Patent GB-484421-A (GB)
Title: Improvements in or relating to protection relays for electrical distribution networks
IPC: H02H1/04
Filed: 1936-12-12
Abstract: 484,421. Protective cut - out arrangements. COMPAGNIE POUR LA FABRICATION DES COMPTEURS ET MATERIEL D'USINES A GAZ. Dec. 12, 1936, No. 34210. Convention date, Dec. 13, 1935. [Class 38 (v)] A device for locking protective relays against operation in case of unstable conditions, such as hunting, comprises locking elements which are sensitive to one or more electrical quantities characterizing a fault and are set to operate before the starting element when hunting occurs. The starting elements may be responsive to voltage, current, or impedance. The locking elements put the protective device out of action either when (1) a constant time has elapsed after passing through the locking values, or (2) a time has elapsed which is greater than a given value between passing through the locking value and passing through the starting value, or (3) more than a given time has elapsed between passing through the operating values of two or more locking elements. The invention is based on the fact that the operating value is reached progressively in hunting conditions, whereas on fault it is reached instantaneously. Since unstable conditions are balanced over all phases of a polyphase circuit, the locking elements are in one phase only, whereas starting elements are repeated in all phases. In Fig. 1, the trip coil 7 is controlled by impedance relays 3, 4, adjusted for an impedance value a little less and a little greater, respectively, than that of the protected section. Relay 3 when operated energizes 7 over closed contacts of directional wattmeter relay 5, and 4 energizes time-relay 6 which also makes the trip circuit over contacts of 5. When hunting occurs, a further time-relay 10 opens the trip circuit before the impedance setting of 3 or 4 is reached, the relay 10 being energized by a further impedance relay 9 with a setting above that of 4, and having a time-delay greater than that of 6. Thus, with hunting, the operating value of 9 is reached a certain time before that of 3 or 4, and if this timeinterval is greater than the setting of relay 10, the latter opens the trip circuit and prevents the subsequent closure of 3 or 4 from producing tripping. In Fig. 2, the trip-coil 3 is energized by the overload.relay 4 and directional relay 5 over the contact of a relay 6, which is controlled over the pilot wires 8, 10 by closure of contacts of remote-end relays 4<1>, 5<1> similar to 4, 5. A similar remote relay 6<1> is provided. On internal fault, all relays 4 .. 6<1> close and make both trip circuits 3, 3<1>, but on the occurrence of hunting, relays 11, 11<1>, having a setting between the normal current value of the line and the setting of relays 4, 4<1>, close and energize time relays 12, 12<1>, which are set to a value less than the time taken during hunting for the current to pass from the setting of 11, 11<1> to that of 4, 4<1>. In Fig. 3, the relay 1 is of the impedance-time type and the locking relays 3, 4 are instantaneouslyacting impedance relays, relay 3 having the higher setting. The time relay 6 when energized opens a contact 7 in the trip circuit and a contact 8, which is in series with the contact of 4 across the winding of 6. On fault, therefore, relays 3, 4 both close their contacts, but the winding of 6 is at once short-circuited by operation of relay 4 and so relay 6 does not operate to open the trip circuit at 7. With hunting, however, relay 3 closes first to energize 6 and, if the latter is set to a time less than that taken by the impedance to pass from the setting of 3 to the setting of 4, contacts 7, 8 are opened to break the trip circuit, and to prevent the short-circuiting of 6, respectively, and will remain open until the impedance rises above the setting of 3. The two relays 3, 4 of this Fig. may be replaced by a simple relay having two contacts operating for two different values of impedance. In one form, Fig. 4 (not shown), in which the time-relay opens trip contacts and its own short-circuiting contacts, the locking relay, at a given impedance value, operates a movable contact from a position in which it short-circuits the time-relay coil and, at a lower impedance, moves it on to a further contact in which the time-relay coil is again short-circuited. With fluctuations, the time occupied in effecting this changeover is long enough to allow the time-relay to operate.. In Fig. 5 (not shown), the systems of Figs. 1, 3 are combined into one system, a relay similar to 4 of Fig. 1 being provided with a second contact, which short-circuits the time-relay winding. The Specification also states that the locking relays need not be sensitive to the same quantities as the starting relays, or, in Fig. 3, as one another.