A question about a sentence in a AC drive manual. 2

[RedSnake]

I have this project with some Spaniards and we have this text from a AC drive manual, it isn't exactly crystal clear to begin with, and we both have a different understanding about what it actually says.
Since neither he or I have English as our first language, I am asking you, what are they actually saying here?

If the load torque will be higher than 20% of motor
nominal torque, or if the machinery is not able to
withstand the nominal torque transient during the ID
run, then the driven machinery must be de-coupled
from the motor during a Normal ID run.

NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[waross]

Hi Anna;
The first question: What is " ID run"
If this is part of the self tuning procedure, then the load torque (and inertia) must be considered.
If this is a load that must be accelerated slowly to avoid breakage, it may wise to disconnect the driven machinery during the drive setup procedure.
This is based on my WAG (Wild ASSet Guess) that "ID" is "Initial something" that is related to commissioning.
In any event, disconnecting the driven machinery during initial commissioning may be the safest action.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RedSnake]

ID run is a built in function in the drive, as you say "self tuning procedure" a program you start that then runs the motor on it's own to determine the slip and the torque and ampere volts and other things it needs to be able to properly drive after the parameter settings you give it afterwards like acceleration and deacceleration.

There is at least four different ID runs you can make, this description is for "Normal" which is the recommended.

NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[RedSnake]

It is mostly this sentence we are bickering about..

If the load torque will be higher than 20% of motor
nominal torque, or if the machinery is not able to
withstand the nominal torque transient during the ID
run

We do not see eye to eye what it actually says..

NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[waross]

Nominal Torque? Torque at rated HP.
Maximum torque? may be 200% or 250% or more of rated torque.
Nominal; In Name, or rated.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RedSnake]

Okay this is what we are bickering about.

He says the sentence means, that the ID Run is going to run the motor to 120% of the motors nominal torque and says that is not good.
Okay I agree it is not.

But my interpretation is that the sentence says, that if the load on the motor from the equipment attached to it is higher than 20% of the motors nominal torque, you need to de-couple it.


And he has at several occasions said that the load from the equipment is only 10% of the nominal torque of the motor.

And another thing is that the motor is only going to run in one direction during this ID run.
And I can’t see how more torque can be put on it then is already there from belts, gearboxes etc. to begin with, only way to do that is to accelerate/break/deaccelerate really fast, but they already do that as it is during production.

I am just not sure if I am getting this right.

NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[waross]

On a DOL start, the torque output of the motor peaks at 200% or higher. This is realized as acceleration.
With a load connected, the load demands acceleration torque also so while the motor still puts out maximum torque, acceleration is slower as the torque is shared by both the motor and the load.
The sentence does not say anything about the motor torque output.
The sentence warns that during ID, the torque output may be enough to damage the load.

And he has at several occasions said that the load from the equipment is only 10% of the nominal torque of the motor.

This raises several questions.
How does "he" know the load torque under acceleration?
Has he, and is he capable of calculating the load torque under acceleration.
The ID run is to determine motor characteristics. If the motor is coupled to a relatively high torque demanding load, the ID information may not be accurate.
And, if the load torque is 10% of motor nominal torquethe motor may be oversized by a factor of 10.
Not to challenge the motor sizing, but his statement;
"that the load from the equipment is only 10% of the nominal torque of the motor." is suspect.
If you can arrange to have some salami delivered to California, jraef can give a better answer than I.
Note: "salami delivered to California" an allusion to a 10 year old tagline that Eng-Tips veterans will recognize. grin

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RedSnake]

"How does "he" know the load torque under acceleration?"
I would say he don't.
Probably he has calculated the torque "load" mechanically with some program I don't really know.

But as son as suggest trying something to see if it will make the drive actually do what you tell it to, he is just like don't touch anything we have always used this parameters and they are right.
Even though they have changed the drive to a larger one, even thought that don't makes so much difference, more that the parameter numbers becoming other ones.

According to his parameters the drive should accelerate and deaccelerate from zero to max 1500 rpm in 0,4 s and it doesn't, and the speed curves look really strange to me.
The motor is 3,3kW.
And the manual says that if you set to short acc deacc times the drive will just handle it as best as it can, on it's own.

I actually have some truffle salami in the fridge not sure how to get it to California though.




NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[stevenal]

Red,

I agree with your technical interpretation as written, but judging the author's intent is a different matter. The remainder of the sentence provides a clue, and my guess is that the 120% interpretation is in line with that intent.

 

[Gr8blu]

"If the load torque will be higher than 20% of motor nominal torque, or if the machinery is not able to withstand the nominal torque transient during the ID run, then the driven machinery must be de-coupled from the motor during a Normal ID run."

Motor nominal torque is rated torque AT RATED VOLTAGE AND FREQUENCY. (Please note that this also translates into "at rated volt/hertz".)
The ID run is the self-tuning test case set up by the drive manufacturer. As you have noted, there may be more than one tuning profile - because the drive is applied across a broad range of applications ranging from variable to constant torque loads, with either low or high starting (break away from standstill) torque requirements.

There are at least two cases where the load torque may be higher than motor nominal torque.
1) The motor is sized for the running load - but the inertia (and/or friction) of the coupled drive train is very high. This leads to a short-term transient overload of the machine to get the drive train moving from a standstill. Once rotational motion occurs, the amount of torque "demanded" by the load/system drops off.
2) The motor is sized for one starting condition (e.g., no load) but the actual starting condition is different (e.g., partial or full load). With a higher-than-expected load on the driven equipment side, the control will demand more torque from the motor to start/maintain rotation - effectively overloading the motor for however long it takes to get within the bounds of the original expectation.

The drive manufacturer is warning the user that during the tuning process, the drive will INTENTIONALLY introduce a step function change in voltage and/or current to the motor such that the result is higher than nameplate to help it determine the magnetic saturation characteristic of the motor and the transient response of the drive train. If the motor or driven load is not capable of withstanding the (very short term) overload then the drive train should be decoupled to minimize damage to the load (by sharply twisting the driven shaft) and to the motor (by reducing the load inertia to something that accelerates easily, thereby limiting the duration of the transient condition).

As to accelerating in 0.4 seconds:
(time to accelerate) = (train inertia in lb.ft2) * (change in rpm) / (308 * applied torque in lb.ft)
This means that to accelerate JUST THE MOTOR to 1500 rpm in 0.4 seconds would require the motor inertia be less than
(wR2 inertia in lb.ft2) = (0.4) * (308 * 4.425 hp * 5252 / 1500) / (1500) = 1.27 lb.ft2 = 0.141 oz.in2

If the motor is still connected to the driven equipment, or its inertia is higher than the value given above, it won't accelerate in the time allotted unless the drive is overloading the motor.


Converting energy to motion for more than half a century

 

[stevenal]

Perhaps folks are not understanding the question? Or just too eager to share all they know regarding motors and torque? 20% of nominal is less than nominal, not more.

 

[waross]

Good catch, Steven.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RedSnake]

Maybe if I given you the whole text, it would have been easier.
This ID run is just necessary because it is driven in Vector mode.

And Gr8blu I am sorry to say but all this old inch, feet and hp's isn't really my thing I live in a meter system. ;-)

Normal
Normal ID run. Guarantees good control accuracy for all cases. The ID run takes about 90 seconds.
This mode should be selected whenever it is possible.
Notes:
• If the load torque will be higher than 20% of motor nominal torque, or if the machinery is not able to withstand the nominal torque transient during the ID run, then the driven machinery must be de-coupled from the motor during a Normal ID run.
• Check the direction of rotation of the motor before starting the ID run. During the run, the motor will rotate in the forward direction.
WARNING! The motor will run at up to approximately 50…100% of the nominal speed during the ID run. ENSURE THAT IT IS SAFE TO RUN THE MOTOR BEFORE PERFORMING THE ID RUN!
_______________________________________________
Reduced
Reduced ID run. This mode should be selected instead of the Normal or Advanced ID Run if
• mechanical losses are higher than 20% (ie. the motor cannot be de-coupled from the driven equipment), or if
• flux reduction is not allowed while the motor is running (ie. in case of a motor with an integrated brake supplied from the motor terminals).
With this ID run mode, the resultant motor control in the field weakening area or at high torques is not necessarily as accurate as motor control following a Normal ID run.
Reduced ID run is completed faster than the Normal ID Run (< 90 seconds).
Note: Check the direction of rotation of the motor before starting the ID run. During the run, the motor will rotate in the forward direction.
WARNING! The motor will run at up to approximately 50…100% of the nominal speed during the ID run.
ENSURE THAT IT IS SAFE TO RUN THE MOTOR BEFORE PERFORMING THE ID RUN!

