Patent GB-410329-A (GB)
Title: Improvements in and relating to the conversion of alternating current of a given periodicity and phase number into alternating current of another periodicity and phase number
IPC: H02M5/00
Filed: 1933-06-19
Abstract: 410,329. Frequency changing. AKT.-GES. BROWN, BOVERI, ET CIE, Baden, Switzerland. June 19, 1933, No. 17411. Convention date, June 17, 1932. [Class 38 (ii).] In a frequency changer for interconnecting A.C. networks, the discharge devices are provided with two grid control systems, one to enable the devices to function as inverters, and the other to enable them to function as rectifiers, and means are provided for rendering effective only one of the controls at any particular instant. This avoids the possibility of short circuits occurring as a result of the simultaneous energization of the grids associated with two anodes. The grids of the discharge device V, Fig. 1 are controlled by rotary distributers C1, C2 which are provided with groups of contacts for inverter and rectifier control. The energization of a particular distributer is determined by means of valves D1, D2 controlled from shunts S1, S2 respectively. For example, when current is flowing in the winding B1 the valve D2 is non-conductive and the valve D 1 conducts to complete the circuit of the distributer C1. In a modification a single distributer having alternate contacts connected with the grids associated with the windings Q1 and Q2 is used. Control is effected by means of a two anode discharge device, by means of which one or the other of the two groups of grids can be rendered ineffective. In another modification (Fig. 4 not shown) the sets of contacts on the distributers C1, C2 are cross connected. With this arrangement the valves D1, D2 are controlled so that D1 is conductive when energy flows from F1 to F2 and D2 is conductive when energy flows from F2 to F1. One method of obtaining such a control to permit interchanges of power at any power factor is shown in Fig. 6. The valves D31, D32 are controlled by light sensitive, cells P1, P2 energized by a light beam reflected from the moving system of an oscillograph L. This oscillograph has a voltage coil and a current coil and the mirror therefore vibrates in accordance with the curve EJ, Fig. 5. During the time interval 1-2 the light falls on the cell P1 and energy is transferred from F1 to F2 ; during the time interval 2-3 the light falls on the cell P2 and energy is transferred from F2 to F1. In a further modification to permit interchange of power at any power factor the distributers C11, C 12, Fig. 7, are connected through pairs of parallel connected valves D42, D44 and D41, D43, each valve having two grids. The grids of these valves are supplied from current and potential transformers T5 and T6. During the period 1-2, Fig. 5 both grids of the valve D41 are positive and the valve conducts to connect the distributer C12 is circuit. Similarly during the period 2-3 the valve D44 conducts ; during the period 3-4 the valve D43 conducts; and during the period 4-5 the valve 42 conducts. So that during the periods 1-2, 3-4 &c. the distributer C12 is energized and during the periods 2-3, 4-5 &c. the distributer C11 is energized. In a further modification in which the control potential consists of a component at the frequency of the network F, superimposed on a component at the frequency of the network F2, the connection of the two grid systems are controlled by a pair of valves the unrequired system being connected to a source of negative bias through a further pair of valves.