How Do You Change Rotation Direction in Three Phase Motors

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A question came in from one of our viewers about HOW to change the direction of a three-phase motor. In the latest episode of Electrician U, Dustin answers this question in addition to explaining to us WHY we are able to do this in the first place!!
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With a single-phase motor, we are relying on 180 degree opposing stators to move the center shaft. In fact, with single phase motors, we are actually applying power to the Capacitor which then relays power so said stator. The reason for that is that the central shaft can become stuck in a center state, thus not moving when power gets applied. But by utilizing a capacitor, that capacitor causes a shift when it starts up (sort of acting like a kick starter on a dirt bike motor) that moves the rotor a bit and allows the opposing coils to actually do their job. A three-phase motor operates a bit different. In lieu of having the 2 poles 180 degrees apart, since we are using 3 phases, those poles are 120 degrees apart. Instead of one pole strongly pushing and the other strongly pulling the rotor, on a 3-phase motor, one of the poles is strongly pushing while the other two are each sharing the pull function. As the pushing pole winds down, the other 2 poles are picking up speed/strength and the rotor’s momentum can be kept going until it hits the next pushing pole thus making the motor much more efficient and really negating the need for a capacitor.
So, onto the reason of why and how we can make a three-phase motor spin the opposite direction. The answer lies in the phases we just spoke of above. As the rotor is spinning, the pole that has been strongly pushing, is transitioning to pulling less, while one of the others that has been strongly pulling is transitioning to strongly pushing. If we swap two of the three phases, this causes power to be applied in a slightly different sequence thus causing the motor to spin the other way!
We can utilize this ability to shift in a positive way. If we hook up a three-phase motor only to find it is spinning backwards to the way we want it to do, we can simply swap two of the three phases and have that motor spin the way we want it to! And it can be any of the three phases, not just two in particular. We can swap A & B, or A & C, or any combination of. There are even meters available (called phase rotation meters) that we can connect to a three-phase circuit to see which way it is going. These meters are useful when we are replacing a piece of existing gear feeding equipment! Simply check the rotation BEFORE removing the gear, hook up the new gear in the same phasing as the old (A, B, C= Black, Red, Blue for instance), and then recheck BEFORE you energize any equipment on the new gear. If it is not spinning the same way, just swap two of the legs feeding the gear and you are in business!! To change a motors rotation, you needn’t necessarily do it IN the gear that is feeding the motor, you could do it anywhere between the gear and the motor. Keep in mind, that if you change it on the line side of said gear, you will be changing ALL the load side feeders feeding OUT of that gear, and that could change rotation on OTHER pieces as well! To combat that, just change two of the three wires on the load side of the specific equipment’s breaker only!
We hope this has been an informative look into the way a three-phase motor operates and how you can change the rotation of a three-phase motor! Is there an electrically related topic you would like to see discussed here on Electrician U? Leave a comment in the comment section below and let us know what you would like to see. Please continue to follow Electrician U and Dustin’s adventures as we are constantly adding new content to help our followers be the best electricians they can be!
#electrician #electrical #electricity #terms of trade #customers questions #journeyman tips

Опубликовано:

26 июн 2022

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Комментарии : 93

@ericharrelson32 2 года назад

This is one of the best explanations I've seen; good job.

@bradunderhill157 2 года назад

Great refresher! 👍 love how you break everything down! The one thing I was waiting for you to say was why you wouldn't need a neutral because the circuit is in balance. BALANCE is key! Love you brother good work! 👍

@kennylavay8492 2 года назад

Another good educational video explained very well, keep em coming.

@notgoing2lie 2 года назад

Awesome video, thanks for the explanation it helps me understand it a little better. I'm an apprentice and knew that flipping and 2 wires causes a reverse rotation but didn't quite understand why. Keep the Awesome videos coming because you are providing a ton of knowledge to people and knowledge is power! ⚡️💡

@Crazypug-eh7xi 2 года назад

Outstanding!! Great explanation! Thanks for the info

@morganyoung8272 2 года назад

good god your videos on phases just helped me so much dude i cant thank you enough!!!! journeyman was talking about rotation and i was not understanding anything he was saying lmao it never occurred to me that the generators on the utility side decide your rotation, we were hooking up a generator to a switch gear in a mall and we weren't sure what the generators rotation was and he was explaining it to me and how to check it and ive been confused for 3 days lmao, a 3rd year and i (only 5 months in btw) looked at eachother "yeah rotation 3 phase yeah makes total sense" lmao i havnt even started class yet and i feel like i understand sine waves, cant wait to be completly wrong haha THANKS AGAIN!!

