GB1194151A - Improvements in or relating to Voltage Stabilising Arrangements. - Google Patents

Abstract

1,194,151. Transmission line arrangements. GENERAL ELECTRIC & ENGLISH ELECTRIC COMPANIES Ltd. 21 April, 1969 [24 Jan., 1968], No. 3685/68. Addition to 1,123,582. Heading H2H. [Also in Divisions G2, G3 and H1] The voltage stabilizing arrangement of Specification 1,123,582 is modified to comprise two or more similar groups of primary saturated reactors combined in a single unit having a plurality of cores, corresponding to the number of cores in each group, wound with insulated primary windings in the manner employed for magnetic frequency multiplication, each core comprising a plurality of sections, corresponding to the number of groups combined, and carrying secondary windings connected so as to provide the required phase displacement of the core fluxes as well as mesh windings arranged to be loaded by a saturated compensating reactor. The two-group arrangement shown in Figs. 1 and 2 comprises three parallel-wound laminated cores A, B, C each formed of back-toback D-shaped core sections A1 A2; B1 B2; C1 C2 lying one on each side of a central plane common to all the cores. Corresponding core sections are interconnected by yokes to outer unwound limbs 2 providing additional flux paths. Cores A, B, C carry primary windings H connected by terminals T1a, T1b, T1C to the high voltage A.C. supply line, and the core sections are wound with respective secondary windings L1 L2 connected in Π15 degrees zig-zag to provide the required displacement of the core fluxes. The core sections also have additional secondary windings H1, H2 corresponding ones of which are connected in open mesh to supply output terminals VA, VB for connection to the respective windings of the compensating reactor unit. Terminals T2a, T2b T2c may be used to supply a low-voltage load for which the reactor will then automatically act as a transformer with a fixed turns ratio. The core sections and windings may be turned through 90 degrees, Fig. 3 (not shown); the connections remaining unaltered. Application of the invention to a treble-tripler involves the use of three generally triangular core sections having parallel laminations, Fig. 4 (not shown), three parallel core sections, Fig. 5 (not shown), or three generally triangular core sections whose laminations are radially disposed and which have flux return sections providing a shell-type core arrangement, Fig. 9 (not shown). A preferred winding scheme for the trebletripler is described and discussed, Fig. 10 (not shown). If the magnetic characteristics of the core sections are not identical, the windings carrying the flux-shifting current are liable to carry an equalizing current. To prevent this, a balancing transformer is added to the circuit so that the required flux-shifting ampere-turns are balanced by the ampere-turns taken from the primary circuit via a series transformer. To match the phase displacement between the primary current and flux-shifting current in the balancing transformer, a tapped series transformer is used. A modified arrangement including these balancing and series transformers is described, Fig. 7 (not shown). In the alternative embodiment shown in Fig. 8 the series transformers ST act also as balancing transformers and have star-connected main and auxiliary windings STM, STA respectively connected as shown to the primary windings H and the secondary windings L1 L2. To prevent currents between neutral and earth from interfering with the required trapezoidal flux waveshape of the reactor, an earthing transformer ET is provided for the high voltage windings and is excited through a winding CW which injects a triple harmonic voltage derived from the output of windings H1, H2 and of the appropriate magnitude and phase position to compensate for the swing of the voltage of the neutral. The saturated reactor may be connected to additional stabilizing filters as described in Specification 1,176,415 and a discussion is given of the various methods of connecting such filters according to the presence or absence of series capacitors fitted to the reactor. The present invention may also be used with tap changers which are arranged near the neutral or the line terminal of the high voltage winding. An embodiment using the former arrangement is described, Fig. 6 (not shown), and a modification of Fig. 8 for use with tap changers is discussed, in which low voltage windings are added to the saturated reactor core to eliminate the fifth and seventh harmonics. This group of windings may also provide a controllable booster voltage through the tap changer and a voltage at the terminals T2 in Fig. 2. To ensure voltage stabilization without a series capacitor, a treble frequency circuit of the compensating arrangement is controlled in the range between open and short circuit conditions by use of a treble frequency transductor associated with the treble-tripler reactor and having its main excitation derived from the primary current of the reactor through current transformers and rectifiers. The D.C. control winding of the transductor is subdivided into two parallel branches of equal turn number carrying opposing currents, one of which is proportional to the reactor primary current and the other of which is approximately constant and is derived from the primary or secondary voltage of the reactor. The voltage/current characteristic then lies between the curves corresponding to open and short circuit conditions of the transductor. To prevent reversal of the transductor excitation at low reactor currents, the branches are interconnected by a gate rectifier poled in the direction of current flow in the branch carrying the proportional current, thereby cancelling the difference between the two currents when the proportional one decreases below the value of the constant one. Other modifications are discussed relating to the arrangement and connection of the series and balancing transformers and to the earthing of the preferred treble-tripler arrangement, Figs. 10 and 11 (not shown).