الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
A power system is vulnerable to faults, either due to natural disasters or by mis-operation of the system due to operators’
negligence. This can result in permanent damage to power system
components leading to considerable costs for their replacement
and in longer disconnections of power supply to customers, which
is highly undesirable. This sets a requirement for a power system
to sustain faults, while protection systems should minimize the
damage in important components and the effect of faults as much
as possible. This is achieved by using power system protection
techniques and methodologies.
Microprocessor-based relays have their own algorithms for
monitoring the power system through current and voltage inputs
from CTs and VTs respectively. Protection relays are thoroughly
tested using relay test sets to confirm their reliability and safe
operation before commissioning them in a substation. With the
advent of Real-Time Simulators and compact reconfigurable
input /output (I/O) controllers, large power systems can be
simulated and their behavior can be analyzed in both steady state
and faulted conditions. The purpose of protection relays is to
detect a fault and give a trip order to the switching device that is
closest to the fault location. However, in several cases, the
commonly used algorithms of the digital relays fail in practice to
cope with their functions.
Therefore this thesis presents a programmable microprocessor
based relay for enhancing the operation of the main
protection functions. The investigated modifications for this
objective have been applied to EL-KOBBA 66/11kv substation in
Cairo to check the reliability of the suggested models.
Thus, the basic over-current protection is simulated for
different standard definite and inverse tripping curves and the
protection function is enhanced with the accompanied voltage
dependent current threshold setting. Also, the basic overcurrent
protection function is modified by taking into account the higher
inrush current occurring at operating transformers after outage or
first operations.
The conventional directional protection function requires
the measurement of both the three phase voltages and currents.
Thus the proposed micro-processor based relay presents an
optimized solution for the detection of current direction based on
the current measurement only by monitoring the change of the
currents angles. This enhancement can lead to eliminate the cost
and the space required for voltages measurements.
Further, future distribution systems with the large
penetration of renewable distributed generation at the load side
represent a challenge for the directional protection function. The
proposed micro-processor based relay presents a new technique
based on an advanced tripping curve to take into consideration the
reactive power supplied by the distributed generation.