Excellent starting torque for high inertia loads
. Low starting current compared to squirrel cage induction motor. Speed is the resistance variable over 50% to 100% full speed. Higher maintenance of brushes and slip rings compared to squirrel cage motor.
What type of starter is used with a wound rotor induction motor?
Rotor Resistance Starter
This starter is used with a wound rotor induction motor. It uses an external resistance/phase in the rotor circuit so that rotor will develop a high value of torque. High torque is produced at low speeds, when the external resistance is at its higher value.
How do you start a wound rotor motor?
Wound-rotor motors can be started with low inrush current,
by inserting high resistance into the rotor circuit
; as the motor accelerates, the resistance can be decreased.
Why is the starting torque of a wound rotor motor higher starting of Amprate motor the starting current Amprage is increasing per Amp of starting current due to the resistance in the wound rotor circuit?
This produces
a very small phase angle difference between the magnetic fields of the rotor and stator
. This is the reason that the wound rotor induction motor produces the greatest amount of starting torque per ampere of starting current of any three-phase motor.
What happens to the starting torque of a wound rotor motor when you increase the resistance in series with the rotor windings?
Wound rotor motors are also referred to as “slip ring motors.” … During starting, this resistance is placed in series with the rotor windings. This
added resistance causes the rotor current to run more in phase with the stator current
, which increases the torque that is developed.
How do you test a wound rotor motor?
If you run a wound rotor motor with brushes that are barely contacting the slip rings, the motor may draw high current. An optional test is
to connect the stator leads together
, and run the motor by energizing the rotor leads at the rated secondary voltage.
What is the difference between rotor speed and synchronous speed?
Induction motor with squirrel cage rotor has two different speeds. The synchronous speed refers to the stator rotating magnetic field, which depends on the number of poles and frequency. The other speed is the rotor's. The
rotor speed will be always slower than the stator speed
, we call it slip.
Which single phase motor is fitted with a wound rotor?
Chapter 13 – AC Motors. A wound rotor
induction motor
has a stator like a squirrel cage induction motor, but a rotor with insulated windings brought out via slip rings and brushes. However, no power is applied to the slip rings.
What is the least expensive method of motor starting?
The direct starting (Direct On line, DOL)
is the simplest and most cost-efficient method of starting a motor.
What is the difference between a squirrel cage motor and a wound rotor motor?
Rotor itself automatically adjusts to the
number of
poles as that of stator. Squirrel cage motor consists of cylindrical rotor having skewed slots in which aluminum bars are placed. No windings are present in squirrel cage rotor.
What is the drawback of rotor Rheostatic speed control method?
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. The efficiency is greatly reduced at low speeds because of the higher value of the slip.
Why will the rotor of a wound rotor motor not turn if the rotor circuit is left open with no resistance connected to it?
If the circuit is left open, the current will not flow in the rotor, this leads
to the absence of the magnetic field in the rotor
. Therefore, there will be no torque between the rotor and the field. Hence, the motor will not start.
Which type of motor is used to provide high starting torque and variable speed?
1.
DC Series Motor
. Since it has high starting torque and variable speed, it is used for heavy duty applications such as electric locomotives, steel rolling mills, hoists, lifts and cranes.
How do you control the output of a wound rotor motor?
The speed of the wound rotor or slip ring induction motor can be controlled by
varying the resistance in the rotor circuit
. This method is applicable to slip ring induction motor only. When the motor is running and if the full resistance is connected in the rotor circuit the speed of the motor decreases.
What do you call when a motor is started by connecting it directly across the line?
A larger motor requires a specialized switching unit called a
motor starter or motor contactor
. When energized, a direct on line (DOL) starter immediately connects the motor terminals directly to the power supply.
How can the direction of rotation be changed on a wound rotor motor?
Reversing Rotation
The direction of rotation of a wound-rotor induction motor is
reversed by inter changing the connections of any two of the three line leads
, figure 10.
