# Three phase transformer connection

Three-phase transformer connections are usually, Star Star, Delta Delta, Star-Delta, and Delta Star. These issues of three-phase transformer connection are discussed

## 3 phase transformer connection

3 phase transformers usually have four types of connections

Star - Star Connection ( Y - Y Connection )

Delta - Delta Connection ( D - D Connection )

Star - Delta Connection ( YD Connection )

Delta - Star Connection ( D - Y Connection )

There are also two other types of connections

Open - Delta connection ( V - V Connection )

Scott Connection ( T - T Connection )

### 1. Star Star connection of transformer( three-phase transformer star-star connection ):-

STAR - STAR has easily connected to three single-phase transformers on both sides according to the correct polarity. This type of connection is especially suitable for small, high-voltage transformers.

Because the number of trans/phase and the amount of insulation is less (Since the phase voltage is 1/3 of the line voltage), if each transformer's transformer ratio is the same, then the line voltage of the primary and secondary sides is the same.

It works well in 3 phase balance loads, the secondary Newton of unbalanced loading is slightly removed from the original state.

This is because of very low-quality resistance i.e. resistance like a short circuit, coupling condition occurs in the landscape of secondary and neutral of anyone transformer.

This causes a very small amount of current to flow and the neutral point to move away from the original state. As a result, there is an inequality in the line to neutral voltage.

The amount of voltage decreases as the resistance between the phase and neutral of one of the transformers decreases, but the amount of voltage increases with the other two transformers. Such an error is called floating neutral.

To solve this error, primary neutrality can be solved by art. Moreover, the distortion of secondary phase voltage is eliminated.

parallel operation of transformer>>

#### Advantages of Star Star approach:-

1.It can be used as a step-up or step-down.

2.It works well with a balanced load.

3.It is very effective for small high voltage transformers.

4.Insulation is very low considering the phase because the phase voltage is 1/1 .73 of the line voltage.

5.Insulation stress is 58% of line to neutral voltage.

#### Disadvantages of Star Star system: -

1.The floating neutral error may occur

2.An unbalanced load does not work well

3.Banking cannot be done in parallel with Delta Star or Star Delta

### 2.Delta Delta transformer (three-phase transformer delta-delta connection)

According to the delta-delta connection method, delta connections are made according to the polarity on both sides of the transformer. It usually works well in a complete. It does not have any problem with uneven voltage.

Their line-to-line (primary and secondary) ratios are equal to their own ratios. The biggest advantage of this is that if one of the units breaks down, the service can be continued temporarily on the other two (V-V) connections.

It does not cause floating neutral error The delta-delta connection is suitable for high current because the phase current is 57.7% of the line cont.

Star Connection is not suitable for unbalanced use. This is because an unbalanced load brings the core of the transformer to too much saturation and insulation of the transformer causes too much stress. Except for the impedance drop in both transformers.

In a delta-delta system the secondary windings of the transformer have to be connected to the correct polarity, otherwise connecting to unequal polarity will cause a short-circuit in the system.

Advantages of Delta Delta Connection: -

1.It is suitable for large low voltage transformers.

2.The output voltage becomes sinusoidal.

3.There is no problem with an unbalanced load.

4.One of the banking transformers is damaged but the rest can be used in V-V connection However, it operates at less than 67% of normal capacity and at 58%.

5.There is no phase difference between the primary and secondary voltage.

Disadvantages of Delta Delta Connection: -

1.This increases the number of trans/phases.

2.Neutral connection not found.

3.V - V Connection Full capacity is not available while performing this operation.

4.Parallel banking cannot be done with Star Delta or Delta Star.

5.The third harmonic exciting current flows in the form of a reversal at the delta vending.

### 3.three-phase transformer star delta connection(star-delta transformer)(y delta transformer) :-

The star delta connection method connects the star in the primary and the delta in the secondary. This method is usually used in step-down transformers. Here the primary and secondary line voltage ratios and their own ratios are not equal. There is a 30-degree phase difference between primary and secondary line voltage. Used to reduce the substation voltage at the end of the transmission line.

