Apparatus for measuring temperature at a hot point along an electrical energy transmission cable

An apparatus for measuring temperature at a hot point along an electrical energy transmission cable when the temperature exceeds a fixed limit temperature, said apparatus comprising

• a first tube containing a liquid which is vaporizable in the vicinity of said limit temperature to thereby increase a vapor pressure within said first tube, said first tube having a first tube end and said first tube being disposed in contact with the electrical energy transmission cable over the length of said cable;
• pressure detecting means for detecting an increase in the vapor pressure of said liquid upon vaporizing thereof at at least one point along said tube, said pressure detecting means comprising means connected to said first tube end for detecting an increase in the pressure exerted by said liquid at said first tube end;
• a second tube identical to the first tube and filled with the same liquid, said second tube being disposed in proximity to the first tube and parallel thereto;
• said first tube having said end and said second tube having a second tube end connected respectively to cylinders fitted with moving pistons and a rocker lever, pivotally mounted at its center, and being connected at opposite ends to respective pistons whereby movement of the pistons are rendered equal and opposite by said pivotable rocker lever;
• the end of the first tube being connected to a pressure gauge constituting said means for detecting an increase in pressure exerted by said liquid at said first tube end and to a chamber of adjustable small volume;
• an actuator for exerting pressure on liquid contained in said second tube via the piston connected to the end of the second tube whereby excess pressure is set up therein such that said second tube contains liquid only;
• and
• a servo-mechanism for maintaining a pressure difference between the first and second tubes constant.