- #1
dannygul
- 1
- 0
Hi,
I am trying to understand the concept of the VFD & the AC motors running on three phase . I have briefed about the concept involved with the VFD what i understood;---
Torque --- directly proportionalt to applied V^2
speed --- directly proportionalt to frequency
One way to control the industion motor operation is using following rule :---
volts per hertz
applied voltage to be proportionally adjusted whenever the frequency is changed to draw same current from the supply.
means torque & speed can be adjusted by varying the voltage & frequency.
I am confused at two thing :-----
1> what do we means by the -- motor on load ?
2> how can we find the starting torque required by the motor, when suppose some device is connected to it ?
For 2> i have done following analysis but still stuck at one thing.
Suppose for example i want to rotate the hollow cylindrical attached to shaft of my motor. Then first i need to find out the -- Torque needed to start the rotation of hollow cylinder.
Litle physics :----
Torque = dL/dt = d(I*w)/dt = I*d(w)/dt = I* α
moment of inertia of a uniform hollow cylinder of inner radius b, outer radius a, and mass M.
I = 1/2* M * (a^2 + b^2 )
But how can we calculate the α angular acceleration well in advance when motor is not started ?
Please suggest for these point.
I am trying to understand the concept of the VFD & the AC motors running on three phase . I have briefed about the concept involved with the VFD what i understood;---
Torque --- directly proportionalt to applied V^2
speed --- directly proportionalt to frequency
One way to control the industion motor operation is using following rule :---
volts per hertz
applied voltage to be proportionally adjusted whenever the frequency is changed to draw same current from the supply.
means torque & speed can be adjusted by varying the voltage & frequency.
I am confused at two thing :-----
1> what do we means by the -- motor on load ?
2> how can we find the starting torque required by the motor, when suppose some device is connected to it ?
For 2> i have done following analysis but still stuck at one thing.
Suppose for example i want to rotate the hollow cylindrical attached to shaft of my motor. Then first i need to find out the -- Torque needed to start the rotation of hollow cylinder.
Litle physics :----
Torque = dL/dt = d(I*w)/dt = I*d(w)/dt = I* α
moment of inertia of a uniform hollow cylinder of inner radius b, outer radius a, and mass M.
I = 1/2* M * (a^2 + b^2 )
But how can we calculate the α angular acceleration well in advance when motor is not started ?
Please suggest for these point.
