VSDS
VSDS
(OP)
Hi guys I’m new to this forum and fairly new to the electrical industry. My understanding of VSDS are very limited other than the basic principles of the AC being converted to DC then transferred back to an artificial AC (sorry for my crude explanation)
Now to the question what happens if the parameters of the motor are incorrectly entered into the VSD so say it’s a 50HZ 415 delta connected motor but we enter the drive as 60Hz 415?
Thank you for your help guys
Now to the question what happens if the parameters of the motor are incorrectly entered into the VSD so say it’s a 50HZ 415 delta connected motor but we enter the drive as 60Hz 415?
Thank you for your help guys
RE: VSDS
In your example you will be throwing away about 20% of the motor HP.
If you go the other way if the motor is 60Hz, 415V and you enter 50 Hz, 415V you will exceed the Volts per Hertz ratio of the motor and be in danger of saturation.
In your example motor, 50 Hz, 415 V the Volts per Hertz ratio is 415V/50Hz = 8.3 V/Hz.
As the VFD is dropping the frequency, it is also dropping the effective voltage in the same ratio.
If the V/Hz ratio is too high there is a danger of saturation and rapid motor burnout.
If the V/Hz ratio is too low there is no danger but you are throwing away motor HP capacity.
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
RE: VSDS
Think of the parameters as the instructions the control block uses to instruct the power section what is to be sent to the motor.
It is better to Take Time to get the parameters correct.
Fred
RE: VSDS
The motor (and the connected load) will run at 20% higher speed.
Muthu
www.edison.co.in
RE: VSDS
But I’m my example the motor is 50Hz 415 but been set to 60Hz will this not mean the motor will run faster but not have the correct voltage applied to the windings to increase the motor torque?
I may be confusing myself
RE: VSDS
Muthu
www.edison.co.in
RE: VSDS
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
RE: VSDS
RE: VSDS
It would seem that someone who would be so stupid and careless as to get the motor frequency wrong would also likely fail to set the drive's overload parameter correctly. Most drives are able to drive larger motors than they're applied to a so the extremely important overload function would not even come close to protecting the motor. That could easily result in a motor melt-down. If it's an unattended motor it could burn the whole place down.
Keith Cress
kcress - http://www.flaminsystems.com
RE: VSDS
The speed that the motor runs at is still determined by the frequency output of the VFD. If you tell it to run at 50Hz, it runs at 50Hz. It's just that at 50Hz, it will be getting less torque and may run at higher slip, pull more current to do the same work, which will increase the thermal stress on the motor.
Alternately if the motor is capable of >17% more torque than the load needs anyway, you may never notice the difference.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: VSDS
RE: VSDS
Keith Cress
kcress - http://www.flaminsystems.com
RE: VSDS
The speed/torque curve of a centrifugal motor is a square function, (HP is a cube function).
Just a little bit over rated speed for a loaded centrifugal pump may result in motor burnout.
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
RE: VSDS
RE: VSDS
If you're running a centrifugal pump as the speed increases the hp demand climbs very rapidly yet the motor's torque would be dropping. This would quickly lead to overload or stalling.
Keith Cress
kcress - http://www.flaminsystems.com
RE: VSDS
RE: VSDS
The real current is mainly dependent on the torque demanded by the load.
As the frequency rises, so also does the inductive reactance and as a result the magnetizing current drops.
With less magnetizing current the available torque drops.
Below rated frequency and voltage, the frequency and the voltage rise roughly in proportion.
This allows or causes full magnetizing current and full torque as the Volts per Hertz ratio is maintained.
Assuming that the supply voltage is appropriate for the motor, the motor reaches full HP at rated frequency and rated voltage.
As the frequency rises further, the voltage is unable to increase above the supply voltage and the magnetizing current and torque drop off.
Below rated frequency: Full torque and variable speed, Constant Torque motor characteristics.
At rated frequency: Maximum HP and Full Torque.
Above rated frequency: Speed increases as torque drops, HP = speed x torque so the motor characteristic is Constant Horse Power.
Note:
There are second order effects causing some interaction between real and reactive current, hence the use of the words "mostly", "roughly" and "mainly".
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
RE: VSDS
Yes.
Muthu
www.edison.co.in