Shunt Generator

Shunt Generator

AU: May-04,05,07,09,14,15,17, Dec.-04,08,18

• When the field winding is connected in parallel with the armature and the combination across the load then the generator is called shunt generator.

• The field winding has large number of turns of thin wire so it has high resistance. Let R_sh be the resistance of the field winding.

1. Voltage and Current Relations

From the Fig. 3.19.1, we can write

I_a = I_L + I_sh

Now voltage across load is V_t which is same across field winding as both are in parallel with each other.

ஃ  I_sh = V_t / R_sh

While induced e.m.f E, Still requires to supply voltage drop I_aR_a and bbrush contact drop.

•ஃ E = V_t + I_aR_a + V_brush  Where E = ϕ P N Z / 60 A

In practice, brush contact drop can be neglected.

Ex 3.19.1 A 4 pole lap wound d.c. shunt generator has a useful flux/pole of 0.6 Wb. The armature winding consists of 200 turns, each turn having a resistance of 0.003 Ω, calculate the terminal voltage when running at 1000 r.p.m. if armature current is 45 A. AU: Nov.-04, Marks 8

Sol.

Ex. 3.19.2 A 4-pole, lap connected D.C. machine has 540 armature conductors. If the flux per pole is 0.03 Wb and runs at 1500 r.p.m., determine the e.m.f. generated. If this machine is driven as a shunt generator with the same field flux and speed, calculate the terminal voltage when it supplies a load resistance of 40 Ω. Given armature resistance as 2Ω and shunt field circuit resistance as 450 Ω. Also find the load current. AU: May-07, Marks 8

Sol.

Ex. 3.19.3 A 4 pole DC shunt generator, with a shunt field resistance of 100 ohms and an armature resistance of 1 ohm, has 378 wave connected conductors in its armature. The flux per pole is 0.02 Wb. If a load resistance of 10 Ω is connected across the armature terminals and the generator is driven at 1000 rpm. Calculate power absorbed by the load.

AU: May-09, Dec.-11,18, Marks 13

Sol. The generator is shown in the Fig. 3.19.3.

Ex. 3.19.4 A 4-pole, lap wound d.c. machines has 728 armature conductors. Its field winding is excited from a dc source to create an air gap flux of 32 mWb/pole. The machine is run from a prime mover at 1600 r.p.m. It supplies a current of 100 A to an electric load.

1) Calculate the elctromagnetic power developed.

2) What is the mechanical power that is fed from the prime mover to the generator?

3) What is the torque provided by the prime mover?

AU: Dec.- 08, May-14, Marks 8

Sol.

Ex.3.19.5 A four pole lap wound shunt generator supplies 60 lamps of 100 W240 V each the field and armature resistance are 55 Ω and 0.18 Ω respectively. If the brush drop is 1V for each brush find i) Armature current ii) Current per path iii) Generated emf iv) Power output of DC machine.

Sol : The arrangement is shown in the fig 3.19.4

Review Questions

1. A 110 V, d.c. shunt generator delivers a load of 50 A. The armature resistance is 0.2 Ω and field resistance is 55 Ω. The generator is driven at 1800 r.p.m. It has 6 poles with 360 conductors connected in lap fashion. Calculate

i) The no load voltage ii) The flux per pole

(Ans. : i) 120.4 V ii) 0.011 Wb)

2. A 4 pole, 100 V d.c. shunt generator with lap connected armature having field and armature resistances of 50 Ω and 0.1 Ω respectively, supplied 60, 100 V, 40 W lamps. All lamps are connected in parallel. Calculate the total armature current and generated e.m.f. Assume brush drop to be 1 V/ brush. 

(Ans.: 26 A, 104.6 V)

3. A shunt generator delivers 450 A at 230 V and resistances of shunt field and armature windings are 50 Ω and 0.03 Ω respectively. Calculate the o generated e.m.f. 

(Ans.: 243.638 V)

 4. A 4 pole, lap wound 750 r.p.m. d.c. shunt generator has an armature resistance of 0.4 Ω and field resistance of 200 Ω. The armature has 720 conductors and the flux per pole is 30 mWb. If the load resistance is 15 Ω, determine the terminal voltage. 

[Ans. 262.4757 V]