2007-12-06 00:48:46 · 6 answers · asked by Anonymous in Science & Mathematics ➔ Engineering
The speed of an alternating current (AC) motor is mostly determined by the frequency (hertz) of the power source and the number of magnetic poles created by the coils of wire that are energized by the power source. The motor’s maximum speed, called the synchronous speed, is determined by the formula: Speed = 120 X f / p. Speed is given in revolutions per minute (RPM). The frequency of the power (f) is given in hertz and is usually 50 or 60. The number of poles (p) is an even number because every magnet has a north and south pole. In most motors, there are 2, 4 or 6 poles, but there can be as many pairs of poles as will physically fit. The constant 120 is 2 poles per pair X 60 seconds per minute.
Most AC motors are one or another of the many types of induction motors. Induction motors run at very nearly synchronous speed when the motor is not driving any load. When the motor is loaded, it runs a little slower. As the load increases, the speed decreases. Depending on the motor design, the reduction in speed at full load can be less than 2% or more than 10%. If the voltage is less than normal, that will cause still more speed reduction. Voltage reduction sometimes is used to adjust the speed of a load like a fan, but that is an inefficient type of speed control. Electronically changing the frequency is a very efficient means of AC motor speed control, but it is more expensive.
Some AC motors, called synchronous motors, run at exactly synchronous speed with no variation due to load or voltage. Small synchronous motors are used for clocks. Large synchronous motors are very efficient and are used to drive industrial machinery.
The speed of a direct current (DC) motor is proportional to the voltage applied to the motor. The load also affects the speed to an extent determined by the motor design. The maximum speed is determined by the motor design. If the fixed magnetic field is provided by an electromagnet rather than a permanent magnet, reducing the field magnetism increases the maximum speed of the motor.
Universal motors are DC motors that are designed to operate from either AC or DC power. They are often used for appliances like food mixers because their speed can be inexpensively controlled by adjusting the voltage.
I believe that covers the basics. There are many motor and motor control design variations.
2007-12-06 02:56:43 · answer #1 · answered by EE68PE 6 · 2⤊ 1⤋
There are many types of motors.
If its an ac induction motor (many ac motors are induction type) then the speed is determined by the frequency of the mains and the number of poles in the motor. This gives the speed that the magnetic field rotates, the actual shaft will be slightly slower and varies very slightly with load.
For other motors the answer may be different.
2007-12-06 08:08:51 · answer #2 · answered by Poor one 6 · 0⤊ 0⤋
The construction of the motor has a great influence on motor speed. A motor designed for DC or AC, the number of field poles vs armature windings.
AC motors are typically synchronous and derrive there speed as a function of the electric frequency powering them. To adjust a speed of this type of motor a VFD (variable frequency Drive) is attached between the motor and its power source. The VFD changes the frequency and speed of the motor.
2007-12-06 01:00:54 · answer #3 · answered by MarkG 7 · 1⤊ 1⤋
the speed of a motor is determined the amount of power and we all know that power is I2* R so the amount of current will affect it check DC Machines
2007-12-06 02:43:04 · answer #4 · answered by cliffmosh 1 · 0⤊ 1⤋
The amount of current applied to the magnets in the motor.
2007-12-06 00:52:51 · answer #5 · answered by Anonymous · 1⤊ 3⤋
how fast it goes
dipshit
2007-12-06 00:56:19 · answer #6 · answered by Anonymous · 1⤊ 7⤋