IEEE Power & Energy Magazine - May/June 2019 - 31

outage conditions for line 27. For example, the calculation
of the distribution factor of line 23 with respect to line 19 pro-
ceeds as follows: the power flow on line 23 is increased by
1 MW, accomplished by absorbing 1 MW at the receiv-
ing end of the line and injecting 1 MW at the sending end
(assuming negligible losses), and the associated power
flow change in line 19, ΔPcongestion, is recorded for an
outage of line 27. The distribution factor associated with
line 23 would then be ΔPcongestion divided by 1 MW. once
the distribution factors for all lines are calculated, the best
candidates for ac-to-dc conversion (the ones having the
largest distribution factors) are found to be lines 19, 23,
21, 22, 20, and 29. This procedure can be repeated for any
given contingency.
Following the candidate line preselection, the engineer-
ing considerations discussed here can then be evaluated
to select the most feasible option, taking into consideration
the line's location, conditions of existing conductors and
towers, land available for the converters, and so forth.

Summary
ac-to-dc transmission line conversion presents itself as an
attractive solution to bring bulk energy to large load centers
and eliminate critical network congestion points through the
optimization of existing assets. This is further emphasized
in the present context where utilities and developers are
faced with stringent permitting and environmental require-
ments when looking to acquire new rights-of-way.
This article presented the technical challenges and consid-
erations facing ac-to-dc conversion, including configuration
options, insulation, audible noise, corona, voltage selection,
and planning considerations. a methodology for ranking
conversion options was also presented. ac-to-dc conversion
opens the door to many possibilities and has the potential
to render major development projects economically viable,
which would otherwise be stopped in their tracks. The opti-
mal ac-to-dc conversion solution needs to be considered on
a case-by-case basis and will be a function of many factors,

may/june 2019

such as cost, conditions of existing conductor and towers,
environmental factors, availability of land for the converter
stations and ground electrodes, outage duration requirements,
and operating criteria.

For Further Reading
conseil international des grands réseaux Électriques Joint
Working group B2.41, "guide to the conversion of existing
ac lines to dc operation," conseil international des grands
réseaux Électriques, Paris, France, Brochure no. 583, 2014.
P. Xu, B. Zhang, s. chen, and K. he, "criterion of drip-
ping discharge of falling water droplet on a conductor-t-
ground electrode with ac voltage applied," in Proc. Electrostatics Joint Conf., 2018, pp. 1-10.
a. edris, l. Barthold, d. a. douglass, W. h. litzen-
berger, and d. a. Woodford, "upgrading ac transmission to
dc for maximum power transfer capacity," in Proc. 12th Int.
Middle-East Power System Conf., 2008, pp. 44-49.
l. Barthold, r. adapa, h. clark, and d. Woodford, "sys-
tem advantages in conversion of ac transmission lines to
dc," in Proc. 9th IET Int. Conf. AC and DC Power Transmission, 2010, pp. 1-5.
X. Zhang and l. Yao, "a vision of electricity network
congestion management with FacTs and hVdc," in Proc.
Third Int. Conf. Electric Utility Deregulation and Restructuring and Power Technologies, 2008, pp. 116-121.
X. Zhang, l. Yao, B. chong, c. sasse, and K. r. ged-
frey, "FacTs and hVdc technologies for the development
of future power systems," in Proc. Int. Conf. Future Power
Systems, 2005, p. 6.

Biographies
Tayeb Meridji is with snc-lavalin, Montréal, canada.
Frida Ceja-Gomez is with snc-lavalin, Montréal, canada.
Jose Restrepo is with snc-lavalin, Vancouver, canada.
Ramy Azar is with snc-lavalin, Montréal, canada.
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IEEE Power & Energy Magazine - May/June 2019

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2019

Contents
IEEE Power & Energy Magazine - May/June 2019 - Cover1
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