Linear and Non linear

[The electron man]

Hey guys new electrician here been doing it for 2 year and I've always here the term Linear and Non linear loads , harmonics but having a hard time understanding it , if someone can explain it in a simple form I would greatly appreciate it thanks

 

[LarryFine]

Basics of Current

Understanding basics of current- Type of current, electrical power consumption, Watt, VA

www.leonics.com

Linear and Nonlinear Electrical Loads | Electrical Wholesaler

Want to know the difference between linear and nonlinear electrical loads? Read more from the trusted electrical wholesaler company, Nedlands Group.

nedlandsgroup.com.au

 

[Strathead]

Non linear loads create harmonics on the neutral. I hope you understand what a harmonic is. If so, then know that double triple quad harmonics etc. are all created. Now the complicated part. Where the NEC is concerned is with 3 phase wye systems whenever all three phases share the neutral. What you will read often is “triplen” harmonics. What that means is harmonics divided by three. The why goes back to understanding harmonics. Three phases of triple harmonics on the neutral don’t oppose each other, instead they line up with each other and add together. The 6 harmonics, 9 harmonics etc. do the same. Thes currents add to any linear unbalanced current on the neutral. This can cause currents higher than the current on any of the hots and can exceed the ampacity of the wire. I am curious if this is a, understandable explanation and hope to get critique from the super brains here.

 

[The electron man]

Non linear loads create harmonics on the neutral. I hope you understand what a harmonic is. If so, then know that double triple quad harmonics etc. are all created. Now the complicated part. Where the NEC is concerned is with 3 phase wye systems whenever all three phases share the neutral. What you will read often is “triplen” harmonics. What that means is harmonics divided by three. The why goes back to understanding harmonics. Three phases of triple harmonics on the neutral don’t oppose each other, instead they line up with each other and add together. The 6 harmonics, 9 harmonics etc. do the same. Thes currents add to any linear unbalanced current on the neutral. This can cause currents higher than the current on any of the hots and can exceed the ampacity of the wire. I am curious if this is a, understandable explanation and hope to get critique from the super brains here.

I have no idea what harmonics are lol you lost me

 

[ActionDave]

Before you get to harmonics understand that a linear load would be an incandescent light bulb or an electric baseboard heater, the voltage in the AC circuit rises and falls 120V above zero and below zero and the current used to make light or heat in that circuit rises and falls in sync with that change in voltage, or linearly.

Electronic loads take a bite of current at different points of the voltage rise and fall so the current used in that kind of circuit is not in sync with the change in voltage, in other words, non-linear.

 

[LarryFine]

Loads that are inductive and/or capacitive, jointly called reactive, cause the current wave to be out-of-sync, or non-linear, with the voltage wave.

 

[gar]

230530-2010 EDT

LarryFine:

I have to disagree with your comment.

Neither a capacitive or inductive load on a sine wave voltage sources produces an out of sync or non-linear current.

These do produce a phase shifted result, but that is in sync with the voltage, and the current and voltage waveforms are still sinusoidal of the same frequency as the source voltage.

.

 

[Carultch]

I have no idea what harmonics are lol you lost me

Think about how you can tell the difference between a flute and a trumpet, both playing the same note. Suppose they both play a 220 Hz A-tone. They will both have a fundamental 220 Hz frequency, and a combination of higher frequency tones that are usually whole numbered multiples of it, like 440 Hz, 660 Hz and 880 Hz. This combination of tones adds up to form a wave shape, that isn't a pure 220 Hz tone, but instead a wave shape specific to the instrument's sound. A flute is dominated by the low tones, while a trumpet has a lot more and a lot louder of the higher tones mixed in with it. The lowest (and usually loudest) tone is called the fundamental, which is the 1st harmonic that governs the music note you hear. The higher frequencies (aka overtones) are the harmonic tones of a higher number, like 2nd harmonic, 3rd harmonic, and 4th harmonic.

