Real time digital simulation and testing of generator protection elements.
Date
2018
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Abstract
Power system protection is designed to identify and isolate the system from any type of fault or
abnormal condition which may endanger the equipment and operation of the system as a whole.
Ground faults are the most common types of faults in generators and can damage the stator winding
severely. Stator winding protection therefore becomes one of the crucial protection functions in
generator protection. The grounding method used plays an imperative role in determining which
protection functions are to be employed on the generator. This thesis reviews different types of stator
winding faults that occur for a generator and how the generator is protected against these faults using
different types of protection system. It also presents how the different types of generator grounding
affect generator protection schemes, focusing on high and low impedance grounding. The
development of real time digital simulators has greatly improved the simulation and testing of
protection studies. In the past, mathematical models were not fully compatible for the representation
of the complete synchronous generator stator. The Real Time Digital Simulator (RTDS) has
developed a synchronous generator phase domain model which allows for simulation of generator
stator internal faults. This thesis illustrates the suitability of the third harmonic voltage protection
scheme against stator internal faults. An overview of abnormal conditions that occur on a generator
was also reviewed, how they affect the generator and their protection systems. The thesis focused on
reverse power, over-excitation, and differential and current unbalance protection. The loss of field
excitation in synchronous generators also largely contributes to voltage instability. The large
consumption of reactive power and rapid changes in the system components leads to severe damage
of the generator and jeopardizes system stability. This thesis looks into loss of field excitation events
and how their impacts can be reduced by using the R-X protection scheme. It also illustrates results
based on closed loop testing conducted using hardware generator protection relay and the models
developed on the RTDS. The simulation and testing of generator protection functions were proved to
be theoretically and practically correct which could be used as a guideline for improvements in
protection studies.
Description
Masters Degree, University of KwaZulu-Natal, Durban.