1. NETWORK OPERATING DIVISION Operating Effectiveness Phase Shifters What is a Phase Shifter These transformers create a difference in phase angle between the primary and secondary side of the transformer thus adjusting MW flow.

2. How Phase Shifters Work NETWORK OPERATING DIVISION Operating Effectiveness Phase Shifters

3. Introduction a phase-shifting transformer is a specialised form of transformer used to control the flow of real power on three- phase electricity transmission networks

4. Power Flow Manipulation For an alternating current transmission line, power flow through the line is proportional to the cosine of the difference in the phase angle of the voltage between the transmitting end and the receiving end of the line.

5. Parallel Circuit Capacity Where parallel circuits with different capacity exist between two points in a transmission grid direct manipulation of the phase angle allows control of the division of power flow between the paths.

6. Method of Operation By means of a voltage derived from the supply that is first phase-shifted by 90° and then re-applied to it, a phase angle is developed across the Phase Shifter. It is this induced phase angle that affects the flow of power through specified circuits.

7. Arrangement A Phase Shifter typically consists of two separate transformers: a shunt unit and a series unit. The shunt unit has its winding terminals connected so to shift its output voltage by 90° with respect to the supply. Its output is then applied as input to the series unit, which, because its secondary winding is in series with the main circuit, adds the phase-shifted component. The overall output voltage is hence the vector sum of the supply voltage and the 90° quadrature component.

8. Arrangement Tap connections on the shunt unit allow the magnitude of the quadrature component to be controlled, and thus the magnitude of the phase shift across the Phase Shifter. The flow on the circuit containing the Phase Shifter may be increased (boost tapping) or reduced (buck tapping). Subject to system conditions, the flow may even be bucked enough to completely reverse from its neutral-tap direction.

9. Example The one-line diagram below shows the effect of tapping a phase shifter on a notional 100 MW generator-load system with two parallel transmission lines, one of which features a phase shifter with a tap range of 1 to 19. In the left-hand image, the phase shifter is at its center tap position of 10 and has a phase angle of 0°. It thus does not affect the power flow through its circuit and both lines are equally loaded at 50 MW. The right-hand image shows the same network with the phase shifter tapped down so to buck the power flow. The resulting negative phase angle has transferred 23 MW of loading onto the parallel circuit, while the total load supplied is unchanged at 100 MW.

10. THE END NETWORK OPERATING DIVISION Operating Effectiveness Phase Shifters