GB501258A - Coil-protecting system for indicating leakages between windings or to earth - Google Patents

Abstract

501,258. Indicating faults ; protective cut-out systems. MASCHINENFABRIK OERLIKON. Aug. 26, 1938, No. 25167. Convention date, Sept. 16, 1937. [Class 37] [Also in Group XXXVII] An arrangement for indicating leakage faults between generator windings, and leakage to earth; wherein an auxiliary choke-coil is connected in parallel with the generator terminals, comprises the series connection of the generator and choke-coil neutral points through two transformer coils having their centre point earthed, the resistance to one fault current being larger than that of the other so that both types of fault are indicated by means of a single choke-coil. A three phase choke 2 in parallel with the generator windings I have their neutral points connected through transformer coils 3 ... 5, the midpoint of coils 4, 5 being earthed. For the same current, coils 4, 5 are connected so that no magnetization of the transformer occurs, and a winding leakage causes the small current ia to operate relay 7 through current transformer 6. An earth leakage R sets up a current in coil 4 and a smaller current io in coil 5, the increase in current im thereupon operating relay 8. A winding leakage thus operates relay 7 only, while an earth leakage operates both relays 7 and 8. The chokecoil 2 may be provided with a delta-connected secondary from which the auxiliary voltage Eo can be taken for indicating earth leakage at the neutral point. If such indication is not desired, the coil 3 can be dispensed with but in this case no discrimination between earth leakages and winding leakages is possible.