The personal path and its correlation with electric power systems renewal and expansion

 

Originally the site was built and used for student education at UAS Frankfurt from 1994 on giving them online access to lecture material on foundations of electric power system theory, exercises and system design calculations. For base courses it included small circuit simulations, for advanced studies complete EMT simulation of executed Classic HVDC installations. 

But before that already in the seventies of the last century the author held seminars on HVDC when working as scientific assistant at RWTH Aachen. The author prepared his industrial work and some students later job with these courses. 

After his industry career and returning to the university 15 years later, this time as professor, HVDC systems like the Pacific DC Intertie and Blackwater B2B belonged to the core lectures of the author. The online material was referenced and furthered in running class room sessions conducted via tablet and beamer, stored and excerptwise made available online, material developed and written down in an exchange with the students. The Internet and MS Frontpage offered new ways for individual flexible course design and adaption to the new technologies.

 

A power system simulation lab was introduced for modelling and studying actual HVDC systems, amongst them the a.m. systems and through contractual work Inga-Kolwezi HVDC. The lab was equipped with PSCAD/EMTDC, with MATLAB/SIMULINK and the ANSOFT Field simulator allowing for a setup of a.m. systems and the study of operational questions and certain events. One event concerned converter transformer bushing failure at Celilo converter station. Another one the August 1996 WSCC power system outage. The 3100 MW Pacific DC Intertie, a 1400 km long transmission, embedded in the WSCC system was involved in the outage. 

Similar AC/DC transmission structures develop now in Germany through North-South HVDC links. Despite harnessing different technologies a risk for power system outage exists also here, the reasons even being more intricate due to a multitude of closed-loop control circuits of IBR (Inverter Based Resources), capacitive and inductive impedances, a mixture of rotating masses and virtual inertia realization.

 

The VSCs (Voltage Sourced Converters) used as front end devices of HVDC and directly power injecting IBRs, sometimes called IBMs (inverter based modules), have extreme good control properties allowing for accurate control of voltage and power, and even for virtual inertia implementation if correctly inderstood and applied. As compared to the classic synchronous machine the VSC has no or only minimal transient current carrying capability. In parallel operation with synchronous machines it does not reliably carry part of a load step in proportion to its rating due to current limitation. Its virtual inertia property becomes zero. Other components - VSCs or synchronous machines - must take over. These must not be synchronous generators, synchronous condensors suffice. Required: Thorough understanding of the underlying theory, application verification through EMT simulation. Proof of correctness of grid configuration, suitability of components, their ratings and overload capabilities, controls. If not adequately rated and controlled we have voltage/power stability issues.

 

The a.m. thesis on the WSCC outage was conducted in the nineties of the last century when HVDC played no role in Germany in the normal power system curriculum.

 

A special thesis was conducted on Classic HVDC stability for checking the feasibility of a stabilizer idea, simultaneously assessing and comparing the properties of two different simulators, the PSCAD/EMTDC and the OPAL. Today RTDS and OPAL are amongst those tools offering real-time computations for studying interacting generation, AC and DC transmission and loads of the electric power system under inclusion of real control devices.

 

Our power system lab used the class room version of PSCAD/EMTDC with 20 student places for seminars and four places in the lab room for thesis work.

Students were prepared for the practical world. That meant also to include business and project management courses with the focus on HVDC systems design and grid integration. The courses were elective. 

 

The advent of VSC based HVDC systems and their application for renewable energy usage in the beginning of this century swayed the curriculum. New contents was built, elective courses became compulsory. A drop out of MS Frontpage for site building and maintenance meant that the site was no longer accessible for students. Part of the existing material is now assembled under tutorial for temporary access. A new page is under construction.