scope:

This guide contains information and recommendations pertaining to the analysis and specification of the performance on the dc side of a high-voltage direct-current converter station concerning the electrical noise at harmonic frequencies up to 5 kHz generated by converter stations in a dc transmission system. This guide also contains information and suggestions pertaining to measurement of dc filter performance and noise level induced in wireline communications circuits from harmonic currents on dc transmission lines.

Purpose

Inductive coordination studies for dc transmission lines have two basic aspects:

a) Determination of the number of wireline communication circuits that will suffer unacceptable interference and the costs that would be involved in remedial measures applied to the affected wireline communication circuits.

b) Computation of interference levels that would result with various practical dc filter/smoothing reactor designs and the costs of these filters.

The optimum solution can be obtained by a cost/performance study. A substantial part of the work involves identifying all wireline communication circuits in the vicinity of planned dc transmission lines and calculating probable levels of induced interference for each circuit. These calculations are tedious and time-consuming, even using available computer programs, due to the detailed calculations involved and determining the exact parameters of each exposure. This can be further complicated by changes to the dc transmission line route (due to factors involved in finalizing the dc line right-of-way), which changes the wireline communication circuit exposures to be analyzed; changes in dc filter designs producing changes in harmonic current profiles on the dc transmission lines; difficulties in reaching agreement between power and telephone companies on limits of allowable induced interference; and short dc project construction schedules.

Reaching an optimum solution can be a lengthy, iterative process. Each dc project is unique, so that a solution used previously on a similar dc transmission project is not necessarily the optimum solution for the dc project under study. However, by using a simple, systematic approach to the problem and by selecting boundaries to the variation of each relevant operating parameter, the required studies can be started early in the project and a satisfactory conclusion reached relatively quickly.

One approach (Patterson and Fletcher [B18]) involves de-coupling the calculation of dc filter characteristics and harmonic current profiles on the dc transmission line (the power system analysis) from the calculation of coupling factors at harmonic frequencies between the dc transmission line and each adjacent wireline communications circuit due to harmonic currents on the dc transmission line (the communications system analysis).