A 400V, 50 kVA, 0.8 pf leading Δ-connected, 50 Hz synchronous machine has a synchronous reactance of 2Ω and negligible armature resistance. The friction and windage losses are 2kW and the core loss is 0.8 kW. The shaft is supplying 9kW load at a power factor of 0.8 leading. The line current drawn is

A 50 kW synchronous motor is tested by driving it by another motor.  When the excitation is not switched on, the driving motor takes 800W.  When the armature is short circuited and the rated armature current of 10A is passed through it, the driving motor required 2500 W.  On open-circuiting the armature with rated excitation, the driving motor takes 1800W.

Calculate the efficiency of the synchronous motor at 50% load.  Neglect the losses in the driving motor.