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Which of the following statements are correct for dc shunt motor? 1. Speed of a shunt motor is sufficiently constant 2. For the same current input, its starting torque is not high as that of series motor 3. The motor can be directly coupled to a load such as fan whose torque increases with speed Select the correct answer using the code given below.

Which of the following statements are correct for dc shunt motor? 1. Speed of a shunt motor is sufficiently constant 2. For the same current input, its starting torque is not high as that of series motor 3. The motor can be directly coupled to a load such as fan whose torque increases with speed Select the correct answer using the code given below. Correct Answer 1 and 2 only

Speed of a DC shunt motor:

  • In the case of DC shunt motor, flux is practically constant as the field is parallel to the armature.
  • If the load is increased, then the speed of the motor will remain almost constant because the field current remains almost constant.

 

The characteristics of speed vs armature current are shown below.

Characteristics of DC shunt motor:

[ alt="SSC JE Electrical 77 15Q Full Test 2 Part4 Electrical Machines Part1 Hindi images q7b" src="//storage.googleapis.com/tb-img/production/19/02/SSC%20JE%20Electrical_77_15Q_Full%20Test%202_Part4_Electrical%20Machines_Part1_Hindi_images_q7b.PNG" style=" width: 450px; height: 149px;">

Therefore, Statement 1 is true.

The torque of a DC shunt motor:

In a DC motor, T ∝ ϕIa

In series motor, ϕ ∝ Ia

⇒ T ∝ (Ia)2

In shunt motor, ϕ is constant

⇒ T ∝ Ia

From the above equations, it is clear that for the same current input, the starting torque of a shunt motor is not high as that of a series motor.

The characteristics of torque vs armature current are shown below.

Therefore, Statement 2 is true.

Speed torque characteristics:

The shunt motor cannot be directly coupled to a load such as a fan whose torque increases with speed as the torque of the dc shunt motor does not increase with speed. DC series motor is used for this purpose. The characteristics of both shunt and series motor are shown below.

Therefore, Statement 3 is false.

Characteristics of DC series motor:

[ alt="SSC JE Electrical 77 15Q Full Test 2 Part4 Electrical Machines Part1 Hindi images q7a" src="//storage.googleapis.com/tb-img/production/19/02/SSC%20JE%20Electrical_77_15Q_Full%20Test%202_Part4_Electrical%20Machines_Part1_Hindi_images_q7a.PNG" style="width: 450px; height: 149px;">

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