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Result analysis of Power Flow Control and Line Deicing Using a Bundle-Controlled Line Impedance Modulator in MATLAB/SIMULINK

This paper presents a flexible ac transmission system device under development for the management of power flow under steady-state and dynamic conditions, the bundle-controlled lineimpedance modulator (LIM) in MATLAB/SIMULINK. In its simplest form, an LIM is made of switching modules connected in series with transmission-line segments whose bundles have subconductors insulated from each other. A module contains one switch in series with each subconductor of a bundle and the modules are anchored to dead-end towers in place of yoke plates. Together, with the measurement of sensors and controls, these modules can be used to change series impedances of transmission lines and implement functions, such as deicing and power-flow control. Finally, the LIM performance is analysed.

and detailed review of the different de-icing and anti-icing techniques, already available and in development.
This paper is about a specific application of a new concept of FACTS device, the bundle-controlled line-impedance modulator (LIM), introduced in [2], which is not erected directly on the ground but anchored to a limited number of existing dead-end towers in place of yoke plates. This new technology involves a method for managing the power flow in an electric power network by modulating the series impedance of an HV power line with bundled conductors. More specifically, it is based on the implementation of switching modules (SMs) in segments of a transmission-line phase conductor made of bundled subconductors. A number of these switching devices must be distributed throughout the power grid and controlled in a coordinated way to manage the power flow. The system and method can, in principle, be used for modifying the power flow through an electric grid in static or dynamic mode. As will be explained, the approach to power-flow control with this new FACTS device is to minimize the equipment cost by exploiting the inherent properties of transmission lines and eliminating the foot print by anchoring small SMs to a limited number of transmission towers.

II. MODELLING IN MATLAB/SIMULINK
This MODEL shows two generators and a 10,000 MVA equivalent power system interconnected by three 735-kV transmission lines.
As a rule, on a high-voltage transmission line, several conductors are usually provided for each line phase to reduce corona losses and the impedance. Within a bundle, yoke plates and spacers hold individual subconductors separate from and parallel to each other. Normally, subconductors are short circuited at yoke plates. The line-impedance modulator can operate with any number of subconductors per bundle but, for the purposes of this thesis, we will restrict our discussion to a 735-kV power transmission line with two subconductors per bundle.
As shown in Fig.7.1, the line impedance can be modulated by installing switching modules(SMs) at a number of locations and in all three phases of the line allowing either one, two, or three conductors to be disconnected. One subconductor in each bundle is left unswitched at all times.

III.
RESULTS As a rule, on a high-voltage transmission line, several conductors are usually provided for each line phase to reduce corona losses and the impedance. Within a bundle, yoke plates and spacers hold individual subconductors separate from and parallel to each other. The line-impedance modulator can operate with any number of subconductors per bundle but, for the purposes of this thesis, we will restrict our discussion to a 735-kV power transmission line with two subconductors per bundle. At t=0.5 s, the impedance signal Zcmd ramps from 1 to 1.642 pu as shown by the yellow trace.
For each values of Zcmd, the look-up table provides the corresponding switch combinations. The switch combinations transmitted to the switching modules are sampled here every 0.1 s. This gives the discretized impedance signal Zdisc (magenta).

Power Flow Control
To control power flow, it is desirable to be able to maintain or change quantities such as line impedances, bus voltage magnitudes, and phase angle differences. There are many power controller devices which affect some or all of these parameters. The well-studied FACTS devices are included in this power controller category.

Line Deicing
Graph 3 also shows the switch currents of the phase A switching module located on the bus B2 side. With all switches closed, switch currents are initially 465 A rms.
With all but one switch opened at t=3.9 s, it can be seen that the switch current of subconductor 2 reaches 1533 A rms.
Hence, although the power flow in line L3 has been reduced by 17%, the subconductor current has increased by a 3.3 factor. Such a current is large enough for simultaneously deicing by the Joule effect three subconductors (one per phase) in both 30-km BCL segments.