Maximum undergrounding degree of HV subtransmission networks as dictated by unscheduled power flows

• Published in: IET generation, transmission & distribution Vol. 7; no. 11; pp. 1202 - 1209
• Main Authors: Lauria, Stefano, Palone, Francesco
• Format: Journal Article
• Language: English
• Published: Stevenage The Institution of Engineering and Technology 01.11.2013; Institution of Engineering and Technology; The Institution of Engineering & Technology
• Subjects: active power flow; Applied sciences; Bypasses; EHV system; electric reactance; Electrical engineering. Electrical power engineering; Electrical power engineering; Exact sciences and technology; frequency 50 Hz; HV line reactance; load flow; maximum undergrounding degree; meshed HV subtransmission network; Miscellaneous; Operation. Load control. Reliability; optimum UGC shunt compensation requirement; Overhead networks; power flow simulation; Power networks and lines; power overhead lines; transmission networks; UGC charging power; Underground and submarine networks; underground cable; underground cables; unscheduled power flow; voltage 150 kV; active power flow; underground cable; frequency 50 Hz; power flow simulation; UGC charging power; EHV system; transmission networks; electric reactance; unscheduled power flow; underground cables; voltage 150 kV; power overhead lines; HV line reactance; load flow; meshed HV subtransmission network; maximum undergrounding degree; optimum UGC shunt compensation requirement; Underground cable; Meshed network; Electric energy transportation; Shunt; Parallel; Load flow; Case study; Reactance; Power flow; System simulation; Overhead line; High voltage line; Power transmission line
• ISSN: 1751-8687; 1751-8695
• DOI: 10.1049/iet-gtd.2012.0295

Meshed HV subtransmission networks are subject to undesirable parallel (unscheduled) active power flows from the EHV system. The phenomenon is worsened by conversion of HV overhead lines to underground cables (UGCs), which increases parallel flows through the HV network because of the attendant reduction in HV line reactance; the effect increase with network extension and are compounded by UGC charging power. The study deals with the assessment of the maximum undergrounding degree for a given subtransmission network. An analytical formulation of maximum HV line extension length as a function of EHV power flow and undergrounding degree is given; optimum UGC shunt compensation requirements are evaluated. Application to a typical 150 kV–50 Hz network is presented, showing a very good agreement with power flow simulation. In particular, the case study evidences that complete undergrounding of the HV network is possible if line length is under 50 km; the proposed shunt compensation effectively raises this limit to 70 km.