Assymetry in 3 phase supply
Assymetry in 3 phase supply
(OP)
"Transformers handle negatvie sequence components the same way they handle positive sequence components"
1 .Does that mean that the negative sequence do not have bad effects on transformers such as increased heating?
"zero sequence components affect transformers in a way that depends on their confirguration (i.e. whether delta/wye, wye/wye, etc.) and the presence of a nuetral"
2. What does this mean and what are the exmaples?
3. Can anyone explain the sequence components in a simple and practical way?
1 .Does that mean that the negative sequence do not have bad effects on transformers such as increased heating?
"zero sequence components affect transformers in a way that depends on their confirguration (i.e. whether delta/wye, wye/wye, etc.) and the presence of a nuetral"
2. What does this mean and what are the exmaples?
3. Can anyone explain the sequence components in a simple and practical way?






RE: Assymetry in 3 phase supply
RE: Assymetry in 3 phase supply
I don't see any reason that transformers would experience similar effects since in that case the negative sequence has the same frequency as the positive sequence.
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(2B)+(2B)' ?
RE: Assymetry in 3 phase supply
After doing this, if you have more specific questions, feel free to post them.
Regarding the transformer and negative sequence currents, I agree with Electricpete - the transformer doesn't care.
David Castor
www.cvoes.com
RE: Assymetry in 3 phase supply
RE: Assymetry in 3 phase supply
RE: Assymetry in 3 phase supply
RE: Assymetry in 3 phase supply
A less common way to use them is to describe a system that has harmonics instead of unbalanced currents or voltages. The harmonics 1, 4, 7 ... 3n+1 are positive sequence, 2, 5, 8 ... 3n+1 are negative sequence, and 3, 6, 9 ... 3n are zero sequence. If you are referring to harmonic sequence components, they do have higher heating effect that are solved by using k-factor transformers.
The Whys of Wyes does a great job explaining this other use of symmetrical components and also how the delta/wye configuration impacts zero sequence components.
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This paper has a more in depth explanation of how to denote the different meanings of symmetrical component.
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RE: Assymetry in 3 phase supply
I think this is one of those examples where two EEs can be talking to each other, both using the same words, and yet meaning completely different things.
When electricpete stated "the negative sequence has the same frequency as the positive sequence", my immediate reaction was...WTF?
I was about to send off a hastily worded missive until I suddenly realised that Oh, they're talking about the 'other' sequence currents. I'm someone who works with harmonics on a regular basis and so for me the sequence currents has to do with the harmonic order and it's nice to be reminded (hit over the head with) that there's other ways of looking at things.
RE: Assymetry in 3 phase supply
1. the reason why assymetry will cause increased heating in transformers is purely due to the presence of zero sequence current.(SINCE NEGATIVE SEQUENCE COMPONENTS DONT HAVE ANY EFFECT)
2. Tripple-N harmonics (3,9,15,21,...) can be thought of as zero sequence component.
Am I right or wrong?
RE: Assymetry in 3 phase supply
RE: Assymetry in 3 phase supply
Power frequency negative sequence components have the same heating affects on transformers as power frequency positive sequence components.
Harmonic components will cause extra heating do to frequency dependent losses in the copper and steel. As the frequency goes up, the amount of extra heat generated goes up. For these additional losses, the frequency is important, not a particular sequence.
Zero sequence components passing through a grounded wye/grounded wye transformer would cause additional losses just due to frequency dependent losses.
Zero sequence harmonics cause additional heating as they are trapped by delta/wye transformers and the current circulates in the delta winding. This is in addition to any frequency dependent losses.
RE: Assymetry in 3 phase supply
True, triplen harmonic currents have a higher frequency and higher frequency currents cause more losses. Not all zero-sequence currents are harmonics. An unbalanced fundamental frequency load can cause zer0-sequence currents.
Balanced 5th harmonic currents are negative-sequence. They also have a higher frequency. Does this mean that negative-sequence currents cause more losses than positive-sequence?
Balanced 7th harmonic currents are positive-sequence. They also have a higher frequency. Does this mean that positive-sequence currents cause more losses than positive-sequence?
RE: Assymetry in 3 phase supply
It is true that certain order harmonic currents **behave like** certain sequence currents. But they are not the same thing at all.
David Castor
www.cvoes.com
RE: Assymetry in 3 phase supply