Composite Load Model for Dynamic Simulations - Report 1.0

Correct representation of electrical loads in power system studies has become very important in recent years, as loads are playing an ever increasing role in power system dynamic stability. Western Electricity Coordinating Council (WECC) has long recognized the need for better load modeling and has undertaken significant efforts to improve load representation in dynamic simulations.

An “interim” load model was approved ten years ago and is still in use today in WECC. The model had 20% of load represented with induction motors across the entire system and for all study conditions. The motor load was still connected at a high-voltage transmission bus. The “interim” model was developed to address operational issues on the California-Oregon Intertie raised after July 2 and August 10 1996 outages. During the approval process, WECC emphasized the “interim” nature of the model and argued the need for a more comprehensive load modeling. It was recognized that the advance of computing capability would permit significant improvements beyond the interim model. Experience in the development of new model has confirmed both that the improvements have been possible and greatly needed.

WECC Modeling and Validation Work Group (MVWG) led the development of the composite load model for dynamic simulations. Today, the composite load model is implemented in GE PSLF version 18 and Siemens PTI PSS®E version 32. Comparable models are being developed in Power World Simulator and PowerTech’s SAT programs. The new composite load model has a much more realistic model structure and has been shown to capture a wide range of load dynamics observed in reality. The model has been proven to be numerically stable and robust, as thousands of simulation runs have been made with the model to date.