Patent GB-1030502-A (GB)
Title: Regulation of alternating voltage in a direct current power transmission system
IPC: H02J3/36
Filed: 1963-03-19
Abstract: 1,030,502. Converting. ALLMANNA SVENSKA ELEKTRISKA A.B. March 19, 1963 [March 20, 1962], No. 10740/63. Heading H2F. In a high voltage direct current power transmission system comprising two converter stations 1, 2 each containing grid-controlled rectifier connections 11, 12, 21, 22 in which the grid control of one station (as shown 2, the inverter station) is programme controlled, i.e. is constant or is varied according to some programme, and the grid control of the other station (as shown 1, the rectifier station) is controlled in accordance with some transmission parameter (as shown, current determined by the coil 3 and applied to grid control devices 113) an arrangement is provided whereby the A.C. voltages at the anodes is controlled (for example, in the rectifier station 1 by tap selectors 112, 122), the A.C. voltage in the programme controlled station 2 being controlled in accordance with the D.C. line voltage, and the A.C. voltage in the transmission-parameter-controlled station being controlled in accordance with the delay angle obtaining at that station. In the arrangement shown, the station 2 is connected not to a transformer but to an A.C. machine. A.C. voltage control is therefore effected directly by means of a controller 231 instead of transformer taps 112, 122. In the station 2 a measure of the D.C. line voltage is taken at 41, amplified at 42 and applied to a relay A (not shown) which operates a contact A1 having three positions (Fig. 2, not shown). Figure 3 discloses an arrangement which enables a signal to be applied to terminals 6 or 7, these terminals being connected to terminals on the voltage controller 231 to provide a rise or fall in the A.C. voltage of station 2. A similar arrangement of 41, 42 and Fig. 3 is disposed in station 1, in this station the terminals 6 and 7 are connected to the tappings 112, 122 to provide a rise or fall in the A.C. anode voltage in this station. Reverting then to station 2, if the voltage picked up at 41 is just right the relay A is operated to set A1 in its middle (inoperative position); if it is low (which would have the effect of making the output A.C. voltage too low) then A1 is operated to the position shown to complete a path from 5 to 7, this signal on 7 being applied to controller 232 to order an increase in output voltage. If the voltage at 41 is too high, A1 takes its upper position, terminal 6 is energized and a decrease in A.C. voltage output. In this station, i.e. the programme controlled station, the contact C2 is always in the position shown. Now for the station 1, which is current controlled, in the Fig. 3 circuit arrangement associated with that station the contact A1 is always in the position shown and the contact C2 is always in its lower position. It is therefore clear that the pick-up 41, 42 has no effect on the signals to 6 or 7. However, in this case signals to 6 or 7 which order the selection of the transformer tappings 112, 122 are effected via relay contacts D114, D124. These relays 114, 124 operate on voltages derived from the phase difference between the actual grid control voltages and some ideal value of delay angle. Thus, as the line current changes the delay angle is varied until it reaches a value which operates the relays 114, 124, to effect a switching of the contacts D114, D124 to a position giving a signal to 6 or 7 which in turn alters the transformer tapping and hence anode voltage so that the delay angle may return to some more suitable value. The arrangement disclosed is complicated by the inclusion of two rectifier connections 11, 12 in each station, each of which may be shortcircuited. This involves the need for the two relays 114, 124 and various modifications for adjusting the relay A. The disclosure contemplates (a) either station being rectifier or inverter, (b) either station being programme controlled or parameter control, (c) any of the parameters current, power or frequency being the operative parameter, (d) one, two or more rectifier element connections disposed in each station, (e) the transfer of a normally-programme-controlled station under abnormal conditions to parameter control, with disconnection. of the D.C. line voltage detecting arrangement.