The same thing applies to electricity. 60Hz is the fundamental, and harmonics are components of the waveform of higher frequencies. Most commonly, and most of concern for neutral wire sizing, is the 180 Hz harmonic and multiples of it, called triplen harmonics. This accumulates, rather than cancels. The grid is supposed to be a 60Hz pure sine wave, but it will inevitably accumulate harmonics due to the nature of the loads throughout it.

Some loads simply draw a current that directly follows the voltage waveform the source provides. The current waveform is just a re-scaling of this waveform (and a possibly phase-delay of the waveform, like capacitors and inductors). These are called linear loads.

Other loads draw a completely different shaped current waveform than the voltage waveform they are given. These are non-linear loads. This is common for electronic loads that use semiconductor components instead of just R/L/C linear circuit elements.

 

[EC Dan]

The ChatGPT asnwer:

In three-phase electrical systems, harmonics refer to the presence of frequencies that are multiples of the fundamental frequency. The fundamental frequency is the base frequency at which the system operates, typically 50 Hz or 60 Hz depending on the region.

Harmonics can be generated in a three-phase system due to various factors such as nonlinear loads, switching operations, and unbalanced conditions. Nonlinear loads, such as power electronic devices and certain types of machinery, draw current in a non-sinusoidal manner, resulting in harmonic currents. These harmonic currents can introduce harmonics into the system voltage as well.

The presence of harmonics can have several effects on the electrical system, including:

1. Distortion of voltage and current waveforms: Harmonics introduce additional frequency components, causing distortion in the sinusoidal waveform of voltage and current. This can lead to voltage and current waveforms that are no longer pure sine waves.
2. Increased losses: Harmonics result in increased losses in electrical equipment, particularly in transformers, motors, and cables. The additional harmonic currents lead to increased heating and energy losses in these devices.
3. Overloading of neutral conductors: Unbalanced harmonic currents flowing in the neutral conductor of a three-phase system can lead to overloading of the neutral conductor, causing overheating and potential damage.
4. Interference with sensitive equipment: Harmonics can interfere with the operation of sensitive electronic devices and control systems, leading to malfunctions or inaccuracies in measurements and control signals.

To mitigate the effects of harmonics in three-phase systems, various measures can be taken, including:

1. Filtering: Installing harmonic filters can help to suppress harmonic currents and voltages, reducing waveform distortion and mitigating the adverse effects of harmonics.
2. Proper grounding: Ensuring proper grounding and bonding practices can minimize the circulating harmonic currents and reduce the risk of neutral conductor overloading.
3. Load management: Balancing loads across the phases and avoiding the use of nonlinear loads during peak demand periods can help to reduce harmonics in the system.
4. Compliance with standards: Following international standards and guidelines, such as IEEE 519 or IEC 61000-3-2, can help ensure acceptable levels of harmonics in electrical systems.

Overall, understanding and managing harmonics in three-phase electrical systems are important to maintain system performance, efficiency, and reliability while minimizing the potential negative impacts on equipment and sensitive devices.

 

[xformer]

Before you get to harmonics understand that a linear load would be an incandescent light bulb or an electric baseboard heater, the voltage in the AC circuit rises and falls 120V above zero and below zero and the current used to make light or heat in that circuit rises and falls in sync with that change in voltage, or linearly.

Electronic loads take a bite of current at different points of the voltage rise and fall so the current used in that kind of circuit is not in sync with the change in voltage, in other words, non-linear.

I like to describe current flow like a smooth stream. When loads are linear, the stream is really smooth. Nonlinear loads are like big rocks being dropped in the smooth stream. They cause big ripples to occur. Sometimes those ripples cancel and sometimes they add up to make a sunami of current. Then I describe how the Bose noise canceling headphones work. Wave smashing.

 

[wwhitney]

Hey guys new electrician here been doing it for 2 year and I've always here the term Linear and Non linear loads , harmonics but having a hard time understanding it , if someone can explain it in a simple form I would greatly appreciate it thanks

Linear loads are those which, when energized with a smooth 60 Hz sinewave voltage, will draw a smooth 60 Hz sinewave current. That sinewave current may or may not be in phase with the applied voltage.

