Example for a voltage drop calculation

We calculate for you the voltage drop which occurs when you start your motor/machine combination, if we know the configuration of your feeding grid in addition to the technical data of motor and driven machine. Below you can find a typical example for a calculation. 2 voltage levels (40 kV and 6 kV) are given. The  40 kV grid has a minimal short circuit power of Sk" = 250 MVA. The 40 / 6 kV transformer has the following features:  10.000 kVA power and uk = 8 % short circuit voltage. Further motorical loads of 4.000 kVA run on the 6 kV level beside the motor, which will be started by us. We calculate the voltage drop from these data when starting your machine to 1,5 % on the 40 kV level and 4,5 % on the 6 kV level. The diagrams show the corresponding curves of time, torque, current and voltage during acceleration.


motor rated current In 250   A
motor rated voltage P 2.000   kW
motor start current DOL Ia 5   x In
motor speed (synchronous) nn 1.500   rpm
start time   10   s
min.  short circuit power at 40 kV Sk'' 250   MVA
voltage drop at 40 kV ΔU 1,4   %
feeding transformer 40 → 6 kV        
power S 10.000   kVA
short circuit voltage uk 8   %
parallel motorical load S 4.000   kVA
voltage drop at 6 kV ΔU 4,5   %

network configuration

Netzberechnung Konfiguration




graph: current


graph: voltage

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