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Power Factor and HarmonicsEnergy University Course Transcript

Slide 1Welcome to Power Factor and Harmonics.

Slide 2For best viewing results, we recommend that you maximize your browser window now. The screen controlsallow you to navigate through the eLearning experience. Using your browser controls may disrupt thenormal play of the course. Click the paperclip icon to download supplemental information for this course.Here, you will find a Schneider Electric White Paper, which offers additional information on the topic we willdiscuss today. Click the Notes tab to read a transcript of the narration.

Slide 3At the completion of the course, you will be able to:

List examples of power factor and harmonics phenomena, the common causes and the commonnegative physical and financial impacts

List methods of preventing or mitigating power factor and harmonics problems and describe theirsuitability for particular situations

Perform power triangle calculations, and size the required power factor correction solution for a

given level of correction

List possible locations of mitigation solutions within an electrical network, and identify the pros andcons associated with each location

Slide 4As a member of the Electrical Department staff of your company, you may have asked some of the followingquestions:

How can we reduce the electricity bill without disruption of electricity supply?

Why is our electrical installation victim of nuisance tripping or unexplained disturbances of control

systems?

Should we worry about the influence of electronic equipment such as adjustable speed drives,uninterruptible power supplies, induction ovens, fluorescent lighting, and IT equipment?

What is the origin of those transformer vibrations?

Why did we experience untimely tripping of overload relays of power factor correction capacitors?

How can we avoid neutral conductor overheating?

Should we complain to the utility about light flicker?

If you have asked any of these questions, then this course should be very helpful by providingexplanations and solutions. All these questions are basically linked to the control of Power Factorand Harmonics.

Slide 5Low power factor and harmonics are a frustration for electrical installations like curves and bumps are anuisance for the motorist. On the road, this means that fuel mileage and reliability are not optimal, resulting


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in an increased gas bill and maintenance cost. In electrical installations, this means additional power lossesand reduced energy reliability.

In the context of increasing concern about energy efficiency and energy management, power factor andharmonics are important issues to consider for the management of electrical installations. Power factorcorrection and harmonic mitigation provide immediate benefit in terms of reduced power losses, reducedelectricity bill, and the possibility to use the total system capacity.

Accounting for these problems upfront yields a plethora of significant benefits, including:

Reduction of electricity bill by 5 to 10% typically,

Reduction of power losseswhich helps to prevent transformers and panels from overheating, Reduction of cable size, bringing reduced cost and easier implementation,

Compliance with harmonic emission limits requested by utilities prior to connection,

Improvement in process quality. For example, spot welding for car body assembly is sensitive tovoltage fluctuations linked to poor power factor.

Improvement of system availability and reliability. Harmonics can cause protection devices to trip,

disrupting production and causing nuisance.

Improvement in business performance: Optimized use of electricity, no disruption of operation andlonger equipment life expectation.

Slide 6The presence of harmonics in electrical systems means that current and voltage are distorted and deviatefrom sinusoidal waveforms. Harmonics are superimposed waves, whose frequencies are multiples of thepower frequency. The multiplying factor is called "harmonic order".

Harmonic currents are caused by nonlinear loads connected to the distribution system. A load is said to benonlinear when the current it draws does not have the same waveform as the supply voltage. The flow ofharmonic currents through system impedances in turn creates voltage harmonics, which distort the supplyvoltage. This results in disturbances of sensitive equipment, mainly related to the circulation of currents inthe grounding connections.

Equipment comprising power electronics circuits are typical nonlinear loads. Such loads are increasingly

frequent in all industrial, commercial and even residential installations and their percentage in overallelectrical consumption is growing steadily.

Examples include:

Industrial equipment (welding machines, arc and induction furnaces, battery chargers),

Variable Speed Drives for AC or DC motors,

Uninterruptible Power Supplies,

Office equipment (PCs, printers, servers),

Household appliances (TV sets, microwave ovens, fluorescent lighting, light dimmers).


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Slide 7Voltage fluctuation is a systematic variation of the voltage waveform or a series of random voltage changesof small dimensions, namely 95 to 105% of nominal at a low frequency. The usual origin of voltagefluctuation disturbances are motor start-up and spot welding. An example of a possible impact of voltagefluctuation disturbances is a light flicker.

Voltage fluctuations are the consequences of variable voltage drop along the distribution lines and acrosstransformer windings. This voltage drop is mainly the consequence of the circulation of reactive energyabsorbed by loads such as motors. The advantages of reactive energy compensation or "power factorcorrection" will be shown later in this course; but first, lets talk a bit about power factor.

