Congratulations, your the first person to accurately describe slip ratio and torque curves on electric motors. Most don't understand that no motor (or engine) has a linear torque curve. Slip is part of both. Well done sir!
Hello I would really appreciate it if you could help me resolve this issue. I have a 1000 rpm 160 kw rated 3 phase Delta connected ac motor hooked to an air compressor feeding an oxygen production plant. our phase to phase supply voltage is 380 volts. our maximum running load current at working pressure is 250 Amps. This motor failed as it was running for more than 10 years. Lately we demanded more continuous load due to high demand for medical oxygen effected by covid19 pandemic. I could not find a similar replacement available. However i found another German made motor with same mounting frame and shaft size and also 1000rpm at 50 Hz the name plate says: Delta connection 660 Volts - 260 Amps - 240 KW. my question is : if i supplied this motor 380V with same delta connection will it be able to give me 160 kw power? because its limiting design current is 260 Amps as it says . Thus if am assuming its rated power will be reduced proportionally to the reduction of supply voltage. i it is rated 240 Kw at 660 Volts is it true that it will become a 160 Kw motor under 380 Volts? I am also assuming it will not overheat as the current will not exceed its rated 260 A at my demanded compressor load. Please help me if you have a definitive answer without any speculations. Best regards
I need to know one thing about torque and speed relation , if the torque decreases with speed is it good o not for motor and and if the torque increases with the speed decreases too good or not for motor ?
I don't think that's good or bad. It's just part of the properties of the motor. And by "good" or "bad", do you mean is it dangerous/damaging or not to the motor?
@@abdullaalmosalami I am confusing about that really , because why we consider the torque with speed in choosing a motor for an application ? if the motor increases the speed and the torque decreased is it good or not in the motor performance , or current consumption will be increased or not ? that what am asking
@@wadib3eed7 Ok, so I hope I understood what your confusion is: "... why we consider the torque with speed in choosing a motor for an application ?" If the motor doesn't have the specified torque/speed needed for an application, that application won't run right. For example, motors for wheels on a cart. If the torque/speed is not matched, then the cart moves too slow, or too fast, or doesn't move at all; etc. How do we know these torque/speed numbers? That comes from having a good model of the object we are trying to drive, and the more detailed the model is, the better we will understand the requirements of the motor. "if the motor increases the speed and the torque decreased is it good or not in the motor performance, or current consumption will be increased or not ? that what am asking" Ok, so I'm not fully sure still what you mean specifically by "good" here, but let me say this: torque and current always move together - if torque increases, this is because current increased; if torque decreased, this is because current decreased. This is because current --> magnetic fields --> torque. If the current goes up, is that bad or good? Well, if the current is within the rated specifications of the motor, then it's just fine. However, if you are stalling you motor which causes the torque and current to be also at max, then this is generally not good for the motor, no. What about for performance? Well, the "performance" kind of comes down to can the motor run the application at the needed torque/speed. We just talked about torque. Read onward for speed. Speed comes not from current directly but is the result of the dynamics of the motor + load. This is where modeling comes in. The most basic kind of modeling for example could be done using Newton's laws of rotation on the motor shaft, where (sum of torques on shaft) = (moment of inertia of shaft) X (rotational acceleration of shaft). And we know that (derivative of rotational speed) = (rotational acceleration). This usually results in a system of differential equations that you either solve numerically or analytically, depending on how the torques are modeled. For example, maybe you are running a constant current into the motor, which means a constant torque from the motor. Ok. There is also friction, which is NOT constant and increases with speed (or even the square of speed). Indeed, friction plays a BIG role in what the speed is at the given motor torque output; if friction was truly zero, then actually the speed would keep going to infinity!! You put these into the differential equations above and solve. One final thing I will say is the torque-speed curve shows the numbers once the motor has reached steady-state - once the torque/speed/currents/etc. have stabilized. On the way to this stable state will possibly be other kinds of behavior that are not at all shown in the torque-speed plot, and the only way to know what these will be is by again having a good model of the situation. Also where on the torque-speed curve the motor lands is again dependent on the dynamics of the situation, which will not be obvious and you will need to have your detailed model to have a good guess of what will happen. Even if you know the torque your load needs, the speed may not be determined immediately. Some of the plots shown in the video for example have two speeds that have the same torque - which of these speeds will the motor be in for the application? I don't know. You need your model. Let me know if you still have some confusion. We can work this out.
