There are a multitude of reasons why VVVF drives are superior to mechanical drives (Fluid, solid, Rube-Goldberg, etc.):

1. Program control curve - long overland conveyors require a non-linear starting ramp that is tailored to conveyor and its terrain. Initial strain variations. that are not in agreement with steady-state, must be removed otherwise elastic shock waves will become exaggerated and impose potentially damaging belt line forces.

2. Belt inspection device - allows low creep speed to visually inspect belt

3. Extract belt from plugged chutes with minimum damage

4. Multiplexing of accel/decel control from one drive to many drives (ie each inverter can be shared to many drives if the sole purpose of the startup is to bring conveyor to a fixed speed)

5. Belt can be programmed to various steady-state operating speeds depending on product demand, thereby saving electricity and wear on rotating components

6. Saves electrical slip electricity loss over most other systems

7. Minimizes belt line forces and thereby belt and structural specifications and allows a predictable force distribution

These are some of the positive attributes

The four significant drawbacks are: 1. price, 2. loss of performance with age, 3. loss of reliability with age, and 4. complexity

I am sure others will comment on other features. ■

Pretty good summary by Mr Nordell.

And price is not an issue anymore.

The saving on the belt spec (starting torque close to nominal) will pay for the VFD on long conveyors.

Best Regards

JP ■

Acceleration control is necessary to relate shock waves during starting and stopping. We find the need to increase the belt strength due to high starting torque a very infrequent event.

There are a number of soft-start controls that achieve good starting behavior without increasing the belt rating. Some are:

1.Wound Rotor Motors with optimized resistor step selection

2. Fluid Couplings - fixed fill, delayed fill, and scoop or drain fill

3. Variable Voltage - AB, ...

4. Air and Fluid Clutches - Rockwell Automation (CST), ...

5. Hydraulic Motors - Hagglund, ....

Each have their place in the design of all types of conveyors. The gift is to know -- what, when, where, and how.

VFD drives save power and provide special controls that others find difficlut to achieve.

VFD are the only drive that can be used on many conveyors/motors by one control device. See my 1977 paper on "Multiplexiing" Inverter Drives at La Caridad, Mexico. At La Caridad, we used 4 x 600 hp VFD's to soft-start over 20 motors connected to steel cord uphill (2400 hp) and downhill (-1800 hp) conveyors, as well as many fabric belts ( 1200 hp, 750 hp, 600 hp, 150 hp, and 50 hp). This is the real potential of the inverter in large plants where belt speed is constant.

When VFD are connected to long overlands, their big advantage is in regulating belt speed to product demand such as at the Curragh mine in Australia. Here the 20 km overland has variable speed ranges that are set by receiving plant coal demand. The conveyor has a speed range of 4.5 m/s to 7.5 m/s in specific stages to meet the many design needs. Very big power savings, and belt damage risks mitigation associated with wear and punture protection. ■

There is one school of thought that says you can have a VFD combined with a fluid coupling.

They tried this on an extendable tailings conveyor at Namakwa Sands here in South Africa, and I will find out what happened.

(It was also the topic of one discussion duringBeltcon 13)

Frankly I really can't see the point though.

Cheers

LSL Tekpro ■

Really, due to the characteristics of a traction fluid coupling I would not have thought it worthwhile? ■

Dear Designer..

Exactly so.. That's why I said "Frankly though I can't see the point"

But they did it, and for the life of me I can't see why.

Cheers

LSL Tekpro ■

you can use Baldor CST drive for long conveyor.

br

Pbose

Originally Posted by dhartipatel

sir

in long distance conveying system "IS VVVf drive better than mechanical drive"?

if yes how it is ?

what r the technical resons behind it?

and one another request is how flexible coupling is used in VVVF drine system instade of fluid coupling?

and instade of VVVF drive how we can use AC slip ring motor ?

what r the technical parameters behind it

■