The contents of this thesis describe the results of an investigation into the means by which computer aided design (CAD) may be applied to the protection systems of electrical drives, removing much of the repetitive procedures presently used in determining relay settings. To further this aim, a series of algorithms have been devised which allow exploitation of the concept. The areas chosen for demonstration are, direct-on-line started induction motors and transformer fed variable speed drives. In both cases "standard settings' cannot be implemented as the field of application varies enormously. The text discusses an algorithm which utilises several databases containing motor, fuse and cable parameters. Chapter three uses a program derived from this algorithm which allows data to be extracted from the databases and manipulated in order to determine the optimum circuit components. Subsequent chapters examine the implementation of two types of motor protection relay and discusses the algorithms used in modelling them. The text is supported by applications which demonstrate the effectiveness of the derived programs. Chapter six discusses in depth the application of overcurrent relays for the protection of transformers used on variable speed drive installations. The possibility of using overcurrent elements in two or three phases is examined together with the attendant difficulties which may arise. The algorithms are further expanded to incorporate applications which involve the protection of multi-transformer installations supplied from a common point.

Published Article / A company in South Africa is a three-phase induction motor protection relay manufacturer. The function of the protection relay is to capture running data, to provide protection against possible damage, to control an electric motor and to communicate this data to the System Control and Data Acquisition (SCADA) system in a control room. In the case of remote sites e.g. a pump station, the protection relays are used as standalone units. The protection relays are equipped with communication facilities to be used in an instrumentation environment. If a trip occurs or settings need to be changed a technician has to visit the remote site and address the problem. The ideal cost and time effective solution is to perform these tasks remotely via a reliable wireless network. A study was conducted to ascertain the viability of using the standard GSM cellular networks in South Africa to effectively control electric motors and to communicate with the Motor Protection Relays (MPRs) controlling the electric motors in order to determine the status of a motor, settings of the motor, trips that occurred and time of occurrence. It was shown that a node controller could be used to store all the data from various electric motors at a single location. It was also shown that the data from the different electric motors could be analysed at the node controller and that communication can then be initiated from the controller to a responsible person via the GSM network. It was further illustrated that, by making use of the GSM networks in South Africa together with the short message service (SMS), communication and control can be effectively established. SMSs proved to be a reliable means of communication between cellular phones, an embedded network and MPRs. It was shown that software protocols, although slower in communication speed, proved to be reliable and effective for the purpose of transferring information between the node controller and the motor protection relays connected to the electric motors.