Why 50 percentage of rated current is given as load condition

The electromagnetic devices extract a magnetising current from the source a.c, to establish the workflow. This magnetising current delays the applied voltage by almost 900.

A synchronous motor is a dual excitation machine, its armature winding is energised from a source a.c and its field winding from the d.c. When the synchronous motor is running at constant applied voltage, the resulting air gap flow required by the applied voltage remains constant. This resulting air gap flow is set by both a.c in the armature winding and d.c in the field winding. If the field current is sufficient to establish the airflow, as required by the constant applied voltage, then the magnetising current or the delayed reactive VA required from the ac source is zero and therefore the motor operates with a factor Of unit power. This field current, which causes the operation of the unit power factor of the synchronous motor, is called normal excitation or normal field current. If the current less than normal excitation, ie, the motor is under excitation, then the flux deficiency must be composed of the armature winding m.m.f. In order to do what is necessary, the armature winding draws a magnetising current or reactive VA back from source a.c and as a result, the motor operates at a delayed power factor.