Harmonics in Electrical Power Distribution Systems

hello I'm Ryan Downey principal engineer for a vote training institutes electrical engineering division and for this presentation I will be discussing

harmonics and electrical power distribution systems the discussion will include in detail the I Triple E standard that explains and provides

recommendations and requirements for our monic control also included in the discussion will be the various types of harmonics sources and the cause effect

problems they can create and how they can possibly be mitigated please feel free to send me any questions you may have during the presentation

I may or may not have time to answer the questions as we go but all questions will be followed up via email here's the little information about me I have over 10 years of experience and electrical

engineering I'm currently licensed in 40 states across the u.s. I'm also licensed in Puerto Rico and Alberta Canada I'm an

active member of I Tripoli 1584 which is a standard of I Triple E that provides a method of calculations calculating this and an energy of art flash events I am also an active member

of I Tripoli 1814 which will be a standard of I Tripoli that will provide recommendations for implementing various types of electrical safety standards

techniques into new design projects to improve electrical safety so for our learning objectives we will discuss the following what exactly are power system

harmonics what causes harmonics what are the effects of harmonics what standards or guidelines are available to help control harmonics and how can we

mitigate our mana so just an overview on harmonics the power quality of electrical distribution systems has a drastic effect on power regulation and

consumption our quality includes all aspects of events and the power system that deviates from normal operation which includes our monix this is

especially true nowadays with the computer age we live in and there are all sorts of electronic power sources that can cause distortion in waveforms of the power system

harmonics are distortion on a power system caused by nonlinear type loads such as variable frequency drives are commonly referred to as VF these large

computer systems SCADA systems electronic lighting ballast these types of loads are accounting for a significant portion of the total load

for various types of facilities I Triple E standard 519 which we'll discuss a little later assess the requirements for harmonics and creates limits for

harmonic distortion I'll also discuss different ways that harmonic distortion can be mitigated so what exactly are harmonics well essentially harmonics are

a mathematical way of describing distortion to a way to a voltage or current waveform and you can see here we have a calculus problem which is a

Fourier series collision I'm sure everyone is dying to solve however understanding the math is not important it's an it's important to understand the

harmonics or a steady state phenomenon and repeats with every cycle harmonics should not be confused with transient dips spikes impulses oscillations or

things of this nature also the term harmonic refers to a component of a waveform that occurs at an instant integer multiple of the

fundamental frequency harmonic distortion is the degree to which a waveform deviates from its pure sinusoidal values as a result of the

summation of all the harmonic elements so for a 60 Hertz fundamental frequency waveform the second third fourth and fifth harmonic components will be a 120

Hertz 180 Hertz 240 Hertz and 300 Hertz respectively also an ideal sine wave should have zero

or monic components and you and here you can see what I meant mean by the an ideal waveform having harmonic components the waveform on the left does not have any harmonic

components and is essentially a pure waveform with a linear loads linear loads draw a current that is sinusoidal in nature so they generally do not

distort the waveform nonlinear loads however can draw current that is not perfectly sinusoidal as shown in the figure on the right since the current

waveform deviates from a sinusoidal wave voltage waveform distortions are created as you can see waveform distortions can drastically alter the shape of the

sinusoidal waveform however no matter that a level of complexity of the fundamental waveform it's actually just a composite of multiple waveforms called

harmonics here we have waveforms that show how the harmonic components combined to form a resultant waveform with much distortion the graph on the Left shows the fundamental frequency

waveform combined with that of the fifth harmonic and seventh harmonic waveforms to form the graph on the right and here we have a nonlinear waveform that shows

clipping this type of waveform is common in electronic devices having nonlinear characteristics such as computer based equipment when the sine waves are

distorted symmetrically about their average values then they're composed of odd harmonics only power is supplied by a three-phase system where each phase is

100 degrees to 120 degrees apart this is done for two reasons first it is because motors and/or generators that use three-phase power or more efficient due

to the constant torque the phase of supply second it is because after power supplied to the load the three-phase can theoretically be added onto the neutral

wire and cancels each other out this saves the utility company from creating returned wiring to the powerplant however if the three phases contained third order harmonics the currents will

not fully head to zero or or cancel out as you can see in the graph that third harmonics between the phases add together which creates oscillate

current this results in a sharp increase in the zero sequence current which increases the current in the neutral conductor this effect can require

special consideration and design of an electric system to serve nonlinear loads to avoid third harmonics adding together Delta connections are used and the

current is cycled around the connection instead of a Wye connection most harmonic problems are caused by the third harmonic for the most part harmonics were abstinance of the 1960's

with a coming of age in computer systems and electronics when the beginning of this area harmonics began to surface as I mentioned harmonics are caused by a

nonlinear type loads power sources act as nonlinear loads and draw a distorted waveform that contains harmonics 75% of

all electrical devices in North America operate with nonlinear current draw so here we have a list of devices or components that can cause issues with

our monix as I mentioned variable frequency drives or VFDs universal power supply systems are commonly referred to

as UPS systems DC converters solid-state rectifiers arc welders heater units or furnaces a switch mode power supplies

such as those used on computers electronic lighting ballast PLC systems SCADA systems computer systems all of these are sources of harmonics so let's

talk about the effects of harmonics hour- can have detrimental effects on electrical equipment and power systems unwanted distortion can increase the

current in power systems which results in higher temperatures and neutral conductors and distribution transformers hour- can also cause the overheating of

transformers motors generators capacitors cables of conductors etc which can result in premature failure

harmonics can also cause miss operation of circuit breakers and other types of protective devices as well as malfunction of electronic equipment

harmonics can also result in an infant or incorrect readings on meters which can cause a whole set of other problems and can also cause malfunction and instruments including medical

instruments which can obviously have serious consequences going on with the effects of harmonics harmonics can also result in premature failure of power

supplies due to distortion of the power of the supply voltage harmonics can also result in a low power factor requiring the transformer to be upsizing KVA or

neutral emphasizing harmonics can also cause resonating and heating of power factor correction capacitors which can cause failure the power quality of

distribution systems has a drastic effect on power regulation and consumption another phenomena that related to harmonics that can occur is

system resonance resonance occurs when a harmonic frequency produced by a nonlinear load closely coincides with a power system natural frequency the

likelihood of effects from harmonics occurring greatly increases if a resonant condition exists or occurs the single largest cause of severe harmonic

distortion is resonance a normal harmonic may be amplified ten to twenty-five times if resonance occurs at or near critical frequencies resonance

occurs mainly due to improper use of power factor correction capacitors or because of incorrect application of filters there's two forms of system

resonance parallel resonance and series resonance and we'll talk about those so parallel resonance occurs when the system and inductance reactants noted

here on this drawing minus XL and the capacitance rear reactants noted as XZ are equal at some frequency like the

fifth seventh etc harmonic currents that flow between capacitors and the system inductance are significantly amplified typically up to 10 to 15 times

parallel resonance can lead to capacitor fuse blowing or failure and/or transformer overeating so series resonance is a series combination of

inductance and capacitance it creates a low impedance path for harmonic currents at the natural frequency this results in high harmonic currents through the

capacitors series resonance can result in a high voltage distortion level between the inductance and capacitance

so I Triple E standard 519 was created to establish limits for our mounting distortion and provide direction on billing with harmonics it was intended

to provide direction on dealing with harmonics introduced by static power converters and other nonlinear type loads the standard was written to establish goals for the design of

electrical systems with both linear and nonlinear loads it is presented as a guideline for a power system design when nonlinear loads are present and assumed

steady state operation distortion limits for both current and voltage are defined in order to minimize interference between the electrical equipment the

limits are defined at the point of common coupling which I will discuss the standard is titled recommended practice and requirements for our monic control

and electrical electric power systems and the current standard was released in 2014 so the point of common coupling it's defined as the point in the power system

closest to the user where the system owner or operator could offer service to another user frequently frequently for service to industrial users for example

manufacturing plants via dedicated service transformer the point of common coupling is at the high voltage side of the transformer for commercial users

that are supplied through a common service transformers the point of common coupling is typically at the low voltage side of the transformer the point of common coupling is

basically recognized as the point where any harmonics can migrate onto the utility system and cause problems for other customers so here we have a couple

of diagrams of the location of the point of common coupling and you'll note you'll notice how the it's basically the point of common coupling is basically the point at which another customer

could be served so you can see the different types of scenarios we have so more on the point of common coupling the intention of having the point of common

