Answer / monika hassan

When the magnetic field through the core changes, the magnetization of the core material changes by expansion and contraction of the tiny magnetic domains it is composed of, due to movement of the domain walls. This is a lossy process, because the domain walls get "snagged" on defects in the crystal structure and then "snap" past them, dissipating energy as heat. This is called hysteresis loss. It can be seen in the graph of the B field versus the H field for the material, which has the form of a closed loop. The amount of energy lost in the material in one cycle of the applied field is proportional to the area inside the hysteresis loop. Hysteresis loss increases with higher frequencies as more cycles are undergone per unit time.

Is there a chance for a motor speed to become negative..?? What is the reason for such a phenomenon.? In that case does the motor works as a generator..???

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HELLO EVERYONE, I RECENTLY HAVE FOUND ONE PROBLEM, I WAS TAKING NO LOAD TRIAL OF AN HT MOTOR 920 MOTOR , 1440 RPM , 6.6 KV, WITH AUTO TRANSFORMER. AT 450 V, LOAD WAS 40 AMP AND SPEED WAS 250 RPM. BUT AS WE INCREASE VOLTAGE FROM 450 TO 480V, LOAD BECOME 41 AND SPEED REDUCED TO SOME RPM . SO WHICH PHENOMENON ACTED HERE FOR REDUCING SPEED.?? AND IS IT HAPPENING ALWAYS OR IT IS RARE? I ALSO HAVE FACED SUCH PROBLEM WITH FEW LT MOTOR ALSO.

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