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Power Flow

The document discusses the operation and calculations related to High Voltage Direct Current (HVDC) systems, specifically focusing on monopolar and bipolar links. It includes conceptual discussions on earth return current, solved examples for power calculations in bipolar HVDC systems, and outlines the effects of isolating one pole. Additionally, it presents an unsolved numerical problem for deriving power expressions in HVDC systems.

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kartikbhandoria06
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16 views20 pages

Power Flow

The document discusses the operation and calculations related to High Voltage Direct Current (HVDC) systems, specifically focusing on monopolar and bipolar links. It includes conceptual discussions on earth return current, solved examples for power calculations in bipolar HVDC systems, and outlines the effects of isolating one pole. Additionally, it presents an unsolved numerical problem for deriving power expressions in HVDC systems.

Uploaded by

kartikbhandoria06
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Power Flow with HVDC System

HVDC Monopolar Links


HVDC Bipolar Links with Ground Return Path
HVDC Bipolar Links with Dedicated Return Path
Conceptual Discussion
Q. With the help of a sketch shows that the current in the earth’s return
of a bipolar HVDC line is the difference of the current in pole 1 and
pole 2. How much will be the earth’s return current if pole 2 is
isolated and pole 1 continues to serve?
R. The current in the earth’s return of a bipolar HVDC line is the
difference between the currents in pole 1 and pole 2, and to analyze
the earth’s return current when pole 2 is isolated.
In normal operation:
▪ Pole 1 carries current 𝐈𝟏 in one direction, (say positive pole).
▪ Pole 2 carries current 𝐈𝟐 in the opposite direction, (say negative pole).
▪ The earth return current 𝐈𝐞𝐚𝐫𝐭𝐡 is the difference = 𝐈𝟏 − 𝐈𝟐
❑ If Pole 2 is isolated (𝐈𝟐 = 𝟎)
▪ The entire current in Pole 1 flows through the earth,
𝐈𝐞𝐚𝐫𝐭𝐡 = 𝐈𝟏
Solved Example
1) A bipolar two terminal HVDC link is delivering 1000 MW at
± 500 𝑘𝑉 at the receiving end. Total losses in the DC circuit
are 60 MW. Calculate the following:
a) Sending-end power
b) Power in the middle of the line
c) Sending-end voltage
d) Voltage at the middle of the line
e) Total resistance of the DC circuit.
Answer:
a) Sending-End Power, 𝑃𝑑𝑟 = 1060 𝑀𝑊
b) Power in the Middle of the Line, 𝑃𝑑𝑚 = 1030 𝑀𝑊
c) Sending-End Voltage, 𝑉𝑑𝑟 = 1060 𝑘𝑉 𝑃𝑜𝑙𝑒 𝑡𝑜 𝑃𝑜𝑙𝑒
d) Voltage at the Middle of the Line: 𝑉𝑑𝑚 = 1030 𝑘𝑉
e) Total Resistance of the DC Circuit, 𝑅𝑑𝑐 = 60 𝑜ℎ𝑚
Solved Example
2) A Bipolar HVDC line has sending end voltage, Ud₁ = ± 530
kV, and receiving end voltage, Ud2 = ± 500 kV, and total
resistance of the DC system, R = 60, ohm for two poles.
Calculate power in the middle of a line, power at the
sending end, and power at the receiving end.
Solved Example
3) A Bipolar 2-terminal HVDC Transmission System is operated in
Bipolar Mode with earthing of neutral points of converters at each
terminal. The following voltages were measured:
Pole 1 Rectifier: 501 kV; Pole 1 inverter: 499 kV
Pole 2 Rectifier: 495 kV; Pole 2 inverter: 493 kV
DC Resistance of pole 1 line conductor 5 ohms.
DC Resistance of pole 2 line conductor 5 ohms.
Earth return resistance neglected. Calculate:
a) Pole 1 DC Current, Pole 2 DC Current, and Earth current.
b) DC Power from Pole 1 at the rectifier end and DC Power
received at Pole 1 at the inverter end.
c) Line Loss in Pole 1.
Unsolved Numerical
1) Derive the expression for Power at the sending end and receiving end
of an HVDC pole in terms of sending end voltage, receiving end
voltage, and line resistance.

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