coupling is to prevent a high level of harmonics such as that generated by nonlinear loads generated by one customer from causing distortion at

another customer on the power grid in considering the primary site of a transformer that supplies only one customer the transformers impedance will

decrease the short-circuit ratio this results in an increase in the harmonic current limits the voltage distortion will be higher at the secondary of the

transformer so going over some of the definitions we have in I Triple E 519 standard the short-circuit ratio is the ratio of the short-circuit current

available at the point of common coupling to the maximum fundamental load current this ratio essentially shows a relative size of the load compared to

the utility system the maximum load current is recommended to be the average current of the maximum demand for the preceding 12 months

unfortunately this value is inherently ambiguous making it difficult to derive at the design stage when measured load is not available so looking at this

graph this shows a high short-circuit current and which results in a minimum voltage distortion and you switch over

to this next slide and you compare and on this graph you can see the low the low short-circuit current which results in a significant voltage distortion the

distortion is much more pronounced as we saw than the one on the previous grass so here you can see the larger loads have a greater ability to cause voltage

distortion on the utility system and now let's discuss more of mathematics here we have the equations for total harmonic

distortion and total demand Distortion these equations can be used to describe a voltage or current Distortion the total demand distortion equals the

total harmonic distortion multiplied by the ratio of nonlinear load to the total demand load which includes both linear

and nonlinear loads per the I Triple E is 519 standard these equations consider components up to the fiftieth order

however I'd like to note it also notes that the components of order greater than 50 may be considered as necessary more definitions here the voltage total

harmonic distortion of the waveform is the ratio of the root sum square value of the harmonic content of the voltage to the root mean square value of the

fundamental voltage similarly the current total harmonic distortion of the waveform is the also the ratio of this root sum square value of the harmonic

content of the current to the root mean square value of the fundamental current so these formulas show the total harmonic distortion on a signal the end

result is a percentage comparing the harmonic components to the fundamental component of the signal the higher the percentage the more distortion as

present on the signal will discuss harmonic limits since managing harmonics in a power system is considered a joint responsibility involving both the

supplier and the end-users I Triple E 519 places recommended harmonic limits for both voltage and current the recommended values are based on the fact

that some level of voltage distortion is generally acceptable and both parties must work together to keep actual values within acceptable levels

by limiting the harmonic currents by users the voltage distortion can be kept within acceptable levels I try triple e

5:19 also states that the recommended limits only apply at the point of common coupling and are not to be applied to individual pieces of equipment or at

location within a user's facility in most instances the harmonic voltages and currents that these locations can be found to be significantly greater than

the limits at the point of common coupling due to the lack of cancellation or other phenomena that tend to reduce the combined effects of multiple

harmonics sources so this is a table one that's in its in a I Triple E standard five nineteen twenty fourteen as we as

we can see here that establishes the harmonic limits on voltages as eight percent for total harmonic distortion and five percent of the fundamental

voltage for any single harmonic this is for system levels up to a thousand volts and on this table you can see the limits for system levels between a thousand

volts and up to sixty nine thousand volts have harmonic limits on voltage as five percent for total harmonic distortion and three percent of the fundamental voltage for any individual

harmonic you'll also notice it shows limits for voltage levels up to 160 1000 volts should be noted that even if the voltage

distortion limits are met at the point of common coupling they could very easily be exceeded downstream where connected equipment could be affected

since the voltage distortion as a result of our mana currents passing through the impedance of the power system voltage distortion is always higher downstream where the harmonic currents are

generated and where system impedance is the highest now let's look at the current harmonic distortion limits for power systems with voltage levels

between 120 volts and 69 thousand volts the limits can be found in table 2 of the standard which is shown here I would also like to note that tables 3 & 4

which are not shown here show their current and distortion limits for higher system voltages the table defines total demand distortion current limits as well

as individual harmonic current limits the limits are most severe for short circuit ratios of less than 20 because

this lower ratio indicates a high impedance power system or a large customer or both voltage distortion is

more likely to develop from current harmonics consumed at a point of common coupling where the short-circuit ratio is low there thereby justifying the more

severe limits so discussing further the current harmonic distortion is recommended that the limits be increased by a multiplying factor when actions are

