[boydage]

LS Lg5 2.2kw VFD, 3 phase, 0-400hz to run a 1.5kw Squirrel Cage, 3 phase 50hz, 1400RPM, motor. Is to be installed onto a small lathe to upgrade the torque.

Ive setup a few high RPM spindles, the last one a 6kw 1000hz 24000RPM ATC. I cant say I have setup a 50hz motor before. This one is 1400RPM. I was just going to set the VFD to 50hz but have read I can double that or even a little bit more yet still achieve a good strong speed controlled motor.

Am I wrong? Reading into it, if I increase the frequency to say 100hz and feed it into my motor it will run at 2800RPM, still be able to cool, have torque, and be no way too fast for the bearings. Please tell me if I am wrong on this? I would expect to be able to drop the speed with the VFD to lower the rpm below 1400 by a tad until I cant cool but going faster is possible huh?.

Have I got this wrong? Keen to hear from someone familia with this kind of setup please. Thanks

[Eldon_Joh]

LS Lg5 2.2kw VFD, 3 phase, 0-400hz to run a 1.5kw Squirrel Cage, 3 phase 50hz, 1400RPM, motor. Is to be installed onto a small lathe to upgrade the torque.

Ive setup a few high RPM spindles, the last one a 6kw 1000hz 24000RPM ATC. I cant say I have setup a 50hz motor before. This one is 1400RPM. I was just going to set the VFD to 50hz but have read I can double that or even a little bit more yet still achieve a good strong speed controlled motor.

Am I wrong? Reading into it, if I increase the frequency to say 100hz and feed it into my motor it will run at 2800RPM, still be able to cool, have torque, and be no way too fast for the bearings. Please tell me if I am wrong on this? I would expect to be able to drop the speed with the VFD to lower the rpm below 1400 by a tad until I cant cool but going faster is possible huh?.

Have I got this wrong? Keen to hear from someone familia with this kind of setup please. Thanks

Most motors have a breakdown torque at least twice rated hp at nominal rpm. And they run about 20 percent saturated.

As such, if you drive a 240vac motor at twice its nominal frequency, but at the same 240vac you can get approximately

One forth breakdown torque, which is half of the nameplate torque.. so, the same nominal hp. This is because the torque you can get for a given slip is related to the volts per hz squared.

However, you get on the order of 10% increase because the motor is no longer saturated.

In addition, you can rig up some boost transformers to give your vfd 260 to 270vac and you can get another 10%.+if you program the vfd to deliver 240vac 50hz and 270vac 70hz and above.

You can also easily rewire your motor for 138 double delta instead of 240v (unless you have a 240/415v european motor) and buy a bigger vfd.

I gave a friend of mine a 2hp 3600rpm motor re wired for 138v delta and its driven by a 2hp 240v drive. Works just fine, and will easily deliver 2 hp at 5500 rpm.

[boydage]

Most motors have a breakdown torque at least twice rated hp at nominal rpm. And they run about 20 percent saturated.

As such, if you drive a 240vac motor at twice its nominal frequency, but at the same 240vac you can get approximately

One forth breakdown torque, which is half of the nameplate torque.. so, the same nominal hp. This is because the torque you can get for a given slip is related to the volts per hz squared.

However, you get on the order of 10% increase because the motor is no longer saturated.

In addition, you can rig up some boost transformers to give your vfd 260 to 270vac and you can get another 10%.+if you program the vfd to deliver 240vac 50hz and 270vac 70hz and above.

You can also easily rewire your motor for 138 double delta instead of 240v (unless you have a 240/415v european motor) and buy a bigger vfd.

I gave a friend of mine a 2hp 3600rpm motor re wired for 138v delta and its driven by a 2hp 240v drive. Works just fine, and will easily deliver 2 hp at 5500 rpm.

Thanks. I was able to follow most of that - a double delta connection, am I correct that would be a 12 lead motor? I have not heard of that before. This one is a 3 lead New Zealand manufactured 415v model. I installed it yesterday. Unfortunately my second hand VFD didt come with a keypad so I am waiting for a new keypad to arrive so I can adjust parameters. I did try to connect via the RS485 but gave up.

[joeavaerage]

Hi,
what you have is a two-pole-pair motor, called in other places around the world four-pole. If it were one-pole-pair (two pole) then its synchronous speed
would be 3000 rpm or close to it. In most cases the manufacturer uses the same armature for the two different motors. I will be highly likely your motor
will survive at 3000 rpm, maybe even a little more. Too much and the armature could explode under centrifugal force, so don't go overboard. Also the bearings will wear much harder at
elevated speeds.

Craig

[joeavaerage]

Hi,
should add that in countries with 60Hz AC synchronous speed for a one -pole-pair (two pole) motor is 3600rpm. Its highly likely that the armature in your motor
was designed such that it could be used in a number of different motors, in which case it will tolerate 3600rpm.

Craig