Slide 8What is power factor?

The active power P (kW) is the real power transmitted to loads such as motors, lamps, heaters andcomputers. The electrical active power is transformed into mechanical power, heat or light. In a circuit where

the applied rms voltage is Vrmsand the circulating rms current is I rms, the apparent power S (kVA) is theproduct: Vrmsx Irms. The apparent power is the basis for electrical equipment rating. The Power Factor () isthe ratio of the active power P (kW) to the apparent power S (kVA).

Slide 9For sinusoidal (undistorted) voltage and current, a vector representation is possible and helpful. For mostelectrical loads like motors, the current I is lagging behind the voltage V by an angle phi.

The current vector I can be split into 2 components:

Iais called the "active" component of the current, and

Iris called the "reactive" component of the current.

For sinusoidal voltage and current with a phase angle, the Power Factor is equal to cos of the angle, calledDisplacement Power Factor (DPF).


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The diagram drawn up for currents also applies to powers, by multiplying each current by a common voltageV.

Thus, we define apparent power, active power and reactive power, as you see here.Apparent power: S = V x l (kVA)Active power: P = V x la= V x I x cos phi (kW)Reactive power: Q = V x l r= V x I x sin phi (kvar)


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Its important to note however, in a three phase system, these equations change just a bit. And we see thathere. Apparent power: S = 3 x U x I (kVA) Active power: P = 3 x U x I x cos phi (kW) Reactive power: Q = 3 x U x I x sin phi (kvar) Here, U is the phase to phase voltage.

Slide 10It is important to know how to size the required power factor correction (PFC) solution for a given level ofcorrection. This can be accomplished by working through the power triangle calculation.

Here are some power triangle calculations:kVA2= kW2+ kvar2

kvar2= kVA2kW2

kvar = (kVA2kW2)


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Lets look at the power triangle in more depth.

Slide 11The power triangle shown here is the simplest way to understand the effects of reactive power. The figureillustrates the relationship of active (real) and reactive (imaginary or magnetizing) power. The active power(represented by the horizontal leg) is the actual power, or watts that produce real work. This component isthe energy transfer component, which represents fuel burned at the power plant. The reactive power ormagnetizing power, (represented by the vertical leg of the triangle) is the power required to produce themagnetic fields to enable the real work to be done. Magnetizing power is inherently present in transformersand motors. Reactive power is normally supplied by generators, capacitors and synchronous motors.

The longest leg of the triangle, labeled apparent power, represents the vector sum of the reactive power andthe real power components. Mathematically, this is equal to: kVA = (kW 2+ kVAR2).

As the apparent power is the basis for electrical equipment rating, there is a big benefit to reduce thereactive power, for a given amount of active power transferred to the loads. Thats why utilities are generallyapplying penalties on reactive power, in order to influence customers to lower the reactive powerconsumption.Here we see the typical value of Power Factor for different kinds of electrical equipment.Motor (0.8)Incandescent lamp (1)Compact fluorescent lamp (0.5)Discharge lamp (0.6)Resistance oven (1)Computer (0.65)

Lets move on now and do a couple of example exercises.

Slide 12A facility is operating with a demand of 4000 kW. The 5000 kVA transformer is fully loaded. How many kvarare required to bring the power factor back to unity? Looking at the information we have been given itmakes the most sense to use the power triangle formula:kvar2= kVA2kW2


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And here we see our solution:kvar2= (5000)2(4000)2kvar2= 25,000,00016,000,000kvar2= 9,000,000kvar = 9,000,000kvar = 3,000 kvarLets look at another example.

Slide 13Consider a 200 HP electric motor that has the following information on the name plate:460 volts228 ampsThree phase93% efficientAll at full loadWhat is the power factor of this motor?

Remember the power factor ratio:PF = kW / kVA = active power / apparent power

First calculate the kW rating of the motor from the horsepower using the formula. Remember that thehorsepower given on the nameplate is the output power on the shaft. Therefore you must not only convertfrom horsepower to kW, but must also calculate the input power from the output power.

In countries using metric units, the nameplate would normally give the output power in kW and you would beable to skip the horsepower conversion step.

1 HP = 0.746 kWEfficiency = Output power / Input power

And soInput power in kW = HP x 0.746 kW x Load factor / Efficiency

The data given told us that the motor is at full load, so that is 100% or 1.The efficiency is 93% or 0.93.kW = 200 HP x 0.746 kW x 1 /0.93If we do that calculation, we'll see that we come out to 160.4 kW.

