Standards Development

Scope

This Technical Specification is intended as a guide to all aspects of DC side harmonic behaviour and filters for HVDC transmission systems. It is based on CIGRE Technical Brochure 811 developed by CIGRE Working Group B4.68. CIGRE sought to bring together the experience, and consider the interests, of different sectors of the HVDC community to produce a Brochure of interest to all parties concerned, including utilities, suppliers and consultants.

The objective of the CIGRE Brochure was to provide information to enable informed and intelligent decisions to be made by those concerned. Where there were different possible approaches to some aspect of design, the relative merits were discussed.

Purpose

HVDC systems exist in conjunction with other technical systems. HVDC systems are a potential source of interference where the DC transmission corridors exists. There are also harmonic performance aspects to be considered for satisfactory performance of the HVDC system.

Two major technological changes have transformed the subject area of CIGRE Technical Brochure 811 since publication of the original CIGRE Technical Brochure 92 on the same topic:

a) The replacement of analogue telephone systems by digi tal and optical and mobile (cell phone) technologies has reduced the relevance of inductive interference from HVDC lines, although the re remain areas where local analogue telephone connections may still be affected.

b) The introduction of VSC HVDC converters with inherently lower harmonic generation, and often with underground cable transmission, has largely removed the need for DC side fil ters in HVDC projects using such technology.

The question might therefore be asked – if DC filters may not be required in many future projects, is there a need for this Technical Specification dealing with DC side harmonics and filtering? Strong justificat ions are given below.

c) National or international regulations governing electro -magnetic compatibility (EMC) often demand that no interference shall be caused to third parties, and this may have to be proved to third parties or regulators before an HVDC project can obtain planning permission or enter operation. Definitions of such interference include the frequency range addres sed in the proposed Technical Specification. Studies may be required to reduce the risk to all parties involved in an HVDC project, ev en if the conclusion is that no special mitigation measures are required.

d) There may be a telephone interference issue in regions where analogue technology is still used for the final connection from an exchange to the consumer’s premises, especially where telephone cables and HVDC cables are laid in, or alongside, the same road.

e) Some digital communication may be subject to in terference or safety hazard from induction, even if not affected directly at audible frequencies.

f) Possible resonance of the DC transmission system at harmonic frequencies must always be considered and studied.

g) Coupling with parallel AC transmission lines in the same corridor, or even on the same tower, is becoming increasingly topical due to restrictions on the construction of new overhe ad lines.

h) The owners of older HVDC projects undergoing refurbishment may wish to consider whether their DC filters are still required, and this will necessitate studies.

i) As DC filters and DC side harmonic issues become less common, the expertise in this fi eld will diminish, and therefore the comprehensive record of knowledge encapsulated in the proposed Technical Specification will be a valuable reference.