NETWORK OPERATING DIVISION
Phase Shifters
Operating Effectiveness
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.
NETWORK OPERATING DIVISION
Phase Shifters
Operating Effectiveness
How Phase Shifters Work
Introduction
• a phase-shifting transformer is a
specialised form of transformer used to
control the flow of real power on threephase electricity transmission networks
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.
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.
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.
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.
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.
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.
NETWORK OPERATING DIVISION
Operating Effectiveness
THE END
Phase Shifters