GB385682A - Improvements in or relating to protective systems for ljungstrom generator sets - Google Patents

Abstract

385,682. Protective cut-out arrangements. SIEMENS-SCHUCKERTWERKE AKT.-GES., Siemensstadt, Berlin. Oct. 2, 1931, No. 27465. Convention date, Oct. 20, 1930. [Class 38 (v).] In the protection against fault on one of the generators of two parallel-connected generators (as in Ljungstrom generator sets) the compensating current, which circulates between the generators on fault in one of them, energizes one winding of a wattmeter-type relay, the other winding being energized by the generated voltage or by the load current. By the use of a wattmeter relay incorrect operation at starting, and before synchronism is avoided, and especially by using induction type wattmeter relays in which the torque is not appreciable until the currents almost reach the working frequency. Where the total load current is used in the wattmeter relay its action is made more sensitive with increase of load and where the generated voltage is used it is made independent of the load and yet dependent on the generators having been first run up to speed. In the arrangement shown in Fig. 1, differential protection is provided for by the differential relay 14 which receives energy from the three balancing current transformers 6, 7, 12 in similar phases of each generator A, B and of the load circuit, respectively. According to the invention, one coil of the wattmeter relay 15 receives current from an auxiliarv current transformer 10 in the balancing circuit between the transformers 6, 7. The other coil is connected between the mid-point of 10 and the transformer 12, the circuit being completed by the lead 13 so that this coil of the relay receives a measure of the total current supplied by the set. The relay has a central off position and, at starting, moves ineffectively around this position owing to time-lag action but on fault moves in one direction or the other to trip out the main circuit-breaker 4 and give a signal. In a modification, Fig. 2 (not shown), the second coil of the relay is energized by the output voltage.