GB273278A - Improvements in or relating to relays for automatically switching off electric line sections - Google Patents

Abstract

273,278. Siemens & Halske Akt.- Ges. June 24, 1926, [Convention date]. Cut-out arrangements; induction relays; electromagnetic s w i t c h e s ; switches partly electromagnetic.-For the protection of sections of a line relays, the time of actuation of which increases with increase of voltage and decreases with increase of current, are used. They are adjustable so that the time of release up to an adjustable limit value of the quotient of voltage and current intensity does not exceed a prescribed value, thereby ensuring that a relay never takes longer than this prescribed time to operate when a fault occurs in its section of line, however long the section. Thereafter the ratio of time of release to the value of the quotient is constant irrespective of the adjustment, thereby ensuring that the relays operate in correct sequence when a fault occurs on a distant section of the line and is not cleared by intermediate relays. One form of such relay is shown in Fig. 4. When the current in line 1 becomes excessively great relatively to the voltage, the force on the core 15 overpowers that on the core 17 and core 15 is therefore drawn down, liberating the Ferraris disc 2 which rotates under the action of the driving element 4 and brake magnet 6 at a rate proportional to the current. A voltage coil 10, opposed by a current coil 12 and spring 8, adjusts a curved slide 3 which is eventually engaged by a pair of contacts 7, whereupon these contacts are closed, and cause the associated circuit breaker to open. The adjustment is obtained by shunting the current coil 12 with a variable resistance 13. In a modified relay, Fig. 5, the time delay is introduced by a thermal element 25 carrying a contact 28 which eventually engages a current slide 26 adjusted by a voltage coil. The thermal element is not in circuit until the current reaches such a value as to rock the lever 33, thereby opening a shunt circuit at 32. Actuation of the lever 33 also causes the contact 28 to approach nearer the slide 26 for the element 25 is secured to one end of the lever 33. Adjustment is obtained by altering the pivot pin 36 of the lever 33.