IEEE Power & Energy Magazine - May/June 2019 - 102

Favorable system improvements use advanced transmission
technologies to effectively increase the delivery capability operation
flexibility, and utilization of the existing network infrastructure.
dc systems and facilitating ac voltage transformation or
adjustment. converter transformers are costly and contribute a large portion of the total station energy losses.
technically, it is feasible to implement a subtransmission
hVdc system without converter transformers by considering the favorable conditions in urban grid applications,
including equal ac terminal voltages and strong ac networks. the hVdc can use symmetric monopole dc line
configurations and similar voltage-controlling behaviors
of the two converter stations (either both capacitive or
both inductive) as a result of the short electrical distance
between the two converters.
✔ Circuit conversion to dc operation: subtransmission
hVdc systems could be implemented by the conversion
of existing ac circuits to dc operation. this can achieve
increased power transfer capability using existing corridors without installing new circuits or replacing the
circuits with high-capacity conductors, and it can also
increase network power flow control flexibility. there
are ongoing research activities to investigate the feasibility and technical specifications of converting ac circuits to dc operation. aspects under study include preferred converter topologies that can enable increased
power transmission and hVac cable insulation life issues under dc voltage operation.
✔ Multiterminal systems: subtransmission hVdc intertie solutions for improving urban grid operational
flexibility and resiliency could be extended to multiterminal Vsc-hVdc configurations. recent improvements in breaker actuators have made it possible to
realize mechanical dc breakers for medium-voltage
and subtransmission voltage ranges. the mechanical
dc breaker has very low losses and operating times
almost as fast as those of the hybrid concepts, which
combine semiconductors with mechanical switches.

102

cantly reduced. Vsc-hVdc technology is under continuous
development and improvement. new system design concepts
focus on modular products and compact structures that will
provide the flexibility for urban power grid applications.

For Further Reading
transmission Planning department, "the long-range transmission plan 2018-2028," consolidated edison company, new
York, oct. 26, 2018. [online]. available: https://www.coned
.com/-/media/files/coned/documents/business-partners/
transmission-planning/long-range-transmission-plan-2018
.pdf?la=en
K. K. sen and m. l. sen, "introducing the family of 'sen'
transformers: a set of power flow controlling transformers,"
IEEE Trans. Power Del., vol. 18, no. 1, pp. 149-157, 2003.
r. silberglitt, e. ettedgui, and a. hove, "strengthening
the grid: effect of high-temperature superconducting power technologies on reliability, power transfer capacity, and
energy use," rand corporation, Santa Monica, CA, mr1531-doe, 2002.
J. Pan, r. nuqui, K. srivastava, t. Jonsson, P. holmberg,
and Y.-J. hafner, "ac grid with embedded Vsc-hVdc for
secure and efficient power delivery," in Proc. IEEE Energy
2030 Conf., 2008.
l. shen, X. Ye, w. Xu, Q. tang, t. li, and Y. wang, "operation and correlation of Vsc-based technologies in city
center power grids," in Proc. IEEE Conf. Energy Internet
and Energy System Integration, 2017.
m. callavik, "grid resilience by power electronics: Use
subtransmission hVdc interties for novel emergency power
control of split networks," IEEE Power Electron. Mag., vol.
5, no. 1, pp. 54-56, 2018.
U. riechert, m. callavik, m. salzer, and P. Bergelin,
"compact high voltage direct current (hVdc) transmission
systems," in Proc. High Voltage Symp., 2016.

Summary

Biographies

Future urban grids will require electric supplies that are resilient, reliable, flexible, secure, sustainable, and affordable.
Vsc-hVdc-based subtransmission solutions offer the most
flexible advanced technology option for addressing multiple
expansion issues related to urban power grid enhancement
and modernization. By establishing direct power infeed
into load centers and strengthening intracity power delivery
capability, the operational flexibility and resiliency of urban
power grids can be greatly improved, and the requirements
for local generation and spinning reserves can be signifi-

Jiuping Pan is with aBB corporate research, raleigh,
north carolina.
Magnus Callavik is with aBB grid systems, Beijing,
china.
Peter Lundberg is with aBB grid systems, Vasteras,
sweden.
Lidong Zhang is with aBB corporate research, Vasteras, sweden.

ieee power & energy magazine

p&e
may/june 2019


https://www.coned.com/-/media/files/coned/documents/business-partners/transmission-planning/long-range-transmission-plan-2018.pdf https://www.coned.com/-/media/files/coned/documents/business-partners/transmission-planning/long-range-transmission-plan-2018.pdf https://www.coned.com/-/media/files/coned/documents/business-partners/transmission-planning/long-range-transmission-plan-2018.pdf https://www.coned.com/-/media/files/coned/documents/business-partners/transmission-planning/long-range-transmission-plan-2018.pdf

IEEE Power & Energy Magazine - May/June 2019

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Contents
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