Nonlinear loads can draw a current waveform that isn't a smooth 60 Hz sinewave. But often the current waveform is close to a smooth 60 Hz sinewave. And the difference between the two is often close to a sinewave of a higher frequency. When that higher frequency is a multiple of 60 Hz (such as 120 Hz or 180 Hz), then that higher frequency waveform is called a harmonic.

[The choice of 60 Hz in the above was arbitrary but done to make the description more concrete.]

Cheers, Wayne

 

[Omid]

As I can remember from long time ago:

When you turn on a switch on a light with an incandescent bulbs, in V =I x R the load is always a fixed number. So if you apply that formula at every point of time the shape of current(I) waveform follow the shape of voltage(V) waveform. for example for a 40 watt A bulb R is always I think about 360 ohm and the RMS current is 0.33 Amp. Note that RMS is not the max of the wave form but in a simple terms is like average of that current wave form*.
Now when you change the bulb to a 40 watt CFL the CFL ballast is not a constant load at every point of time so in V = I x R V which comes from POCO remain the same shape but R varies during every cycle of Voltage therefore shape of current waveform is not a smooth sinusoidal form(called it distorted) and does not follow the shape of voltage waveform even though it might still be in the sync of voltage wave form. The RMS (or average) current for a 40 watt CFL also remain the same 0.33 amp because even R varies the average R during one cycle remain 360 ohm.

Now base on a complicated mathematic theory every distorted sinusoidal waveform can be made by (or represented by) a number of sinusoidal waveform which their frequencies is a multiplier of that initial distorted waveform frequency (60 hz) which we call them it's harmonic. so mathematically we can replace or represent that 60 hz distorted current to the multiple waveforms which the first one or first harmonic is 60 hz wave, the 2nd is 120 hz, the 3rd is 180hz, the 4th is 240 hz and so on. the RMS of each one of these waves goes down as their frequency goes up too( I don't know in what rate though but it goes down with such rate that we can eliminate the higher frequency easily).

If you imagine we have a 3 phase panel and with only one circuit per phase and each circuit have only one 40 watt incandescent lamps load. when you add up those 3 current wave that come back to panel from 3 neutral lines to neutral bar at every point of time they add up to zero (you can draw the 3 waveform and each one has 120 degree lag and you will see at any point add up to zero). so the neutral current in service cable is zero. If you change the bulbs to CFL we have a distorted current waveform in all 3 lines and if we replace(mathematically) each current wave to its harmonic waves the first and second harmonic of each line will add up to zero but the 3rd harmonic of each line come to the same phase of each other and will not add up to zero (I know this might sounds complicated). So even though we have same load on all 3 phase but they don't add up to zero and we have load in service cable neutral line.

*Per Google: RMS or root mean square current/voltage of the alternating current/voltage represents the d.c. current/voltage that dissipates the same amount of power as the average power dissipated by the alternating current/voltage

 

[Omid]

*Revised

As I can remember from long time ago:

When you turn on a switch on a light with an incandescent bulbs, in V =I x R the load is always a fixed number. So if you apply that formula at every point of time the shape of current(I) waveform follow the shape of voltage(V) waveform. for example for a 40 watt A bulb R is always I think about 360 ohm and the RMS current is 0.33 Amp. Note that RMS is not the max of the wave form but in a simple terms is like average of that current wave form*.
Now when you change the bulb to a 40 watt CFL the CFL ballast is not a constant load at every point of time so in V = I x R Voltage which comes from POCO remain the same shape but R varies during every cycle of Voltage therefore shape of current waveform is not a smooth sinusoidal form(called it distorted) and does not follow the shape of voltage waveform even though it might still be in the sync of voltage wave form. But the RMS (or average) current for a 40 watt CFL also remain the same 0.33 amp because even R varies the average of R during one cycle remain 360 ohm.

