| 摘要 |
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 Isc.1 and Isc2 affords a number of fixed off-operation time delays (tsc o = const) and at circuit currents higher than setting value of Isc2 release is operating instantaneously (tsc o = 0). In addition, current-limiting reactors are connected to terminals of selective circuit breakers starting from that of second time grading. Reactances Zn of these reactors are chosen so as to ensure that maximal short-circuit current past reactor Ir(n) would amount to (20 - 40)-fold rated current In of circuit breaker of given n time grading. Isc2 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 Ir(n) at reactor output terminals. Newly introduced in releases of all selective circuit breakers is adjustable off-operation integral setting Qsc whose value for circuit breakers of n time grading Qsc(n) depends on off-operation integral Qo(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 Qn = (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 |
