Scott Connection

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Scott Connection:-

Scott connection is also known as the three phase to two phase converter.

By using scott connection we can convert three phase in to two phase or vice-versa.Where two phase supply is required for the any equipment then by using scott connection we can get it.

Two phase supply is needed for following application are,

  • To supply power to two phase electric furnaces
  • To interlink two phase and three phase system.
  • To supply power to 2 phase source from three phase equipment and vice-versa.

Circuit description:-

scott connectionTwo single phase transformer with suitable tapping on both side, are required for the scott connection. They both transformer are following tapping on both side are,

  • Transformer 1 is main transformer and it has 50% tapping.
  • Transformer 2 is teaser transformer and it has 86.6% tapping.

Teaser transformer is connected between center tapping D and Z.D is center tapping of main transformer and it connected across the line X and Y of three phase side. It has secondary PQ and primary XY.

3 phase input power is required for the scott connection. Its provide two single phase outputs. These output are at 90° out of phase and must not be connected in series or in parallel as it creates a vector current on the primary side. teaser transformer has secondary RS ans primary ZX.
Fig shows the phaser diagram of the voltage across primary and secondary.

Phaser Diagram:

phaser of scott connection
Supply line voltage = V
Then, Vxy = Vxz= Vzy  = V
Voltage between Z and D is given by,    (V×√3)/2
No of turn between Z and D is given by,  (N×√3)/2

Since the power factors of the load for the main transformer and  the teaser transformer are equal, the phase angle between the secondary currents is also 90°. The angle between the primary currents I1T and I1M is also 90°. Thus the three line currents Ix ,IY and Iz are displaced from each other by 120° and lag the respective phase voltages by an angle Φ. This proves that if the tow phase load is balanced then the loading on the three phase side is also balanced.
       If we will consider the case of unbalanced tow phase load having different currents and different power factors.
here, figure shows the lagging power factor under two phase load,
lagging pf of scott connection
If any query or suggestion about Scott connection please comment below or Email on sohal@electricalidea.com.

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