Independent thesis Advanced level (professional degree), 20 credits / 30 HE credits
Safe operation of a large synchronous power system as Nordel is not an easy task.
There are several aspects to take into consideration. This thesis focuses on the problems due to voltage collapses in a transmission system.
The ability to foresee an upcoming collapse is vital to maintain stable operation of the grid. The grid operator at Svenska Kraftnät (SvK) uses the computer program SPICA to predict the maximum transfer limit at specified transfer sections. SPICA uses actual states from the grid to predict the transfer limitation, and a quarter later a renewed estimate is produced and so on. This means that the operator can se his transfer limits vary every fifteen minutes.
Our task in this project is to validate the accuracy of the limitations obtained by SPICA. The validation process was carried out as a comparison with another power system analyser, ARISTO. The latter program simulates transient stability as a function of time, and is a versatile tool in many aspects. Another objective of this project is to develop the two programs as we discover disparity.
Our investigations carried out in the CIGRÉ Nordic 32 test system show that, the method of repeatedly updated load flows can in some extent be used to predict the limit of stable operation, in a transfer limiting point of view. Repeatedly investigations show that the prediction seems to be more accurate, the closer the actual point of operation, is to the physical transfer limit.
Further investigations with ARISTO as a guide, we discovered that this behaviour depended on the way to express the reactance in the generator model, which in case of a net failure causes SPICA to produce a value some few percent too high.
During the process we also discovered a couple of improvements of the software involved, which were immediately implemented by the system administrator. The continuous upgrades have led to an iterative process of the analysis. The project also involved production of a tool for converting network-databases between ARISTO-SPICA, This has been made by ordinary staff at SvK by our requirements.
2004. , 102 p.