Special:Badtitle/NS90:Milestone-Proposal talk:Virginia Smith HVDC Converter Station with Integrated AC Voltage Control Function/HVDC converter station/reply

Munich, September 23, 2014

Dear Mischa Schwartz,

Please allow us to refer to our proposal texts under the headlines: What is the historical significance of the work (its technological, scientific or social importance)? and: What obstacles (technical, political, geographic) needed to be overcome? and: What features set this work apart from similar achievements?

Also, please allow us to add the below explanations in response to your questions!

Yours with sincere thanks and best regards,

Gerhard Juette

What makes this system unique? The system is one of several back-to-back HVDC interconnections between the western and eastern US ac grids. Typically, these interconnections are located at weak points of the ac grids, i.e. far from regions with strong generation and heavy load. Therefore, ac system voltages are impacted by the load flow itself. As a result, reactive power compensation is required for voltage control.

Before Sidney, separate reactive power compensating devices (synchronous condensers or static VAr compensators) were used for ac bus voltage control on both sides of the converter. They represented a significant cost factor of these interconnections. With Sidney, the converter itself is designed to operate at variable power factors, i.e. variable reactive power consumption, independent of and up to the maximum dc load. Ac bus voltage control is achieved by varying the reactive power consumption of the converter. Thus, in addition to transmitting power, the converter itself provides control of the ac bus voltages. No separate hardware is required anymore for dynamic ac voltage control.

In addition to this dynamic ac voltage control and as another innovation specific to the Sidney HVDC Converter Station, limitation of transient overvoltage is accomplished by banks of rapidly switched MOV surge arresters.

Is it the first of a kind? Yes, it is: Both of the above-described unique features have first been realized with the Sidney HVDC Converter Station.

How significant was it to interconnect the two networks, as stated? The interconnection provides significant improvements in performance, flexibility, strength and reliability of the electric power supply within the affected areas.

Was it a difficult engineering job? Yes, especially the combination of the different interacting control algorithms required expertise, innovation, and accurate modeling to confirm and demonstrate the new concept.

What is the specific engineering accomplishment? Significant reduction of hardware necessary for back-to-back HVDC interconnections is accomplished.