Tag Archives: Reactive Power

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.

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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,

And,

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 www.pqindia.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!

Doctor_Character-71

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

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:

Picture3

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.

IMG_1

The calculation for this case would go as follows:

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

The average current,

IMG_2

Maximum deviation from Iavg = 352-233.67 = 118.33A

Therefore,

IMG_3

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.

Picture1

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.

Picture2

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!

Doctor_Character-71

 

Thanks for reading…if you have questions don’t forget to ask me. You could write to me to info@inphase.in 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.