And the ID run that has been performed is this one.

Standstill
Standstill ID run. The motor is injected with DC current. With an AC induction (asynchronous)
motor, the motor shaft is not rotated.
With a permanent magnet motor, the shaft can rotate up to half a revolution.
Note: This mode should be selected only if the Normal, Reduced or Advanced ID run is not possible due to the restrictions caused by the connected mechanics (e.g. with lift or crane applications).

NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[Marke]

The drive runs a routine called ID Run, or Auto-Tune whereby it feeds different waveforms/frequencies to the motor in order to determine what the motor characteristics are.
Often, there are two choices, a static ID Run where the motor does not turn, and a rotating ID Run where the motor tunes, but should normally be open shaft or decoupled from the load.
This paragraph implies that the load can be connected as long as the required shaft power to turn it is less than 20% of rated torque. Usually, the criteria is open shaft due to a) the torque requirement and b the inertial loading affecting the motor response or reaction time.

I would recommend that you run static if you can not decouple the load, and only run rotating of dynamic if you can run the motor open shaft.
Anything connected to the shaft will affect the results measured and will impact on the motor modeled parameters. This in turn will affect the optimum performance in open loop vector or speed estimating control.


Mark Empson
Advanced Motor Control Ltd

 

[jraef]

As per usual, Marke is spot on correct. A rotating autotune (aka “ID run” in ABB speak) is best done with as little load on the motor as possible. So you (RedSnake) were right, they were telling you not to do it with more than 20% of the motor nominal torque connected, which boils down to pretty much a coupling.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[RedSnake]

I am not intending to do the normal ID run unless they say so.
I do not feel they have all the calculations "facts" for that.
And I certainly have not.

Another thing I did suggested just to see how it would impact the acc deacc speed was to change parameter 21.01 Vector start mode, which now it is set to Const time 500ms which is default to Automatic not sure whether that can cause any damage?

Const time The drive pre-magnetizes the motor before start.
The pre-magnetizing time is defined by parameter 21.02 Magnetization time.
This mode should be selected if constant pre-magnetizing time is required (e.g. if the motor start must be synchronized with the release of a mechanical brake).
This setting also guarantees the highest possible break-away torque when the premagnetizing time is set long enough.
WARNING! The drive will start after the set magnetizing time has passed even if motor magnetization is not completed.
In applications where a full break-away torque is essential, ensure that the constant magnetizing time is long enough to allow generation of full magnetization and torque.

Automatic
Automatic start guarantees optimal motor start in most cases.
It includes the flying start function (starting into a rotating motor) and the automatic restart function.
The drive motor control program identifies the flux as well as the mechanical state of the motor and starts the motor instantly under all conditions.

NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[Marke]

Hi

A bit more information would be a great help in providing the best advice.

If the manufacturer recommends that you do an ID Run, then there could be a valid reason for this.
1. There are many variations on two themes when it comes to the waveform generation within the drive. Essentially, most are a derivative of a space vector modulation (PWM) type of waveform generator which can be run in totally open loop, or one of a variety of closed loop topologies.
The alternative is the DTC type waveform generator where the output waveform applied to the motor is dynamic and is based on the immediate and instantaneous feedback from the motor. The motor is an integral part of the waveform generation and so its characteristics must be known by the drive.
2. In the case of the standard PWM drives, the motor characteristics are not a critical part of the actual waveform generation and so a motor ID run is not essential except where you need an improved performance at low speed and/or high torque.
3. In the case of a true DTC waveform generator, the motor characteristics are an essential part of the waveform generation algorithm and so the motor ID Run is essential in order to get the unit to run properly.

In both cases, if there is a need for high torque as less than 5Hz (sometimes 10Hz) then a motor ID Run is highly recommended.
In the case of a variable torque load, (Torque increases as the speed is increased) then only the DTC drive needs to be ID Run.

A static Auto-Tune will give some estimation, particularly of the stator characteristics. A rotating Auto-Tune will give a much more accurate estimation of both the rotor and the stator characteristics.
NB : Rotor characteristics affect the speed estimation loop.

Mark Empson
Advanced Motor Control Ltd