Motors

Question 1

What is the rule for the developed force for the motors?

Answer 1

F=(l*ß)*i

Question 2

What is the eqn for the induced torque in the motors?

Answer 2

T_ind=(i*L*ß)*r

Question 3

Describe the theory of operation of the DC motor?

Answer 3

• A DC supply is applied to the field winding(stator) this inuces a magnetic field
• A DC supply is applied to the rotor through the comutator and the brushes causing a DC current to pass in the rotor circuit
• Therfore a torque will be produced on the armature winding

Question 4

What is the Eqn for the developed torque?

Answer 4

T_d=K_a*Ø*I_A

K_a=(2P/2a)*Z/2π

Z is number of conductors

T_d=K*I_f*I_A

Question 5

Draw the power flow diagram of the DC motor and label it and state the EQNS?

Answer 5

Question 6

What are the types of DC motors?

Answer 6

Self excited:

• DC shunt
• DC series
• DC compound

Seperatly excited motors

Question 7

Draw the separatly excited DC motor?

Answer 7

Question 8

Draw the DC shunt motor?

Answer 8

Question 9

Draw the speed torque charcatristics of separtely and shunt DC motors and derive the eqn of the slope?

Answer 9

Question 10

What are the applications of the DC shunt motors?

Answer 10

• It is used when the speed needs to be constant from no load to full load
• belt driven applications
• Drills
• Machine tools
• Spinning and weaving machines

Question 11

Draw the series DC motor?

Answer 11

Question 12

Draw the torque speed charactristics of series DC motors and derive the slope?

Answer 12

Question 13

What are the applications of series DC motors?

Answer 13

• Elevators
• Electric cars

Question 14

Draw the DC short compund motor?

Answer 14

Question 15

Draw the DC long compund motor?

Answer 15

Question 16

What are the advantages and disadvantages of armature voltage speed control?

Answer 16

Advantages:

1. Wide range of speeds
2. No resistance losses

Disadvantages:

1. Expensive
2. Only used for values below base speeds

Question 17

What are the advantages and disadvantages of field current speed control?

Answer 17

Increasing field resistance leads to decrease in field current and decrease in the flux and so the speed increases

Advanatges:

1. Cheap
2. Low power loss

Disadvantages:

1. Only for speeds below base speed

Question 18

What are the advantages and disadvantages of armarure resistance speed control?

Answer 18

Avantages:

Disadvantages:

1. High losses
2. Poor regulation
3. low effciency

Not commenly used

Question 19

What is the name of the compund DC machine if both fields are in the same direction and if they are in the opposite direction?

Answer 19

Same direction is cumulatively compound and different directions deferrentialy compound.