Simulation methodology for DC GIS

Dimensionning of DC isulation is relatively complexe and need to take into account must more effects and parameters than in AC. This paper presents simulation methodology to applied for DC GIS and GIL.

HVDC (High Voltage Direct Current) shows great interests for high power transmission thanks to its opportunity to transmit the electrical energy over long distances with very low losses and to guarantee higher system stability. Advantage provided by Gas Insulated Substation (GIS) and Gas Insulated Line (GIL) on footprint impact and environmental aspects make those component  valuable solution for high voltage substations.

To reduce costs of this kind of installation, one of the solutions consists in minimization of its dimensions. The design of a reliable and compact GIS requires complete reliable information about electric field distribution in the equipment. However, it is well known that electric field distribution of insulating materials subjected to a DC voltage are very different from AC one. When the electric field distribution in HVAC GIS is controlled by insulating materials permittivity and system geometry, in HVDC GIS field distribution depends also on the conduction currents. These currents play an important role and need to be considered.

This paper focuses on electric field simulation methodology for insulating materials under DC stress in order to obtain a reliable model for the conception of HVDC GIS apparatus. Under DC stress, both permittivity and conductivity (surface and volume conductivities) of insulating materials influence the field distribution and thus have to be taken into account for the assessment of DC steady state and transient. These electrical characteristics are not constant and depend on the electrical field and the operating temperature. The field distribution also depends on equivalent gas conductivity that may vary in a wide range through the number of charge carriers and their associated mobility. Different physical phenomena are at the origin of charge carriers. The influence of each parameter as well as that of the type of models for computing the electrical field distribution is discussed.

Moreover, the electric field shifts from capacitive to resistive distribution within time that can vary from few seconds to several months. This aspect is important for testing procedures and can be also evaluated by calculation. Hence, the transient field simulation must also be included in order to predict the most critical case which needs to be taken into account for the design of GIS apparatus.

Cong-Thanh VU (1), Paul VINSON (2), Alain GIRODET (3), Abderrahmane BEROUAL(4)

1 : SuperGrid Institute, 130 rue Léon Blum, 69100 Villeurbanne, cong-thanh.vu@alstom.com
Université de Lyon, Ecole Centrale de Lyon, AMPERE CNRS UMR 5005
2 : SuperGrid Institute, paul.vinson@alstom.com
3 : SuperGrid Institute, alain.girodet@alstom.com
4 : Université de Lyon, Ecole Centrale de Lyon, AMPERE CNRS UMR 5005,
SuperGrid Institute, Abderrahmane.Beroual@ec-lyon.fr