# 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