J
Johan Bengtsson
>First things first....... Break means to damage as in destroy, damage,
>cause (irreversible) negative change, I don't think this is what you
>mean, try Brake, which is to slow down/stop.
OOPS! sorry! of course!
>> It was, however, not what I meant. What I was talking about was that
>> if the motor is still connected to the drive, but rather when the
>> drive gets disconnected from the power grid (or if the power grid
>> fails).
>The drive may or may not be disconnected from the power grid, the real
>question is where if anywhere will the energy be dissapated, if there
>are Braking resistors the power may be converted to heat in the
>resistors, i.e. there is still an electrical path present which will
>disharge the accumulated energy. If the power grid is disconnected the
>energy may still be discharged in your neighbours
>toaster/airconditioner/HiFi system, or anything else which is locally
>connected.
Exactly
>> The drive would not die completely immediately (since it have
>> capacitors holding a considerable amount of energy) and if it would
>> try to stop the motor in case of a power failure it could very well
>> succed with that because of regeneration without any external power
>> availiable.
>
>
>The amount of energy the capacitors store and are thus able to
>discharge is immaterial, what is of coincern is can they absorb the
>Kinetic energy you want to change to (potential) some other form of
>energy and thus dissapate as heat.
Partly true, they will need to hold enough energy for the drive to begin stopping the motor, but since that don't take very long time the energy needed isn't that high. But if you remove them completely it won't work.
>> A too long delay would - of course - kill the drive and after that
>> there would be no hope of electrically breaking since electrical
>> power - as you say - need to be availiable.
>
>Kill the drive ??? what does this mean, inanimate objets are not to
>good at dying, the issue here is, is there a discharge path for the
>energy.
What I mean if of course that it needs energy to work, no energy = no work done = not able to stop the motor. Ok, I am not a language expert (I have never pretended beeing one either <grin>) but of course a thing like that don't die but isn't it quite common to call it dead when it doesn't do what it is expected to do?
>> In order for it to work the drive have to be connected to the motor
>> all of the time, and operational. It could (theoretically at lest)
>> stay operational on the power regenerated for as long as it take to
>> stop the motor since there would be more energy regenerated than is
>> needed by the drive. (why would you otherwise need a breaking
>> resistor).
>
>
>It does not (necessarily) take power to stop the motor, it takes
>conversion of the stored kinetic energy to some manageable form, and
>subsequent dissapation of this energy, it does not/should not matter if
>the drive is "powered" up as the motor generates the power, the DC link
>if it is powered up should keep the electronics going, and the
>transistors/thyristors firing, and allow the dissapation of the above
>mentioned energy to proceed, by the time there is no more energy left
>to realise this, it does not neccessarily matter anymore as the motor
>is stationary.
You definitely need power to electrically stop an asynchronous motor, that is what Phil Corso tryed to say all the time, and he is completely right about that. The power is availiable since it is possible to pull it from the kinetic energy stored in the motor, but not unless you have some amount of electrical energy to begin with.
As opposed to brake with a DC current trru one winding, that will also stop the motor, but you need to feed electrical energy into the motor until it does. All this energy are then transfered to heat inside the motor.
The matter is completely different with a syncronous motor or a DC motor since they work as generators all by themself (if they are rotating of
course) and just short circuiting them make them stop rather quickly (too quickly perhaps ... but that is another story)
>Bye
>Donald Pittendrigh
/Johan Bengtsson
Do you need education in the area of automation?
----------------------------------------
P&L, Innovation in training
Box 252, S-281 23 H{ssleholm SWEDEN
Tel: +46 451 49 460, Fax: +46 451 89 833
E-mail: [email protected]
Internet: http://www.pol.se/
----------------------------------------
>cause (irreversible) negative change, I don't think this is what you
>mean, try Brake, which is to slow down/stop.
OOPS! sorry! of course!
>> It was, however, not what I meant. What I was talking about was that
>> if the motor is still connected to the drive, but rather when the
>> drive gets disconnected from the power grid (or if the power grid
>> fails).
>The drive may or may not be disconnected from the power grid, the real
>question is where if anywhere will the energy be dissapated, if there
>are Braking resistors the power may be converted to heat in the
>resistors, i.e. there is still an electrical path present which will
>disharge the accumulated energy. If the power grid is disconnected the
>energy may still be discharged in your neighbours
>toaster/airconditioner/HiFi system, or anything else which is locally
>connected.
Exactly
>> The drive would not die completely immediately (since it have
>> capacitors holding a considerable amount of energy) and if it would
>> try to stop the motor in case of a power failure it could very well
>> succed with that because of regeneration without any external power
>> availiable.
>
>
>The amount of energy the capacitors store and are thus able to
>discharge is immaterial, what is of coincern is can they absorb the
>Kinetic energy you want to change to (potential) some other form of
>energy and thus dissapate as heat.
Partly true, they will need to hold enough energy for the drive to begin stopping the motor, but since that don't take very long time the energy needed isn't that high. But if you remove them completely it won't work.
>> A too long delay would - of course - kill the drive and after that
>> there would be no hope of electrically breaking since electrical
>> power - as you say - need to be availiable.
>
>Kill the drive ??? what does this mean, inanimate objets are not to
>good at dying, the issue here is, is there a discharge path for the
>energy.
What I mean if of course that it needs energy to work, no energy = no work done = not able to stop the motor. Ok, I am not a language expert (I have never pretended beeing one either <grin>) but of course a thing like that don't die but isn't it quite common to call it dead when it doesn't do what it is expected to do?
>> In order for it to work the drive have to be connected to the motor
>> all of the time, and operational. It could (theoretically at lest)
>> stay operational on the power regenerated for as long as it take to
>> stop the motor since there would be more energy regenerated than is
>> needed by the drive. (why would you otherwise need a breaking
>> resistor).
>
>
>It does not (necessarily) take power to stop the motor, it takes
>conversion of the stored kinetic energy to some manageable form, and
>subsequent dissapation of this energy, it does not/should not matter if
>the drive is "powered" up as the motor generates the power, the DC link
>if it is powered up should keep the electronics going, and the
>transistors/thyristors firing, and allow the dissapation of the above
>mentioned energy to proceed, by the time there is no more energy left
>to realise this, it does not neccessarily matter anymore as the motor
>is stationary.
You definitely need power to electrically stop an asynchronous motor, that is what Phil Corso tryed to say all the time, and he is completely right about that. The power is availiable since it is possible to pull it from the kinetic energy stored in the motor, but not unless you have some amount of electrical energy to begin with.
As opposed to brake with a DC current trru one winding, that will also stop the motor, but you need to feed electrical energy into the motor until it does. All this energy are then transfered to heat inside the motor.
The matter is completely different with a syncronous motor or a DC motor since they work as generators all by themself (if they are rotating of
course) and just short circuiting them make them stop rather quickly (too quickly perhaps ... but that is another story)
>Bye
>Donald Pittendrigh
/Johan Bengtsson
Do you need education in the area of automation?
----------------------------------------
P&L, Innovation in training
Box 252, S-281 23 H{ssleholm SWEDEN
Tel: +46 451 49 460, Fax: +46 451 89 833
E-mail: [email protected]
Internet: http://www.pol.se/
----------------------------------------