GB1114868A - Improvements in or relating to electrical on-load tap-changers - Google Patents

Abstract

1,114,868. Transformers, heavy current switches. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 21 Oct., 1966 [21 Oct., 1965], No. 44630/65. Headings H1N and H1T. A tap changer arrangement includes at least one tap selecting switch Mx or My (Fig. 1) and at least one vacuum switch X (or Y) arranged for connection in circuit with the tap selecting switch during a tap changing operation, the selector switch being a quick action switch or a separate quick action switch being connected in series with the vacuum switch so that the current can be interrupted even if the vacuum switch fails to open. Transitional resistor R may be shorted by a switch closed on completion of tap changing. Fig. 2 shows another arrangement, suitable for heavy currents and for alternating direction of power flow, in which quick acting switches a, b, c and d are capable of taking over interruption of the load from vacuum switches X and Y. In this arrangement change from tap 4 to tap 3 is effected by the sequence: open X, open a, close b, close X, open Y, open c, close d and close Y. Another arrangement using only one vacuum switch and one transitional resistor is descried (Fig. 3, not shown). The tap changing mechanism may comprise three sets of quick action tap selector switches, one set for each phase, separated by and carried between parallel vertical plates 41 (Fig. 1B) in an oil filled tank 33 secured to the wall 31 of the associated transformer. Each set has parallel contact bars 1-11 and alternately movable contacts 63x, 63y mounted on rotatable insulating tubes 66x, 66y as described in Specification 604,632. Each pair of plates 41 has a bracket 49 carrying a pair of vacuum switch X, Y (of which only X is shown in Fig. 1B) and also a transition resistor R connected between contact 63y and vacuum switch Y. Vacuum switch X is connected through a slip ring to contact 63x. Two insulating tubes 66x, 66y carry the moving contacts 63x, 63y for all three phases and are driven by a twin Geneva mechanism 71 (Fig. 1A, not shown). The shaft carrying Geneva mechanism 71 is driven by a motor provided with limit switches through a quick-motion mechanism of the kind described in Specification 1,032,116 (Fig. 1D, not shown). This shaft also drives camshaft 95 (which is divided by insulating couplings between the phases) carrying a pair of cams 97 for each phase through which the spring biased vacuum switches X, Y are opened. Malfunction producing arcing causes gas passing through pipe GP to actuate a warning device. Movable contact 61 (Fig. 1C) of each vacuum switch is normally spring biased closed on fixed contact 57 in high vacuum chamber 51 the contacts being opened at appropriate times by the cams 97. In another arrangement (Fig. 2B) the contacts D of the two selector switches of each phase set are operated through separate Geneva mechanisms having their operation pins 180 degrees apart, drive being from a shaft H having insulating couplings (S, Fig. 2A, not shown) between phases through 2 : 1 gearing. Vacuum switches X, Y for each phase are operated through cams on square shaft O which also carries cams operating quick acting diverter switches a, b, c, d. Shafts H and O are chain driven from a motor drive, the latter being coupled through a quick motion device (QM) (Fig. 2A, not shown) and both shafts making one revolution per tap change during which, in each phase, one or other of the selector switches DB is changed slowly and the four diverter switches a, b, c, d are operated quickly. A similar arrangement (Figs. 3A and 3B, not shown) has only one vacuum switch (V) per phase, three quick action diverter switches (X), (Y), (Z) (or, instead a make-before-break switch) and two changeover switches (ab, Cd). Switches X, Y, Z and cd are spring closed and operated by a common cam-shaft (O) while the movable arm of (a, b) is carried on the tap selector drive shaft, is operated by a crank-pin (CP) on the selector Geneva operator shaft and is moved from one contact to the other when the Geneva wheel is turned 180‹.