What is the relation between maximum torque and starting torque?
the ratio of the starting torque to the full-load torque (b.) the motor speed and slip at which the motor develops maximum torque (c.) the maximum torque developed by the motor as a percentage of the full-load torque. Thus, the motor provides 180% of the full-load torque at startup.
Can an induction motor be started with a full load connected?
In general as the stator voltage is constant, the magnetizing current is constant and independent of load. Therefore, stator current depends mainly on the rotor current. Maximum starting torque corresponds to full load and hence maximum starting current.
How is load torque calculated?
To calculate load torque, multiply the force (F) by the distance away from the rotational axis, which is the radius of the pulley (r). If the mass of the load (blue box) is 20 Newtons, and the radius of the pulley is 5 cm away, then the required torque for the application is 20 N x 0.05 m = 1 Nm.
Which starting method is best for induction motor?
1. Direct On Line Starter
- It is simple and cheap starter for a 3-phase induction motor.
- The contacts close against spring action.
- This method is normally limited to smaller cage induction motors, because starting current can be as high as eight times the full load current of the motor.
Which starting method is best method in induction motor?
Starting of an Induction Motor
- Direct on-line starter. The direct on-line starter method, of an induction motor, is simple and economical.
- Star delta starter. The star delta starter method of starting three-phase induction motors is very common and widely used among all the methods.
- Autotransformer starter.
How to calculate the torque of a squirrel cage motor?
To obtain higher starting torque in case of squirrel cage induction motor another cage is applied on the rotor and the motor is called a double cage motor. The maximum torque is denoted by T m and occurs at s = R 2 /X 2. The value of slip which corresponds to maximum torque is denoted by s m.
How does a squirrel cage induction motor start?
In this method of starting of a 3-phase squirrel cage induction motor reduced voltage is obtained by means of resistors (or reactors) that are connected in series with each stator lead, as shown in Fig. 1.68, during the starting period. The voltage drop in resistors (or reactors) causes a reduced voltage across the motor terminals.
How does the torque of an induction motor work?
Hence to obtain maximum (higher) at the start some external resistance is added in the rotor circuit which is only possible in the case of slip ring induction motors. Once motor picks up speed this external resistance is reduced to zero and slip rings are short-circuited.
How to start a polyphase cage induction motor?
Primary Resistor (or Reactor) Starting: This method of starting of a polyphase cage motor is very simple and provides smooth acceleration of the motor.