperes should match.


  • Press  Power parameter mode key, the above screen will appear.
    • Check the Actual Power (W), Apparent Power (VA),
    • Both values should be in Positive (+ve).
    • If the values are Negative (-ve) invert the CT probe direction fixed in the breaker panel.
    • Check for the Phase Sequence/CT probe direction in Breaker panel.


  • Press Harmonics mode key, the above screen will appear.
  • We can see the harmonics in % and in terms of Amperes for voltage as well as current by using navigation keys in the screen.
  • Use corresponding Function key for seeing Voltage Harmonics (U) / Current Harmonics (A).
  • Till 50th order voltage and current harmonics recording available.


  • Press button and select Trend mode the above screen will appear.
  • This is for selection of parameters we wanted to record.
  • Use corresponding Function keys to Select/Unselect the parameter.
  • After selecting all the parameters, Press Return button for the previous screen.
  • Then select Trend mode key for Start the recording.

TREND MODE is the function used to Start Measurements & Monitor the readings.

  • After selecting Trend mode key recording list screen will appear.
  • Select the Function key for Recording schedule, the above screen will appear.
  • Enter the Record Name, Star & Stop time by using Navigation Keys.
  • Period is the sampling time for data recording.
    • 20s (seconds) means the analyser will record every 20 seconds per data.
    • The data will be the Minimum, Maximum & Average of 20 seconds data.
    • In Krykard ALM-32/33/35 the Interval limit from 1s (Seconds) to 15 mins (Minutes).
  • After entering all the details Press this button to start.
  • After starting the recording the below screen will appear.

  • During recording time, we will be able to see THD, RMS, Current & Voltage Phase sequence, Crest Factor, Power Parameters by selecting Function keys & Mode keys.

  • After reaching STOP TIME / Finishing the measurement, it will SAVE automatically.
  • If we want to STOP in between the measurement Press in Trend mode screen, it will stop immediately and save the records. We can stop the measurement in between the record time.
  • In that Trend mode select the recording list will appear. In this we can see the recorded measurements and the waveform of the record by Enter the selected record.

Check out:  Fluke-435 Tutorial

Thanks for reading this article. Will see you again with a new article. Until then bye from Dr. InPhase!!! For any feedback contact us 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.

Active Harmonic Filter Technology History, Evolution and Future


Doctor_Character-04-1Hello Readers, this article discusses the evolution of active filters as a harmonic mitigation solution and where it is getting to in the future. 


With the increasing number of power electronic equipment’s in the power system, the need to maintain sinusoidal line voltages and currents have become the need of the hour.

Harmonics in power system is caused by both domestic and industrial loads. Traditionally, harmonic distortion has been dealt with the use of passive LC filters. However, their application may result in parallel resonances with the network impedance, over compensation of reactive power at fundamental frequency, and poor flexibility for dynamic compensation of different frequency harmonic components.

Therefore, to overcome these problems and to provide adaptability to load variations in network and instantaneous adjustable solutions, Active Harmonic Filters were implemented. They regulate terminal voltage to improve voltage balance, compensate harmonics and reactive power and suppress flicker in electrical systems. The controller is the most indispensable part of the Active harmonic filter. The performance and reliability of the system greatly relies on it.


Starting from 1971, a number of configurations, such as the active series filter, active shunt filter, and combination of these filters have been developed and materialized for UPS applications. From 1976, a significant number of publications have reported on three phase three wire Active Harmonic Filter’s. Active shunt, active series, and combinations of both, named as active power quality conditioners, as well as passive filters combined with active shunt and active series Harmonic Filter’s are some typical configurations used. These configurations are used to resolve the problems of excessive neutral current, unbalanced load currents, heating issues and the previously mentioned problems which mainly occur due to nonlinear unbalanced loads and other power quality issues.


Passive Harmonic Filter


One of the major factors in advancing the Active Harmonic Filter technology was the invention of fast self-commutating solid-state devices. With the introduction of IGBT’s, the evolution of Active Harmonic Filter technology got a real boost and, at present, they are considered as ideal solid-state devices for Active Harmonic Filter’s. The improved sensor technology has also contributed to the enhanced performance of the Active Harmonic Filter. The next breakthrough in the evolution of Active Harmonic Filter development has resulted from the microelectronics revolution. Now, it is feasible to implement complex algorithms online for the control of the Active Harmonic Filter at a reasonable cost.

igbt                  18722-3172117


Selection of the Active Harmonic Filter for a particular application is an important task for end users and application engineers. There are widely varying application requirements, such as single-phase or three-phase, three-wire and four wire systems, requiring current-or voltage-based compensation. Moreover, there is a number of Active Harmonic Filter configurations which may cater to the needs of individual users. The proper rating of a passive harmonic filter must be concluded from the rating of a non-linear load without a harmonic filter and that of an active harmonic filter based on rectifier parameters without a filter. Selecting an Active Harmonic Filter of the correct size is the key to achieve optimum cost/benefit ratio, i.e. desired current harmonic reduction with minimum filtering effort.

Some of the leading Active Harmonic Filter manufacturers of today’s market are COMSYS, MERUS POWER, INPHASE POWER, SCHAFFNER and ABB. The InPhase Power Active Harmonic Filter stands out in the crowd in a number of ways. InPhase Power which is an Indian company provides 100% indigenous technology with up to 1000A in a single equipment. It has emerged as the only one in the market to provide Direct High Voltage Compensation with advanced DSP control and INPHASE CLOUD Computational system for online monitoring of faults in electrical systems with SMS alert facility. Application of LCL filters and rigorous algorithm for better compensation makes it the right choice power quality issues. InPhase Power also offers direct 690v Active Harmonic Filters  typically used in Furnace kind of applications. To top it all InPhase Power won the Ministry of MSME Award for Innovation in Renewable Energy & Power Quality Solutions which shows the reliability and dependability of InPhase Power products.

       ahf                                                    Active Harmonic Filter                                              


Today, Active Harmonic Filter technology is well matured, and a number of manufacturers are producing Active Harmonic Filter’s with large and varied capacities. The utilities in the long run will induce the consumers with nonlinear loads to use the Active Harmonic Filter’s for maintaining the power quality at acceptable levels. Many Active Harmonic Filter configurations are available to compensate harmonic current, reactive power, neutral current, unbalance current and harmonics these days.

With the advent of new and improved technology implementing faster devices the filter size and its performance can greatly improve, increasing the reliability and adaptability to perturbations in our power system network. The future looks promising as the IGBT technology  which is the key system component in Active Filters are evolving very faster and with robust capability.  The futuristic Active Filters might be compact, modular with ability to compensate higher orders and respond much quicker. Not leaving the reliability of these Active Filters will also be high in comparison to the current generation filters with more rugged capability for Industrial environments. InPhase as a pioneer in power quality and as a manufacturer of Active Harmonic Filter is working towards bringing these latest generation products to your door steps.

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.


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.