What does it mean ia is measured to be 12 A when w=850 rpm ? What it is going to

Question

What does it mean ia is measured to be 12 A when w=850 rpm?

What it is going to be if the motor were started with additional resistance in series or parallel with the amature?

Please provide the key concepts and equations involved with this problem to solve similar problems.

The armature circuit of a dc motor may be modeled as a voltage source in series with a resistor. The field of the motor is supplied by a shunt field winding as shown below. 2 2 S2 250 LOAD 500 Vdc vb SUPPLY 50H For a particular field strength, the back vo directly proportional to the motor speed co. steady state, under a particular load, the current ia is measured to be 12 A is and at 2 A, if the motor were started with no additional resistance in i is 2 A. With field current (amperes) would be most nearly: series with the armature, the initial current ia (A) 12 (B) (C) 12 (D) 250

Explanation / Answer

a) Ia means the armature current when the corresponding speed is 850 RPM.

b) at the time of starting of a dc motor, the back emf or counter emf(Eb) is zero.

because of speed is zero.

so the armature current is very high.

c) we know DC motor equation, V=Eb+Ia*Ra.

Ia=(V-Eb)/Ra.

at the time of starting,Eb=0.

so Ia=V/Ra.

to limit the armature current we are inserting additional resistance.

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.