The document contains examples and problems about a simple rotating loop electrical machine. Example 1 part (a) asks what happens when a switch connecting the machine to a battery is closed. Parts (b) through (e) calculate machine parameters like starting current, speed, and power under different load and operating conditions. Problem 1 provides additional machine specifications and asks questions about whether it is operating as a motor or generator, and how current and power output would change with different rotor speeds.

1. IE243 ELECTRICAL MACHINES–I
[Cr. Hrs = 3+1] [Marks: 100+50]
By
Asif Ahmed Memon

3. Example 8-1. Figure 8--6 shows a simple rotating loop between curved pole faces
connected to a battery and a resistor through a switch. The resistor shown models the
total resistance of the battery and the wire in the machine. The physical dimensions and
characteristics of this machine are
r = O.5m R = 0.3Ω VB = 120 V I = 1.0m B = O.25T
(a) What happens when the switch is closed?
(b) What is the machine's maximum starting current? What is its steady-state angular
velocity at no load?
(c) Suppose a load is attached to the loop, and the resulting load torque is 10 N· m.
What would the new steady-state speed be? How much power is supplied to the shaft of
the machine? How much power is being supplied by the battery? Is this machine a
motor or a generator?

4. (d) Suppose the machine is again unloaded, and a torque of 7.5 N • m is applied to the
shaft in the direction of rotation. What is the new steady-state speed? Is this machine
now a motor or a generator?
(e) Suppose the machine is running unloaded. What would the final steady-state
speed of the rotor be if the flux density were reduced to 0.20 T?

5. Example 8-1. Figure 8--6 shows a simple rotating loop between curved pole faces
connected to a battery and a resistor through a switch. The resistor shown models the
total resistance of the battery and the wire in the machine. The physical dimensions and
characteristics of this machine are
r = O.5m R = 0.3Ω VB = 120 V I = 1.0m B = O.25T
(a) What happens when the switch is closed?
At starting As the rotor
rotates

6. Example 8-1. Figure 8--6 shows a simple rotating loop between curved pole faces
connected to a battery and a resistor through a switch. The resistor shown models the
total resistance of the battery and the wire in the machine. The physical dimensions and
characteristics of this machine are
r = O.5m R = 0.3Ω VB = 120 V I = 1.0m B = O.25T
(b) What is the machine's maximum starting current? What is its steady-state angular
velocity at no load?

7. Example 8-1. Figure 8--6 shows a simple rotating loop between curved pole faces
connected to a battery and a resistor through a switch. The resistor shown models the
total resistance of the battery and the wire in the machine. The physical dimensions and
characteristics of this machine are
r = O.5m R = 0.3Ω VB = 120 V I = 1.0m B = O.25T
(c) Suppose a load is attached to the loop, and the resulting load torque is 10 N· m.
What would the new steady-state speed be? How much power is supplied to the shaft of
the machine? How much power is being supplied by the battery? Is this machine a
motor or a generator?
If a load torque of 10 N m is applied to the shaft of the machine, it will begin to slow
down. But as ω decreases, eind decreases and the rotor current increases. As the rotor
current increases, ζind increases too, until ζind = ζLoad at a lower speed ω

8. At steady state
Voltage induced
at the rotor
To calculate the
speed of the
shaft
The power
supplied to the
shaft is
The power out
of the battery is

9. Example 8-1. Figure 8--6 shows a simple rotating loop between curved pole faces
connected to a battery and a resistor through a switch. The resistor shown models the
total resistance of the battery and the wire in the machine. The physical dimensions and
characteristics of this machine are
r = O.5m R = 0.3Ω VB = 120 V I = 1.0m B = O.25T
(d) Suppose the machine is again unloaded, and a torque of 7.5 N • m is applied to the
shaft in the direction of rotation. What is the new steady-state speed? Is this machine
now a motor or a generator?
If a torque is applied in the direction of motion, the rotor accelerates. As the speed
increases, the internal voltage eind increases and exceeds VB, so the current flows out of
the top of the bar and into the battery. This machine is now a generator. This current
causes an induced torque opposite to the direction of motion. The induced torque
opposes the external applied torque, and eventually ζind = ζLoad at a higher speed ω.

10. At steady state
Voltage induced
at the rotor
To calculate the
speed of the
shaft
The power
supplied to the
shaft is
The power out
of the battery is

11. Problem 8-1, The following information is given about the simple rotating loop shown in
figure 8--6:
B = 0.8T l = 0.5 m r = 0.I 25 m VB = 24 V R = 0.4Ω
ω = 250 radls
(a) Is this machine operating as a motor or a generator? Explain.
(b) What is the current i flowing into or out of the machine? What is the power flowing
into or out of the machine?
(c) If the speed of the rotor were changed to 275 rad/s, what would happen to the
current flow into or out of the machine?
(d) If the speed of the rotor were changed to 225 rad/s, what would happen to the
current flow into or out of the machine?

12. Problem 8-1, The following information is given about the simple rotating loop shown in
figure 8--6:
B = 0.8T l = 0.5 m r = 0.I 25 m VB = 24 V R = 0.4Ω
ω = 250 radls
(a) Is this machine operating as a motor or a generator? Explain.

13. Problem 8-1, The following information is given about the simple rotating loop shown in
figure 8--6:
B = 0.8T l = 0.5 m r = 0.I 25 m VB = 24 V R = 0.4Ω
ω = 250 radls
(b) What is the current i flowing into or out of the machine? What is the power flowing
into or out of the machine?

14. Problem 8-1, The following information is given about the simple rotating loop shown in
figure 8--6:
B = 0.8T l = 0.5 m r = 0.I 25 m VB = 24 V R = 0.4Ω
ω = 250 radls
(c) If the speed of the rotor were changed to 275 rad/s, what would happen to the
current flow into or out of the machine?

15. Problem 8-1, The following information is given about the simple rotating loop shown in
figure 8--6:
B = 0.8T l = 0.5 m r = 0.I 25 m VB = 24 V R = 0.4Ω
ω = 250 radls
(d) If the speed of the rotor were changed to 225 rad/s, what would happen to the
current flow into or out of the machine?

16. Commutation in Simple Four
Loop DC Machine