Recommended VFD rating for 415 V, 16 HP, 25 Amps hoist duty motor 5

[edison123]

Our present 10 ton hoist motor is two speed two winding rated for 415V, 12/4 HP, 1440/465 RPM with electrically operated spring brake as shown below.

To reduce the high inrush current of about 80 Amps, I plan to rewind the motor for single speed 16 HP/25 Amp/1440 RPM and use a VFD.

The VFD will have two speed settings for 1500/600 RPM with pendant and as well radio controls. The exiting electrically operated brake will be retained.

The duty cycle max is 15 minutes ON (up and down continuous as well as inching) and 45 minutes OFF in an hour and the rewound motor will have ample thermal reserve.

What is the recommended VFD capacity for the hoist? 25 Amps or more?

Would a standard off the shelf VFD do or do I need one rated for hoist duty?

Muthu

http://www.edison.co.in

 

[jraef]

A VFD rated for 25A minimum and rated as “Heavy Duty” or “Constant Torque” (same thing) is fine. It appears to be a right angle gearbox, which should be self locking to a certain extent, so Sensorless Vector Control might be fine, but I would look for one with Flux Vector Control and capable of “torque proving” to coordinate with the brake release.

Make sure the brake is separately powered.


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

 

[edison123]

Thanks, Jeff.

I will go for 30 Amp VFD. Since there are only two preset speeds, is flux vector control necessary?

Yes, brake is separately powered.

Muthu

http://www.edison.co.in

 

[edison123]

The electromagnetic spring loaded disc brake is attached to the hoist motor NDE as shown below. The 3 ph AC brake coil is energized when the Up/Down contactor is ON and the brake gets disengaged and then gets reengaged via springs with the Up/Down contactor is OFF.

Muthu

http://www.edison.co.in

 

[FacEngrPE]

You must have a mechanical load brake as part of the hoist if you are using a "normal" VFD. This is true even if there is a right angle worm gear drive as part of the lineup. Jeff's recommendations work for this case. I would still use vector control, but with 2 fixed speeds encoder feedback should be unnecessary. The special thing about the load break is that the motor can never see any regeneration energy requirement beyond what is needed to decelerate the rotor.

If your hoist does not contain a load brake the VFD must be designed for hoist duty, and specifically rated for 4 quadrant operation.

The braking resister on a 4 quadrant drive needs to be sized to handle the regeneration energy of lowering a test weight (125%) the full distance from the upper limit to the floor in one motion. The duty cycle can consider the time needed to hoist back to the upper limit.
The VFD should be able to accelerate a test weight upwards, so drive current rating needs to be high enough that the drive thermal limit is not exceeded by the the upward motion to the upper limit with a test weight.
The motor thermal should be OK unless you see a need to spend enough time at low speed where the shaft fan will be ineffective.

On VFD operation the electrical brake is operated by the VFD.
[ul]
[li]When approaching stop, the brake will set when the shaft speed approaches zero.[/li]
[li]When starting motion the VFD will build to some minimum torque (adjustable) before releasing the brake. Once the brake releases the VFD needs to match load torque to VFD output. Torque matching is faster when using a shaft position encoder for feedback.[/li]
[/ul]

You might think the above is overly conservative. I have seen some abusive crane operations.

 

[edison123]

FacEngrPE

There is no counterweight on this hoist and the lift is only 12 meters. Since it already has a shaft mounted mechanical brake, is VFD with braking resistor needed? Since the operation is not continuous, 4 quadrant drive may be too much?

I am planning to go for attached Fuji drive 20 HP/31 A (page 2).

Any idea what HND/VT/LD and HHD/CT/HD mean?



Muthu
www.edison.co.in

 

[edison123]

https://www.manualslib.com/manual/1197732/Fuji-Electric-Frenic-Ace-Series.html?page=597

10.4 Selecting an Inverter Drive Mode (ND/HD/HND/HHD)

10.4.1 Precaution in making the selection
The FRENIC-Ace is available in four different drive modes--ND and HD modes for general load and HND and HHD
modes for heavy duty load, which allows users to switch the drive modes on site.

