VFD 460 vs 480

Macbeth

Member
Location
Livonia NY
Enter what is on the name plate. Lets say the name plate ratings are 50Hp, 460v, 60hz, 3ph, 65a, 1756rpm, this is what the motor is rated for and what the VFD needs to know. if you input different voltage you then need to recalculate hp, and amps for the voltage you are entering. its just way easier to enter nameplate. The VFD uses motor data for protection calculations.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Enter what is on the name plate. Lets say the name plate ratings are 50Hp, 460v, 60hz, 3ph, 65a, 1756rpm, this is what the motor is rated for and what the VFD needs to know. if you input different voltage you then need to recalculate hp, and amps for the voltage you are entering. its just way easier to enter nameplate. The VFD uses motor data for protection calculations.
Pretty much what I had assumed, although the need to recalculate manually hadn’t occurred to me.
Easier is close enough.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Are you saying the VFD does not give you an option for entering 460V? Seems odd if that's the case. Must be a foreign drive, they often don't understand how things work here.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
then program it for what the MOTOR nameplate says, should say 460V. that is what determines the V/Hz pattern the VFD puts out to the motor, you want that to match.
 

garbo

Senior Member
I usually enter the nameplate voltage of the motor, 460, into the VFD parameters. The VFD we have would accept 480. Is there a reason not to use 480 and/or is there an advantage to using 480?
At the large hospital/research/office building that I retired from the 2 separate companies that we paid for starting up all new drives always used 480 volts. That is what the over maybe 500 drives were feed from. The few hundred dollars these great service companies charged extended the free parts & labor warranty to 3 years. Always entered the motor nameplate amps into drive parameter. Salesmen that I always ordered replacement drives always wanted to know motor amps. He said drives are rated for ampere and not HP but drive labels always had a maximum HP on their label
 

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
... He said drives are rated for ampere and not HP but drive labels always had a maximum HP on their label
UL requires a HP value on the label. But he was right, you MUST look at amps, not HP. VFDs are generally sized for the HP of a 4 pole motor, knowing that the FLA of a 2 pole motor will be less, so that's fine. But where you can get in deep kimchee is if your motor is 6 poles or more.

I once had to look into a problem with some "250HP" 12 pole motors that had a motor nameplate FLA of 421A! The contractor had bought the drives based on HP, but the 250HP drives were rated for 302A max. So they would go into current limit and not allow the motors to run full speed. The contractor had no choice but to buy new 350HP drives that were rated for 430A. That was an expensive lessen for him.
 

garbo

Senior Member
UL requires a HP value on the label. But he was right, you MUST look at amps, not HP. VFDs are generally sized for the HP of a 4 pole motor, knowing that the FLA of a 2 pole motor will be less, so that's fine. But where you can get in deep kimchee is if your motor is 6 poles or more.

I once had to look into a problem with some "250HP" 12 pole motors that had a motor nameplate FLA of 421A! The contractor had bought the drives based on HP, but the 250HP drives were rated for 302A max. So they would go into current limit and not allow the motors to run full speed. The contractor had no choice but to buy new 350HP drives that were rated for 430A. That was an expensive lessen for him.
Wow a 12 pole motor. In my 50 years as a sparky a 6 pole was the most poles that I ever came across. a 12 pole motor running on 60 Hertz would run around 600 RPM. Motor with 12 poles guess cost a lot of money but for a slow speed operation might be able to get away with a small or no gearbox. While I was an apprentice back in early 70's my company purchased a 125 HP Syn. motor from an old movie theater to drive an ammonia refrigerant compressor. I told them they were wasting money on a 50 year old motor. Had to send motor out to a rewound shop then sent control panel out several times for a white elephant that could not start under load and cost over 8 grand in total repairs along with a crane rental and never ran more then a hundred hours before burning up.. That motor ran slower then the average 4 pole 1760 RPM motor but not sure how many poles it had. Right before I retired they got a pumping station that they had the 2 10 or 15 HP pump motors programed for VFDS to run 10% higher then motor nameplate speed. I complained that this mostly likely would shorten the life of the motors but they stated they do that all the time. we did PM"s on all VFD"s from once to 4 times a year but I never got a chance to see if they set motor amps higher then nameplate amps due to higher speed.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Meh, not a good plan. On a centrifugal pump, load on the motor increases at the CUBE of the speed increase. So running the pump at 10% over speed results in the motor load being 1.1 cubed, or 133% of what it was at full speed. But once you go over the design speed, the motor HP becomes flat (Constsnt HP), so if your load required 10HP at base speed, you will be overloading the motor on a continuous basis. Now if your load only required 7HP at full speed and you have a 10HP motor, that could be fine. But why would the pump mfr have a 10HP motor on a pump that needed 7HP?
 

