21-09-2013, 03:55 PM
FLEXIBLE AC TRANSMISSION SYSTEMS
FLEXIBLE AC TRANSMISSION.docx (Size: 153.25 KB / Downloads: 49)
Aim:
Simulation for performance of uncompensated transmission line
To understand the performance of uncompensated transmission line, let us consider a simple case of lossless transmission line connecting a source Vs to a load. It is clear that Between the sending and receiving end voltages, a magnitude variation as well as a phase difference is created. The most significant part of the voltage drop in the line reactance is due to the reactive Component of the load current. To keep the voltages in the network at nearly the rated value, two Control actions are possible:
1. Load compensation
2. System compensation
LOAD COMPENSATION
It is possible to compensate for the reactive current Ix of the load by adding a parallel Capacitive load so that Ic = Ix. Doing so causes the effective power factor of the combination To become unity. The absence of Ix eliminates the voltage drop ΔV1, bringing Vr closer in Magnitude to Vs; this condition is called load compensation. Actually, by charging extra for supplying the reactive power, a power utility company makes it advantageous for customers to Use load compensation on their premises. Loads compensated to the unity power factor reduce The line drop but do not eliminate it; they still experience a drop of ΔV2 from j IrXl.
SYSTEM COMPENSATION
To regulate the receiving-end voltage at the rated value, a power utility may install a reactive power Compensator. This compensator draws a reactive current to overcome both components Of the voltage drop ΔV1 and ΔV2 as a consequence of the load current Il through the line Reactance Xl. To compensate for ΔV2, an additional capacitive current, ΔIc, over and above Ic that compensates for Ix, is drawn by the compensator.
Circuit Diagram:
The circuit diagram shows the equivalent pi- model of a transmission line 300 Km long and divided in two pi sections of equal length. The line is supplied at sending end by ac generator. The generator Supplies 800 MW power at 500 KV and 60 Hz of frequency.
By simulation of the above circuit with the help of MATLAB simulink blocks, it is clear that the
Midpoint voltage and receiving end voltage are not equal to the sending end voltage due to the Absence of any compensation in the line. The various waveforms for the Vs, Vm and Vr are shown Below.