@matthewclemons1574 2 года назад

In hvac we refer to “jogging” motors as “bumping” motors or compressors. On other topics I always found single phase vfd interesting.

@Mr.Sparks.173 2 года назад

In my machining days, "jogging" ment asking the machine to move an axis or two into a hopefully useful position as fast as the machine and physics would allow. And yes, that is definitely one situation where Dustin's little rotation meter would be invaluable- cause those stepper motors can run either way, but the lead screw and table its attached to would have some complaints if spun too far on their extremes. Definitely in the tens of thousands of dollars level of complaints, to say nothing of potentially damaging the machine's ability to hold a tight tolerance permanently.

@2011craggie 2 года назад

Awesome info!! Thank you for my daily dose of electrons!!!

@freddybee4029 2 года назад

3rd year electrical apprentice knowledge. Great refresh video for all electricians.

@UMBRELLAUNIVERSE888 9 месяцев назад

I love This Chanel Started watching 2 Weeks Ago and It’s best The Best

@emmanuelmata 2 года назад

damn this is the best explanation on 3-phase I've seen thanks man

@An0nAm0nda 2 года назад

Thank you!

@dilanruwanthilaka2739 Год назад

Excellent explain 👍

@Ruben-is3re Год назад

The 😂 the pecker head of the motor.! ❤ much love bro that’s what we call the compartment where the wires hook up on a Copeland compressor. Lol great content please keep it going. Your the best for sharing your knowledge with us. Thank you

@gcg9056 10 месяцев назад

very, very good,,, thx

@michaelwheatley3064 2 года назад

Great video

@markchidester6239 Год назад

This also gave me a better understanding of why a three phase motor draws such a low current when unloaded.

@jim878 Год назад

This is perfect.

@Merescat 2 года назад

From light bulbs to moths! Gotta love it!

@elc2k385 2 года назад

I like the white writeable screen with the black background and you in the foreground.

@danielfranchette5547 2 года назад

Good presentation, for those who are interested the theoretical bases of rotating magnetic fields are established in three-phase by the theorem of Ferraris (1847/1897) which shows the creation of a rotating magnetic field. single-phase by Leblanc's theorem (1857/1923) which shows the creation of two magnetic fields which rotate in opposite directions, due to the impossibility of correctly operating single-phase high-power machines (> qq kW).

@MrTooTechnical 2 года назад

This a great video. The push/pull concept is a little misleading and not the complete picture. Thanks again.

@RJ-ej1nr 2 года назад

Recently there was an extended power outage where the local utility hooked up temp power. Connected generator output phase A to substation output phase A, B to B, and C to C. And the water pumps started going backwards. Turns out with the generators and utility, the spec for one was clockwise and the other was counterclockwise. They powered down and swapped A and C and then it was good.

@michealplater9007 2 года назад

They do not have phase failure relays that trip if the phase rotation is incorrect ?

@JohnThomas-lq5qp 2 года назад

On most VFD 'S there is a parameter that you can change to reverse direction. Do not use this on drives that have bypass because if you run it on bypass ( contactor M3 ) bypasses the drive and motor would run in opposite direction. Yes I came across this a few times.

@electricianslife1984 2 года назад

Love it

@E74RKTrishal Год назад

Nice

@kelpshake421 2 года назад

hey bossman, can you make a video on how to read prints? just started my ibew apprenticeship and want to get ahead of the game before school starts. thanks for getting me interested in the trade!

@marietonik 3 месяца назад

Thanks for the presentations it was very helpful! So I have a question: In quadcopters using bldc motors, it is necessary that 2/4 motors only have a CW direction and other 2 a CCW direction. If I have bought 4 motors with only 1 type of direction, the cabling of the 3 phases will solve the problem with the rotation or the flight controller software control?

