Transformers with Scott connection

The connections between two different electrical circuits or between a receiver and electric network are often made with using of intermediating elements. Such devices adjust the parameters of electric energy or supply network configuration to the receiver’s needs. The Scott circuit is an example of such intermediating system in the network-receiver connection.
The Scott circuit consists of 1-phase transformers working in configuration presented on the figure below. It is an example of adjusting the 3-phase supply network and 2-phase receiver or the group of 1-phase receivers.


Diagram of transformer Scott connection
Description: Odbiornik - Receiver

The transformers, i.e. basic transformer (Tb) and booster transformer (Td) are 1-phase transformers of the same powers. There is a tap on the middle of the primary winding of Tb transformer, which serves for connection with the end of Td transformer primary winding. In order to obtain equal secondary voltages (Ud and Ub) of both transformers they must be supplied (in respect of module) from symmetrical network, and the number of turns of primary windings must fulfill the following proportion:

If above proportion between the primary turns of transformers is ensured by their construction, then the secondary voltages of transformers will be identical (Ud=Ub), provided that the numbers of secondary windings are equal (Z2d=Z2b ). In such a case the current modules I1U, I1V and I1W will be equal, and the phase angle between them will be 2π/3.


Topographic diagram of voltages and vector diagram of the system

An important advantage of Scott circuit is the fact that with symmetrical 2-phase load also the 3-phase supply network will be loaded symmetrically. 

The transformers working in Scott circuits are widely applied in electric heating engineering.

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