Alstom Design Manager, Antero Kahkonen, who undertakes system studies for reactive power compensation projects, is the inventor of the Main Reactor concept, which has now been patented. “At the end of the last decade, the general requirements for SVC specifications exceeded the capabilities of conventional SVCs. The biggest obstacle was meeting grid codes in terms of harmonic performance. But also items such as losses, space and availability requirements demanded innovations. The conventional SVC needed a facelift.
"I was preparing the technical proposal for the Beauly substation SVC [see sidebar], when I realised we were facing a brick wall. We had examined all possible conventional configurations without finding an acceptable solution. That’s when I started to write equations for impedances and current amplifications. I modelled my calculations and found we could solve a number of problems by adding just one reactor to the topology. The concept was examined using commercial simulation tools, with very good results. Subsequently, our design tools were updated with the ability to calculate Main Reactor configurations. Based on recent experience, this SVC innovation is well suited to today’s FACTS market."
Indeed it is, if the Beauly substation in Scotland is to be taken as the example. The planned expansion of the substation (to operate a new 400 kV transmission line between Beauly and Denny) required the installation of a new SVC to help operate the transmission network within quality limits. A standard SVC could not meet the harmonics requirements. However, this innovative SVC configuration – complete with the Main Reactor – fully satisfied the criteria for this strategic substation. It has been in operation since the summer of 2013. Other countries such as Brazil and Saudi Arabia are now showing interest in this promising solution.
Three questions to Neil Thomson, Engineering Manager, SHE Transmission
Could you briefly describe the SHE Transmission network and the role of the Beauly substation?
Scottish Hydro Electric Transmission plc (SHE Transmission) is responsible for the electricity transmission network in the north of Scotland, which serves around 70 percent of the landmass of Scotland. SHE Transmission has to ensure there is sufficient network capacity for those seeking to generate electricity from renewable and other sources. Beauly substation is a major transmission hub in the Scottish highlands. It has recently had its 275 kV compound rebuilt and a 400 kV compound added as part of the Beauly-Denny project. Beauly is a strategic hub for power generated from renewables in the north of Scotland. The Beauly-Denny 400 kV replacement transmission line project is replacing the 132 kV transmission circuits between Beauly and Denny, in central Scotland, to allow a greater transfer of renewable power from the highlands to the load centres in the central belt and further south.
The need for voltage control at Beauly was identified at an early stage of the project. A +150/-150 MVAr SVC was installed and connected to the 275 kV busbars, along with tertiary connected 90 MVAr reactors on the supergrid transformers and two 45 MVAr mechanically switched damped capacitor networks (MSCDN) on the 132 kV busbar.
What was the attraction of the SVC with Main Reactor?
We know that SVCs fitted with TCRs generate harmonics, and our specification detailed limits on the generation of these harmonics and amplification of existing harmonics. When Alstom offered its Main Reactor as part of its SVC offer, we saw its advantages and did wonder why such a simple idea had not been thought of before! The detailed studies submitted showed that the SVC’s harmonic performance complied with our requirements, so, as a company that is keen to encourage innovation and open to new ideas, we saw no reason not to proceed with a Main Reactor solution.
What has been your experience with the Beauly SVC with Main Reactors?
The SVC has been in operation since early summer 2013 and we have had no issues with its operation to date. We have had several faults on the network over that time, which the SVC has responded to well within the response criteria we specified. The SVC is in operation 24/7 and has quickly become an important part of the transmission network in the north of Scotland.