@Elisummit845 2 года назад

HVAC guy here. I had a 3ph RTU (rooftop unit) that had 3 compressors. Got a call, ac not working. Got there and found 2 out of the 3 compressors where spinning the wrong way. Was the weirdest thing ever. Switched the wires and boom, all good. All you electricians, if you turn on (you really shouldn't lol) a 3ph ac, listen if the compressor sounds weird. Ps I used to be an electrician before switching to AC. Yes I love HVAC more lol.

@soranuareane 2 года назад

About the moths, here's what I was taught: in nature they come out at the full moon to mate and make little moths via the whole egg shindig. Artificial lights throw that off and so the moths go to the artificial lights looking for the moth-y equivalent of a Good Time. I have no idea if the pulsing affects this!

@justink7269 2 года назад

You just keep getting smarter and smarter Dustin. For a while I thought you were just generating content, but now all your videos have great substance

@MP57719 2 года назад

Do you have a rotation meter? Would love to see a video on one.

@ptrick213 Год назад

In the single phase sine wave diagram, what does the red line represent vs the black line?

@jasongillean44 2 года назад

As soon as you brought up moths being able to see light pulse 🤯🤯🤯

@TR4Ajim 2 года назад

Dustin when you mentioned how a light bulb actually flashes 60 times a second, is that the same thing as “60 cycle hum”? I’ve played electric guitar (single coil pickup) for many years and always heard a humming sound from my amplifier when not touching the guitar strings. In some clubs the hum would be very slight, but in others it was pretty loud. What causes that hum? Also why do “humbucking” pickups (with 2 coils) prevent or minimize that hum?

@spen.surrr1199 2 года назад

Yes. It’s because the hum of the power conductors are being inducing voltage on the signal wires and sometimes strings. Humbuckers don’t pickup this sound because it’s two coils wired in reverse so it cancels out the hum.

@ronburn 2 года назад

At some point can you talk about Wye vs Delta 3-phase and where you would use one vs the other?

@carultch 2 года назад

It has to do with whether the three windings of the transformer are wired sequentially across phases (delta), or whether they are wired to a common point in the middle that we assign as the neutral (WYE). This property is called transformer topology. You may also see it called the vector group. It is called Delta and Wye, because it looks like the Greek letter Delta, and the Latin letter Y, when you draw out the configurations. It is unrelated to Delta standing for difference in mathematics, and only relates to Delta's appearance. You may also hear WYE called "star". If there were four-phase, it would be Square and Plus. For six-phase, it would be Hex and Star. I'd like to see Epsilon (center-tap) and Iota (no center-tap) catch on to mean the equivalent thing for single phase, but so far it hasn't. Wyes are the most common to set up a grid, since it gives us two voltage values to work with, and symmetry among the phases. Deltas are used where it is unnecessary to fix the voltages relative to ground. You may also see mixed topology transformers, where the grid-side primary is delta, and the load side secondary is wye, because it mixed topology transformers have the advantages of harmonic cancelling and efficiency. At one point, there was a trend to install high-leg delta services, so that you could have 120V available for the minority of the loads, and 240V available to power the majority of big ticket loads on a 3-phase service. These are a lot less common, in favor of 120/208V wye systems instead.

@johnwalker890 2 года назад

And another thing about one of the comments, A single phase to Three phase converter is called a static converter, and it contains a few capacitors to make up the phase lost, it is sometimes easier to do transformer banking or more reliable.

@TnTBLACK95 2 года назад

Incadescent light bulbs do not pulse 60 times a second, they pulse 120 times a second. In one cycle you sine wave crosses zero twice, there is a positive and negative sequence. Incandescent bulbs are resistors and do not care the direction of flow.

@dustinbergeron7508 2 года назад

Hey I have a generator that runs but doesn’t put out any electricity I checked every fuse all good I checked the breakers I’m not even getting power to the breaker. What else can I check and how do I check it

@44R0Ndin 2 года назад

With most generators there's some electronics between the actual generator and the 120/240v AC output. Probably need to check and/or repair/replace that. Expect that electronics board to be either expensive or not available. If it's not that, it's the brushes and/or slip rings in the generator (the part that lets electricity into or out of the generator's rotor).

