Electrical power transmission

A connection-and-protection device for a power-transmission cable having two capacitively connected conductors respectively connected in use to a supply cable at one end and a load cable at the other end, the connection-and-protection device comprising:

• an earthable conductive housing;
• three connection terminals, each being rated to provide for termination at elevated voltage insulation from the housing and an internal connection point within the housing:
• one of the connection terminals being for insulated termination and internal connection of either of the supply or load cables,
• the others of cable terminals being ones of a pair for insulated termination and internal connection of the respective capacitively connected conductors, or interconnecting pieces of cable from the terminals to the respective conductors,
• a direct connection within the housing between the one of the connection terminals and one of the pair of cable terminals, the other of the pair of cable terminals not normally being connected to the one of the connection terminals, and
• connection means in the housing for connecting the other of the pair of cable terminals to the one of the connection terminals to protect the capacitive connection of the two conductors, in the event that the voltage between the pair of cable terminals exceeds a threshold.

A connection-and-protection device in combination with a power-transmission cable having two capacitively connected conductors respectively connected in use to a supply cable at one end and a load cable at the other end, the connection-and-protection device comprising:

• an earthable conductive housing;
• three connection terminals, each being rated to provide for termination at elevated voltage insulation from the housing and an internal connection point within the housing:
• one of the connection terminals being for insulated termination and internal connection of either of the supply or load cables,
• the others of cable terminals being ones of a pair for insulated termination and internal connection of the respective capacitively connected conductors, or interconnecting pieces of cable from the terminals to the respective conductors,
• a direct connection within the housing between the one of the connection terminals and one of the pair of cable terminals, the other of the pair of cable terminals not normally being connected to the one of the connection terminals, and
• connection means in the housing for connecting the other of the pair of cable terminals to the one of the connection terminals to protect the capacitive connection of the two conductors, in the event that the voltage between the pair of cable terminals exceeds a threshold:
• the connection means being rated for not more than 20% of the elevated voltage, and
• the connection means being adapted to be operated by low voltage control,
• event detection means for detecting the voltage between the pair of cables exceeding a threshold of more than 20% of the elevated voltage,
• a low voltage power supply in the housing, and
• a low voltage controller in the housing for causing the connection means to effect the said connection in the event of detection of the said voltage exceeding the threshold.

A power-transmission cable protection-and-control arrangement for a capacitive power-transmission cable, the arrangement comprising:

• at a one end termination of the cable:
• a load or supply terminal for a load or supply cable,
• a pair of cable terminals for a pair of conductors of the capacitive power-transmission cable, the conductors being connected directly or via extension conductors to the terminals in use,
• one of the pair of cable terminals being connected by a rail or busbar to the load or supply terminal,
• an electromagnetic or electronic switch between the rail or busbar and the other of the pair of cable terminals, and
• at the one end or at another end termination of the cable:
• measuring means for measuring the differential voltage between the pair of cable terminals, i.e. between the capacitive cable conductors in use, and
• switch controlling means for controlling the switch to close in the event that the differential voltage exceeds a threshold below dielectric breakdown of the capacitive cable,
• wherein
• the switch controlling means is adapted to control the switch in a second or third event or separate switch controlling means is provided therefor,
• the second event is that the current in the busbar or rail is below a certain threshold and
• the third event is that the current in the busbar or rail is above a certain threshold.