Now base on a complicated mathematic theory every distorted sinusoidal waveform can be made by (or represented by) a number of sinusoidal waveform which their frequencies is a multiplier of that initial distorted waveform frequency (60 hz) which we call them it's harmonics. so mathematically we can replace or represent that 60 hz distorted current to the multiple undistorted waveforms which the first one or first harmonic is 60 hz, the 2nd is 120 hz, the 3rd is 180hz, the 4th is 240 hz and so on. the RMS of each one of these waves goes down as their frequency goes up too( I don't know in what rate though but it goes down with such rate that we can eliminate the higher frequency easily for simplicity).

If you imagine we have a 3 phase panel and with only one circuit per phase and each circuit have only one 40 watt incandescent lamps load. when you add up those 3 current wave that come back to panel from 3 neutral lines to neutral bar at every point of time they add up to zero (you can draw the 3 waveform and each one has 120 degree lag and you will see at any point add up to zero). So the neutral current in the service cable is zero. If you change the bulbs to CFL we have a distorted current waveform in all 3 lines and if we replace(mathematically) each current wave to its harmonic waves the first and second harmonic of each line will add up to zero(because line A, B and C have phase different) but the 3rd harmonic of each line come to the same phase of each other and will not add up to zero. So even though we have same load on all 3 phase but they don't add up to zero and we have current in service cable neutral line which return to POCO transformer.

*Per Google: RMS or root mean square current/voltage of the alternating current/voltage represents the d.c. current/voltage that dissipates the same amount of power as the average power dissipated by the alternating current/voltage

 

[GoldDigger]

I agree with Omid that the single defining characteristic of a linear load is that the current is constant multiple of the voltage. This is easy to understand where purely resistive loads are concerned. If the value of R in the equation V=IR is a constant over time and voltage the load is linear. Both inductive and capacitive loads loads are not linear by this definition since the voltage is proportional to either the first derivative or the first antiderivative (integral) of the current. But for the specific condition of a single frequency sinusoidal voltage or current function you can represent the phase relationship by considering the amplitude of both current and voltage as a complex number and the impedance as a complex number too.
If you have a sinusoidal waveform and you double the current, you double the voltage at each point in time. This is the extended definition of linearity.
If you look at DC or changes in the amplitude of an AC waveform, a light bulb in NOT a linear load because of the temperature coefficient of the filament resistance. If you double the sine wave voltage you do not double the sine wave current. But for the purpose of evaluating waveform distortion we still often call a light bulb filament a linear load. The key is that the thermal characteristics of the filament cause the temperature, and therefore the resistance, to be very close to constant at all points in the waveform.
If I apply a sine wave with a frequency of .1 Hz to a common light bulb you will see that it no longer acts like a linear load.
A typical motor behaves as a linear load as long as you do not drive the magnetic circuits into saturation.

 

[drcampbell]

Remember this?

Serious question. How often or when really would you ever need to know most things taught in AC theory levels 1 through 4 out in the field? To me it all seems unnecessary

AC THEORY

Serious question. How often or when really would you ever need to know most things taught in AC theory levels 1 through 4 out in the field? To me it all seems unnecessary

forums.mikeholt.com

This is why you need to study AC theory. If you learn the theory, you also learn linear and nonlinear loads. If you don't learn the theory, it's almost impossible to explain.

 

[Strathead]

I have no idea what harmonics are lol you lost me

We like to get really deep here, I am trying to keep it simple for you. Carultch gave you a somewhat complex answer to harmonics, but...
Very basically a sine wave, (look this up if you don't know, it refers to the mathematical shape of a sine wave.) A pure electrical wave is a sine wave that completes a full cycle 60 times in 1 second. (Carultch) alluded to music notes also being sine waves. So is light, microwave, radio waves, etc.

Now 60 hz sine wave goes from 0 volts to +170 volts to 0 volts to -170 volts to 0 volts 60 times in 1 second. If I have a sine wave that does that 120 time in a second, it would cross zero and peak at the same time that the 60 hz sine wave does. (It would also peak and cross 0 two more times in that same time frame). That is a harmonic. 240 Hz same thing. They are each harmonics of 60 Hz.