Now, calculate the kVA.In a three phase system, kVA = 3 x U x I (and remember - U is the phase to phase voltage)kVA = 1.73 x 460/1000 x 228kVA = 181.7

Take that one step furtherPF = 160.4/181.7 = 0.88h


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Slide 14For many types of electrical equipment the difference between apparent power (VA) and active or realpower (W) is very slight and can be ignored. However, for some equipment such as computers and compactfluorescent lamps, the difference is very large and important.

Many desktop personal computers present a nonlinear load to the AC supply. This is inherent to the powersupply design known as "capacitor input, switch mode power supply". In a study done by PC Magazine, itwas found that typical personal computer systems exhibit a power factor of .65 which means that theapparent power (VA) was 50% larger than the active power (W)!

Information Technology equipment including servers, routers, hubs, and storage systems almost universallyuse a different power supply design known as "Power Factor Corrected". These devices present a verylinear load to the AC supply and do not generate harmonic currents. In fact they are one of the cleanestloads on the power grid and generate less harmonic current than many other devices such as fluorescentlighting or variable speed motors. Ten years ago, these devices were nonlinear loads like personalcomputers, but today all of these loads are subject to international regulation IEC 1000-3-2 which requirethem to be made with the "Power Factor Corrected" design.

Lets move forward and discuss how power factor and harmonics relate to energy efficiency.

Slide 15The maximum active power is transmitted to a load when voltage and current are undistorted and in phase.

When voltage and current are phase-shifted, the instantaneous power (P = V x I) is negative when thesignal signs are opposite. The average power is then reduced.

With a distorted current, the instantaneous power is negative or close to zero during a significant period oftime. The average power is then also reduced.


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Slide 16Let's compare three different situations. In the first, ideal situation, voltage and current are purely sinusoidalcurves, and in phase. For a given transferred active power, the rms current is equal to I.

In the second situation, voltage and current are purely sinusoidal curves, but phase-shifted by an angle phi.With displacement power factor (abbreviated to DPF) = cos phi = 0.7, the rms current is equal to 1.43 x I, soit is increased by more than 40% for the same active power.

In the third situation, the current is distorted, such that the Total Harmonic Distortion (THDi) is equal to100%. THDi is an indicator of the amount of distortion on the signal. Then, by using calculations notdetailed in this course, the resulting rms current is equal to 1.41 x I, so again increased by more than 40%for the same active power.


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Slide 17The higher current means additional losses, more CO

2emissions, premature aging of equipment, higher

electricity cost, nuisance tripping of over-current detection relays, higher equipment cost, and possiblevoltage fluctuations. The circulation of harmonic currents through the system impedance creates voltageharmonics resulting in voltage distortion.

That is why power factor correction (PFC) and proper harmonic mitigation contribute to improvecompetitiveness of companies in different ways:

Reduced overloading on the electrical system, thereby releasing useable capacity. This couldavoid the installation of an additional transformer in case of extension of the installation,

Reduced system losses and demand power,

Reduced risks of outage, and

Extended equipment lifetime.Lets take a closer look at the benefits of power factor correction and harmonic mitigation.

Slide 18Some of the benefits include:

Reduced overloading on the electrical system, thereby releasing useable capacity

This could avoid the installation of an additional transformer in case of extension of the installation

Reduced demand power Reduced risks of outage, and Extended equipment lifetime

Other benefits include: Reduced electricity bill

Low power factor and harmonics are resulting in increased power demand and reactive energyconsumption. Both aspects are part of the electricity bill paid to the Electricity utility.

Reduced power lossesLow power factor and harmonics are responsible for increased current for a given active power and foradditional losses.

Reduced cable sizeThe cable size is determined according to the electrical current requirements, so reduced current meansless expensive and easier-to-install cables.

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Improved process qualityProcess quality or machine operation may be impaired by voltage fluctuations linked to variations of reactiveenergy. The same problems may be produced by a high level of distortion, producing disturbances ofsensitive equipment (computer management system, sensors)


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Improved business performance

Capex is reduced by lower cost of equipment such as transformer, cables, and switchgear.Opex is reduced by reduction of power losses, reduction of subscribed power, and elimination of reactiveenergy penalties.System availability and reliability are improved.

Now that we have discussed the benefits of power factor correction and harmonic mitigation, lets talk abouthow best to mitigate those problems.

Slide 20Lets look at diagnostics and solutions!

