5.1 Important features of a slip-ring motor. The external resistance adds up to the total impedance of the motor windings and limits the starting current. It also improves the starting power factor.
What is the effect on slip as we add some external resistance to the rotor of slip ring induction motor?
Placing the slip-rings and variable resistance, rheostat, or permanent resistance in series to add external resistance or modulating the feedback current increases the slip and produce higher starting torque. The external resistance equals the total impedance of the motor windings.
What is the effect of external resistance in the rotor circuit of a 3 phase srim?
If the resistance in the rotor circuit is increased, the slip is increased and the speed of the rotor is decreased.
What is the purpose of connecting external resistor to slip ring induction?
The slip rings in a wound rotor motor form a secondary, external circuit. Inserting resistance to this circuit allows the motor to produce very high torque at start-up, which is necessary for moving loads with high inertia.
How does the external resistance of slip ring induction motor influence the motor performance?
Effect of Adding External Resistance
The external resistance reduces high resistance as soon as the motor obtains normal speed and increases the starting torque of a motor. The tweaking of external resistance also aids in decreasing of rotor and stator current but improves the power factor of a motor.
What are the applications of slip ring induction motor?
A slip ring induction motor is capable of maintaining the highest torque at any slip. Even a high braking torque can be maintained easily. It is mainly used for high starting torque which makes use of an external resistance. They can help in speed control for lifts, railway traction, elevators, etc.
What are the advantages of slip ring induction motor?
Slip rings Induction motor provides some advantages like provides high starting torque, low starting current and it improves the power factor. We can add external variable resistance to the rotor of this type of motor. So, we are able to control the speed of this type of motor easily.
What are the advantages and disadvantages of rotor resistance control?
Advantages and disadvantages of rotor resistance control
- Absence of in-rush starting current.
- Availability of full rated torque at starting.
- High line power factor.
- Absence of line current harmonics.
- Smooth and wide range of speed control.
What are the advantages and disadvantages of rotor resistance control method?
It is possible to have a large starting torque, low starting current, and large values of the pullout torque at a small value of slip. The major disadvantage of the rotor resistance control method is that the efficiency is low because of the additional losses present in the resistors connected within the rotor circuit.
How is rotor resistance calculated?
As for the proportion of the stator and rotor leakage reactances, empirically, X l s = X l r = 0.5 X B for Design A and D types, X l s = 0.4 X B , X l r = 0.6 X B for Design B type, and X l s = 0.3 X B , X l r = 0.7 X B for Design C type .
How do electrical slip rings work?
HOW DOES A SLIP RING WORK? A slip ring passes electrical signals and power across a rotating interface using sliding electrical contacts. These contacts are typically a rotating ring and a stationary brush, or wiper, that slides along the ring surface during rotation.
What is the method of starting a 3 phase slip ring induction motor?
The three-phase induction motor may be started by connecting the motor directly to the full voltage of the supply. The motor can also be started by applying a reduced voltage to the motor. The torque of the induction motor is proportional to the square of the applied voltage.
Why do we use slip rings in AC generator?
The function of slip ring in an AC generator is that these are the hollow rings that are connected to the ends of the armature coil. They help in rotation of the coil. … A slip ring in an electric motor is used an electrical joint to transmit power. It acts as a bridge between a still component and a rotating element.
How does slip Help for rotation of induction motor?
“Slip” in an AC induction motor is defined as:
As the speed of the rotor drops below the stator speed, or synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the rotor’s windings and creating more torque.
Which DC motor is preferred for constant speed?
Explanation: Rotary compressor generally demand constant speed operation throughout the load. Sometimes, DC machines are not able to produce constant speed throughout the process hence, synchronous machine is used. 4.
Which type of starter is used in a slip ring induction motor?
Rotor resistance starter is used for slip ring induction motors of high ratings.