Three-phase short circuit selectivity
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answer90
viewsIn a three-phase circuit there are 4 three-phase circuit breakers installed, the closest to the load (9 kW load, switched on via a contactor) is a 25 A circuit breaker, 25 A after it, 40 A behind it and an input 50 A. How can I make this circuit selective during a short circuit? Now at short all machines are turned off, which creates inconvenience. Thank.
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Good afternoon, Marat. Your power supply circuit contains an excessive number of machines and is contrary to the basic principles of power supply.
Let me explain: let's say the first one, 50 amperes, is located in a substation, the second 40 amperes is an introduction to the switchboard of the workshop. Then two 25-amperes go sequentially - why? Power supply circuits from substations always provide for loop powering of workshop distribution points or installation of a basic distribution point, from which other switchgears are fed via radial lines.
The next question is where short circuits occur, in which part of the circuit? Without specificity, the answer will be worse than divination on coffee grounds.
You need to upgrade the power supply circuit, recount the currents K.Z. on sections of the circuit, check the correct selection of the settings of the machines
As an option to resolve the issue - the installation of fuses, for example, instead of a 50-amp automatic machine.