Monitoring is the best diagnostics tool! It provides: An early warning of impending problems which may appear after a change of circuit configuration Determination of the nature and origin of a disturbance. For example, monitoring can indicate whether thedisturbance originates inside or outside the installation Validation of quality contract compliance

Some examples of Monitoring Equipment include: Power monitors and circuit monitors: PowerLogic PM, CM, and ION Series Protection relays: Sepam Trip units: Micrologic

Some examples of solutions include: Capacitor banks: Varset Transient-free capacitor switching: Varset Fast Harmonic filters: Accusine, Sinewave Fast reactiveenergy compensators: Accusine, Sinewave

Lets discuss these solutions in further detail.

Slide 21Capacitor banks are the basic solution for power factor correction. The main objective is to avoid reactiveenergy penalties charged by the utility. Equipment may be connected at different levels in the installation:MV substation, LV main switchboard, LV secondary switchboard, and machine terminals.

Compensation of an installation is determined in 4 steps:1. Calculation of reactive power

2.

Selection of compensation mode (global, by sector, local)3. Selection of compensation type (fixed, by steps, dynamic)4. Consideration of harmonics

Slide 22The first step is calculation of reactive power. The objective is to calculate the reactive power Qc (kvar) tobe installed to increase the cos phi to the targeted value. This is based on the formula we see here: Qc = P(tan phitan phi')


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Lets look at an example.A facility has a demand of 3500 kW and a power factor of 0.78. What size ofcapacitor would be required to improve the power factor to 0.9?

As we learned earlier in this course, DPF is equal to cos phi. Here we see that is 0.78, and the tan phi is 0.8.

The improved cos phi' is 0.9, which means tan phi' equals 0.48.

Looking at our formula, the reactive power to be installed is Qc = 3500 * (0.80 - 0.48) = 1120 kvar

Slide 23The second step is selection of compensation mode (global, by sector, local).

When looking at global compensation, the capacitor bank is connected at the supply end of the installation.This is ideal for stable and continuous loads.

When looking at compensation by sectors, the capacitor bank is connected at the supply end of the sectorto be compensated. This is ideal for extended installations including workshops with varying load systems.

When looking at individual (or local) compensation, the capacitor bank is directly connected to the terminalsof the machine (generally motors). This is the best technical solution because reactive energy is suppliedwhere it is needed.

Slide 24The third step is selection of compensation type (fixed, automatic by steps, or dynamic)

Different types of compensation shall be adopted depending on the performance requirements and

complexity of control: Fixed, by connection of a fixed-value capacitor bank,

Automatic, by connection of different number of steps, allowing the adjustment of the reactiveenergy to the requested value,

Dynamic, for compensation of highly fluctuating loads.


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First, well talk about fixed compensation.This arrangement uses one or more capacitor(s) to provide a constant level of compensation. Control maybe either:

Manual: by circuit-breaker or load-break switch,

Semi-automatic: by contactor,

Direct connection to an appliance and switched with it.

These capacitors are applied:

At the terminals of inductive loads (mainly motors),

At busbars supplying numerous small motors and inductive appliances for which individualcompensation would be too costly, in cases where the load factor is reasonably constant.

Now well discuss automatic compensation.

This kind of compensation provides automatic control and adapts the quantity of reactive power to the

variations of the installation in order to maintain the targeted cos phi. The equipment is applied at points inan installation where the active power and/or reactive power variations are relatively large, for example:

At the busbars of a main distribution switch-board,

At the terminals of a heavily-loaded feeder cable.

Where the kvar rating of the capacitors is less than, or equal to 15% of the supply transformer rating, a fixedvalue of compensation is appropriate. Above the 15% level, it is advisable to install an automatically-controlled bank of capacitors. Control is usually provided by contactors. For compensation of highlyfluctuating loads, fast and highly repetitive connection of capacitors is necessary, and static switches mustbe used.

And finally well discuss dynamic compensation.

This kind of compensation is requested when fluctuating loads are present, and voltage fluctuations shouldbe avoided. The principle of dynamic compensation is to associate a fixed capacitor bank and an electronicvar compensator, providing either leading or lagging reactive currents. The result is a continuously varyingand fast compensation, perfectly suitable for loads such as lifts, crushers, and spot welding.

Slide 25Now lets look at the final step: Consideration of harmonics.

When capacitor banks are installed in the presence of harmonics, two parameters shall be considered:Gh: Total power of the nonlinear loadsSn: Rated power of the supply transformer

Different types of equipment must be selected depending on the level of the network harmonic emission.The selection is based on the value of the Gh/Snratio, as illustrated here.

