GB990293A - Starting arrangement, especially for impedance protecting devices - Google Patents

Abstract

990,293. Protective systems. BROWN, BOVERI & CO. Ltd. Feb. 7, 1962 [Feb. 9, 1961], No. 4768/62. Heading H2K. In an impedance protective arrangement, a starting relay 11 has its coil connected for energization by a first component in the operating direction and proportional to the current (IT) in one phase, a second component in the operating direction and proportional to the interphase voltage (U RS ) between the other two phases and a third component in the restraining direction and proportional to the voltage (U T ) of the first phase. As shown, the relay coil is connected in a rectifier bridge circuit in which a rectifier 10 is supplied with the first component through an auxiliary transformer 7 from current transformers 4, a rectifier 8 is supplied with the second component through an auxiliary transformer 5 from a potential transformer 3 and a rectifier 9 is supplied with the third component through an auxiliary transformer 6 from the transformer 3. Resistors 12, 13 have magnitudes such that the relay is restrained by a current proportional to three times the phase voltage less the interphase voltage (3 UT -U RS ), a rectifier 18 preventing this current from ever acting in the operating direction on the relay. A zero sequence component may be supplied to the relay by using any or all of auxiliary transformers 14, 15 and an additional primary winding on the transformer 7. A " compounding " current component may be added to the phase voltage component by an auxiliary transformer 16. The auxiliary transformers 14 . . . 15 may saturate at half their normal rating. It is stated that two such starting arrangements would provide adequate protection for any fault condition in a three-phase system.