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# Looking for lecture for plus null minus system [solved]

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#### Grossel

##### Well-Known Member
Hi forum.

I do not know the correct english term for the subject (maybe not the greatest way to start off a thread).

I want to get a push in right direction where I can learn about theory about null/plus/minus (system ?) in 3 phase systems? Any teaching book/course you recommend?

null/plus/minus (system ?) in 3 phase systems?
Sorry, but I have never heard that expression before.

What does it do?

JimB

I was afraid of that - it is fully possible that it cannot be directly translated into english. What I do know is that it is a way of simplifying a 3 phase system before or while doing calculations.

Sorry, that rings no bells with me.

JimB

I'm not sure what you mean either. Are you referring to a so-called 'modified sine wave', such as used in many inverter circuits and where the waveform is +V, 0, -V, 0, +V, 0, -V ..... ?

Thanks for trying to help. If I do find an english terminology for this, I'll try to find this post and reply

I also do know this - from years back at school: Student that doesn't study specific for electrical engineering (3 phase system / power grid theory) here won't normally touch this topic. I assume that is the same for most other countrys as well.

Are you referring to "per-unit analysis"?

Thanks dknguyen, but it is not the per-unit analysis I'm looking for. That is btw pretty much the same in norwegian anyway.

My biggest problem here is that Google doesn't give any sensible returns when I do search for "null system" "plus system" "minus system". So I'm actually completely stuck as to be enable to provide enough info so that any one probably would know what I ask for. The poor results from Google searches indicates for me that the topic is named something fundamentally different in english.

I do beleive (but have never learn in school) that "nul system" is when in a three phase system, one phase is considered as one phase system where neutral is threated as ground. That is a guess.

Is this what you're looking for?

Yes, but perhaps the general analysis method could be used in other disciplines?

Thank you, but no - that paper is for oil/seismic only.

Eureka - At last I found what it is named on english: symmetrical components fault analysis - that it is

it is named on english: symmetrical components fault analysis

Hmmm...

Maybe I have led a sheltered life, but I have never heard of it.

JimB

Eureka - At last I found what it is named on english: symmetrical components fault analysis - that it is
That...doesn't sound like the translation at all lol.

In 3 phase system symmetrical component analysis, fault currents are separated into three components: positive sequence, zero sequence, and negative sequence. Those were the 3 terms Grossel was having trouble finding the translations for. The positive sequence current has the same phase rotation as the power system. The negative sequence currents have a phase rotation in the opposite direction, and the zero sequence have no phase rotation at all.

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