Oversized capacitors must be selected when Gh/Snexceeds 15% because harmonic currents will beresponsible for increased stress. When Gh/Snexceeds 25%, a series reactor is necessary to limit thecirculation of harmonic currents, harmful to the capacitors. This is called a detuned reactor becausecapacitors and reactor are set up in a resonant circuit configuration, not tuned to the frequency of anyharmonic order. Passive filters are implemented when power factor correction is requested with a high levelof existing harmonic distortion. They consist of reactors and capacitors set up in a resonant circuit


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configuration, tuned to the frequency of the harmonic order to be eliminated. A system may be composed ofa number of filters to eliminate several harmonic orders.

Here we have discussed consideration of harmonics when selecting a capacitor bank for power factorcorrection. But what if you need to mitigate harmonics in the rest of your site? Lets move on now anddiscuss the various forms of filters.

Slide 26First, we have active filters. Active filters are systems employing power electronics, to provide the harmoniccurrents required by nonlinear loads and thereby avoiding distortion on the power system. The active filterinjects, in opposite phase, the harmonics drawn by the load, such that the line current remains sinusoidal.

Slide 27Then there are hybrid filters. Hybrid filters are systems including a passive filter and an active filter in asingle unit. They cumulate the advantages of both technologies, providing a high performance and costeffective solution.

Slide 28Active or hybrid filters are also capable of compensating the fluctuations of reactive energy. In this mode ofoperation, they are also known as "Static Var Compensators" (SVC) or "Hybrid Var Compensators" (HVC).

Lets move on now to discuss mitigating variable speed drive (VSD) power problems.

Slide 29Capacitor-less (C-less) technology, combined with an advanced control algorithm, decreases the THDi by50% compared to traditional technology. This solution, which is dedicated to centrifugal pumps, fans and

HVAC machines, has been adopted by leading manufacturers.

Slide 30AC-Line or DC-link reactors (chokes) are commonly used with drives up to about 500 kW unit power in orderto smooth the line current and so reduce the distortion. When a large number of drives are present within aninstallation, the use of AC-line or DC-link chokes for each individual drive is recommended. This measureincreases the lifetime of the drives and enables use of cost effective mitigation solutions at installation level,such as active filters for example.


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Slide 31A special configuration called "Multi-pulse arrangement" is usually used for drives above 400 kW.Precondition is a dedicated transformer directly supplied from the MV network, with a 3-windingarrangement. This limits the harmonic emission considerably and usually no further mitigation is necessary.Multi-pulse solutions are the most efficient in terms of power losses. Compliance to the most stringent ofstandards is also easily achievable.

Slide 32The best performing solution concerning harmonic mitigation with drives is an electronically controlledcircuitry, called "Active Front End" (AFE), limiting the THDi below 5%. All the applicable standardrequirements can be met. No detailed system evaluation is necessary, making this solution the easiest toimplement. In addition to harmonic mitigation, power regeneration and power factor correction are inherent.

Slide 33As we conclude lets review how appropriate design affects energy efficiency.In electrical installations three different aspects should be considered:

Energy savings: reduction of energy consumption,

Energy cost optimization: reduction of the cost of energy paid to the utility, and

Availability and reliability: minimize the risk of outage, and also sustain an efficient equipmentoperation.

Power factor correction and Harmonic mitigation have an impact on all 3 aspects, since these allow:

Reduction of the power losses in transformers, cables, switchgear, motors, capacitors, up to 5%,

Eliminate utility charges for reactive energy (kvarh)

Reduction of the demand power (in MVA), resulting in lower tariffs,

Use of the total system capacity, without risk of overload, nuisance tripping or premature aging ofequipment.

Slide 34To summarize lets review some of the information that we have covered throughout this course.

Power factor and harmonic phenomena include power losses, overloading of the electrical system,light flickers, disturbance of sensitive equipment, and nuisance tripping of circuit breakers

The impacts of these phenomena include increased utility bills for reactive power and powerlosses, inability to use the full electrical system capacity, loss of production due to power outage,and reduced equipment lifetime

Common causes of low power factor include motors, fluorescent lamps, discharge lamps, personalcomputers


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Common causes of harmonics include variable speed drives, welding equipment, and fluorescentlamps

Power factor and harmonic phenomena may be mitigated by capacitor banks, detuned reactors,passive, active or hybrid filters

Use the power triangle calculations to know how to size the required power factor correctionsolution for a given level of correction

kVA2= kW2+ kvar2 kvar2= kVA2kW2 kvar = (kVA2kW2)

Capacitor banks may be located at the medium voltage substation, low voltage main switchboard,secondary switchboard, or machine terminals

Slide 35Thank you for participating in this course.

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