A 230 V shunt motor has a nominal armature current of 60 A. If the armature resistance is 0.15 ohm, calculate the following: a. The counter-emf [V]. b. The power supplied to the armature [W]. c. The mechanical power developed by the motor, [kW] and [hp]. d. The initial starting current if the motor is directly connected across the 230 V line, and the value of the starting resistor needed to limit the initial current to 115 A.

a)

b) P = 13,800 W

c)

di)

dii)

Explanation:

Voltage, Vt = 230 V

Armature current,

Armature Resistance,

a) The back emf is calculated as follows:

b) The power supplied to the armature (W)

P = 230 * 60

P = 13,800 W

c) Mechanical power developed by the motor

= Power supplied to the armature - Power lost in the armature

Power lost in the armature,

d)( i)The initial starting current if the motor is directly connected across the 230 V line

At starting, there is no back emf,

ii) Value of the starting resistor needed to limit the initial current to 115 A

answer:

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