We have a number of recognized transmission and distribution experts serving on our board of "Grid Masters." Several times each month we’ll post what we judge to be the toughest questions that also have high interest to our readers. At least one of our experts will respond. Want to challenge our Grid Masters for a chance to win?

This week’s question and answer:

Q: What would pre-conditions & challenges to have interconnection of grid from two different countries operating on 50 & 60Hz frequency? How can synchrophasors help here & which parameters do they monitor for providing grid stability? Also if role of power electronic devices can be elaborated, appreciate it.

Anon (India)

A: Linking large power systems of different frequencies (like 50 and 60 Hz) as well as linking two power systems which are not in synchronism (like East and West of the United States and North-East United States and Canada) is routinely done with the HVDC links. HVDC provides an opportunity to transfer power in both directions between two dissimilar systems. HVDC link consists of two terminal stations and a DC transmission line. The two terminal stations convert AC to DC and vice versa and are based on Power Electronics DC valves.

HVDC links are also used for applications where HV ac cable's reactive power makes the alternating current prohibitive to transmit large amounts of active power.

Dr. Mietek Glinkowski, P.E
Global Head of Technology
ABB Inc.

We have done this in the past and most notably in 2009. We didn't do this amongst two countries but we did it in a microgrid system where we linked two military bases together, one US Base and the other a New Zealand Base. We used power electronics to solve the problem not PMU's. Our PowerStore product is a grid stabilization, we use in microgrids, and it is there to regulate voltage, power and frequency. I am attaching the case study as well as some PPT slides for reference.

Brad Luyster
VP/GM Smart Grid

HVDC transmission can asynchronously interconnect different systems including those with different frequencies. Often these interconnections are comprised of back-to-back HVDC converter stations, e.g. interconnections between Brazil and Argentina and within Saudi Arabia. They can also be used for long distance transmission, e.g. Itaipu in Brazil were hydro generation is at 50 Hz and consumption is at 60 Hz. Converter firing controls are synchronized to their respective grids using phase locked loops. Power electronics is used to for AC/DC conversion. Either line-commutated, current sourced converters (LCC/CSC) with thyristor valves or forced commutated, voltage sourced converters (VSC) with insulated gate bipolar transistors (IGBT) can used. The latter is of interest when AC systems are weak relative to the transmitted power.

Michael Bahrman
HVDC Business Development

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