garbo

Senior Member
Amazing how some companies try to get over. Made one company spend a day moving a control panel that had 3' of pipes & pumps directly in front of panel. Might be okay if you had a sparky with 4' long arms to teach over this.
 

paulengr

Senior Member
UL requires a HP value on the label. But he was right, you MUST look at amps, not HP. VFDs are generally sized for the HP of a 4 pole motor, knowing that the FLA of a 2 pole motor will be less, so that's fine. But where you can get in deep kimchee is if your motor is 6 poles or more.

I once had to look into a problem with some "250HP" 12 pole motors that had a motor nameplate FLA of 421A! The contractor had bought the drives based on HP, but the 250HP drives were rated for 302A max. So they would go into current limit and not allow the motors to run full speed. The contractor had no choice but to buy new 350HP drives that were rated for 430A. That was an expensive lessen for him.

A 12 pole, 250 HP motor will have a very high no load current. At full load it’s still going to be around 90%+ efficiency so FLA isn’t going to be dramatically different from a 4 pole motor. BUT that motor physically will be HUGE. The torque will be 300% higher than a 250 HP, 4 pole motor. The frame size and rotor are going to be similar to a 4 pole, 800 HP motor. With all that steel needless to say expect no load current equal to 50-75% of FLA. Below about 80% of FLA the power factor will quickly drop to 0.5 and drop quickly to under 0.1.

BUT once you are at 90%+ of load this motor will be no different than any other 250 HP motor. It will still draw 207 kw and FLA at 0.85 power factor (worst case) is still 306 A. This is outside NEMA so doubting your 421 A number. That’s just not anything close to high pole motors I’ve ever seen. Power factor is bad but that’s DC drive bad. The only reason you may need a huge drive is to achieve heavy duty starting so at 150% that would be indeed a 458 A drive but you don’t maintain that continuously. Usually drive manufacturers specify 135% continuous or 150% for 30 seconds which is a 413 A drive. Granted there may not be a size available in the range from 413 to 458 A. So the drive size doesn’t sound unreasonable.
 

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Here's a 24 pole 300HP pump I worked on a few years decades ago, it's lifting water out of the Sacramento River into an irrigation ditch.

300HP, 407A 250RPM, so fairly high slip too.
IMG_0348.jpg

Here she is in all of her glory...
IMG_0347.JPG
The device on the right with the fan in front of it was the "one Armed Bandit" starter for it, called a "Manual Compensator" which, if you have never seen one, is like an Autotransformer starter, except without contactors. It has a 3 position manually operated switch with a big handle on the side, kind of like a slot machine. You push the handle forward to Start through the transformer, then after the motor winds up and 'sounds about right", you pull the handle back through the Off position and into Run, which puts it Across the Line.

The two red things on the front are the "Dash Pot" overload relays. The ammeter on the front was DIRECT READING, no CTs!

This is the pump station, there were 4 of these inside, but only 3 still in service. We were replacing the Manual Compensators with solid state soft starters. One of my all time favorite projects, it was like working in a museum of our industry. The gear was built in 1908.
IMG_0343.JPG
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Now that's a motor. Must have had some good maintenance over the years to still be going. And I notice it was mfg in my back yard.
 
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