Regulation of the alternating voltages in a direct current power transmission

Claim 1

A HIGH VOLTAGE DIRECT CURRENT POWER TRANSMISSION SYSTEM CONNECTING TWO A.C. NETWORKS AND COMPRISING A D.C. TRANSMISSION LINE AND A CONVERTER STATION AT EACH END OF SAID LINE; EACH CONVERTER STATION BEING PROVIDED WITH A RECTIFIER CONNECTION AND A FIRST CONTROL MEAND FOR SAID CONNECTION; SAID FIRST CONTROL MEANS INCLUDING MEANS FOR PROVIDING THE RECTIFIERS OF SAID RECTIFIER CONNECTION WITH CONTROL PULSES WITH A CERTAIN DELAY ANGLE; SAID FIRST CONTROL MEANS IN A FIRST OF SAID STATIONS HAVING AN INPUT CIRCUIT SETTABLE TO A CERTAIN DESIRED VALUE OF A CERTAIN TRANSMISSION MAGNITUDE; SAID FIRST CONTROL MEANS IN THE SECOND OF STATIONS BEING CONTROLLED IN ACCORDANCE WITH A CERTAIN PROGRAMME INVOLVING A CERTAIN MINIMUM OR MAXIMUM VALUE OF SAID DELAY ANGLES CORRESPONDING TO RECTIFIER OR INVERTER OPERATIONS, RESPECTIVELY, OF SAID SECOND STATION; ON STATION; SAID POWER TRANSMISSION SYSTEM BEING CHARACTERIZED IN THAT: IN EACH OF SAID STATIONS SAID RECTIFIER CONNECTION HAS AN A.C. SIDE CONNECTED TO THE A.C. VOLTAGE OF SAID A.C. NETWORK; EACH STATION INCLUDES A FURTHER CONTROL MEANS FOR CONTROLLING SAID A.C. VOLTAGE CONNECTED TO THE A.C. SIDE OF SAID RECTIFIER CONNECTION; SAID FURTHER CONTROL MEANS HAVING AN INPUT SIDE; MEANS IN SAID FIRST STATION FOR MEASURING THE DELAY ANGLES OF THE RECTIFIERS OF THE STATION; THE INPUT SIDE OF SAID FURTHER CONTROL MEANS OF SAID STATION BEING CONNECTED TO SAID DELAY ANGLE MEASURING MEANS AND CONTROLLED FROM SAID MEANS IN RESPONSE TO THE DEVIATION OF SAID DELAY ANGLES FROM A CERTAIN DESIRED VALUE OF SAID DELAY ANGLES; MEANS IN SAID SECOND STATION FOR MEASURING THE DIRECT VOLTAGE OF SAID TRANSMISSION LINE; THE INPUT SIDE OF SAID FURTHER CONTROL MEANS OF SAID SECOND STATION BEING CONNECTED TO SAID DIRECT VOLTAGE MEASURING MEANS AND CONTROLLED FROM SAID MEANS IN RESPONSE TO THE DEVIATION OF SAID DIRECT VOLTAGE FROM A CERTAIN DESIRED VALUE OF SAID DIRECT VOLTAGE.