Select the inverter capacity appropriate to the user application, considering the motor capacity, overload
characteristics, and ND/HD/HND/HHD mode, referring to "10.4.2 Guideline for selecting inverter drive mode and
capacity."

ND mode for general load
Apply to equipment where the inverter's load current in normal operations is less than the inverter rated current and
the load current in overcurrent operation is less than 120% of the rated current for 1 minute. (fan, pump, etc.)

HD mode for heavy duty load
Apply to equipment where the inverter's load current in normal operations is less than the inverter rated current and
the load current in overcurrent operation is less than 150% of the rated current for 1 minute. (wire drawing machine, etc.)

HND mode general load
Apply to equipment where the inverter's load current in normal operations is less than the inverter rated current and the load current in overcurrent operation is less than 120% of the rated current for 1 minute. This mode is for applications which require running the motor under low noise conditions or running the inverter with high responsibility. (fan, pump, centrifugal machine, etc.)

HHD mode for heavy duty load
Apply to equipment where the inverter's load current in normal operations is less than the inverter rated current and the load current in overcurrent operation is less than 150% of the rated current for 1 minute and 200% for 0.5 second. This mode is for applications which require running the motor under low noise conditions or running the inverter with high responsibility. (compact hoist, winding machine, etc.)

Muthu

http://www.edison.co.in

 

[FacEngrPE]

The counterweight in the picture is not usually a feature of a hoist. Here is another picture of the concept

Steady state operation of a hoist is in quadrant 1 and 4. Operation in 2 and 3 occurs when accelerating the load.
Lowering a load when a load brake is present, the torque is absorbed by the load brake, and the hoist motor never sees any regeneration energy from the load (quadrant 3 operation). On stopping, dumping the energy of the spinning motor can be handled the same with the new VFD as it is currently, by setting the motor brake whenever power is removed from the motor.

For a hoist with a load brake, where only a small number of speeds will be available for selection. I would use a hoist rated drive programmed for constant torque operation. Encoder feedback is not necessary, and neither is torque proving (the load break takes care of the issues torque proving solves). Most hoist rated drives have connections for the motor shaft brake. A breaking resistor may still be needed, it's VFD design specific, but if needed will be small, as only the rotational energy of the rotor and the components on the motor side of the load brake can end up in the resistor. The resistor is to prevent any possibility of a drive trip on DC Bus overvoltage.

Fuji Electric Inverter FRENIC-Ace series you call out in the post above appears to have the features I consider important for this application. I would use the HDD setting, this appears to be the one used for constant torque applications.

 

[edison123]

Thanks FacEngrPE.

Drive supplier also advised DBR for the hoist loads and will go for it.

Another question

We will be running 4x160 A copper DSL busbars with current collectors for the long travel of 200 feet.

The crane supplier says it is standard to mount the drive on the crane bridge and feed the drive from the 415 V DSL busbars via current collectors and feed the motor via cables (for cross travel, which is manual). So, the VFD will be in the moving bridge. This means, we need to climb up to the crane bridge for any drive servicing.

What if we fix the drive on the ground level and run cables from the drive output to the DSL busbars? This of course means, the bus bar voltage will be variable and thus I need to run a separate 415 V supply for the electromagnetic brake for the entire long travel, which is not a big issue.





Muthu

http://www.edison.co.in

 

[jraef]

What if we fix the drive on the ground level and run cables from the drive output to the DSL busbars? This of course means, the bus bar voltage will be variable and thus I need to run a separate 415 V supply for the electromagnetic brake for the entire long travel, which is not a big issue.

NO! Don’t do that, ever. The high frequency pulsed DC output of the VFD will rapidly damage the collectors and make the output unreliable. Yes, bridge and crane drives require being on the bridge to service them, that’s just part of the deal.

