Question

1.   The following test data apply to a 208-V, 6-pole, Y-connected, three-phase induction motor:
-   No-load test: Power input = 336W, line current = 2A at rated voltage
-   Blocked-rotor test: Power input = 600W, line current = 20A at the line voltage of 30-V
-   The friction and windage loss is 36W. The resistance between any two lines is 0.2.

Determine:
a)   The equivalent circuit parameter of the motor.

2.   This motor is connected to a distribution feeder. The driving point impedance of the feeder is 0.15+j0.3 per phase. The line-to-line voltage of the source is 208V. Determine the level of the voltage sag at motor starting.

Answer 1

Solution:

The wye connection reduces the starting voltage to 57 percent of the system line-line voltage; starting current and starting torque are reduced to 33 percent of their values for full-voltage start.

If we do in line-line voltage calculations we get

V_min = 208x600/300+600 = 138.66 (V)

why I have considered the phase value I have given a reason for it in the only for above 2nd solution while in first solution line values are considered as per the condition of tests conducted that no load and blocked rotor test current values are of line values at rated voltage in no-load test and given specified voltage at blocked rotor test. So, dont get confused.