Patent GB-1350128-A (GB)
Title: Load current control arrangements incorporating saturable reactors
IPC: G05F1/38
Filed: 1971-05-11
Abstract: 1350128 Automatic current regulation V P LEPP K M SIBGATULIN and J N CHERKASOV 11 May 1971 14200/71 Heading G3X An electric load current control arrangement comprises an unbiased saturable reactor having two magnetic cores carrying respective control windings connected in series-opposition for D.C. energization by a D.C. control signal, each magnetic core also carrying one or more additional windings, the said additional winding or one of the said additional windings on each core being A.C. energizable in series-aiding connection with a corresponding winding on the other core, and switching means to disconnect from A.C. energization part of each said additional winding or all of each said one additional winding at each saturation instant of the reactor and to reconnect the disconnected said parts or windings when the A.C. energization next reverses polarity, the other said parts of the additional windings or the other said additional windings on the cores being connected to supply a load. In a basic embodiment, Fig. 1 (not shown), each core has one additional winding tapped to provide unequal-turn portions of which those having the greater number of turns are short-circuited by a change-over or tap change switch at the instant of saturation. Prior to this both windings are in series between an A.C. supply and a load which receives the no-load current of the reactor. After the saturation instant of one of the cores, the load current rises to operate the switch and flows through the lesser-turn portions for the remainder of the A.C. half cycle. At the current zero the switch resets and then operates again when the other core saturates in the next half cycle. Load current flow in the lesser-turn portions, Fig.3 (not shown) induces in the control windings currents of the same polarity irrespective of which core is saturated, Fig.4 (not shown), the arrangement being such that if the mean value of these induced currents changes from the mean value of control current set by a D.C. source connected to the control windings, then the instants of core saturation are automatically adjusted to maintain the load current at a value determined by the D.C. control current. The relationships between the number of control winding turns, the number of turns of the winding portions, the total number of winding turns, the reactor voltage, current and power gain and its time constant and speed of response are discussed. The embodiment shown in Fig.5 has cores 11, 12, D.C. control windings 8, 9 supplied by a D.C. source 10, winding portions 2, 3 and 5, 6, an A.C. source 1, a load 7 and a switch constituted by silicon controlled rectifiers 19, 20, the current in each half cycle flowing through members 2, 21, 3, 5, 20 (gate-cathode) and 6 or 6, 22, 5, 3, 19 (gate-cathode) and 2 until core 11 or 12 saturates to fire the rectifier 20 or 19 to short-circuit the portions 3, 5 The embodiment shown in Fig. 6 uses an arrangement similar to Fig. 5 to supply current to a transformer 25 which alternately switches transistors 23, 24 on and off, the load 26 being connected through these transistors and the winding portions 2, 6 to D.C. source 27. A.C. source 1 may be of low power and high frequency to produce alternate conduction of transistors 23, 24 when the rectifiers 20, 19 are alternately fired, with D.C. pulses of corresponding time and frequency to the load 26, Fig.7 (not shown).