Patent GB-1303634-A (GB)
IPC: G05F1/33
Filed: 1969-04-29
Abstract: 1303634 Automatic voltage regulation and control GENERAL ELECTRIC CO Ltd 29 April 1970 [29 April 1969] 21810/69 Headings G3R and G3X The voltage of a three phase network is stabilized by an arrangement comprising a primary A.C. saturated reactor having a plurality of core limbs carrying primary windings connected in shunt with the network and wound in series zigzag form as for the primary windings of a magnetic frequency multiplier, wherein suppression of harmonics is provided by secondary turns on the limbs arranged and inter-connected so as to form a closed polyphase mesh as for a short-circuited output winding of the comparable frequency mulitplier, the total phase number being any multiple of three and the mesh sequence of the secondary turns being so arranged as to provide points at which a symmetrical three-phase output voltage of treble frequency is available and to which there is connected a three-phase treble frequency secondary reactor. In Fig.1 the series zig-zag primary windings No are connected in star to the network 1, 2, 3 and effectively form three groups as described in Specification 1123582. The secondary turns N 3  form a mesh closed with respect to the ninth harmonic to represent a short circuit for all such harmonic fluxes in the nine limbs of the reactor core PR. Tapping points Q, R, T provide a symmetrical output voltage V 3  and are connected to the primary winding N 3 , of a secondary three-phase saturated reactor SR having short circuited secondary mesh turns N 9 . Winding N 3 ,  3 carries a third harmonic current I 3,   3  and the turns N 9  carry a current I 9  to ensure short circuiting of the ninth harmonic on the reactor SR and to counteract the tendency of the mesh N3 to over-compensate the seventeenth and nineteenth harmonics, the latter function ensuring that the currents in the windings No and the network are nearly sinusoidal. Point P may be connected to a neutral point N, isolated or earthed if turns ratio N 3 /No is suitably selected. In a modification to the reactor SR, Fig.2, (not shown), six wound limbs carry a three-phase starconnected primary winding connected to the points Q, R, T and the short circuited mesh turns are connected to a D.C. supply which is variable to provide a desired relationship between the primary voltage and current and so give an additional degree of voltage stabilization. In the embodiment of Fig.3 the primary windings are inter-connected to ensure that adjacent ones of the limbs linked by flux paths carry fluxes whose mutual phase displacement is 120‹ electrical of the three phase network R, Y, B to be stabilized. Unwound limbs UL alow for reduction of the cross-section of the iron core. The winding N 3 ,  3  of the reactor SR may be controlled by a tap changer TC in response to network voltage variations to provide the additional degree of voltage stabilization. The core arrangement of the primary reactor of Figs.1 and 3 may be sub-divided into a number of separate sections each with its magnetic circuit continuity maintained by the addition of an unwound limb at the point of separation but with inter-connected turns as required for the number of limbs used. Each section may be housed in a separate oil-filled tank. Other modifications include the connection of network terminals 1, 2, 3 to the respective turns on the three middle limbs of the core and the achievement of the Œ 20‹ phase displacement between the zig-zag groups either with an equal internal connection and external reversal of the phase sequence (as in Fig.1) or with the same phase sequence on both groups if the internal zig-zag connection is reversed. The embodiments of Fig.3 and Fig.2, (not shown), may be used in conjunction with series capacitors as described in Specifications 1123582 and 1288741, although such capacitors can be dispensed with by gradual control of the transition between open circuit and short circuit conditions of the treble frequency circuit. Fig.4 illustrates such an arrangement and uses as the secondary reactor a transductor T.D. having three-phase windings and two control windings CW1, CW2 with an equal number of turns. Winding CW1 has an excitation I 3 a derived through members CT, RI from the primary current I 1  and proportional thereto with the factor of proportionality chosen so that without any correcting influence the compensating current I 3  would be greater than the ideal current I 30  giving optimum wave shape and a characteristic Vc between the open and short circuit voltage characteristics V I0  and V IS  shown in Fig.6. Thus by appropriate control of I 3  a characteristic which is constant over a wide range of primary current I 1  will be obtainable. To this end the control winding CW2 carries a biassing current I 3 b opposed to I 3 a and obtained from the secondary voltage V 3  of the primary reactor PR through members VT, R2, or alternatively from the primary voltage V 1 . To prevent premature decay of the characteristic Vc at low values of I 1  (see dotted line in Fig.6), caused by I 3 a approaching zero with I 3 b remaining constant, a gate rectifier GR is arranged to carry current only in the direction of the current I 3 a so that if the latter is greater than I 3 b both currents can flow independently, but if I 3 a tends to become less than I 3 b any difference between the currents is prevented and the ampere-turns will be forced down to zero below this critical current, Fig.5, (not shown).