How can 400V & 690V on e-motors result in the same power
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Connection possibilities.


On a 400 V phase-to-phase supply the motor windings are connected in delta (from the Greek 'D' or &Delta;).
On a 690 V phase-to-phase supply the motor windings are connected in star or wye (from the American letter 'Y').
From trigonometry you can show that the orange lines in Figure 1b are \$ \sqrt 3 \$ times the length of the black lines. \$ 400 \times \sqrt 3 = 692.8 \$.








simulate this circuit

Figure 2. Connection options.


  How can two 3-phase ratings on the same motor result in the same output power?


In each case the voltage across each winding is 400 V so the same current will flow in each winding and the same power will be produced.