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08-18-2013 09:35 PM

unbalanced load distribution among three phases in a building

What can be the effects of unbalanced load distribution among three phases in a building?

Can it cause any problem to the Equipment s connected?
08-18-2013 10:08 PM
Top #2
08-18-2013 10:08 PM
Unbalanced loading may result in unbalance voltage drop and thus unbalanced voltage levels for rotating 3 phase motors. If the unbalanced is substantial it increases rotor heating due to negative sequence magnetic flux generated in the stator counter to the rotor rotation, which induces negative seq voltage on the shorting bars and hence negative sequence short circuit current in the rotor.
08-18-2013 10:09 PM
Top #3
08-18-2013 10:09 PM
Most cases when you have 3phase into the same building and it is unbalanced depending on the level of imbalance,the first sign is drop in voltage level of the overloaded line.If the imbalance is small,you may not physically notice anything except you take measurement or are using sensitive load. But the consequences of imbalance could be felt by the other consumers all the way to the transformer,the voltage will drop.If the imbalance is huge,the circuit breaker will trip or fuse will rupture.It impacts on 3phase load more as Raymond has earlier described.
08-18-2013 10:10 PM
Top #4
08-18-2013 10:10 PM
Unbalance affects power factor, sometimes overload the transformers, overloads the neutrals, the active and reactive power behavior does not comply with the known rules of the power triangle, etc.

Under balanced load power triangle is ok, but under unbalance load is not right and you should use the buchozlt equations or the CPC theory in order to study your power system.

I would like to recommend you a book: "Power definitions and the physical mechanism of power flow" by Alexander Eigeles Emanuel, specially dedicated to study unbalanced systems with and without harmonics.

I wrote a paper some years ago regarding this issue. Paper deals with practical applications of the CPC and Emanuel theories applied to industrial power systems under unbalanced loads if you wish i can send you a copy.
08-18-2013 10:12 PM
Top #5
08-18-2013 10:12 PM
Unbalanced loads create power losses i.e when the phases aren't symmetrical harmonics is generated and their is current on the neutral phase. This hence causes a cumulative current of (4 phases)R,Y,B,N instead of the 3 phases.The resultant power is high than the ideal power hence power wastage
08-19-2013 09:10 PM
Top #6
08-19-2013 09:10 PM
You can easily separate those from people who have been in the field, as distinct from those who may not have practiced their electrical engineering at the 'sharp end' - that is, in the field. All the views were relevant, though.

1. If you are faced with the negative effects of an unbalance 3-phased problem, the first sign is annoying tripping of protective systems like circuit breakers or alarms.
2. Usually this tripping will occur even when the highest current reading in one of the phases is less than the current rating of the supply source - say generator set. You could spend valuable time trying to find the faulty equipment or circuit. You won't find it - because there is none!
3. The imbalance will cause a resultant current to flow to earth, via the neutral point. Most protective systems monitor the level of current flowing through the neutral line. if this exceeds a certain level, the system will trip on earth fault.
4. The other noticeable effect is felt more in the telecoms industry - that is the harmful effects of harmonics.
So, if you don't want to lose your hair, keep your circuits balanced!
08-21-2013 09:39 PM
Top #7
08-21-2013 09:39 PM
Unbalanced loads cause crappy power factors, and will effect the peak demand billing by the supplier, you will probably pay a much higher rate.
The neutral in a 3 phase system caries the differential in load, and as in most cases the "neutral conductor" is the same size as the phase conductors you will never get oerheating???????
Wow??? and the volt drop?? please take into account cable distance when designing airconditioning or any other circuit for that matter, and you should never have voltage dropp (in an ideal world, agreed) but the levels should never xceed 10% anyway if correctly designed Bla Bla Bla, Uh waht was the question again?????
I will let all you experts tackle that one!!!!
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