A dc shunt generator has a speed of 800 rpm when delivering 20 A at 22

1.	A dc shunt generator has a speed of 800 rpm when delivering 20 A at 220 V. If this machine is run as a motor and takes a line current of 20 A at 220 V supply, the speed will be:-1. 800 rpm2. more than 800 rpm3. less than 800 rpm4. zero
Answer» Correct Answer - Option 1 : 800 rpm Concept: In a DC shunt generator, generated emf is given by Eg = Vt + IaRa In a DC shunt motor, back emf is given by Eb = V_t – IaRa Where Ia is armature current Ra is armature resistance N is speed E ∝ N Given: Speed of generator (N_g) = 800 rpm Terminal voltage (V_t) = 220 V Armature resistance (Ra) = 0 Ω Armature current (I_a) = 20 A Eg = V + IaRa = 220 + 20 (0) = 220 V Eb = V - IaRa = 220 - 20 (0) = 220 V \(\frac{E_g}{E_b}=\frac{N_g}{N_m}\) \(\frac{E_g}{E_m}=\frac{220}{220} = 1\) E_m = E_g = 800 rpm

A dc shunt generator has a speed of 800 rpm when delivering 20 A at 220 V. If this machine is run as a motor and takes a line current of 20 A at 220 V supply, the speed will be:-1. 800 rpm2. more than 800 rpm3. less than 800 rpm4. zero

Answer» Correct Answer - Option 1 : 800 rpm

Concept:

In a DC shunt generator, generated emf is given by

Eg = Vt + IaRa

In a DC shunt motor, back emf is given by

Eb = V_t – IaRa

Where Ia is armature current

Ra is armature resistance

N is speed

E ∝ N

Given:

Speed of generator (N_g) = 800 rpm

Terminal voltage (V_t) = 220 V

Armature resistance (Ra) = 0 Ω

Armature current (I_a) = 20 A

Eg = V + IaRa

= 220 + 20 (0) = 220 V

Eb = V - IaRa

= 220 - 20 (0) = 220 V

\(\frac{E_g}{E_b}=\frac{N_g}{N_m}\)

\(\frac{E_g}{E_m}=\frac{220}{220} = 1\)

E_m = E_g = 800 rpm

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