Wide area measurements have been widely used in the energy management systems (EMS) of power systems for monitoring, operation, and control. In recent years, the advent of synchronized phasor measurements has added another dimension to the field of wide-area measurements. At the same time, the field of protection systems has been dominated by computer based relays, which make it relatively easy to communicate with relays and thus include them in many innovative protection systems. Special Protection Systems (SPS) or Remedial Action Schemes (RAS) are one example of integration of communication and protection systems. In recent years-due to operational demands imposed on transmission networks by deregulation it has become clearer that wide-area measurements and their integration in protection and control systems is a necessity. This paper documents the state-of-the-art in modern sensor, communication, and protection technologies which show great potential for innovations in protection and control systems for the future.

This paper describes the performance of the protection system used for the first commercially operated sixphase transmission line in the world -New York State Electric & Gas's 93 kV (phase to phase and phase to ground) line from Goudey Station to Oakdale Substation during faults in the winter of 1993.The paper briefly describes the basics of the HighPhase Order Transmission Demonstration Project and the integration of available state of the art microprocessor based relays, with a programmable logic relay (designed for the protection of conventional three-phase systems) in a hierarchical six-phase protection system. The operation of the protection system during two faults on the line in January and February 1993 is reported. The modeling of the six-phase line in a conventional three-phase short circuit study program is also considered and a comparison between the measured and calculated fault currents is presented.

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