Along with the restructuring of the power sector and the dissemination of the system automation and the information and communication technology, the power utilities have been encouraged to deliver more and more information to their consumers, grid operators and regulation agencies concerning the performance of the power system. This paper presents the application of protective digital relays to assist the power quality evaluation of a power system. Recommended power quality indices are used to measure the severity of short-duration voltage variation. The indices are calculated based on the registers of digital relays of different characteristics and compared to the indices calculated from a disturbance analyzer. Although the sample rate of the relays is smaller than that of the disturbance analyzer, the numeric relays can be used to assess the power quality of electric power systems.

To ensure consistent reliability and proper operation, protective relay equipment must be evaluated and tested. This paper presents the requirements for testing the ac and d.c. auxiliary power supply of protective relays and the test results. The test severity levels, test setup , test procedures and test report are presented according to the IEC60255-11 Ed.2.0. A numerical relay commonly found in the power distribution systems is used for testing. The tests are carried out to determine the ability of the relay to withstand a variety of disturbances as specified in the international standard.