@duenge 2 года назад

About 8 years ago, I was a drawbridge operator, and my bridge was having its electrical control system replaced. Most of the new gear was placed before the old was removed. One of the electrical contractors was looking to find if something was right-handed or left-handed. Could this be the directionality that you referred to? He ended up using a meter to determine....

@Ephesians-ts8ze 2 года назад

The rotation is typically referred to as either clockwise or counterclockwise. It sounds like they’re talking about something else but maybe they are referring to phase rotation but using different terminology? I would call clockwise right-handed and counter clockwise left-handed if those were the terms used to depict direction of rotation

@Headbanger9000 11 месяцев назад

Left hand rule and right hand rule has to do with the direction that the magnetic field is moving in. Left hand means that magnetic flux is moving clock wise, right hand is counter. When working with 3 phase motors, typically you have to switch phases A and C to change magnetic polarity, which is what changes the direction of the motor.

@jamestoy426 2 года назад

Explain run capacitors along with start capacitor

@II-tp4rm 5 месяцев назад

If the motor spun the other way for about 20 seconds will that mess it up and if so how

@carlosgiron3834 2 года назад

8:18 reminds me of a rotary engine

@mackfisher4487 2 года назад

Nice explanation, great joke about the moths you probably start a new Internet legend.

@lockpickingvlad 2 года назад

How does 1-phase to 3-phase converter work?

@alecdacyczyn 2 года назад

It's AC-to-DC-to-AC3ph conversion.

@kc9scott 2 года назад

Modern units typically work as Alec mentions, and they’re also known as VFDs (variable frequency drives). But there are also a couple of older technologies. One is a rotary converter, which is much like its own separate motor, that spins to create the 3 phase power; I don’t know the details of how it works. The other type uses capacitors and perhaps also an inductor to shift the phase. At least with the capacitor-based ones, the motor you run from it will have less HP capability than its original rating.

@lockpickingvlad 2 года назад

Thanks for the information guys! 👍🏻

@TnTBLACK95 2 года назад

For a static phase converters2 hot legs of a single phase service will power 2 of the 3 phase. You will derive a 3 "phase" from the 2 existing phases and a start capacitor. Once running the 3rd phase will drop out and the motor will run on 2 phases.

@tommywatterson5276 11 месяцев назад

In generator the field rotates, the rotor is stationary

@kahlil4745 2 года назад

Do LED lights pulse? Do drivers go from ac to dc? Because bugs will fly around LED lights too.

@mattfleming86 2 года назад

Some do. Others do not. Both attract moths :-D

@noiseismymiddlename5669 2 года назад

6:00: 😆! But they are attracted to flashlights which are DC!

@slingblade05 2 года назад

Good point lol

@wilburrrrr742 2 года назад

I saw the title and said to myself... this is gonna be a 3 min video

@warnieday 2 года назад

Lol Dustin Stelzer aka Moth 🤣 really lmao

@briandillard8125 Год назад

Swap A and C everytime and never have to worry about high leg

@josueayalallanas7142 6 месяцев назад

The light bulb is actualy pulsing 120 times per second since one hert is 0 to peak positive back to 0 then peak negative then back to 0

@baverdi 2 года назад

Moths fly into candles.

@thebigd6249 Год назад

End of a motor where the wire leads are is referenced as the lead end and will be exemplified as LE. The other end is the SE which is shaft end. I know you know this Justin. I'm just helping some of your viewers because it also sounds better than pecker end. Lol.

@ikerivers1795 Год назад

The ends of a motor are; Drive End (back) and Opposite Drive End (front). The Drive End being the one that has the shaft. The connection box locations are F1 (left) F2 (right) and F3 (on top). Those are the NEMA terms. You are referring to fractional single phase motors used for fans and HVAC.

@thebigd6249 Год назад

@@ikerivers1795 hmm, I wonder why my 3 phase 9 lead motors say LE and SE on them?

