Patent GB-596907-A (GB)
Title: Improvements in or relating to electrical relay arrangements for the automatic control of electrical systems
IPC: G05F1/00
Filed: 1944-07-20
Abstract: 596,907. Electromagnetic relays. NALDER BROS. & THOMPSON, Ltd., and LIPMAN, C. L. July 20, 1944, No. 13925. [Class 38(v)] [Also in Group XXXV] A relay comprises two or more devices energised from a common circuit and each having a movable member to effect a switching operation. One of the devices operates when a change takes place in the direction or sense of an electrical quantity in the common circuit while a second device operates only when a change in the electrical quantity takes place in the opposite direction. Any number of such devices may be employed and may be arranged to operate on different power, current, voltage or frequency settings. Four devices may be used for example two of which respond to power flow in one direction, the other two responding to power flow in the opposite direction. The power or current setting of one device of each pair may differ from that of the remaining devices. Devices of different kinds may be combined, responding for example to power, kilovoltamperes, voltage, frequency or power factor. A relay for the automatic correction of power factor may comprise three devices two of which respond respectively to a lagging and leading power factor, the third being a non- directional over-current device responding only to the magnitude of the current. Fig. 1 shows a relay comprising three devices for the automatic control of the flow of power in a circuit S1, S2. Two of the devices W1, W2 are of the wattmeter type, the third A being an overcurrent device. The current coils C1, C, C2 of the three devices are joined in series with the line S2 which with the line S1 interconnects the two sources of supply GA, GB. Currentlimiting resistances RA, RB, and a choke L in series with the coils C1, C2, C are normally short-circuited by contacts whose operating coils X, Y, Z are energised from a local supply through normally closed contacts a b<1>, c b<1>, b bl, d bl and e bl. Normally the power in the lines S1, S2 is insufficient to affect any of the relay elements. If, however, a sudden peak load develops at station GA power is supplied from station GB and the overcurrent element A and wattmeter W1 commence to operate causing the sectors TA, TW1 to rotate and open the contacts a b<1>, c b<1>, b bl and d bl and thus insert the choke L and resistance RA in the line S2. The sectors TA, TW1 continue to rotate till the former strikes a stop Q and the latter joins two contacts g, g<1> which control a local circuit to cause an increase of power output from station GA and thus reduce the power delivered from station to GB to station GA. When normal conditions are re-established the sectors return to their initial positions after suitable time delays determined by the gear ratios of the operating pinions PA, PW1 and the sectors and by the brake effects of permanent magnets MA, MW1. If the power generated by station GA exceeds the demand so that the power tends to flow from GA to GB the wattmeter device W2 commences to operate and closes contacts j, g<1> thereby reducing the power output of station GB. To prevent hunting the voltage coils V1, V2 of the two wattmeter devices are electrically interlocked through rotary passing contacts I1 and I2 comprising insulating drums carrying conducting strips engaged by contacts connected to the line S2 and the voltage coils VI, V2 as shown in Figs. 1 and 2. The drums I1, I2 may be concentric with the sectors or connected thereto by cranks. The width of the conducting strips on the drums is arranged so that the connection to the voltage coil V2 at the contacts on drum I1 is cut off when the sector TW1 reaches the last third of its angular movement towards the contacts g, g<1>. Coil V1 is similarly cut off before the sector TW2 reaches the contacts g<1>, j. The contacts g, g<1> and g<1>, j are consequently never closed at the same time and hunting is prevented. In order to avoid damage by mechanical shock to the main spindles of the rotating parts of the various elements of the relay an idle toothed wheel O, shown in the meter A in Fig. 1, is arranged to engage the driving pinion PA. The field strength of the magnet MA is greater than the field strength of the wattmeter magnets so that the time lag for the resetting of the overcurrent device is longer than the time lag for the resetting of the wattmeter devices. The number of devices in the relay may be varied and the overcurrent device A may be omitted. The resistances and impedance RA, RB, L may also be omitted together with the corresponding interlocking contacts or they may be replaced by condensers, inductive coils or current consuming or controlling devices. Specification 560,053 is referred to.