“Torque proving” that I mentioned earlier means that the drive will put out an output to the motor with enough torque to hold it in place, BEFORE giving the signal to release the brake, so that the load doesn’t move when the brake was released. It’s an added safety feature. Right angle worm drive gearboxes often don’t need this because the load generally will not allow the worm gear to transfer rotational energy backward into the motor shaft. If that is the case now, it will remain the same and you might not need torque proving.


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

 

[edison123]

Thanks, Jeff. Will follow the tradition for drive location.

Another question about DBR. This won't work when the incoming power to the drive is cut off, right? So, a mechanical brake is still needed?


Muthu

http://www.edison.co.in

 

[jraef]

Yes, absolutely! No power = no Dynamic Braking.

That's also why you ENERGIZE an electro-mechanical brake to RELEASE IT, because if power fails, it the brake SETS so that the load doesn't fall and kill someone.


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

 

[edison123]

Jeff - So, what would justify the additional cost, footprint and maintenance hassle of having a DBR?

Muthu

http://www.edison.co.in

 

[FacEngrPE]

DBRs are sized (speaks to footprint) for the dutycycle and energy needing to be dissipated. In your case this is very dependent on the presence or absence of a mechanical load break. The DBR for the hoist in the photo will be rather small. Your drive manual will have the correct sizing information for your drive.

I have seen the arrangement you ask about - all controls on the ground - only on DC MILL cranes in locations where the shop overhead was unsafe to work in unless the shop was completely idled. DC Resistor drive systems are very tolerant of all sorts of electrical noise, but are much more expensive to purchase and operate that modern equipment.

To add to Jeff's statement, the longer the current path the more likely you are to create resonance in the drive - motor feeder. When resonance occurs the motor terminals can see several times the DC bus voltage. Sliding power collector shoes are electrically noisy, and using a cable festoon the length of the runway adds more cable length.

I completely agree the drive belongs on the crane bridge, best place is likely where your existing panel is.

 

[edison123]

Thank you, FacEngrPE.

My vendor said DBR (Aluminum resistors) footprint is very small, and it will be mounted on the top of the drive panel for better cooling.

He will be submitting offer for both 15 and 20 HP Fuji drives with DBR. If not much price difference, I will go with 20 HP Fuji drive.

I once again thank you and Jeff for your advice and tips.

Muthu

http://www.edison.co.in

 

[jraef]

So, what would justify the additional cost, footprint and maintenance hassle of having a DBR?

Saves wear and tear on the EM brake pads, shoes etc. Basically, the EM brake becomes a HOLDING brake and emergency brake, the hard day-to-day work is done electrically.


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

 

[LionelHutz]

In case it wasn't clear, part of the VFD software/setup should be that it controls the mechanical brake contactor. That way, it can match what it's doing to having the brake on or not.

 

[edison123]

Got it, Jeff.

Thanks, Lionel.

Since the hoist has to stop almost immediately, what is the ramp down braking time before the EM brake is activated by VFD? Is it settable in the drive?


Muthu

http://www.edison.co.in

 

[FacEngrPE]

Depends on the drive.
My experience is with much larger hoists on bridge cranes. These hoists always use quadrature encoder feedback to the VFD for speed and shaft position.
In that application the VFD ramps the hoist speed to zero, and sets the brake when the speed reaches zero before torque is turned off. Ramp rate does not impact the brake setting point as the brakes set while the motor is still holding the load.

Tuning torque proving is where the choices are. Torque is developed at zero speed before the brakes release, but the VFD does not know how much torque is needed, you need to chose that as a setting (sometimes it is a default, not adjustable). Depending on the balance between motor torque and load torque the motor will rotate when the brake releases until the VFD adjusts the torque to match the torque demand. Typically less than 1/4 turn of the motor shaft.

On a small hoist such as the one being discussed in this thread, I expect you will need to adjust torque proving settings to get the best results.

The best ramp rates between speeds (and stop) to use are a balance between fast enough to ensure safe load handling, and not so fast that the rigging is overloaded by excessive acceleration. Get your rigger involved in the tuning process.