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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.
How do you test a brake rotor assembly?
How to Test an Alternator Rotor Remove and disassemble the alternator as indicated in your vehicle’s maintenance manual. Visually inspect rotor shaft, slip rings and windings. Connect one probe of the ohmmeter to a slip ring and the other to the shaft.
How blocked rotor test is performed?
A blocked rotor test is conducted on an induction motor. It is also known as short circuit test, locked rotor test or stalled torque test. From this test, short circuit current at normal voltage, power factor on short circuit, total leakage reactance, and starting torque of the motor can be found.
What is a wound rotor type motor?
A wound-rotor motor, also known as slip ring-rotor motor, is a type of induction motor where the rotor windings are connected through slip rings to external resistance. Adjusting the resistance allows control of the speed/torque characteristic of the motor.
How can the stator windings be tested?
For the electrical insulation component, an insulation resistance (IR) instrument is used to validate the condition of the winding relative to ground (outer case of the stator winding). Insulation resistance testers apply high DC voltage which causes a small current through the insulation being tested.
Why We Do Blocked Rotor Test?
A blocked rotor test is conducted on an induction motor. From this test, short-circuit current at normal voltage, power factor on short circuit, total leakage reactance, and starting torque of the motor can be found.
At what speed will the maximum torque occur?
So, when slip s = R2 / X2, the torque will be maximum and this slip is called maximum slip Sm and it is defined as the ratio of rotor resistance to that of rotor reactance. NOTE: At starting S = 1, so the maximum starting torque occur when rotor resistance is equal to rotor reactance.
Why are there no load and blocked rotor tests?
Thus no load and blocked rotor tests are performed on the motors. The synchronous speed can be achieved by taking slip = 0 which creates infinite impedance in the rotor branch. This test gives the information regarding no-load losses such as core loss, friction loss and windage loss.
What are the starting characteristics of a wound rotor motor?
Wound Rotor Induction Motor Qualities 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.
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.
How do you reverse 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. This procedure is identical to the procedure used to reverse the direction of rotation of a squirrel-cage induction motor.
How do you test a motor stator?
Insert each probe into a stator socket. You should read around 0.2 to 0.5 ohms. If you show an open circuit with the “Open” or infinity reading or have higher resistance, then the stator is bad and you must replace it. If these tests all produce positive results, then the stator itself is good.
How do you check motor windings?
You should test the windings for a “short to ground” in the circuit and open or shorts in the windings. To test your motor for short to ground, you’ll need to set the multimeter to ohms and disconnect the motor from its power source. Then inspect each wire and look for infinite readings.
How much resistance should a motor have?
Earth Continuity and Resistance Test A good motor should read less than 0.5 ohms. Any value greater 0.5 ohms indicate trouble with the motor.
Why is locked rotor current important?
The locked rotor current (information) is used to choose the overcurrent protection device (circuit breaker / fuse). An electrician has to install the correct breaker, or fuse, to prevent tripping on motor startup, as well as to protect the motor. Knowing the locked rotor current is certainly not useless.
What causes locked rotor?
Something as simple as a broken wire or weak capacitor can generate a lock rotor condition.
What is the locked rotor current?
The very high current or amperage a motor draws when power is first applied, due to low counter emf. It is usually five to six times the running load amperage.
Under what condition the torque is maximum?
Maximum torque occurs when θ = 90º and sin θ = 1.
How do you get maximum torque?
Note that the torque is maximum when the angle is 90 degrees. A practical way to calculate the magnitude of the torque is to first determine the lever arm and then multiply it times the applied force. The lever arm is the perpendicular distance from the axis of rotation to the line of action of the force.
What is pull out torque?
: the maximum torque a motor will carry without an abrupt drop in speed.
Which arrangement is done for blocked rotor?
The Blocked Rotor Test of an induction motor is similar to the short circuit test of a transformer. In this test, the shaft of the motor is locked so that it cannot move and the rotor winding is short-circuited. In the slip ring motor, the rotor winding is short-circuited through the slip rings.
Which loss in the motor is significant in no load test Why?
As the motor is running at no load, the total input power is equal to the constant iron loss, friction, and windage losses of the motor. Since the power factor of the induction motor under no-load condition is generally less than 0.5, thus the Wattmeter reading of one of the Wattmeter will show a negative reading.
How do you test an induction motor rotor?
HIGH CURRENT ROTOR TEST – This test is performed by applying high current through the shaft of the rotor (rotor out of stator) and thermally scanning (infrared or thermoscan) the rotor O.D. searching for shorted laminations. These shorted laminations cause localized hot spots which cause uneven heating of the rotor.
