How Does Armature Voltage Affect the Speed of a Separately Excited DC Motor?

In summary, the conversation discussed a 180V separately excited DC motor with an armature resistance of 1.2ohm and an armature current of 10A at 1200rpm. The questions asked for the mechanical torque and power developed in the motor assuming constant torque at all speeds, as well as the speed of the motor when the armature voltage is increased to 200V with unchanged magnetic flux. The solution involved calculating power loss, power developed, and mechanical power, as well as using the equation ω=V/KΦ to find the speed. After correcting a calculation error, a speed of 1334rpm was found, which is more than 7 times the original speed.
  • #1
Jasonpys
2
0

Homework Statement


A 180V separately excited DC motor has an armature resistance of 1.2ohm. When the note runs at 1200rpm,t he armature current is 10A.
1) Assuming that motor torque is constant at all speeds,d determine the mechanical torque and power developed in the motor.
2)Find the speed of motor when the armature voltage is increased to 200V and magnetic flux is kept unchanged.

Homework Equations


P=VI
P=I²R
Mechanical power=torque•angular speed
ω=V/KΦ[/B]

The Attempt at a Solution


I had tried the question few times,and not sure if I was doing it correctly.Here's my solution:

1) power loss=I²R=120W
Power developed in the motor=VI-I²R=1800-120=1680W
Mechanical power=ω•torque
ω=(2π•1200rpm)/60=125.7rad/S
Since electrical power=mechanical power, 1680/125.7=13.7Nm

2)ω=V/KΦ
Since magnetic flux is kept unchanged, therefore KΦ is constant, KΦ=V/ω

V1/ω1=V2/ω2
180/125.7=200/X
X=838rad/s=8002rpm

[/B]
 
Last edited:
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  • #2
Jasonpys said:
X=838rad/s=8002rpm
That's more than 7 times the original speed. Check this calculation.
Jasonpys said:
180/125.7=200/X
 
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  • #3
cnh1995 said:
That's more than 7 times the original speed. Check this calculation.
I recalculated the whole thing,and found out that I did some calculating error. The speed I found was 1334rpm. Does it make sense?
 
  • #4
Jasonpys said:
I recalculated the whole thing,and found out that I did some calculating error. The speed I found was 1334rpm. Does it make sense?
Yes.
 

1. What is a separately excited DC motor?

A separately excited DC motor is a type of electric motor that uses direct current (DC) to convert electrical energy into mechanical energy. It consists of a stator, which is the stationary part of the motor, and a rotor, which is the rotating part. The motor is called "separately excited" because the field winding is supplied by a separate power source, allowing for independent control of the motor's speed and torque.

2. How does a separately excited DC motor work?

A separately excited DC motor works by using the interaction between the magnetic fields of the stator and rotor to produce motion. When an electrical current is passed through the field winding, it creates a magnetic field that interacts with the magnetic field of the rotor. This interaction causes the rotor to rotate, and the direction and speed of rotation can be controlled by varying the amount of current supplied to the field winding.

3. What are the advantages of a separately excited DC motor?

One advantage of a separately excited DC motor is its ability to provide precise speed and torque control. This makes it ideal for use in applications that require accurate and consistent movement, such as robotics, electric vehicles, and industrial machinery. Additionally, separately excited DC motors are relatively simple and reliable, with a long lifespan and low maintenance requirements.

4. What are the limitations of a separately excited DC motor?

One limitation of a separately excited DC motor is its dependence on a separate power supply for the field winding. This can add complexity and cost to the motor system. Additionally, the speed and torque control can be affected by changes in the supply voltage, which can lead to inconsistent performance. Finally, separately excited DC motors are not as efficient as other types of motors, such as brushless DC motors or AC induction motors.

5. What are some common applications of separately excited DC motors?

Separately excited DC motors are commonly used in a variety of applications, including electric vehicles, industrial machinery, robotics, and small household appliances. They are also frequently used in variable speed drives, where precise control over speed and torque is required. Additionally, separately excited DC motors are often used in renewable energy systems, such as wind turbines and solar panels, to convert the generated electricity into usable mechanical power.

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