Patent GB-654624-A (GB)
Title: Devices for determining the contact time of periodically actuated contacts of switching devices
IPC: H02M1/26
Filed: 1946-04-25
Abstract: 654,624. Rectifying; automatic control systems. AKT.-GES. BROWN, BOVERI, & CIE. April 25, 1946, No. 12543. Convention date, April 25, 1945. [Classes 38 (ii) and 38 (iv)] [Also in Group XXXVI] For determining the contact time of periodically operated contacts of switching devices which are equipped with auxiliary devices for producing an interval with a low current for the sparkless opening of the contacts, especially in moving contact current converters, means are provided which give a measuring value for the instant of the contact opening during the lowcurrent interval. The contact bridges a1, a2, a3, Fig. 1, of a moving contact current converter co-operate with stationary contacts connected to the A.C. network b through switching choke coils e1, e2, e3 and a switch s; they supply the D.C. network c. The contact bridges a1, a2, a3 are periodically raised and lowered by a device d. A grid-controlled discharge tube h has its anode circuit switched in and out synchronously with the contacts a1, a2, a3. The anode circuit includes an ammeter g and a variable resistance k. The control grid of the discharge tube is controlled by a winding f arranged on the switching choke coil and in dependence on the voltage variations occurring in the choke coil serving to produce the low-current interval. The anode circuit is periodically interrupted by the bridge a3 in synchronism with the opening of the contacts. The control grid, which is negatively biassed from an auxiliary voltage source i, receives from the winding f a positive control impulse during the low-current interval so that the tube is switched in from the beginning of the low-current interval until the contact is opened. A current of periodic impulses with constant amplitude flows through the tube during this period and the average D.C. value measured by the ammeter g indicates the time of the opening of the contact a3 after the beginning of the interval. The measuring circuit can be applied in succession to the other contacts al, a2. The contact time may be controlled by using the potential drop across the resistance k. This is applied to an amplifier l having an output resistance m. The voltage across this is compared with the constant voltage obtained at a potential divider n by means of a relay p, which actuates a motor q and gearing r for adjusting the contact duration of the contacts. In a modification, Fig. 2, the relay p is directly operated by the amplified measuring value. The discharge tube h is connected in parallel with the current converter contacts a1 a2, a3 and is switched successively on to the contacts by switches t1, t2. As shown in Fig. 3, the measuring value can also be used to regulate the value of the current through the contacts when these have a constant current duration, i.e. to maintain the overlap constant. This is achieved by altering the premagnetization of the choke coils e1, e2, e3 which produce the low-current interval. The relay p varies a resistance r and thus alters the D.C. premagnetization current through windings v1, v2, v3. The A.C. premagnetization is varied by an induction regulator u through windings x1, x2, x3 with series impedances z1, z2, z3 and is adjustable both in magnitude and phase. Combined D.C. and A.C. premagnetization may be provided. The resultant premagnetization of the switching choke coils may be arranged to remain constant during the opening of the associated contacts, whilst it is regulated during their closing.