//Appareillage électrique haute tension

Design and validation tests of 320kV HVDC GIL/GIS

2019-11-21T10:37:01+01:00novembre 21st, 2019|Appareillage électrique haute tension, Publications|

This paper gives an overview of electrical DC phenomena in GIL/GIS, the influence of insulating properties of SF6 and filled epoxy resin, and design of new support insulator for 320kV HVDC GIL/GIS. The busbar system including the insulator was designed not only to satisfy all standard requirements such as mechanical, temperature rise, heating cycle performance but also particular requirements for HVDC applications such as superimposed impulse tests. Finally and for the first time at actual scale, type test according to CIGRE JWG D1/B3.57 was conducted in EDF R&D Les Renardières laboratory to verify the design and insulating performance of the 320kV HVDC GIL/GIS system. The satisfactory results allow to confirm the high technology readiness level of HVDC GIL/GIS.

Phd Raphael CHASSAGNOUX « Dielectric study of liquid and boiling nitrogen – Application to a superconducting fault current limiter »

2019-11-15T15:24:29+01:00novembre 14th, 2019|Appareillage électrique haute tension, Phd|

The increasing number of interconnections in electrical networks and the massive integration of renewable energies nowadays comes with an increase of short circuit currents, and more constraints on high voltage circuit breaker during the current clearance. To solve this problem, a solution consists in inserting a fault current limiting device on electrical lines. Among the available technologies, the superconducting fault current limiter is ideal from the perspective of transmission system operator. However the design of this device is non-trivial, especially the electrical insulation, which is very specific to this apparatus: electrical insulation in a cryogenic environment (liquid nitrogen at - 196°C), superconducting tapes inducing electric field reinforcement, and strong transient heating generating numerous vapor bubbles.

Phd Alexis FOUINEAU « Medium Frequency Transformers design methodologies for high voltage grids and railway grids »

2019-11-15T15:25:48+01:00novembre 13th, 2019|Appareillage électrique haute tension, Phd|

Medium Frequency Transformers (MFT) are an innovative technology compared to low frequency transformers, with the promise of reduced volume and increased efficiency. This PhD thesis focuses in particular on their design for high voltage, high power applications, such as high voltage and medium voltage DC networks, as well as railway networks. In these applications, MFTs are used in converters that can generate specific constraints to be taken into account during their design: non-sinusoidal signals, polarization voltage, target inductance values.

A DC voltage source for long term GIS testing designed by SuperGrid Institute

2019-11-07T17:33:49+01:00octobre 29th, 2019|Appareillage électrique haute tension|

As part of its research, SuperGrid Institute studies the phenomena of partial discharge under DC voltage. Environmental issues emphasised in the European project PROMOTioN encourage the exploration for possible replacement of SF6 gas and remains a strong component of the study at SuperGrid Institute.

Electric field computation for HVDC GIS/GIL spacer under superimposed impulse conditions

2019-10-21T17:08:39+01:00octobre 21st, 2019|Appareillage électrique haute tension, Publications|

This paper evidences the influence of different parameters on the electric field on DC spacers in GIS/GIL and thus their dielectric withstand under S/IMP tests. A notable difference in term of electric field can be observed in function of impulse polarity, load condition (with/without heating current) and insulating material’s properties. For example, an overstress of 0.3pu was obtained on spacer’s surface in case of superimposed impulse test with opposite impulse polarity, high load condition and high leakage current in gas. Contrary to AC system where the simple LI tests were enough, S/IMP tests with both impulse polarity, ZL and HL conditions are mandatory to verify the insulating performance of HVDC GIS/GIL spacer. This paper gives a better understanding of the electric field distribution in HVDC GIS/GIL and helps for the design and tests

Liquid spray injection in the expansion volume of a CO2 high voltage circuit breaker

2019-09-06T14:03:25+01:00septembre 6th, 2019|Appareillage électrique haute tension, Publications|

Most high voltage gas circuit breakers (HVCB) in operation use SF6 as the arc interruption medium because of its high dielectric strength and good arc interruption properties. However, SF6 also displays a high global warming potential which motivates the investigation of possible alternatives to this gas.

Numerical modelling and influence of defects on space charges in epoxy resin under HVDC stresses

2019-08-26T09:10:27+01:00août 29th, 2019|Appareillage électrique haute tension, Publications|

Space charge accumulation on High Voltage Direct Current Gas Insulated Substations can produce electrical field reinforcements in the insulation that need to be taken into account in the equipment design. The TSM (Thermal Step Method) is one of the experimental techniques allowing to determine space charge distributions in insulating materials. However localized defects (i.e. microvoids, delaminations etc) cannot usually be detected by this technique. A new numerical approach to study the influence of structural defects on Thermal Step Method currents is proposed. The method is based on a Finite Element numerical simulation allowing to simultaneously solve electrical and thermal equations. The effect of three different defects were studied. It results that ring defects, with diameters smaller than 0.4 mm, produce less than 10% of change on TSM current signals. This confirms the difficulty to detect small defects by this method. It was also observed that delaminations can produce variations in signal as high as 70%, and even generate signals of opposing sign from the case without defect.

Characteristics of creeping discharges along epoxy surface in fluoronitrile/co2 gas mixture under lightning impulse

2019-09-02T15:13:42+01:00août 26th, 2019|Appareillage électrique haute tension, Publications|

This paper deals with creeping discharges propagating over solid insulator samples in presence of a fluoronitrile mixture consisting of 10% of fluoronitrile and 90% of CO2, under positive and negative standard lightning impulse voltages, in point-plane geometry. The solid samples used are disks made of filled epoxy resin used for real GIS insulators. The experimental results are compared with those obtained with SF6 at pressure ranging 0.1 to 0.3 MPa, while the pressure of fluoronitrile mixture is chosen to match an equivalent dielectric strength of SF6. Different characteristic parameters are investigated namely the maximum length of creeping discharges versus the gas/mixture pressure and voltage polarity. In SF6, two regimes of discharges that depend on the voltage polarity are evidenced. Under positive impulse, the mixture presents similar properties as SF6. However, under negative polarity the maximum discharge length in SF6 is much longer than in the fluoronitrile mixture.

SuperGrid Institute hosts the 11th Quarterly review of NanocompEIM 2

2019-07-25T17:34:46+01:00juillet 25th, 2019|Appareillage électrique haute tension, Systèmes de câbles & jonctions HVDC|

Since October 2016, SuperGrid Institute has been involved in the NanocompEIM 2 project. The goal of the project is to develop nanocomposites (Nanocomp) for electrical insulation materials (EIM) in order to reduce CO2 emissions and improve system reliability and availability. Financed at 50% by Innovate UK, a government organisation dedicated to research and innovation in the United Kingdom, the overall budget of the project is around 1M£ (1.1M€).

Phd Priscillia DANIEL « Electrical properties study of cross-linked polyethylene insulated cables in presence of gaseous cavities aged under DC or DC with harmonic voltages »

2019-07-09T16:00:06+01:00juillet 5th, 2019|Appareillage électrique haute tension, Phd, Systèmes de câbles & jonctions HVDC|

This study aims to examine possible impact of these harmonics in presence of microcavities. Depending on their size and on the electrical field, partial discharges (PD) can occur in these microcavities. Two types of cables have been aged: a medium voltage AC (MVAC) cable with millimetric cavities induced artificially and a model cable with an HVDC XLPE grade.