Driver for the local display unit of a protection relay

Sašo Vrbinc (2009) Driver for the local display unit of a protection relay. EngD thesis.

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Abstract

Local display unit functions as a user interface of the protection relay. It is therefore an indispensable part of the relay, used for monitoring and controlling of the relay and,consequently, of certain power grid elements. Local display unit is composed of two parts: a standalone peripheral display unit (the master device), and a software driver (the slave) running on the protection relay control unit. The thesis describes a software driver which is incorporated into the existing architecture of the 'rcman' information-communication system, and runs on the protection relay. The software driver communicates with the master device using the Modbus protocol over an RS-232 interface. The two key requirements to be met in preparation of the thesis were a high data throughput, on one hand, and a simple extensibility of the driver on the other hand. During the initial development phase it was established that the implemented subset of Modbus functions is not sufficient for communication between the driver and the peripheral display unit. Therefore,certain Modbus functions had to be modified at the expense of losing their compatibility with the standard Modbus protocol. The result is a working software driver that meets the above mentioned requirements and provides the peripheral display unit with the data describing alarms, events, analogue measurements,LED indications, and the status of digital input lines.

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