exercise: test electric motor

[gadec]

Hello, everyone!
I am studying mechanical measures and are taking the following exercise:

"define the specifications for a measuring chain to be used for testing an electric motor from 11 kw to 3000 rpm"

now I make the various conversions in the s.i and I find the couple in nm..
but I don't understand one thing the electric motor acts as a brake? ?
should I define the characteristics curves according to the load regulation? ?
If there is someone who knows about electric motors and has studied mechanical measurements maybe could help me set it up properly...
thanks anyway for any answers!

france

 

[zeigs]

Usually you put the motor on a test bench, connect it to a brake and feed it. at that point you do the various tests to vacuum, to rotor blocked and to various load regimes to verify the characteristics of performance and torque delivered. this as a basis. then obviously the measures to do and the test conditions depend on what type of electric motor it is. In this case it is not specified, so I would say that the professor is more interested in the way you do the measurements.
In my opinion I would put a tree-side torquemeter, an electric side wattmeter and a counter.
for the choice of the wattmeter (and any amperometric calipers) but you have to know if it is an ac or dc motor (9 out of 10 is ac seen the kw, but it is not said)
consider that the blocked rotor test causes currents 7-9 times the nominal ones and a couple 2-3 times (for an asynchronous, this always for the choice of tools)

 

[Fulvio Romano]

attention...you are doing an exercise for an exam, not a design. Leave the real world alone, let alone what you do normally.

when in a university exercise it is said to "define the specifications" or "design", the specific meaning of the term is never understood.

For example, when testing automatic controls "designing a controller" simply means calculating the transfer function, and not "designing" the hardware architecture.

In your case, it depends on the exam and the professor. So, look for a similar exercise already done by some of your colleagues or maybe just the professor's dispenses, and see him what he means with "definite the specifications".

probably just wants you to find the numerical value of a small set of parameters that are studied at the course.

if you ask here on the forum and follow the tips, risk making an effort a hundred times larger, do a perfect job, and do not pass the exam because it was not what you were asked.

I've seen so many finishing up like this...instead of following the lessons, studying from wikipedia, and then at the exam talking about something else.

 

[gadec]

thanks for the answers.

Meanwhile I wanted to clarify that "like" examples on the book are not there otherwise I would not have asked for your help.
I followed the lessons with dispenses followed but the lucids were "equal" to what is written on the book and the topic of electric motors are 2 pages and 3 graphs, it is not here of electrotechnics, so to make an example.

This is an exercise and not a design you are fulvio reason perhaps the prof intends to make load adjustments and determine the characteristic curves.
in lesson obviously exercises are not carried out because they are part of the "written " before the oral.

 

[PaoloColombani]

now I make the various conversions in the s.i and I find the couple in nm..
but I don't understand one thing the electric motor acts as a brake? ?

Of course, an electric motor can generate work (the windings are crossed by the power current) but can also absorb it (the windings are crossed by the induced current).
negative work is absorbed and dissipated by joule effect on electrical resistance as mechanical brakes dissipate on mechanical resistance ( friction).

 

[Fulvio Romano]

Meanwhile I wanted to clarify that "like" examples on the book are not there otherwise I would not have asked for your help.

Can't go to the professor's reception and try to figure out what he wants?

 

[gadec]

Can't go to the professor's reception and try to figure out what he wants?

Yes, of course, but before Wednesday, he can't receive so if you have any other ideas/suggestions are welcome.

meanwhile I'm thinking about the electric brake to parassite currents and the one to dust to see if it could go well

 

[Fulvio Romano]

electric brake to parasite currents? I mean?
is it not only used to brake...liquids?

 

[MBT]

electric brake to parasite currents? I mean?
is it not only used to brake...liquids?

No...
On the contrary!
at the time of the start one of the engines of the test room was precisely braked by a brake to parasite currents! :finger:
(Good times...)

 

[zeigs]

There are different types, including parasite currents, pliers, belt or viscous liquids. It's the powder I've never heard.
from that I remember the parasite current is one of the best as adjustment and constancy of torque. in other pennies is that a disc that rotates in front of a pair of electromagnets, the braking effect is given by the currents that induce in the disk (and that heat it)

 

[gadec]

There are different types, including parasite currents, pliers, belt or viscous liquids. It's the powder I've never heard.

powder brake has a stator and rotor similar to those of the current brake parasite the only difference lies in the traferro where there are magnetic powders that accumulate and increase more the braking torque for friction

 

[Tequila]

...in other pennies is only a disc that rotates in front of a pair of electromagnets, the braking effect is given by the currents that induce in the disk (and that heat it)

would it be a classic as.triphase autofrenating motor, or is it another thing this brake to parassite currents?

 

[PaoloColombani]

would it be a classic as.triphase autofrenating motor, or is it another thing this brake to parassite currents?

once it was called a pharaoh's record; Basically it's what you just described zeigs.

 

[zeigs]

from what I saw the autofrenants have a sort of mechanical brake that blocks them when the power is missing.
No, it's another thing. It consists of a disk that is cast on the motor shaft in test, usually it is aluminum for low electrical resistance, and an electromagnet (a u with a coil) that vents it frontally and is fixed. switching current (continuous) into the coil creates a magnetic field that concatenates with the disc.
nothing happens, but if the disk is rotated, parasite currents are created in the disc that cause the braking effect (the same effect that rotates the rotor of an asynchronous motor), much more marked as high is the current in the coil (from which the regulation)
Of course he can't lock the rotor, but he doesn't even wear it.