Can VSDs used for Slurry pumping duty

[arsmith]

Hi guys
Iwould like to know whether Variable speed drives can be used in motors that drive Slurry pumps. Also I would like to know the following details.
1. Can VSD controlled motors develop sufficient torque to clear chocked delivery lines.
2. Is it advisable to install a VSD for above said duty. Please comment from both operational and econimical point of view
3. Can a VSD automatically increase the RPM of motor based on the torque load devloped by the pump. If not is there any other equipment available in market
Eqpn Details:
VSD we are having : SIEMENS Midimaster 37 KW
Motor : SIEMENS 50 HP 3P 50HZ
Pump : 4/3 WARMAN Slurry pump
Duty : Sand Slurry (Load varries from 35 tph to 50 tph (Dry Solids)
Present Loading : 40 Amps at 2100 pump RPM (50 tph solids)

Iam just new to your forum and so please dont mind if the same question was already asked by some one else.

 

[gsimson]

Motor controlled by VSD can develop 100% of full load torque at all speeds below the rated speed unlike the pullout torque occuring at only at one speed by a Sq. Cage motor with DOL/Soft starter.
On operational point of view Motor with VSD can be used in any applicaion. If the torque required for clearing the choke is more than the rated torque then an inverter duty motor & flux vector drive can be used. This system can deliver app. 420% of the rated torque even though the motor is designed only for about 2oo% POT
Economy is generally based on the 'Energy saving' potential.

 

[dpc]

The VFD will work if it's big enough. Make sure the drive is current-rated for "constant torque" type applications, even though this isn't really a constant-torque load.

When suppliers see the word "pump" they are going to think of a typical centrifugal pump and may supply a variable-torque type drive that will overload when your slurry gets thick. Ignore any drive "horsepower" rating and focus on the continuous output current capapbility.

I have seen this problem with raw sewage pumps that trip drives on overload when "ragging" occurs.

Warman pump engineers should be able to offer some assistance in drive selection.

 

[ozmosis]

The VSD you mention is rated for Variable Torque and Constant Torque depending on the settings you make. As dpc says, a constant torque setting would be advisable in this instance to ensure you can achieve the higher overload (VT setting only provides 110% overload for 1 min whereas the CT setting will provide approx 150% for 1 min). Check the nameplate as there will be a VT and CT rating, if it is 37kW CT then you should be ok but if it is VT @ 37kW then effectively this is only 30kW CT but again, as dpc points out, check the current rating not the kw's.
An interesting function in the latest Siemens VSD's(4th Generation ones) is a feature that allows the drive to go, momentarily, in reverse if the load is blocked and then after a few seconds run forward again to try and release the blockage. The drive monitors torque and uses a bit within the drive to activate a reverse run, this in turn activates a timer for a second or two(adjustable) then the bit changes state to tell the drive to run forward again. Quite a useful feature but you need to first check with the pump manufacturer to make sure the pump is ok going in reverse. You don't want to unscrew the impeller!

 

[BJC]

arsmith

In my limited experience ( with variable spped and pumps and ash ) the veolcity of the slurry was a critical factor. Even though the amount of ash in the slurry went down periodically the velocity of the water had to remain high. If the flow rate went low enough everything "fell out" and the pipe clogged.

 

[arsmith]

BJC
Its true that if rpm runs down the line will get clogged. But I think the VSD frequencies minimum level can be set so that the velocity imparted by the pump will be above the limit settling velocity.

Still iam bit confused by the overload factor discussed above. Does the overload mentioned by sed2devloper means current overload or torque overload. Iam asking this because my thinking is that VSD's motor torque rises gradually.so even if the motor cannot induce more torque it can still show more current

 

[jbartos]

Suggestion to arsmith (Mining) Feb 15, 2004 marked ///\\Hi guys
Iwould like to know whether Variable speed drives can be used in motors that drive Slurry pumps.
///Yes, appropriate ones for a type of slurry pumps.
Also I would like to know the following details.
1. Can VSD controlled motors develop sufficient torque to clear chocked delivery lines.
///Yes.\\2. Is it advisable to install a VSD for above said duty. Please comment from both operational and econimical point of view
///Generally, VFDs are better to motor and motor load than other starts. However, the cost to procure, maintain and operate them may or may not be affordable at a specific point of the time. Also, ofte VFD incorporation requires a review of overall power supply quality for potential higher harmonic content, spikes, etc.\\3. Can a VSD automatically increase the RPM of motor based on the torque load devloped by the pump.
///Yes.\\ If not is there any other equipment available in market
Eqpn Details:
VSD we are having : SIEMENS Midimaster 37 KW
Motor : SIEMENS 50 HP 3P 50HZ
Pump : 4/3 WARMAN Slurry pump
Duty : Sand Slurry (Load varries from 35 tph to 50 tph (Dry Solids)
Present Loading : 40 Amps at 2100 pump RPM (50 tph solids)

 

[ozmosis]

For info to arsmith: the Siemens Midimaster (if rated as Constant Torque 37kW drive) is designed for an output of 72A continuous with 150% for 1 min (you also have 200% for 3 secs too). If the same drive is configured for Variable Torque(by setting a parameter to configure it to operate on a quadratic volts/frequency curve)then effectively this drive will be 'rated' as a 45kW drive (suitable for centrifugal fans/pumps) with an output current of 84Amps continuous but the overload is restricted to 110% for 1 min. A torque limit can be utilised but only when this particular drive is setup for, what is known as, vector control mode. Then motor torque produced is then a function of motor current.