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ElectricalPower System

Two six pulse converters used for bipolar HVDC transmission system, are rated at 1000 MW, ± 200 kV. What is the dc transmission voltage?

200 kV

400 kV

500 kV

100 kV

Correct Answer

⚙️ TE • Technical Concept & PrincipleElectricalPower System

Option B

400 kV

Quick Summary:

In a bipolar HVDC transmission system, two converters are connected to two independent poles, one operating at a positive potential ( $+V_d$ ) and the other at a negative potential ( $-V_d$ ) relative to ground. The total transmission voltage is defined as the potential difference between the two poles, which is calculated as $|+V_d| + |-V_d|$ .

⚙️TETechnical SolutionConcept & Principle

💡 Explanation

🔢 Key Formulas

$V_{total} = V_{pole1} + |V_{pole2}|$ — Calculation of total DC transmission voltage in a bipolar system

⚙️ Working Principle

In a bipolar configuration, each converter terminal acts as one pole. Since the system is rated at $\pm 200\text{ kV}$ , the positive pole is at $+200\text{ kV}$ and the negative pole is at $-200\text{ kV}$ with respect to the neutral ground. The total voltage across the transmission lines is the difference between these potentials, resulting in $200 - (-200) = 400\text{ kV}$ . This configuration is preferred in HVDC as it allows each pole to operate independently if one line fails.

📌 Key Points

▸
Bipolar transmission uses two conductors, each carrying opposite polarity.
▸
The ground acts as a return path only during unbalanced conditions or single-pole operation.
▸
The total voltage rating is the line-to-line DC voltage between the two poles.
▸
Bipolar HVDC is more reliable than monopolar systems due to redundancy.

✅ Advantages

▸
Improved reliability as one pole can operate independently
▸
Reduced ground current under normal balanced operation
▸
High power capacity for long-distance transmission

❌ Disadvantages / Limitations

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Increased cost due to two sets of converters
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Complex insulation requirements for the transmission towers

🛠️ Applications / Uses

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Long distance bulk power transmission
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Asynchronous interconnection of AC grids
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Submarine power cables

📄 Additional Information

▸
Standard bipolar HVDC systems use the formula $V_{line-to-line} = V_{pole} \times 2$ .
▸
Option A (200 kV) refers to the voltage of a single pole relative to the ground, which is a common distractor.

📊 Diagram / Illustration

✅

B is correct — In a bipolar HVDC system, the total transmission voltage is the potential difference between the positive and negative poles, resulting in $200\text{ kV} + 200\text{ kV} = 400\text{ kV}$ .

Core Concepts Used

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HVDC Converter Topologies Bipolar Transmission Systems DC Potential Difference

💡 EXAM TIP

Always verify if an HVDC system is monopolar (rating is equal to pole voltage) or bipolar (rating is the sum of magnitudes of both poles).

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