In this arrangement the X0 neutral tap is part way up on the secondary teaser transformer (see right). This is a cost-saving in the lower-power transformers due to the two-coil T connected to a secondary two-coil T instead of the traditional three-coil primary to three-coil secondary transformer. The Scott-T transformer connection may also be used in a back-to-back T-to-T arrangement for a three-phase to three-phase connection. Back to back arrangement Scott Connection 3 φ to 3 φ The instantaneous difference in loading on the two sections will be seen as an imbalance in the three-phase supply there is no way to smooth it out with transformers. This will not result in balanced current on the three-phase of being equal. In modern times people have tried to revive the Scott connection as a way to power single-phase electric railways from three-phase Utility supplies. Since the typical two-phase load was a motor, the current in the two phases was presumed inherently equal during the Scott-T development. However if a two-phase load is not balanced (more power drawn from one phase than the other), no arrangement of transformers (including the Scott-T transformers) can restore balance: Unbalanced current on the two-phase side causes unbalanced current on the three-phase side. Two-phase motors draw constant power, just as three-phase motors do, so a balanced two-phase load is converted to a balanced three-phase load. The other side of the transformers then connect directly to the two pairs of a two-phase four-wire system. Its centre tap then connects to one end of the lower turn count side of T2, the other end connects to the remaining phase. The centre-tapped side of T1 is connected between two of the phases on the three-phase side. Technical details Standard Scott Connection 3 φ to 2 φĪssuming the desired voltage is the same on the two and three phase sides, the Scott-T transformer connection (shown right) consists of a centre-tapped 1:1 ratio main transformer, T1, and a √ 3/2(≈86.6%) ratio teaser transformer, T2. (Three phase power can be transmitted with only three wires, where the two-phase power systems required four wires, two per phase.) Both 2 φ and 3 φ components coexisted for a number of years and the Scott-T transformer connection allowed them to be interconnected. However, as transmission distances increased, the more transmission-line efficient three-phase system became more common. ![]() Nikola Tesla's original polyphase power system was based on simple-to-build two-phase four-wire components. This was valuable for getting equal voltage drop and thus feasible regulation of the voltage from the electric generator (the phases cannot be varied separately in a three-phase machine). Interconnection Īt the time of the invention, two-phase motor loads also existed and the Scott connection allowed connecting them to newer three-phase supplies with the currents equal on the three phases. Scott in the late 1890s to bypass Thomas Edison's more expensive rotary converter and thereby permit two-phase generator plants to drive three-phase motors. The Scott three-phase transformer was invented by Westinghouse engineer Charles F. ![]() ![]() The Scott connection evenly distributes a balanced load between the phases of the source. ![]() A Scott-T transformer or Scott connection is a type of circuit used to produce two-phase electric power (2 φ, 90 degree phase rotation) from a three-phase (3 φ, 120 degree phase rotation) source, or vice versa.
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