The Life of Nikola Tesla. Electrons to Waves and Beyond. A two-value capacitor motor is a capacitor motor with different values of capacitance for starting and running.
Speed control of a universal motor is achieved by a varying field flux with tapped field windings b connecting rheostat in series c applying variable voltage by means of silicon controlled rectifier d applying variable voltage by means of variable auto-transformer e all of the above methods Ans: This magnetic field passes down perpendicularly through the disc, inducing circular eddy currents in the plane of the disc centered on the field. Note the change in motor torques at the transition point at which the starting switch operates.
Polyphase Electric Currents and Alternate-current Motors. The repulsion-start induction-run motor is used because of a good power factor b high efficiency c minimum cost d high starting torque Ans: When the motor is at rest, a spring acts on the sliding rotor and forces the brake ring against the brake cap in the motor, holding the rotor stationary.
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. The repulsion-start induction-run motor is used because of a good power factor b high efficiency c minimum cost d high starting torque Ans: When the speed of the motor is sufficient to overcome the inertia of the load, the contacts are opened automatically by a centrifugal switch or electric relay.
Each of these four half-poles carried a coil, and the coils of diagonally opposite half-poles were connected to a pair of terminals. 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. A universal motor can run on a A. Which of the following statements regarding a reluctance motor is incorrect? 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: Timeline of the electric motor Ball bearing motor Barlow's wheel Lynch motor Mendocino motor Mouse mill motor.
Which of the following motors is inherently self starting? Single phase induction motor usually operates on a 0. Evolving Technology and Market Structure: There is no additional brake control required. The 'permanent' connection to the capacitor in a PSC motor means that changing rotation is instantaneous. If a conventional squirrel-cage rotor has flats ground on it to create salient poles and increase reluctance, it will start conventionally, but will run synchronously, although it can provide only a modest torque at synchronous speed.
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The current-to-torque and frequency-to-speed relationships of BLDC motors are linear. This type of capacitor motor usually has a tapped main winding and a high-resistance rotor. Keeping in mind that the effective speed of the travelling magnetic field in the gap was constant, placing the poles nearer to the centre of the disc made it run relatively faster, and toward the edge, slower. Another variation is the permanent-split capacitor or PSC motor. An aluminum cup supports the magnet.
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. If connections to the rotor coils of a three-phase motor are taken out on slip-rings and fed a separate field current to create a continuous magnetic field or if the rotor consists of a permanent magnet , the result is called a synchronous motor because the rotor will rotate synchronously with the rotating magnetic field produced by the polyphase electrical supply. It should be recognized that, with this type of motor, the speed change is obtained by letting the motor speed slip down to the required low FIGURE 1. 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: The most common design is the two-speed motor, which has three windings:
A special version of the capacitor motor is used for multiple-speed fan drives. For a given capacitor-start motor, the effect of adding a running capacitor in the auxiliary winding circuit is as follows: Nikola Tesla , The Franklin Institute. In a ceilingfan employing capacitor run motor a secondary winding surrounds the primary winding b primary winding surrounds the secondary winding c both are usual arrangements d none of the above Ans:
3-phase AC induction motors
A reversible shaded-pole motor was made by Barber-Colman several decades ago. The motor used for the compressors is a d. This is known as a reluctance motor. The high starting torque and low inertia of the conical rotor brake motor has proven to be ideal for the demands of high cycle dynamic drives in applications since the motor was invented, designed and introduced over 50 years ago.
AC motor DC motor. A single-phase motor has no revolving field at standstill and therefore develops no locked-rotor torque. Synchronous motors are valued in any case because their power factor is much better than that of induction motors, making them preferred for very high power applications.
Conical rotor brake motors are also used to power micro speed drives. For this reason, ordinary squirrel-cage motors run at some tens of RPM slower than synchronous speed. Applying AC to the coil created a field that progressed in the gap between the poles. These are two-phase induction motors with permanent magnets to retard the rotor so its speed is accurately proportional to the power passing through the meter. Actual RPM for an induction motor will be less than this calculated synchronous speed by an amount known as slip , that increases with the torque produced. When stopped and restarted, the poles are likely to form at different locations.
The rotor of a hysteresis motor is made of a aluminium b cast iron c chrome steel d copper Ans: In all, this creates a repeating sequence of four poles, unshaded alternating with shaded, that creates a circumferential traveling field to which the rotor's magnetic poles rapidly synchronize. 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.
This initial design change also shows the shortest payback period. Small single-phase AC motors can also be designed with magnetized rotors or several variations on that idea; see Hysteresis synchronous motors below. When the speed of the motor is sufficient to overcome the inertia of the load, the contacts are opened automatically by a centrifugal switch or electric relay. After the starting winding of a single phase induction motor is disconnected from supply, it continues to run only on a running winding b rotor winding c field winding d compensating winding Ans: Two-phase servo motors are inherently high-speed, low-torque devices, heavily geared down to drive the load. Comparison of this performance with the performance shown in Table 1.