Phase Rotation 2

[Lenz81]

Hello Everyone

Is that true that Phase Rotation in UK is Negative Sequesnce ? If so why !!!

Thanks
Lenz

 

[cranky108]

Why would that be important? The phase rotation in parts of the US is ACB (negative sequence).

 

[rbalex]

Motors rotate, some magnetic fields rotate, phasors rotate; but phases don't rotate - they oscillate in a specified peaking sequence.

As cranky108 noted, several US utilities have adopted an ACB phase sequence.

If equipment is installed in the US, phase sequence is mandated by various sections of the NEC; e.g. 408.3(E).

 

[Lenz81]

Thanks guys , i know Phase is not Rotating and just Oscillating , i am trying to find out if there is an historic reason behind that or any technical advantageous .

 

[electricpete]

There is no technical advantage of ABC vs ACB power system.
Our power system is ACB, and I experience modest difficulties communicating my rotation needs with motor repair shops (you’d think it’d be simple), but nothing that can’t be overcome. As a result of a few historical mis-steps, we spend a little more effort... in some cases where bump check for rotation after installation is not acceptable, we do our own on-site rotation checks of large motors.

Also, for an ACB power system, I personally would call ACB positive sequence and ABC negative sequence. Because for example our negative sequence relays will sense the component of current flowing as ABC. As long as you know what you’re doing, I guess it doesn’t matter what you call it.


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(2B)+(2B)' ?

 

[rbalex]

There is no inherent advantage either way. Basically, it is simply local convention which was probably a 50-50 toss up at the time.

 

[jraef]

I once worked for a mfr of solid state motor control equipment and one of our new product design engineers added a phase sequence protection feature without thinking it needed to offer either sequence, it always looked for ABC input. It turned out to be a MAJOR omission, none of our products would work in much of the Western US!

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[ScottyUK]

In the UK our phases have an R-Y-B sequence on the HV system, and thanks to Europe the LV system has a U-V-W sequence. Makes sense. Sort of.


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If we learn from our mistakes I'm getting a great education!

 

[cranky108]

The biggest problem is when you order equipment like switchgear. And if you have both rotations, the switchgear manufactures get really confused.

And even some relay manufactures have been confused.

That's the biggest drawback.

The rotation issue started as a nameing issue. The left wire is A, and the Right wire is C.

Now you should ask how many utilities are 30 degrees different from there phase A and the neiboring utilities phase A.

 

[Lenz81]

Thanks Scotty ,Rotation is clock wise ?

 

[Marmite]

In the UK "National Standard" phase rotation on the transmission system is anti clockwise, sequence RYB. There are some networks belonging to the distribution Companies that have clockwise phase rotation for historic reasons.
Regards
Marmite

 

[davidbeach]

No, electrical phasors, by definition, always rotate counter- (anti-) clockwise. They may rotate in an A-B-C order or they may rotate in an A-C-B (substitute any other phase designation desired) order, but always counter clockwise. Some systems are A-B-C and some A-C-B (C-B-A), but always CCW. Some utilities have voltages that are A-B-C while other voltages are A-C-B, while others are all A-B-C or all A-C-B. In the US it is likely to be far more of a mess than in Europe. The total devastation of much of Europe following WWII made it easy to apply a few standard broadly. Nothing like that has ever happened in the states and we are left with an interconnected hodge-podge of systems that were once all stand-alone. Some of it makes more sense than other portions.

 

[sibeen]

In Australian cities in can go one way in the central business district (a-c-b) and be the opposite (a-b-c) in the suburbs. Can be an absolute pain in the arse trying to explain to the sparkies that you need to have two of the phases swapped.

In both scenarios the definition is widershins

 

[rcw retired EE]

ABC, UVW, RST, red-blue-yellow, red-orange-yellow, black-red-blue, brown-orange-yellow, red-white-blue, T1-T2-T3 are all phase designations we have come across with further confusion by calling for counter-clockwise or clockwise rotation.

Is that rotation of the phasors, the spin direction of the phase rotation meter dial, the motor, turbine or generator rotation? From which end? (A major turbine supplier looks at the turbine and the generator from the coupling. The turbine rotates CW and the generator rotates CCW on the same shaft.)

The best description is "The voltages on terminals U1, U2, U3 will reach their positive maximum in the following sequence: U1, U2, U3." If my U1 connects to your phase C, and U2 to B it is ACB sequence.

Then we confuse ourselves by saying Phase A is on the left. Is that looking out from the substation to the line or looking into the substation? On double ended subs, either A needs to be on the right at one end or a phase swap occurs in the middle.

Bottom line, it's just names and we call the same thing different names with different reference points. When interconnecting make sure you communicate with your counterparts. Draw a vector diagram with a rotation arrow. On substations, sketch a phasing diagram. It is a real pain to swap the buswork.

 

[Skogsgurra]

LPS for you Curt!

The problem is that most people want it short and simple. Motor runs backwards. That is a simple statement.

Why does it run backwards? Because someone wired it the wrong way! Or Because someone defined phase sequence the wrong way! Or Because my definition is right and yours isn't! It starts getting complicated already.

And then we haven't even started talking vectors and vector rotation and the fact that all rotating systems have negative (CCW) vector rotation defined as positive - simply because angles grow positive when rotating "backwards" in cartesian and polar diagrams. And so on.

Many of the posts in this thread start somewhere between motor shaft and definition of poistive angle in a polar diagram. That does not make the the issue any clearer. Personally, I think it is a non-issue.

I used to make sure the phase sequence was always "right" when commissioning new industries or new parts of an existing industry. Then I made sure that the phase sequence definitions and rotation definitions were understood by everyone involved.

After that, we walked through all motors and marked their intended rotation with permanent ink. Then we corrected all drawings and wiring diagrams/tables.

A very common remark was "It doesn't matter - more than half will still run wrong direction" They didn't. We saved lots of time and I got a reputation to be good at commissioning factories. Which I thought was good.

Also, reconnecting a heavy gauge cable ruined the good work made by the electrician and avoiding that results in a more reliable plant in the long run.



Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.