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relays usually offers some sort of stabilization against false the assumed corrections and testing the relay with the
tripping. The simplest solution is an appropriately insensitive resulting new transient data.
setting of the restraint characteristic parameters. Or there
might be dedicated blocking functions for this case, with CONCLUSION
related parameters. But how to set these parameters? Here Modern measurement and test equipment enables the
the described testing approach can be used to stimulate commissioning staff to comfortably carry out tests related
the relay with the saturation-distorted signals according to to on-site conditions which also allow the assessment of
the CT and burden data at the ends of the protected zone relay performance under CT saturation during high-current
and the grid data controlling the short current, and you can faults. This is a complement to the parameter-oriented test
now optimize the restraining or blocking parameters of the and adds confidence where without this kind of test you
relay to ensure stable operation at the expected worst- would either have to just hope for the best accepting the
case through-fault conditions without setting them to possible saturation (as was often done in the past), or you
inappropriately high values that might impair tripping when would refrain from using these assets due to the expected
needed. So this is some sort of parameter testing, but
not in the formerly described sense of verifying predefined saturation and unknown consequences.
parameters but to evaluate the proper parameter settings
needed for the application. There is no other equally LITERATURE
convenient way to do this verification. [1] IEC 60044-6
[2] CM-Line Catalog; http://www.omicron.at
Once the CT and burden data have been gathered the
simulation test may alternatively be carried out ‘in the office’ Eugenio Carvalheira received his BSc in Electrical
with an identical relay unit with identical settings, in order Engineering from the Federal University of Pernambuco,
to verify the saturation behavior. Of course the classical Brazil and his MSc in Computational Engineering from the
parameter and connection test still has to be done with University of Erlangen-Nuremberg, Germany.
the target relay on site. He started his career as a Project Engineer at ESC Ltd
responsible for the design, planning, implementation and
If the result is that the saturation influence leads to commissioning of protection and control systems for
unacceptable relay performance then diverse remedies electrical substations and power plants. In 2008 he joined
can be considered, such as using a greater cable cross- OMICRON in Germany as Training & Consulting Engineer
section to reduce the burden of the connection between designing and developing test automation solutions
CT and relay (the cables usually contributes much more for protection relays and responsible for the IEC 61850
to the external CT burden than the connected relay input). training courses at OMICRON. He is presently Application
Engineer and Training Manager (Latin America) with
Incidentally, the expected influence of changed burden is OMICRON electronics Corp. USA in Houston, TX.
easily studied beforehand by feeding the simulation with

INDUSTRY JOURNAL 38