Capability charts for power systems.
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis extends the concept of the traditional synchronous generator capability chart to describe the steady state performance of transmission lines, HVDC links, and entire AC/DC power systems. Each capability chart depicts an operating region on the complex power plane that represents the real and reactive power that may be supplied to a load from a particular busbar. The boundaries of the operating region are defined by a web of contours that represent the critical operating constraints of the system. The charts for small systems can be constructed by manipulating the operating equations into a form suitable for drawing loci on the complex power plane. This technique is used in this thesis to construct charts for generators, transmission lines, and HVDC links. The operating equations of large systems are not easily manipulated, so a different approach is used to construct charts for large systems. This approach involves iterative powerflows and contour plotting to avoid the formulation of explicit closed form locus equations. Two algorithms for drawing the capability charts of large AC power systems are described. The first algorithm uses a contour tracing technique to plot the constraint loci. The knowledge gained from the use of this algorithm was then used to design the second, faster algorithm that uses a region growing technique to help plot the constraint loci. Capability charts for large AC/DC systems are also discussed. The operating constraints of the AC/DC converters require special treatment due to discontinuities in the converter operating equations. An offshoot of the work on AC/DC charts is the development of an improved sequential AC/DC powerflow algorithm. A practical example of the use of the capability charting algorithms is given by drawing charts for a proposed second New Zealand HVDC link. The capability charting algorithms will make suitable additions to existing power system interactive graphics programs. On-line displays of capability charts in system control centres could also provide useful information to human dispatchers.