A method of building an insulation system around a naked conductor section of a power cable, which power cable has a conductor which includes the naked conductor section and which power cable comprises an insulation system already provided around a majority of the conductor, which insulation system comprises an inner semiconducting layer arranged around the conductor, an insulation layer arranged around the inner semiconducting layer, and an outer semiconducting layer arranged around the insulation layer, and wherein the method comprises: a) placing the naked conductor section in a mould, and b) moulding an insulation system around the naked conductor section, wherein the moulding of the insulation system involves injecting a first semiconducting compound into a first mould cavity to form an inner semiconducting layer around the naked conductor section, injecting an insulation compound into a second mould cavity to form an insulation layer around the inner semiconducting layer, and injecting a second semiconducting compound into a third mould cavity to form an outer semiconducting layer around the insulation layer, wherein step b) of moulding involves using several mould inserts, one for each layer, wherein for each layer that is being moulded a mould insert is placed in the mould forming a respective mould cavity, wherein step a) further comprises placing the naked conductor section in a first mould insert in the mould, characterised in that each mould insert is provided with a respective ring-shaped runner system, each having a ring-shaped runner that extends circumferentially 360 degrees around the respective mould cavity, and a sprue connected to the ring-shaped runner, wherein the ring-shaped runner in the beginning of each mould cycle only has a single gate opening, which single gate opening is located opposite to the sprue, and wherein each ring-shaped runner system comprises a movable sleeve arranged in a first position at the beginning of the corresponding mould cycle thereby forming the single gate opening, wherein the method comprises moving the respective sleeve axially along a central axis of the power cable from the first position to a second position to obtain a gate along the entire circumference of the ring-shaped runner, wherein the respective sleeve is moved from the first position to the second position when any of the first semiconducting compound, the insulation compound and the second semiconducting compound has reached the single gate opening. a) placing the naked conductor section in a mould, and b) moulding an insulation system around the naked conductor section, wherein the moulding of the insulation system involves injecting a first semiconducting compound into a first mould cavity to form an inner semiconducting layer around the naked conductor section, injecting an insulation compound into a second mould cavity to form an insulation layer around the inner semiconducting layer, and injecting a second semiconducting compound into a third mould cavity to form an outer semiconducting layer around the insulation layer, wherein step b) of moulding involves using several mould inserts, one for each layer, wherein for each layer that is being moulded a mould insert is placed in the mould forming a respective mould cavity, wherein step a) further comprises placing the naked conductor section in a first mould insert in the mould, characterised in that each mould insert is provided with a respective ring-shaped runner system, each having a ring-shaped runner that extends circumferentially 360 degrees around the respective mould cavity, and a sprue connected to the ring-shaped runner, wherein the ring-shaped runner in the beginning of each mould cycle only has a single gate opening, which single gate opening is located opposite to the sprue, and wherein each ring-shaped runner system comprises a movable sleeve arranged in a first position at the beginning of the corresponding mould cycle thereby forming the single gate opening, wherein the method comprises moving the respective sleeve axially along a central axis of the power cable from the first position to a second position to obtain a gate along the entire circumference of the ring-shaped runner, wherein the respective sleeve is moved from the first position to the second position when any of the first semiconducting compound, the insulation compound and the second semiconducting compound has reached the single gate opening.