Gas insulated substations (GISs) are broadly used for transmission and distribution in electric power networks. Very fast transient overvoltage (VFTO) caused by SF₆ discharge during switching operations in a GIS may threaten the insulation of electrical equipment. In this paper, a novel VFTO suppression method with great prospects in engineering, called the spiral tube damping busbar, is proposed. The suppressing mechanism of the new method is analyzed. The structure and the design characteristics of the damping busbar are introduced as well. Moreover, a calculation method for the self-inductance of the damping busbar at high frequency is presented. According to the structural characteristics of the damping busbar, the inductance effect on suppressing VFTO is analyzed. A further improvement in damping VFTO is investigated by designing a spiral litz coil connected in series with the busbar, which increases the damping effect. The simulation results show that the improved damping busbar has a significant suppressing effect on the amplitude and the frequency of VFTO.

The corona discharge pulse current has double exponential distribution characteristics. On this basis, the electromagnetic radiation model of corona discharge is established by using the theory of electric dipole. The corona discharge characteristics are analysed and compared with the measured results of 1000kV UHV ac transmission line. The results show that the electromagnetic field strength increases first and then decreases with time, and at the same time, the electromagnetic field strength decreases exponentially with distance. The simulated and predicted corona discharge radiation characteristics have the same variation law as the measured data, which verifies the correctness of the model.

This paper focus on the research about the probability and practicability of 330 kV GIS structure design with three phase in one tank， which represents the miniaturisation and compact developing trend of GIS. The design principle is proposed according to the volume of three phase in one tank (structure A) is generally smaller than that of the sum volume of three single phase (structure B). Then, the dimension size of 330 kV GIS with structure A is presented. To solve the weak insulation‐level problem between phases of structure A, which prevents it from being used in high‐voltage power system especially above 330 kV, an electromagnetic‐temperature‐flow multi‐physical field coupling model considering eddy effect and skin effect is established to analyse the influencing factors on the insulation level of internal GIS. Therefore， the insulation level between the phases of structure A is calculated under the condition of power frequency and short circuit, respectively. The results show that the insulation margin of 330 kV GIS with structure A is enough and completely meet the insulation requirement of GIS. Furthermore, compared with structure B, structure A has lower temperature rise and energy consumption .

To meet the special insulation demand of the DC transmission system with the highest voltage in the world, a new kind of ±1 100 kV DC voltage divider is designed. The reliability of the new structure voltage divider under the action of lightning impulse is studied. To achieve the voltage and electric field strength distribution of the voltage divider, a 3D transient electric field calculation model is established and a lightning impulse test for the prototype is carried out. The results reveal that (1)The voltage and electric field strength distributing on the voltage divider changing with time show a cumulative effect. (2)The maximum electric field strength occurs at the junction where the first grading ring connecting to the internal bushing. (3)The maximum current of resistance occurs at the peak voltage of lightning impulse with the corresponding time is 1.2 µs. (4)The voltage distributing on the capacitance imply that the capacitance really does play the role of equalisation voltage when the voltage divider suffering lightning impulse. (5)The prototype of HVDC voltage divider passing through the lightning impulse test successfully strongly demonstrates the correctness and reliability of the new structure ±1 100 kV voltage divider voltage.