Machines used for this purpose are easily identified as they have no shaft extensions. Froehlich; Allen Kent One of the pair of discs distributes the coil's flux directly, while the other receives flux that has passed through a common shading coil. In contrast, the synchronous motor does not rely on slip-induction for operation and uses either permanent magnets, salient poles having projecting magnetic poles , or an independently excited rotor winding.
A spring-loaded auxiliary manual starting switch connected power to this second motor for a few seconds. Both shading coils were probably closer to the main coil; they could have both been farther away, without affecting the operating principle, just the direction of rotation. Assuming power is flowing to the load, the flux from the left current coil crosses the disc upwards where the eddy current flows radially toward the center of the disc producing by the right-hand rule a torque driving the front of the disc to the right. Several methods are commonly used:.
The synchronous motor can also be used as an alternator. In case of a shaded pole motor the direction of rotation of the motor is a from main pole to shaded pole b from shaded pole to main pole c either of the above depending on voltage d either of the above depending on power factor Ans: An AC servo amplifier, a linear power amplifier, feeds the control winding. Polyphase Electric Currents and Alternate-current Motors. The current-to-torque and frequency-to-speed relationships of BLDC motors are linear.
The direction of rotation is determined by the connection between the main winding and the start circuit. The Gateway to Understanding: A split-phase watthour meter has a stator with three coils facing the disc. Views Read Edit View history. Representative are low-torque synchronous motors with a multi-pole hollow cylindrical magnet internal poles surrounding the stator structure.
This produces a low level rotating magnetic field which is large enough to turn both the rotor and its attached load. The axial component overcomes the spring force, releasing the brake; while the radial component causes the rotor to turn. In a repulsion motor, the armature brushes are shorted together rather than connected in series with the field, as is done with universal motors. Conical rotor brake motors are also used to power micro speed drives. As the rotor picks up speed the torque builds up to its full level as the principal magnetic field is rotating relative to the rotating rotor. Applications included tape recorder capstan drives the motor shaft could be the capstan , and, before the advent of crystal control, motion picture cameras and recorders.
Locked rotor current of a shaded pole motor is a equal to full load current b less than full load current c slightly more than full load current d several times the full load current Ans: The brushless wound-rotor doubly fed motor is a synchronous motor that can function exactly at the supply frequency or sub to super multiple of the supply frequency. Most of the fractional horsepower motors have either a hard and annealed bearings b ball or roller bearings c soft and porous bearings d plain or sleeve bearings Ans:
A conical rotor brake motor incorporates the brake as an integral part of the conical sliding rotor. Single phase induction motor usually operates on a 0. As a result, the induction motor cannot produce torque near synchronous speed where induction or slip is irrelevant or ceases to exist. Two-phase servo motors are inherently high-speed, low-torque devices, heavily geared down to drive the load. The shaded pole motor is used for a high starting torque b low starting torque c medium starting torque d very high starting torque Ans:
It thus appears to the supply to be a capacitor, and could thus be used to correct the lagging power factor that is usually presented to the electric supply by inductive loads. In a split-phase watthour meter the voltage coil is connected between the two hot line terminals V in North America [ citation needed ] and two separate current coils are connected between the corresponding line and load terminals. Which of the following motors is preferred for tape-recorders? Their distinguishing feature is their rotor, which is a smooth cylinder of a magnetic alloy that stays magnetized, but can be demagnetized fairly easily as well as re-magnetized with poles in a new location. Several types of repulsion motors have been manufactured, but the repulsion-start induction-run RS-IR motor has been used most frequently. They have a Nd or other rare-earth permanent magnet.
Hysteresis refers to how the magnetic flux in the metal lags behind the external magnetizing force; for instance, to demagnetize such a material, one could apply a magnetizing field of opposite polarity to that which originally magnetized the material. Because of AC's advantages in long distance high voltage transmission, there were many inventors in the United States and Europe during the late 19th century trying to develop workable AC motors. Nearly all universal motors are series-wound because their stators have relatively few turns, minimizing inductance.
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Very low voltages at very high currents are typical in the bars and end rings; high efficiency motors will often use cast copper to reduce the resistance in the rotor. These induced currents are proportional to the time derivative of the magnetic field, leading it by 90 degrees. Repulsion motors are wound-rotor single-phase AC motors that are a type of induction motor. If the capacitor of a single-phase motor is short-circuited a the motor will not start b the motor will run c the motor will run in reverse direction d the motor will run in the same direction at reduced r. In case of a shaded pole motor the direction of rotation of the motor is a from main pole to shaded pole b from shaded pole to main pole c either of the above depending on voltage d either of the above depending on power factor Ans:
It had a single field coil, and two principal poles, each split halfway to create two pairs of poles. Thank u sir, Please send me question in pdf Pky gmail. Electronically commutated EC motors are electric motors powered by direct-current DC electricity and having electronic commutation systems, rather than mechanical commutators and brushes. A universal motor is a design that can operate on either AC or DC power. The RS-IR motor has a centrifugal switch that shorts all segments of the commutator so that the motor operates as an induction motor once it is close to full speed.
Which of the following motors can be run on AC. The 'permanent' connection to the capacitor in a PSC motor means that changing rotation is instantaneous. For a given design, torque at synchronous speed is only relatively modest, and the motor can run at below synchronous speed. Electrons to Waves and Beyond. When the rotor is not rotating in sync with the magnetic field, large rotor currents are induced; the large rotor currents magnetize the rotor and interact with the stator's magnetic fields to bring the rotor almost into synchronization with the stator's field. They have a Nd or other rare-earth permanent magnet.
PSC motors are the dominant type of split-phase motor in Europe and much of the world, but in North America, they are most frequently used in variable torque applications like blowers, fans, and pumps and other cases where variable speeds are desired. Ferraris demonstrated a working model of his single-phase induction motor in , and Tesla built his working two-phase induction motor in and demonstrated it at the American Institute of Electrical Engineers in    although Tesla claimed that he conceived the rotating magnetic field in Universal motors are widely used in small home appliances and hand power tools. The magnetic circuit is completed by a C-shaped core of permeable iron. The speed control of universal motor used for sewing machines is by a friction b varying the resistance c tapping the field d centrifugal mechanism Ans: Various other designs use a small induction motor which may share the same field coils and rotor as the synchronous motor or a very light rotor with a one-way mechanism to ensure that the rotor starts in the forward direction.
In case of a shaded pole motor the direction of rotation of the motor is a from main pole to shaded pole b from shaded pole to main pole c either of the above depending on voltage d either of the above depending on power factor Ans: Which motor is normally free from mechanical and magnetic vibrations? This magnetic field passes down perpendicularly through the disc, inducing circular eddy currents in the plane of the disc centered on the field. These coils connect the supply to the load, producing a magnetic field in phase with the load current.
As the rotor picks up speed the torque builds up to its full level as the principal magnetic field is rotating relative to the rotating rotor. If the load supplies power to the grid, the disc rotates backwards unless prevented by a ratchet, thus making net metering possible. Which of the following single-phase motors is suitable for timing and control purposes? Applications included tape recorder capstan drives the motor shaft could be the capstan , and, before the advent of crystal control, motion picture cameras and recorders. Nearly all universal motors are series-wound because their stators have relatively few turns, minimizing inductance.