@ikerivers1795 Год назад

@@thebigd6249 In HVAC, LE/SE terms are used. Because the motors are in an “enclosure” and do not need a raceway i.e. conduit. Motors outside of HVAC or enclosures use different nomenclature. I wrongly stated single phase fractional HP motors. That is incorrect, I went with the generalization. My bad. Certainly there are some 3 phase full HP motor in HVAC.

@johnwalker890 2 года назад

You need to get back in the field Dustin, and leave those moths and bugs alone. Just kidding, haha.

@alecdacyczyn 2 года назад

Lights flash 120 times per second.

@slingblade05 2 года назад

Well they go off 60 times and on 60 times so technically the flash is 60 times a second

@mg30ebay 2 года назад

@@slingblade05 They brighten at the positive peak, dim at the zero crossing, brighten at the negative peak, and dim at the next zero crossing. Two flashes per cycle.

@slingblade05 2 года назад

@@mg30ebay thanks for clearing that up

@lujitsu1251 Год назад

Ouch.

@JayVeeEmm.07 2 года назад

First!

@highvoltage1979 2 года назад

How is single phase 180° out of phase with it self. That is not true.

@TnTBLACK95 2 года назад

Single phase, referring to a residential single phase pot. You tap the secondary winding in the middle for your neutral, now your 120v lines are 180⁰ out from one another.

@highvoltage1979 Год назад

It may appear that way on a scope depending on how your leads are referenced, but single phase does not oppose itself in that way. If it was actually 180° out of phase you would have 120 volts from L1 to N and 120volts from L2 to neutral , but L1 to L2 would cancel itself out and be 0 volts

@TnTBLACK95 Год назад

@@highvoltage1979 no sir, they are 180⁰ out from one another. You have 2 halves of the same winding that are wound opposite of each other from the neutral tap. If you were to use a phasor diagram the 2 legs of a split bank would directly opposite of one another. Then using trig, in this case simple math, if given voltage and phase angles you can find any phase to phase voltage.

@rogerpenske2411 2 года назад

I’ve never been able to figure out why 220/240 two phase, is called single phase

@acog_quarks8753 2 года назад

I believe it’s because you have a single phase to phase reading. So you just have phase A and B reading, then your phase to ground. But in 3 phase you have readings for AB, AC, and BC. Plus the phase to ground

@JohnThomas-lq5qp 2 года назад

You appear to be confused. Any electrician would never call 240 volts two phase unless it was a now obsolete ( but still in use in Philly, Detroit & some other large old cities ) two phase that usually was 240 volt with both center point of the two phase connected together & grounded to provide 120 volts. ( Total of 5 wires ) In one old plant they had 2,300 volt two phase 3 wire feeding a separate building. They connected one lead from phase A & one lead from phase B. Johnnie homeowner often gets confused with the 3 wire 120/240 volt Edison system common in the USA. It's just single phase with a center tap in transformer supplying the neutral conductor.

@rogerpenske2411 2 года назад

@@JohnThomas-lq5qp Chicago

@RJ-ej1nr 2 года назад

The 240v wave form is single phase. There is no other 240v wave form in the system to be considered a second phase. Would you call a high leg delta a four phase system? There, the utility is only bringing in 3 phases.

@44R0Ndin 2 года назад

It's because it's single phase, center grounded, 240V hot to hot (and 120v hot to ground or neutral). There is no phase shift between the two hots in a 220/240v system. Or if you want to think about it as 2 phases of 120v each, there's a 180 degree phase difference between them so that when one's at max positive voltage the other's at max negative voltage, and vice versa. But the main thing to take away from it is that you can't get a motor to turn on single phase unless it's got a segmented armature that means it would also work on DC (and if you have a vacuum cleaner and 10 12v car batteries, you can make it work just fine on DC if you put all those batteries in series, this kind of motor is called a "universal motor" because it doesn't matter what kind of electricity it gets, it'll always spin the same direction). Whereas in a 208v three phase system, the phase difference between any two adjacent phases is 120 degrees, which makes it really easy to make electric motors turn using three phase electricity (that's why it's so common in commercial/industrial spaces).

@michaelwells7348 4 месяца назад

~ Personally I think that the Moths are Attracted to the light Cuz thats how U get to Heaven ...... Move into the light, and they are Tired of Being a Moth...