A terminal bushing sealing element is adapted to be fitted between a terminal bushing and a barrier element. The sealing element is elastic, has an annular shape, and includes a wall with an inner surface and an outer surface. A first opening is provided at a first end of the sealing element and a second opening is provided at a second end of the sealing element, which is opposite to the first end and the wall extends between the first end and the second end. The wall includes a first wall portion that is inclined such that a diameter of the sealing element increases from the first end in the direction towards the second end. The sealing element provides for improved sound attenuation while maintaining a long creepage distance and may be used in sound attenuation casings that are included in power capacitor arrangements.