i really need to knowww
2007-01-22 11:46:05 · 5 answers · asked by Shenty H 1 in Science & Mathematics ➔ Other - Science
You need to be more specific in your question.
In an electric motor, there are two magnetic fields generated. One is 'stationary', in that it is generated by passing current through windings that are embedded in the part of the machine that does not rotate. The other is 'rotary', in that it is generated by passing current through windings that are embedded in the rotating portion of the machine.
A Direct Current (DC) machine has both stationary and rotary fields powered by DC voltages and currents. A Synchronous machine has a DC rotor field and an Alternating Current (AC) stator field. An Induction machine has AC fields on both rotor and stator.
In general, the relative strengths of the magnetic fields define the speed of the machine. A stronger relationship means the machine will turn slower, while a weaker one will increase rotational speed.
For a DC machine, this is pretty easy to discover. Holding the voltage constant for the main field supply maintains the strength of the stationary field. If the armature (rotor) voltage is then increased, the motor will speed up - because the stationary field is weaker with respect to the rotating one. Alternatively, reducing the rotor voltage will slow it down. Now ... hold the rotor voltage constant. Raising the voltage on the stator field makes it a stronger magnet ... and will slow the machine down. Lowering the voltage on the stationary field will speed up the rotation.
A synchronous machine works kind of the same; raising the DC voltage on the rotor while holding the stator voltage constant will generally make the rotor generate a stronger magnetic field, thereby trying to slow the machine down. However, the relative strength of the fields is such that the pull of 'synchronism' overcomes the rotor tendency and the net result is the ability to generate higher torque before stalling. Reducing the DC rotor field voltage would have the opposite effect. Raising the AC voltage on the stator while holding the rotor DC voltage constant will generally generate more stator field strength - again, it shows up as increased torque capability rather than actual speed change. Reducing the voltage reduces the torque capability.
Induction machines behave similarly to Synchronous machines; higher stator field strength generally occurs at higher voltages, and results in higher torque before stall - rather than a noticeable speed change. There is only an induced field on the rotor - so what actually happens is that an increase in stator voltage will slightly decrease the rotor speed by a couple of rpm (maybe 1 or 2 out of 1800!). Alternatively, lowering the stator voltage will achieve a very slight speed increase (again 1 or 2 rpm) and a reduced peak torque capability.
2007-01-23 01:35:21 · answer #1 · answered by CanTexan 6 · 1⤊ 0⤋
Yes. Just about anything like a motor or something will turn faster if the voltage is increased.
2007-01-22 12:19:01 · answer #2 · answered by Anonymous · 0⤊ 0⤋
A DC motor does -- its speed is relative to the voltage (assuming you don't go over the maximum voltage).
An AC motor doesn't -- increasing the voltage to an AC motor will increase its torque (the force it can turn when attached to a load), but not its speed.
2007-01-22 11:55:47 · answer #3 · answered by Anonymous · 1⤊ 0⤋
I believe that a contributing factor to the rpms of an electric motor
is the frequency
2007-01-22 12:05:48 · answer #4 · answered by osinamunatum 2 · 0⤊ 1⤋
Direct current yes.. Alternating current is different because the magnetic lines change to fast to see a noticible difference.
2007-01-22 11:51:06 · answer #5 · answered by segabill 3 · 0⤊ 0⤋
I would answer this but 'CanTexan' nailed the answer.
2007-01-23 15:50:28 · answer #6 · answered by Brendan R 4 · 0⤊ 0⤋