MULTIPLE THREE-PHASE ELECTRIC CIRCUITS PROTECTION SYSTEM FROM REMOTE SHORT CIRCUIT CURRENTS Russian patent published in 2009 - IPC H01H7/00 H01H73/00 

FIELD: electrical engineering.

SUBSTANCE: invention relates to protection systems for electrical circuits with long lines from the remote short circuits in case powerful electric motors are available in the circuits. Multiple three-phase electric circuit protection systems includes protection device, e.g. switch, with current sensors and semi-conducting release. There is a comparison unit in the release to compare current flowing through the unit with current setting by short circuit current I_sd. The unit is designed so that low setting level I_sd can be set up within (1.5÷3) from the unit operating current I_r. Long mainline electric line is connected to the draining terminals of protection unit. Feeder lines with different types of loads are connected to the above mainline electric line along the whole length. The feeder lines are also connected to electric motor. Short circuit current value at the end of mainline line I_sc is equal or lower than the value of start-up current in motor I_sm coupled with the beginning of middle parts of mainline, but it is higher or equal to the current setting value I_sd-(I_sm≥I_sh≥I_sd). In addition, protection unit release includes the control unit of current sum of squares for all three phases {Si²(t)} and comparison of maximum current sum of squares value relation {S_maxi²(t)} to its minimum value {S_mini²(t)} in the first period of current occurrence exceeding the setting I_sd,. It also includes logic unit, which automatically increases current setting value I_sd to I_sd1 value equal to 1.1÷1.5 of startup current value I_sm -I_sd↑{I_sd1=(1.1÷1.5)I_sm} under condition that the above relation expressed by the coefficient K_s={S_maxi²(t)}/{S_mini²(t)} is equal or more than 1.4 (K_s≥1.4).

EFFECT: improving protection reliability of long lines from remote short circuits and ensuring uninterrupted power supply during electric motor start-up not affecting fire safety class and protection system cost.

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