 

[The electron man]

Thanks to all you guys , lots of learning to do

 

[Omid]

I think out of sync or out of phase is NOT the same as nonlinear. Out of sync means the current waveform is lagging or leading the voltage wave this happen when you have a load like motors, or a bank of capacitors. The current wave form still has the same waveform which I think they call it fundamental waveform. If you have a 3 equal motors each in separate phases (A,B,C) the sum of currents from 3 line (both active and reactive *) on neutral would be zero same as a 3 phase motor you don't need to have a neutral line for it.

But non-linear load such as electronic ballast or electronic dimmer change the shape of current waveform. It can still be in sync with voltage or not but the shape is different. This type of load as I explained above create an additional current on neutral line even if you perfectly balance your load between your phases. For example if you run a multi line circuit to 3 set of fluorescent lights on phase A, B and C and each set has 10 equal lights even your 3 phase are balance but you still have current in neutral line.

Understanding the physical meaning and effect of voltage and current being out of sync

In alternating current, we may have inductors and capacitors which make voltage and current become out of sync. At the beginning, I was stuck because how can it be that there is first voltage and ...

physics.stackexchange.com

https://www.researchgate.net/figure/Distorted-Waveform-Composed-of-Fundamental-and-3_fig1_314079514

* Those type of current can mathematically represented by 2 current wave active and reactive.

 

[gar]

230601-2356 EDT

If I have two signals that are in sync, then a plot on a dual channel scope where one signal is used to sync the scope time base to said signal, then the second signal will display in some fixed time relationship to the first signal.

Otherwise the signals are out of sync with each other.

The two signals do not need to look alike to be in sync.

.

 

[Jraef]

Here’s my try.

In “traditional” AC loads, meaning BEFORE the age of electronics, the load will pull current from the AC line in the same way that the AC sine wave cycles back and forth. That is what we refer to now as “linear” loads, because the current is drawn in line with the voltage. This term “linear” was not used until there was something to compare it to, so it’s still not really that relevant unless discussing the alternative below.

With the advent of electronics that use DC power, you must convert the AC to DC using a “rectifier”. Part of the rectifier is a device, usually now a diode, that is like a “one-way valve” for electrical current flow, meaning it only conducts in one direction, it blocks current flow when the sine wave reverses. Multiple diodes configured back to back in what’s called a “bridge” will allow converting both sequences (positive and negative) if a sine wave to be used to produce the DC. But the main problem with a diode is that it dies not conduct continuously throughout the rise and fall of the sine wave voltage. A diode has thresholds of voltage in which it conducts, called “conduction thresholds” or “biases”. So if we imagine a sine wave of a 120VAC circuit, a diode on that circuit will not conduct until the sine wave rises to 90V, then stops conducting when the sine wave drops below 90V (this is over simplified to illustrate the point). But a load on the DC side of the rectifier will want to PULL the current that it needs regardless of whether the diodes are supplying it or not. So the rectifier will have capacitors that store and discharge their energy to ride through those non-conducting periods in each sine wave cycle ahead of the diodes. That then means that ALL of the current needed by the load must be pulled through the diodes in short gulps or “pulses” of current that occur only at the peaks of each incoming sine wave. So because the current in NOT pulled by the load on the linear fashion described above, it is referred to as “non-linear” current, or a “non-linear load”. So ANYTHING that is using DC that is supplied by an AC source is referred to as “non-linear”.

Harmonics are an EFFECT of non-linear loads on the AC supply source. The pulsing of the current causes reverse ripples in the spline waves of the source voltage. These ripples then can cause other equipment being fed from the same source to have to content with the added heating effect these ripples cause, which is why we need to be concerned. If you want to demonstrate this to yourself, put a pistol grip spray nozzle on your garden hose, turn on the water, then squeeze and release the grip so that you make the water pulse as rapidly as you can. Then while doing this, take a look at the hose behind you, you will see it jumping and dancing around at rate commensurate to your pulsing. That is a “harmonic” created on that supply source. It has little effect on a hose, but it’d that were wires or windings in a transformer, the harmonics react with the resistance (impedance) in those AC components to create additional unwanted heat.