Introduction to Static Var Compensator.pdf

# Note that only odd harmonic components are produced

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Figure 16. Note that only odd harmonic components are produced because the waveform of current ܫ ்஼ோ flowing in each inductor of a TCR, although chopped, remains symmetrical. Figure 16. Curves of the rms value of the harmonic components in the current ࢀ࡯ࡾ flowing in each inductor of a TCR as a function of the firing angle of the thyristors. Figure 16 confirms that no harmonic components are generated in the current ܫ ்஼ோ flowing in each inductor of the TCR between a firing angle ߙ of 0° and 90°. As the firing angle ߙ increases above 90°, the values of the various harmonic components generated in the current ܫ ்஼ோ fluctuates between 0% and about 14% of the nominal rms value of the current ܫ ்஼ோ,ଵ௙ . Note also that, as the firing angle ߙ reaches about 140°, the combined value of the harmonic components generated in the current ܫ ்஼ோ becomes about as important as the value of the current ܫ ்஼ோ,ଵ௙ (compare in Figure 16 the rms values of the harmonic components other than the fundamental with the rms value of current ܫ ்஼ோ,ଵ௙ ). Such a high percentage of harmonics is undesirable because harmonics have negative effects on the system to which the SVC is connected, such as increasing the current flowing in the system and increasing the power losses (i.e., the ܴܫ losses). A number of different methods exist to reduce the importance of the harmonic components generated in the current ܫ ்஼ோ flowing in each inductor of a TCR. For example, all base 3 harmonics ( ܫ ்஼ோ,ଷ௙ , ܫ ்஼ோ,ଽ௙ , ܫ ்஼ோ,ଵହ௙ , etc) generated by the TCR can be eliminated by correctly balancing the three legs of the delta- connected TCR. Also, harmonic filters can be added to the TCR in order to dampen the remaining prevalent harmonics (notably ܫ ்஼ோ,ହ௙ and ܫ ்஼ோ,଻௙ ) generated by the TCR. However, no matter the techniques used, it is generally impossible to completely eliminate the harmonics generated in the current ܫ ்஼ோ flowing in each inductor of a TCR. RMS value of the harmonic components in current ܫ ்஼ோ (% of nominal rms value of current ܫ ்஼ோ,ଵ௙ ) Firing angle ߙ of the thyristors (°) 0 5 10 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 ܫ ்஼ோ,ଷ௙ ܫ ்஼ோ,ହ௙ ܫ ்஼ோ,଻௙ ܫ ்஼ோ,ଽ௙ ܫ ்஼ோ,ଵଵ௙ ܫ ்஼ோ,ଵଷ௙ 0 15 ܫ ்஼ோ,ଵ௙

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Main Components of a Static Var Compensator (SVC) Discussion Static Var Compensator (SVC) 17 Thyristor valves The largest currently available thyristors can block voltages of up to about 9 kV and carry currents of up to about 6 kA. Although high, these ratings are insufficient for the high voltages and currents at which SVCs operate. Because of this, when designing a TCR (and TSCs , as will be seen in the next section of this exercise), it is necessary to connect more than one thyristor in series (generally, from 10 to 20 thyristors). Such thyristor arrangements are called thyristor valves and consist of a number of thyristors stacked on one another. Figure 17 shows a
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• One '14
• Electric power transmission, AC power, TCR, Static VAR compensator

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