Answer / bharadwaj.gajula

generally harmonics means ,the unwanted response at the output
....coming to electrically ,the 3rd harmonic components are
eliminated by connecting the alternator 3-phase windings are
in delta or star...but the star connection most preferable
compare delta ,because of the 3rd harmonics components
produces circulating currents,. it results to increase the cu
losses and heat due to that efficiency decreases .so star
connections most preferable

Answer / dinakar

As the question is what use we can make of 3rd
harmonic....even though it is an unwanted component but is
used in transformer to produce sinusoidal flux...by having
this 3rd harmonic in magnetizing current...i.e due to hysteresis

Answer / sidda raghavendra

actually Harmonics are unwanted frequencies but if we
needed pure dc we can add as much as harmonics such that
the sinsoidal wave becomes more flatter
If we use inverter it can reduce the efficiency.

Answer / ketul

Yy connection without neutral wires with both primary and
secondary connected in
star no closed path exists. As the triplen harmonics are
always in phase, by virtue
of the Y connection they get canceled in the line voltages.
Non-triplen harmonics
like fundamental, become rt3 times phase value and appear
in the line voltages. Line
currents remain sinusoidal except for non-triplen harmonic
currents. Flux wave in each
transformer will be flat topped and the phase voltages
remain peaked. The potential
of the neutral is no longer steady. The star point
oscillates due to the third harmonic
voltages. This is termed as ”oscillating neutral”.

Yy connection with neutral wires When a neutral wire is
provided the triplen har-
monic current can flow and the condition is similar to the
single phase case (with a star connected 4 wire source or
with the system earth).The neutral wire carries three
times the triplen harmonic current of one transformer as
these currents are co-phasal.
Unloaded secondary neutral will not be operative. In a Yy
connection, to obtain third harmonic suppression one may
provide a third
winding which is connected in mesh, which can be an
unloaded winding. It is called a
tertiary. This winding improves the single phase to earth
fault detection also. Further,
this winding can be used to feed some permanent station
loads also. Such transform-
ers are designated as Yyd transformers. If the neutral
wires are provided and also
mesh connected winding is present, then triplen harmonics
are ’shared’ between them
depending upon their impedances.

Answer / guest

It is increased the frequency 3 time more than supply frequency. For eg. Supply frequency is50hz then due to harmonics it will 150hz.

I need the recommended size for a 3 phase transformer at 13.8 KV Primary and connected loads of 3000 kVA at 4200 volts and 2375 kVA @ 480 volts AC.

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