Answer / prashanth kumar hg

Apart from the Primary & Secondary windings, there
sometimes placed a third winding in power transformers
called "Tertiary Winding".
Its purpose is to provide a cirulating path for the
harmonics (especially third harmonics) produced in the
tranfmormers along with power frequency (50Hz. third
harmonic means 150 Hz oscillations).

Answer / amit sharma

In delta-delta, delta-star and star-delta transformers all
voltages are balanced and there is no floating of neutral.
The floating of neutral is developed in the case star-star
connection only. The transformers are sometimes constructed
with three windings. The main windings are connected to
form star-star connection and the third winding known as
tertiary winding is used to make a closed delta connection
to stabilize the neutrals of both primary and secondary
circuits. The tertiary winding carries the third-harmonic
currents.

HARMONICS are caused because of use of high flux densities
in the core. If the core gets saturated during part of the
sinusoidal wave, then secondary wave will be non-
sinusoidal. This may be due to inadequate core area or
characteristics of core material.

Harmonic currents result in higher copper loss, core loss,
magnetic interference and interference with communication
systems.

Harmonic voltages result in increased dielectric loss,
interference with communication systems and resonance
between inductance of the winding and capacitance of
transmission line.

Answer / deepak

Its purpose is to provide a cirulating path for the
harmonics (especially third harmonics) produced in the
tranfmormers.as well as harmonics it may be use for loading
purpose.

Answer / raghu

Its purpose is to provide path for 3rd harmonic currents.
Along with that it can be used for interconnection of power
systems operating at different MVA level.

Answer / abhidewas

tertiary winding is provided for ELIMINATION OF HARMONICS.

also it is always connected in DELTA.
bcaz in delta the harmonics are eliminated by circulation.

Answer / pradeepkumar

Apart from the Primary & Secondary windings, there
sometimes placed a third winding in power transformers
called "Tertiary Winding".
Its purpose is to provide a cirulating path for the
harmonics (especially third harmonics) produced in the
tranfmormers along with power frequency (50Hz. third
harmonic means 150 Hz oscillations

Answer / sri

some more information about tertiary winding

ref:
http://answers.yahoo.com/question/index?qid=20090731083908AADwAY1

One purpose may simply be to provide an additional terminal,
often at a different voltage. While the use of 'three
winding transformers' is relatively unusual, it can be a
powerful tool is system architecture.

The other objective for a tertiary winding is to provide a
closed-circuit path for zero-sequence currents/fluxes. That
is most typically the case with transformers that, for
system reasons, must be connected wye-wye (star-star for
those in the IEC world). With a wye-wye transformer, the
only path for zero-sequence flux is the tank of a
transformer (and if the three-phase bank is comprised of
three single-phase units, even that does not exist). The
tank is a high-impedance path, so the result is that the
zero sequence impedance seen looking into the transformer is
very high. Also, the circulation of zero sequence current
through the tank will cause the tank to heat and lead to
paint failure. A tertiary winding presents a low impedance
path to zero sequence currents, thereby reducing the zero
sequence impedance presented to the outside world, while
avoiding the problem of tank heating.

Answer / subhajit saha

tertiery winding of a transformer is connected in delta and
having lowest KVA rating.(transformer containing 3 windings
is not having same kva rating for primary and secondery.
Primary kva rating is maximum, tertiary lowest and secondery
intermediate.)
The main advantage is to suppres the 3rd hermonics mainly
generated in case of unbalanced load in a star star
transformer.So as to keep the system stable.

It may also be used to supply substation auxiliaries at a
voltage different of those primary or secondary.

It reduces the impedence offered to the zero sequence
currents to allow sufficient earth fault current for proper
operation of protective relays.

To supply power from two sources where continuity of supply
is required.

Answer / anil prajapati

TERTIARY WINDING

In Δ - Δ, Δ -λ and λ - Δ transformers all voltages are balanced and there is no floating of neutral. The floating of neutral is developed in the case λ- λ connection only. The transformers are sometimes constructed with three windings. The main windings are connected to form λ- λ connection and the third winding known as tertiary winding is used to make a closed Δ (Delta) connection to stabilize the neutrals of both primary and secondary circuits. The tertiary winding carries the third-harmonic currents and zero sequence currents (3I0).
HARMONICS are caused because of use of high flux densities in the core. If the core gets saturated during part of the sinusoidal wave, then secondary wave will be non-sinusoidal. This may be due to inadequate core area or characteristics of core material.
Harmonic currents result in:
1. Higher copper loss
2. Higher Core loss
3. More Magnetic Interference
4. Interference with Communication Systems.
Harmonic voltages result in:
1. Increased dielectric loss
2. Interference with communication systems and resonance between inductance of the winding and capacitance of transmission line.

Importance:
Importance of tertiary winding is given below:
1) To supply small additional load at a different voltage.
2) To supply phase compensating devices such as capacitor for power factor improvement which can work at different voltages.
3) In Delta connected tertiary winding reduces Zero sequence impedance and allow adequate current for operation of protective device in order to limit voltage imbalance which may be produced when in balance in load.
4) It indicate voltage in high voltage transformers.
5) It limits the fault current to flow.

Answer / nhasan

1. It provides a path for third harmonic currents.
2. It helps stabilize voltages in the Y-Y primary-secondary connection.
3. It provides a grounding bank action by providing a path for zero sequence currents.
4. It provides the necessary voltage taps for regulating the low-side
voltage.

why we have to particulary use ACB for below ratings,even available of MCB,MCCB with that range ?

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