Vector group

In Case of Dyn11 - Phase displacement b/w windings is 30deg

In case of yyno - Phase displacement will be "o"

Just keep in mind clock position.

ADVANTAGES OF THE Y-Y CONNECTION:

1. The primary and secondary circuits are in phase; i.e., there are no

phase angle displacements introduced by the Y-Y connection.

2. Since the phase-to-neutral voltage is only 57.7% of the phase-to phase

voltage, the windings of a Y-Y transformer require fewer

turns to produce the same level of excitation in the core compared

to windings connected across the phases.

3. If the neutral end of a Y-connected winding is grounded, then there

is an opportunity to use reduced levels of insulation at the neutral

end of the winding.

DISADVANTAGES OF THE Y-Y CONNECTION:

1. The presence of third (and other zero-sequence) harmonics at an

ungrounded neutral can cause overvoltage conditions at light load.

2. There can be a large voltage drop for unbalanced phase-to-neutral

loads.

3. Under certain circumstances, a Y-Y connected three-phase transformer can produce severe tank overheating that can quickly destroy the transformer.

4. Series resonance between the third harmonic magnetizing reactance

of the transformer and line-to-ground capacitance can result in severe

over voltages.

5. If a phase-to-ground fault occurs on the primary circuit with the

primary neutral grounded, then the phase-to-neutral voltage on the

unfaulted phases increases to 173% of the normal voltage.

6. If the neutrals of the primary and secondary are both brought out,

then a phase-to-ground fault on the secondary circuit causes neutral

fault current to flow in the primary circuit.

ADVANTAGES OF THE D-Y CONNECTION:

1. One of the major advantages of the D-Y connection is that it provides

harmonic suppression. Recall that the magnetizing current must contain odd

harmonics for the induced voltages to be sinusoidal and the third harmonic is

the dominant harmonic component.

2. Another important advantage of the D-Y connection is that it provides

ground current isolation between the primary and secondary circuits.

3. A transformer-connected D-Y with the neutral of the Y grounded is

sometimes referred to as a grounding bank, because it provides a local source

of ground current at the secondary that is isolated from the primary circuit.

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Thanks for your valuable information.