---
title: "T/F: HVDC converter reactive power need"
subject: "Transmission and Distribution System Design"
chapter: 1
key: "semester_8/transmission_and_distribution_system_design:tf-hvdc-reactive-power"
source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-hvdc-reactive-power
site: BCT Engineering
---

# T/F: HVDC converter reactive power need

Transmission and Distribution System Design · Chapter 1: Introduction

- Asked in: 2072 Magh, 3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-hvdc-reactive-power
- Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-1

## Question

State whether the following statement is TRUE or FALSE. Justify your answer with a brief explanation: HVDC converter station requires huge amount of reactive power support.

## Short answer

True. Line-commutated converters draw lagging current due to firing and commutation angles, consuming reactive power up to 50–60% of real power. Converter stations need large shunt capacitor banks, filters, or SVCs to supply this support.

## Answer

**TRUE.**

- Line-commutated (thyristor) converters always draw current that lags the voltage, both as rectifier (firing angle $\alpha$) and as inverter (extinction angle $\gamma$), plus extra lag due to commutation overlap $\mu$.
- The reactive power consumed is roughly $Q \approx P\tan\phi$ with $\cos\phi \approx \frac{1}{2}[\cos\alpha + \cos(\alpha+\mu)]$; in practice $Q$ is **50–60% of the transmitted real power** at each end.
- This reactive power is supplied by AC filters (which also remove harmonics), shunt capacitor banks, synchronous condensers or SVC/STATCOM at the converter station.

So a 1000 MW HVDC terminal needs about 500–600 MVAr of local reactive support. (Voltage-source converter HVDC does not have this need, but the statement refers to conventional HVDC.)

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. For conventional HVDC the statement 'converter station requires huge reactive power' is:
   A. False
   B. True
   C. True only for inverter
   D. True only for VSC
   Answer: B. Line-commutated converters always draw lagging current and consume large reactive power. (Key point: Verdict)

2. Reactive demand of a conventional converter is about what fraction of transmitted real power?
   A. 5-10%
   B. 50-60%
   C. 150%
   D. Zero
   Answer: B. Q is roughly 50-60% of P at each end, e.g. 500-600 MVAr for 1000 MW. (Key point: Magnitude)

3. How is the converter's reactive demand supplied?
   A. By the DC line
   B. AC filters, shunt capacitors, synchronous condensers or SVC/STATCOM
   C. By series reactors
   D. By the thyristors themselves
   Answer: B. Local reactive support is provided at the converter station; filters also remove harmonics. (Key point: Sources of Q)

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