Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Electrical and Computer Engineering


Induction machines, which make up more than half the loads in most power systems, exhibit dynamic characteristics especially after system disturbances. This phenomenon is not well modeled by the commonly used static load models but is easily and accurately predicted by some induction machine models. This dissertation develops a method that models a group of induction machines and their connected mechanical loads at a bus by an equivalent induction machine and a mechanical load. Criteria are also developed for deciding which machines could be grouped together into equivalents with acceptable error levels;The equivalent machine draws active power from the source that is equal to the sum of the active power drawn by all the induction machines it replaces. Similarly, it draws reactive power and current equal to the sums of the reactive power and current drawn by the individual machines. It delivers mechanical power equal to the sum of the power delivered by the machines it replaces;The equations of the individual induction machines in the O-d-q axes are used in deriving the equivalent machine. This requires the knowledge of the parameters of the individual machines. In practical systems where this knowledge is not available for all the machines, a method of obtaining the equivalent is suggested;The equivalent machine has been tested for voltage and frequency disturbances. It is found to accurately predict the variations in the active power, reactive power and the current drawn by the machines in the transient, dynamic and steady states. The equivalent induction machine is found for a large number of induction machines and used as part of the load in a transient stability study done on the WSCC 9-bus power system. The loads exhibit significant amounts of dynamics in both the active and reactive power compared with purely constant impedance and constant current load representations.



Digital Repository @ Iowa State University,

Copyright Owner

Kodzo Obed Abledu



Proquest ID


File Format


File Size

134 pages