Advantages of Star Delta Connection: -

1.Suitable for high voltage to low voltage methods.

2.Suitable for low voltage distribution circuits.

Disadvantages of Star Delta Connection: -

1.Banking cannot be done in parallel with Delta Delta or Star Star.

### 4.Delta Star transformer connection (delta to star voltage conversion):-

The Delta Star connection method connects the primary delta and the secondary star. This method is used to increase the voltage.

Especially used at the beginning of the primary transmission line Only 58% of secondary insulation work can be run in the absence of Star. Star winding for low-current, high space factor.

The floating neutral error does not occur in an unbalanced load. At this connection, the voltage web is without distortion. The golden ratio of line voltage is not the same, as it is according to the transformer ratio of each transformer.

This method of connection of the distribution transformer (where the voltage is usually step down) is typically used to take a single-phase supply from the secondary to the neutral. Their primary and secondary line voltage ratios are not equal to their own ratios. The transformer ratio of each transformer is 1 / 1.732 times.

Advantages of Delta Connection: -

1.The amount of insulation is less, only 58% of the insulation work can be done

2.Floating neutral error does not occur in unbalanced load

3.Voltage web is without distortion

4.Nowadays, it is very popular as a distribution transformer, because from secondary to Newton, single-phase supply is available.

Disadvantages of Delta Star connection: -

1.Primary and secondary line voltage of 30 degrees due to the phase difference, Delta Delta or Star Star can not be parallel Banking.

### Open Delta connection (open delta transformer connection)

In the open delta system, the supply of 3 phases can be maintained by banking of two single-phase transformers called open delta connections.

If one of the three transformers is removed during power supply in the Delta Delta system, or one of the three transformers breaks down for any reason, the remaining two transformers can continue the 3 phase work.

Advantages of Open Delta Method: -

1. If a transformer of the Delta system breaks down for some reason, power can be supplied uninterruptedly with the help of the other two.

2. Repair of remaining transformers is available while supplying power in the open delta system.

3. Three-phase power supply can be provided easily with the help of two transformers if required You don't have to bother with the Scott connection.

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Disadvantages of open delta approach: -

1. The value of the average power factor is lower than the note power factor Its value is 86.6% of the balance lord factor.

2. Two transformers have different power factors when the load is not balanced with a single power factor.

3. Increased load often tends to cause the secondary terminal voltage to be uneven It happens even under balanced load.

4. Load cannot be supplied at full capacity.

5. When working on unity power factor load, one transformer is in lagging and the other is in transformer lead in open delta connection, so the output voltage is unbalanced. Even with load impedance and input voltage balance, this problem occurs.

### Scott connection (Scott transformer connection)

3 phase power can be supplied in the Scott method and with the help of two single-phase transformers. There are two transformers in this system, one called Main Transformer and the other called Teaser Transformer. Only 86.6% of the winding of the teaser transformer is used.

A terminal of both the primary and secondary of the teaser transformer is electrically connected to the primary and secondary midpoints of the main transformer, respectively. It looks a lot like the English letter "T", so this connection is called the "T-T" connection.

#### Q1. What type of connection is provided to the distribution transformer and why?

Ans;- The Delta Star connection of the distribution transformer is provided, as it requires a single phase to connect the customers.

#### Q2. Why is the Delta Star connection suitable for more current?

Ans:- Delta Star connections are connected to the customers as there is a Star connection in Delta and Secondary in the primary, so this connection is suitable for more current.

#### Q3. What is Open-Delta or V - V connection?

Ans:- The method by which three single-phase transformers can be maintained by banking two single-phase transformers are called open delta or V - V connection.

#### Q4. Where is the application of the T - T connection method?

Ans:-
1. To supply three-phase with two single-phase transformers.
2. To supply from three-phase to three-phase, from three-phase to two-phase, from two-phase to three-phase.

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