الفهرس 
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Abstract
HYDC cables start playing more important role in interconnecting national grids. Investment in High Voltage Direct Current (HYDC) transmission will increase by 44% over the next five years, rising from $8.4 billion in 2010 to $12.1 billion in 2015. Many utility companies are turning to HYDC because HYDC lines do not require as much space as overhead alternating current (AC) transmission lines and line losses is lower. HYDC has become the preferred technology for long-distance transmission.
This thesis deals with different concepts of the calculation of electric fields in HYDC cables. The calculation of fields in HYDC cable is far more complex than the equivalent case in HY AC cables. The calculation of electric fields in cables under dc voltages is more complex and depends on the conductivity. the geometry of the cable and the applied voltage while the conductivity depends highly on temperature and electric field.
One of the concepts will take into consideration some important aspects of steady state thermal stability in the insulation of HYDC cables. The resistively graded electric field distribution and the temperature distribution, under steady state. in dc cables, are interrelated. The dc conductivity is known to be a function of stress as well as of temperature. Reasonably convincing theories of electric stress and temperature distribution are now available in the literature. Until recently. the thermal runaway was believed. primarily. to be a consequence of an inordinate run away in the sheath temperature due to dynamic interaction with the ambient. The field distribution in HYDC cable may be of a capacitive. intermediate (and time¬dependent) or resistive nature. Usually. the effect of heating of the insulation by the leakage current may be disregarded. However. in certain cases. i.e. the cable temperature and applied voltage are high enough; the field distribution is influenced by these insulation losses. They even may lead to an instability that causes breakdown of the cable. The calculation of the field distribution in this situation also is carried out also HYDC cables play an important role in a growing number of HVDC links. For almost all of these cables. mass impregnated paper is used as electrical insulation. The electrical conductivity of this insulation is given by a commonly used empirical formula; this formula takes into account the temperature and stress dependency of the conductivity.
This work derives a physics-based equation describing ionic conduction. In good approximation this theoretical formula simulated using MA TLAB M-file and SIMULINK toolboxes that give the same results as the empirical one. This makes it most likely that the conduction in paper mass impregnated cables is of the ionic kind.