SELECTIVE PROTECTIVE SYSTEM FOR FORKED ELECTRIC CIRCUITS Russian patent published in 2005 - IPC

FIELD: selective short-circuit protection of forked electric circuits.

SUBSTANCE: proposed system designed, in particular, to protect low-voltage power installations of up to 1000 V against short-circuit currents incorporating K number of time gradings starting reading from power supply has instantaneously-tripping circuit breakers at last K grading and selective circuit breakers with releases at gradings from first to (K - 1) one which have definite adjustable current settings in region of short-circuit currents; selectivity characteristic of release in the range of short-circuits between I_sc.1 and I_sc2 affords a number of fixed off-operation time delays (t_{sc o} = const) and at circuit currents higher than setting value of I_sc2 release is operating instantaneously (t_{sc o} = 0). In addition, current-limiting reactors are connected to terminals of selective circuit breakers starting from that of second time grading. Reactances Z_n of these reactors are chosen so as to ensure that maximal short-circuit current past reactor I_r(n) would amount to (20 - 40)-fold rated current I_n of circuit breaker of given n time grading. I_sc2 setting of each selective circuit breaker disposed at time grading from second to (K - 1), inclusive, amounts to (1.1 - 1.5) of maximal current I_r(n) at reactor output terminals. Newly introduced in releases of all selective circuit breakers is adjustable off-operation integral setting Q_sc whose value for circuit breakers of n time grading Q_sc(n) depends on off-operation integral Q_{o(n + 1)} of circuit breaker disposed at lower time grading (n + 1) maximal for this very time grading in short-circuit protection proceeding from equation Q_n = (1.5 - 2)Q_(o(n+1).

EFFECT: enhanced speed of response, reduced probability of heat loads on cables and other parts of installation caused by arcing current, enhanced reliability of protective gear, and reduced fire probability in installation.

1 cl, 15 dwg