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21Symmetra MW II 1200 kW 3 x 400/230 V Installation - 990-1979E-001
Output and downstream breakers
In the absence of a proper breaker coordination study and if only the actual Ip on the unit’s input
terminals is known, this table must be used to optimize the instantaneous trip setting or to choose a
breaker with a usable fixed instantaneous trip value.
22 kA is the maximum peak let-through current (including safety factor) present during clearing of an
internal fault in a 200 kW section or a power module. This maximum peak let-through current is based
on and applicable to utility with prospective short-circuit currents (Ip) up to 200 kA.During or after a
controlled fault clearing, none of the breakers are allowed to trip on the instantaneous trip setting below
the specified value. This is also applicable to the upstream breakers, and a check of the instantaneous trip
setting in this part of the installation is required.
The instantaneous trip setting calculated by a professional engineer in a breaker coordination study must
not disable the functionality of clearing and surviving an internal fault unless there is a written agreement
between APC by Schneider Electric and the customer.
By ensuring the unit’s fault clearing ability (survival skills) i.e. using the correct instantaneous trip
settings in the switch gear (installation), maximum power availability in normal operation is obtained for
the critical load.
Note: The instantaneous trip setting can be calculated when utility Ip is known. An incorrect
trip setting can result in limiting the system functionality and jeopardize the load support.
Q2, Q4, Q6
Duration [S] Current [A] Total load [%] Event/Operation
< 0.005 22 kA -- Internal fault clearing.
60 3464* 200 Overload on-line
600 2165* 125 Overload on-line
1732 100 On-line
* In the absence if a coordination study conducted by a professional engineer, the recommended
instantaneous trip setting for breakers Q1, Q2, Q4, Q5, and Q6 is 22 kA
** Only applicable to Q2 and Q4
Ip* [kA] I peak let-through [kA] I setting [kA]
200 16 18
140 14 16
100 13 15
50 10.5 12
30 9 11
* Ip = Abridgment for Prospective short-circuit current.
This is the current that would flow in the fault circuit is the fuse was
replaced by a link with an infinitely small impedance
∞