1.OPEN DELTA CONNECTION: In this type of connection one phase remove from three phase delta connection,thus remains two phase form an open delta circuit.
By removing one phase from delta,remains two phase from V-shape.Thus it is also known as three phase V-V transformer.
The given below images show open delta connection type transformer.
Open delta connection
Uses: The use of open delta connection type transformer is given below:
1.When three phase load on transformer is much less than rated capacity of transformer and no small capacity transformer is available.
2.When one phase of delta connection type transformer is damage and thus we can use this type of connection.But load on the transformer should be 58% of the rated capacity of transformer.
3.When at starting the load on transformer is less.But in future it will be increase.So we use this type of connection.
Drawbacks:The drawbacks of this type of connection is given below:
1.The capacity of this type of transformer is 58% of delta-delta connection transformer.
2.The power factor of this type of transformer is less (86.6%).
3.On increasing load the voltage will become unbalanced.
2.INTER CONNECTED STAR CONNECTION: The connection of this type of transformer is like zig-zag.So this connection is also known as zig-zag connection.
In this type of connection primary winding may be star or delta connected,but secondary is in the form of zig-zag.Thus be obtain different phase by this connection.
The given below image shows the inter connected star connection:
Inter connected star connection
3.SCOTT CONNECTION: This connection is introduced by Charles F.Scott.So this connection is known as Scott connection.
This type of connection is mainly used to convert three phase supply into double phase and double phase supply into three phase.So this is also known as phase changing supply transformer.
The given below images show the scott connection transformer:
Scott connection
This type of transformer made by the combination of two single phase transformer.In above image horizontal transformer is known as main transformer and the vertical transformer whose one end of primary winding is tapped with mid point of primary winding of main transformer is known as teaser transformer.Thus we get the supply from secondary of these transformer.
At the time of scott connection the main point should be remembered in mind:
1.The number of turns in primary winding of teaser transformer is 86.6% of the number of turns in primary winding of main transformer.
2.The number of turns in secondary of both the transformer is always same.So we gets the same voltage.
3.On three phase side the tapping is done at 50% on primary winding in main transformer and in teaser transformer the tapping is done at 86.6% on primary winding.
4.If number of turns in primary winding N1 and secondary winding N2.
Than transformer ratio of main transformer is,
K = N2/N1
and the transformation ratio of teaser transformer is,
K = N2/0.866N1
= 1.15 K
Uses: This type of transformer is used for those machines which works on double phase supply or single phase machines run separately (like: ac arc welding,ac traction,ac arc furnace etc).
Drawbacks:
1.The main and teaser transformer works on different power factor,which is undesirable.
2.It works on only 86.6 capacity.
3.TERTIARY WINDING: In star-star connection type transformer.The third harmonic waves are more effective.So we cannot get pure sinusoidal wave with this transformer and also in unbalanced load the neutral point shift towards one of the phase.Due to this an extra delta winding is used in Y-Y transformer it is third winding of this transformer,So it is called tertiary winding.
The given below image shows the tertiary winding of a transformer.
Tertiary winding
Uses: The uses of tertiary winding in transformer is given below.
1.For the supply of phase compensating devices.
2.For the interconnection.
3.For the use of voltage winding in testing transformer.
→ In delta-delta,delta-star and star-delta transformer neutral is fixed.So we get pure sinusoidal wave with this transformer,because delta winding is a close circuit and it reduce the effect of third harmonic waves.
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