  This paper analyses and explains from the systems point of view,
microprocessor based protective relay (MBPR) systems with emphasis on
differential equation algorithms. Presently, the application of protective
relaying in power systems, using MBPR systems, based on the differential
equation algorithm is valued more than the protection relaying based on any
other type of algorithm, because of advantages in accuracy and implementation.
MBPR differential equation approach can tolerate some errors caused by power
system abnormality such as DC offset. This paper shows that the algorithm is a
system description based and it is immune from distortions such as DC-offset.
Differential equation algorithms implemented in MBPR are widely used in the
protection of transmission and distribution lines, transformers, buses, motors,
etc. The parameters from the system, utilized in these algorithms, are obtained
from the power system current i(t) or voltage v(t), which are abnormal values
under fault or distortion situations. So, an error study for the algorithm is
considered necessary.
