Introduction to HVDC.pdf

When the firing angle is 90 the bridge dc voltage is

Info icon This preview shows pages 14–17. Sign up to view the full content.

When the firing angle is 90°, the bridge dc voltage is approximately null (zero). In this particular example, the bridge dc voltage passes from -0.01 pu to -0.06 pu as the bridge dc current passes from the minimum value to the nominal value. When the firing angle is 170°, the bridge dc voltage is approximately the nominal negative value (-1.0 pu). In this particular example, the bridge dc voltage passes from -0.99 pu to -1.04 pu as the bridge dc current passes from the minimum value to the nominal value. The nominal value of a pa- rameter is equal to 1.0 per unit (1 pu) . For example, when the value of a parame- ter is twice the nominal value, the parameter value is equal to 2.0 pu. When the value of a parameter is half the nominal value, the parameter value is equal to 0.5 pu. Bridge dc current, I dc (A) Bridge dc voltage, E dc (V) α ൌ 30° Voltage Regulation and Displacement Power Factor (DPF) in Thyristor Three-Phase Bridges -Discussion
Image of page 14

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

HVDC Transmission Systems 15 Figure 12. Voltage-versus-current relations at the dc side of a thyristor bridge, for different firing angles (smoothing inductor of infinite inductance value). As previously discussed, the voltage-versus-current relations in Figure 12 are valid for a smoothing inductor of infinite inductance value. Since real smoothing inductors have a finite inductance value, they cannot keep the current flow continuous at low bridge dc current values. Consequently, the voltage-versus- current relations actually look more like those shown in Figure 13. Near the origin (i.e., for low dc current values), the relations have a curved section indicating that the bridge dc voltage does not decrease linearly with current because current flow is discontinuous . The curved section of each relation ends when the bridge dc current is high enough to ensure continuous current flow in the bridge. Past that point (i.e., for higher dc current values), each relation follows a linear downward slope since current flow remains continuous. α ൌ 30° α ൌ 15° α ൌ 0° α ൌ 45° α ൌ 60° α ൌ 75° α ൌ 90° α ൌ 105° α ൌ 120° α ൌ 135° α ൌ 150° α ൌ 165° Bridge dc current, I dc (pu) Bridge dc voltage, E dc [1 pu ൌ1.35 ൈ Line voltage ܧ ௅ି௅ ] α ൌ 170° Voltage Regulation and Displacement Power Factor (DPF) in Thyristor Three-Phase Bridges -Discussion
Image of page 15
16 HVDC Transmission Systems A Figure 13. Voltage-versus-current relations at the dc side of a thyristor three-phase bridge, for different firing angles (smoothing inductor of finite inductance value). As the dashed line in Figure 13 shows, the curved section at the beginning of the relations increases in length as the firing angle passes from 0° to 90°. The length of the curved section is maximum at firing angle 90°. As the firing angle passes from 90° to 170°, the curved section of the relations shortens, reaching the minimum length at firing angle 170°. To ensure continuous current flow over the entire firing angle range, the current must be kept above the minimum current ensuring continuous current flow at firing angle 90°. In Figure 13, for example,
Image of page 16

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

Image of page 17
This is the end of the preview. Sign up to access the rest of the document.
  • One '14
  • High-voltage direct current, Electric power transmission, HVDC transmission systems

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern