الفهرس 
Performance of High Voltage Direct Current Circuit Breaker during and after Arc Interruption Process
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Abstract
The applications of High Voltage Direct Current systems have increased lately with the
great demand for electric power and the integration of the new renewable power plants. To
ensure the reliability of the High Voltage Direct Current systems it must be able to clear faults
very fast. This is mainly done by circuit breakers. High Voltage Direct Current Circuit breakers
are different from AC Circuit breakers for that in AC systems the existence of the zero crossing
facilitates the interruption process. This thesis studies the interruption process of a High
Voltage Direct Current pole to ground fault.
First, the circuit analysis method is carried out using a Mayr arc model to simulate the
arcing process and find the interaction between the arc and different circuit components. This
type of analysis gives a good view on the arc current and Circuit breaker voltage during and
after the fault interruption process. Also, it gives a good idea about the different factors
affecting the arc from circuit paraments to fault conditions and arc model parameters.
Second, the Finite Element Method is used to develop a physical arc model. This method
uses a Circuit Breaker geometry as a base for the simulation then the magnetohydrodynamic
equations are used to simulate the arcs interaction with the fluid flow. This type of simulation
gives a good idea about the electric field, pressure and temperature generated during and after
the interruption process.
To ensure the best results both methods are coupled to have a complete and conclusive
view on the arcs properties and interaction with circuits connected to the circuit breaker and
the Circuit breaker geometry. The coupling is made by taking the results of arc current and
circuit breaker voltage during the fault interruption process as an input to the Ansys Fluent
program to continue the simulation.
We found out that the increase in arc time constant value leads to an increase in the arcing
time, which decreases the di/dt and also increase the RRRV. The increase in cooling power
value would increase the di/dt and decrease the RRRV.
We investigated corona discharge around the arcing contact after arc interruption, the
discharge is mainly caused by the high temperature low pressure dissociated SF6 gas left after
the arcing process, it was found that the discharge at the lower part of the hollow contact can
retain up to 300 μs from moment of arc interruption.
We also investigated the effect of CB geometry on interruption process, we found out that:
It’s better for the interruption process, to have big solid contact as possible as it will help block
the gas flow leading to an increase in gas pressure inside the nozzle so the arc would face a
high dielectric strength and the thermal dissipation of the arc would be better, also we found
out that the increase in hollow contact thickness will not cause any change in arc temperature
and pressure distribution inside the CB during the interruption process.