How to choose a circuit breaker for a group of 9 motors?
There is a group of consumers in the form of 9 asynchronous electric motors, data from one motor (11 kW, In 26A, Ip 156A). All engines will be powered through starters and a thermal relay, but the question arose of how to calculate the opening machine for the entire group. If according to the rated current, then 9 * 26 = 234A, but the inrush current is 156. Will the 250A circuit breaker with characteristic D not work? If it is permissible, 8 engines will work and the 9th will start. Motors rotate the mixers. Starting conditions are not yet known. Please share the methodology or literature.
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Characteristic D - frequency response of the electromagnetic release 10-12. That is, the current at which the electromagnetic release of the machine will trip is 2500-3000 A. As for the current, it is better to measure the operating and starting currents in order to have accurate values. If the engines will run under different loads, it is necessary to measure the current of each motor in order to choose the right machine.
In the cabinet there will be 9 automatic motor protection circuit breakers of the type ABB MS161, is it possible in this case to replace the input circuit breaker.
After a knife switch comb and 9 Automatic motor protection.
All electric motors operate at the same load.
And yet, I correctly think that the maximum setting of a thermal relay should be no more than In * 1.25? According to the PUE.
It is impossible to replace the input automatic machine with a knife switch. These two switching devices have different purposes.
Thanks, but there is still a question.
Such automatic machine Compact NSX NSX250N TM-D,
I correctly understood that he can be set
the multiplicity of short-circuit current is 5 ... 10 x In, then there is a maximum setting of 2500A, which in my case is enough when all EDs are started simultaneously. 1400A. Although no one will let them at the same time.
And you can tell by the machine. What are the settings.
(time delay during overload)
15 s 6 x Ir
120 ... 400 s 1.5 x In
AND
long delay range
0.7 ... 1 x In
The time delay during overload is the time during which the machine will operate in case of overload - exceeding the rated current. This is necessary for selectivity of operation of circuit breakers - the input circuit breaker must have a longer delay time than the machines of the outgoing lines. The range of long operation delays is also a parameter for adjusting the selectivity of automatic machines, if I am not mistaken, the parameters of operation during a short circuit are adjusted.
And how to calculate the cable on the outlet line taking into account the short-circuit current. A terminal block with 27 taps per phase will be installed on the input machine. There you can hold a maximum of 10-16mm2. then 9 automatic machines on 25A. What cross-section of a cable to choose for a section from the input to each automaton 25A, so that it survives a short circuit? Introductory 250A Har. D, multiplicity 10.