taken by the user to reduce low order harmonics and as we can see in this this is table 5 the multipliers in the second column are to be used when steps have

been taken to reduce the harmonic order shown in the first column please know however that the low order harmonics currents must be kept below 25 percent

of the current harmonic distortion values shown in table 2 so power factor must include the distortion factor to

account for harmonics so here we can see how the distortion factor is determined the distortion factor decreases as our

monix increases true power factor may be lower when the effects of harmonics are considered so here we have a couple of

graphs the graphic on the left shows a typical power factor diagram and the graph on the right shows a power factor diagram with harmonics included you'll

notice how the harmonics are factored in to the equations as well real power is useful work producing power reactive power is on

useful non-work producing power as an example imagine you have a full glass of beer the foam at the top is not very useful just as reactive power however

the beer below that is very useful just as real power so the class of example of a nonlinear load is a rectifier with a

capacitor input filter where the rectifier diode only shows first excuse me only allows current to pass to the load during the time that apply

voltage exceeds the voltage stored in the capacitor which might be a relatively small portion of the incoming voltage cycle the characteristic current

harmonics produced or determined by the pulse number and here you can kind of see the equation so here's an example of

a six-pulse rectifier with harmonics present you'll notice how the fifth

seventh eleventh 13 17 19 and so on are monix are present the current is quite distorted and the typical full load

current harmonic distortion at the transfer transformer primary can be anywhere but from 25% up to 48 percent

depending on the network impedance even with a three percent reactor and here we have an example of a 12 pulse rectifier with harmonics present you'll notice

that the fifth and seventh harmonics are not present as we saw in the six pulse rectifier the typical full load current

harmonic distortion at the transformer primary is between 8% and 12% and here we have an example of an 18 pulse

rectifier you'll notice that the 11th and 13th harmonics are not present as we saw on the 12 pulse rectifier at the typical full load current harmonic

distortion at the transformer primaries between 4% and 6% this shows the effect of increasing the AC

input percent impedance on the input current harmonics the six pulse rectifier cannot reduce the input current total harmonic distortion below

25 percent even with an input AC reactor with 10 percent impedance and you can see that the 12 volts and 18 post rectifiers can achieve an input current total

harmonic distortion of less than 10 percent with the addition of an input AC reactor of 1 to 2 percent impedance so

as we have seen 12 posts or better yet 18 post drives are preferred over 6 pulse drives due to the reduction of harmonics

as a rule of thumb the magnitudes of the harmonic currents will be the fundamental current divided by the harmonic number for example the magnitude of v or money would be

one-fifth of the fundamental current VFDs also producer Munn occurrence at the output of the inverter which are

seen by the motor so let's talk about harmonic mitigation with the increasing demand of nonlinear type of equipment and loads mitigation of harmonics

becomes more and more important if harmonic study or testing indicates excessive harmonic levels or a potentially harmful resonance condition

mitigation must be considered depending on the specific situation there are often several different methods to look into for mitigating the harmonics so

what are some of the methods we can utilize to mitigate the harmonics well of course we could limit the amount of nonlinear loads but this is typically

not an option with the necessity of these loads with limited resources line reactors and motor drive isolation

transformers use reactive harmonic attenuation effect to reduce the actual current distortion at the input terminals to the drives line reactors

are more commonly commonly used because of their size and cost as we discussed earlier we could replace six post drives with higher pulse drives such as twelve posts

or 18 post drives harmonic filters can be used to mitigate problems as well they are used in applications with a high nonlinear load

to overall system ratio to eliminate the harmonic currents they can be tuned to specific harmonic such as the third fifth seventh eleventh etc to meet the

requirements of the I Triple E five nineteen standard active filters in certain negative harmonics into the network thereby eliminating the

undesirable harmonics on the network passive filters are a combination of capacitors inductors or reactors and resistors they're the most common and

are available for all voltage levels a resonance problem indicates removal or relocation of power factor correction capacitors overall it's important to

understand how the various system components interact with each other and with the power system it is essential that a coordinated solution be provided

which meets total harmonic distortion levels system performance demands and power system requirements correcting or mining distortion problem in the field

after installation can be very challenging time-consuming and very costly so now I'll go over a few of the

different filter types available for harmonics mitigation harmonic filters can be used to mitigate harmonic problems as well they generally consist of one or more

