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Torque is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist to an object. Mathematically, torque is defined as the cross product of the lever-arm distance vector and the force vector, which tends to produce rotation.
The speed of an object is the magnitude of its velocity (the rate of change of its position). The average speed of an object in an interval of time is the turning cycles travelled by the object divided by the duration of the interval. The instantaneous speed is the limit of the average speed as the duration of the time interval approaches zero.
Efficiency is the ratio of average output power divided by average input power over the same time period, times 100%. With a motor, the mechanical output power is equal to the motor shaft speed times the shaft torque, and is often expressed in kilowatt. The input power is equal to the input volts times input amps, and is often expressed in Watts.
The difference in these power values is caused by motor losses during the electro-mechanical transduction process. These losses include load dependent losses like the motor winding (I2R), speed (or frequency) dependent losses like the iron losses (magnetic hysteresis and eddy currents), shaft contact friction and windage friction.
Temperature rise is the increase in temperature above ambient. Ambient temperature iss the temperature of air (or other cooling medium) in the area surrounding the motor, frequently termed as room temperature. The sum of ambient temperature and the temperature rise is the overall, or "hot" temperature of the motor. Insulation temperature classes are based on the overall temperature.
The critical limitation on winding temperature is the hot or overall temperature. In large part, the load determines the rise. The other key factor that must be dealt with is ambient. From the temperature rise, we can decide the motor size is sufficient or not.
Direct current (DC) is the unidirectional flow of electric charge. Direct current is produced by sources such as batteries, switch power supply, solar cells, and commutator-type electric machines of the dynamo type. In alternating current (AC, also ac), the movement of electric charge periodically reverses direction. In direct current (DC, also dc), the flow of electric charge is only in one direction.
Electric current produces a magnetic field. The magnetic field can be visualized as a pattern of circular field lines surrounding the wire that persists as long as there is current. Magnetism can also produce electric currents. When a changing magnetic field is applied to a conductor, an Electromotive force (EMF) is produced, and when there is a suitable path, this causes current.
Most electrical power is transmitted via AC waveforms. A measure of how efficiently that power is being transmitted is called power factor, which is the average power divided by the "apparent" power. The apparent power is calculated by taking the RMS value of the voltage and current independently, and multiplying them together.
For sinewaves, if the voltage and current are in perfect phase with each other, the power factor is unity. This represents a very efficient way to transmit power. The power factor is reduced as the phase relationship changes, and goes completely to zero for a 90 degree shift. Under this condition, the average power delivered to the load is zero, but current is still flowing in the power lines, resulting in heat dissipation.
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