tuned inductor inductor capacitor legs which specific harmonic currents away from the power system they also offer

that it benefit of supplying leading reactive power and thus provide power factor correction here we have an active

filter front end with a LCL filter the active filter line and removes low frequencies less than one kilohertz the SEL filter which you can

see all this on the diagram LCL filter is a passive filter removes high frequencies greater than one kilohertz

current and voltage the SEL filter is inserted between the rectifier and the three-phase power supply this attenuates the full Smith width modulation

harmonics so the proper voltage and current total harmonic distortion levels are obtained for this particular setup no transformer is required and

performance is actually not affected by line imbalance a parallel active filter is an option to help mitigate or monix

it works by sampling the distorted current and uses fast-acting transistors to generate harmonic currents and inject them 100 degrees 180 degrees out of

phase the pros of using these filters are their size - harmonic content only they maintain good performance at light

loads the cons of using these filters are they're expensive they're susceptible to background voltage total harmonic distortion and imbalance also

the complexity requires start-up and regular service by the manufacturer another option to help mitigate

harmonics is to use a VFD with an active front-end or also known as an active rectifier the six pulse diode bridge rectifiers replaced by a fully

controlled transistor bridge the pros of using this device are it ideally achieves the lowest current total

harmonic distortion it can provide regenerative regenerative braking the cons of using this device are it is

expensive it can introduce higher order harmonics and it can result in higher electromagnetic radiation as well the

complexity requires start-up and regular service the manufacturer so here we have an overview of the effectiveness of

different types of harmonics mitigation methods no mitigation can typically result in a 72% total harmonic current

distortion that's what doing nothing the percent harmonic reduction is based on the current total or a harmonic distortion for a given method as compared to no mitigation at all

so looking down the list you can see how different methods are more effective than others so harmonics can also be

measured or monitored using specific metering equipment a digital oscilloscope shows the wave shape total harmonic distortion and amplitude of

each harmonic a true RMS Multi multi meter gives correct readings for distortion free sine waves and typically read flow when the current waveform is

distorted the instruments used to measure harmonics should comply with the IEC specifications which are detailed in

I Triple E v 19 2014 standard their requirements for the measurement window in cycles to properly display the spectral components there are also

requirements for measurement of harmonics over daily and weekly observations so it's important to check the I Triple E 519 for these

requirements so harmonics and analysis is a mathematical way of simulating or predicting harmonic distortion levels

and potential resonances based on the power system data the electrical distribution system is modeled using proven engineering software and

harmonics analysis performed in conjunction with other power systems analysis such as short circuit analysis

etc it is recommended that the analysis be performed by definitely should be performed by a qualified person preferably a licensed electrical

engineer also mitigation myth can be analyzed to determine the effects of adding different types of equipment

to limit or eliminate the harmonics so when should a power distribution system be monitored or evaluated for harmonics

well it is it is always best to perform an evaluation of harmonics during the design stage this is very true if large capacitor banks which are typically used

for power factor correction or other harmonics generating equipment will be used also if capacitor banks will be incorporated into an existing system

harmonics analysis or evaluation should be considered especially if 20% of or more of the load includes other harmonic generating equipment it is recommended

that a harmonic analysis and power system modeling be performed in the event that large nonlinear loads will be added to a large facility especially if

the new loading comprises twenty twenty-five percent or more of the existing load if the facility has a history of harmonic related problems

such as brownouts voltage flicker capacitor fuses being blown or some of the other things I previously mentioned an evaluation should definitely be

considered so in conclusion harmonics can result in decreasing power system reliability understanding the causes

potential effects and mitigation methods can reduce or eliminate our Monica type problems mitigation should be considered

if nonlinear loads are significant portion of the total system load which we went over also in conclusion applying the harmonic limits for I

Triple E 5:19 can be challenging and it's important to understand the requirements mitigation methods can be determined with a proper harmonics

analysis it is recommended that the harmonics analysis be performed by qualified personnel and it is essential that a coordinated solution be provided which makes

the total harmonic distortion levels system performance demands and power system requirements and that concludes the presentation once again I appreciate

your time and I apologize if I was unable to answer any other questions however I will follow up with an email to each and every questions that were

submitted and thank you