Somewhat depends on how you chose to use the motor and how accurate you calculate the motor demand power.

1. No dynamic braking: set reserve motor size that surges will not exceed. Usually, the nameplate should be about >20 % over demand or say 75 kW. However, how was the -60 kW derived. Could be the treatment was flawed. Fabric belt (kW) guesses are usually low and consume more power (ie less regenerative) than say CEMA unless the 2/3 kY rule is used zero idler seal drag. Steel cord belt can be more regenerative (ie. lower rolling resistance) due to the power influenced by the bottom/pulley cover thickness. What happens when the belt wears? This will increase the regen. demand.

2. With dynamic braking - may use more torque with demand regenerative capacity beyond steady-state operation such as with an inverter. Here you can pull back the frequency and if the VFD is designed for 4 quadrant operation the dynamic stopping action will pump the excess energy back to the grid or regen resistor bank. Here the motor size depends on how fast you want to stop. The motor selection depending on the design of the motor torque signature curve and number of loaded stops. A good bet is still in the range of 15-20% over full regenerative demand. This could be higher with faster stopping time.

I am sure others will offer sage advice beyond these points that relate to their experiences. I often must examine calculation methods of others in an audit role. I urge you to set up a design criteria that you and others follow. Leave room for others to comment on the efficacy of your procedure and recommend an alternative based on their experiences. There are too many items to suggest them all in this response.

Wishing you success,

Lawrence Nordell

Conveyor Dynamics, Inc.

www.conveyor-dynamics.com ■

It is difficult to describe here in this forum, the drive selection procedure in detail. However, salient points are as below :

1) You have to decide conveyor power for varied operation situations, such as empty, 25% load, 50% load, 75% load, 100% load, etc and again all these for varied values of conveying friction coefficient, part length loading etc.

2) For decline conveyor of negative power, again the conveyor will have positive power when being empty or partially loaded. Therefore, conveyor drive will be operating in positive to negative mode.

3) Drive motor type can be 3-phase slip ring or squirrel cage motor. If you have maximum negative power of 60 kW at drive motor, you can use 60kW motor. This motor will be operating below synchronous speed during positive power mode, and above synchronous speed when during negative power mode.

Thus, the motor at any time will be operating say 97% to 103% of synchronous speed (excluding starting and stopping). The motor exact speed in above range will depend upon the magnitude of mtph. The motor operation above synchronous speed has negative torque (restraining torque) which creates balanced speed operation.

4) The motor and its power supply system should be suitable for regenerative mode operation.

5) The issue has been taken care in my book on belt conveyor. It includes numerical examples of practical application and calculations for varied operational conditions.

Trust this provides the basic answer to your query.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Contrary to Mr. Mulani:

I disagree with your advice to size downhill conveyors on the calculated kW. I have never heard of such a practice as to select the drive on the demand or calculated rating. How do you propose to set the governing values to be weighed in this analysis. Arguing that the motor shaft power is significantly influenced by the gear losses is pretty subtle and not very relevant as well as the super-synchronous speed albeit you get more cooling.

Downhill analysis has many contrary methods of analysis: CEMA, DIN 22101, ISO, AS, JIS, Goodyear, Contitech, and many others.

In the calculation procedures, stock must be taken of new and of worn or future state of the equipment. Standards differ as does the equivalent friction factor such as:

CEMA says to eliminate the seal drag in idlers, pulleys skirts and cleaners, and to reduce the belt induced drag by 1/3. Often this can result in a overall drag factor of DIN f < 0.012. DIN 22101 does discuss a similar value down to f = 0.012. Taking these conditions as they apply to small belts is conservative (ie f>0.012) and larger belts the values can drop below f = 0.0085.

Temperature also can have a dramatic influence.

In summary, you argue the point of a few percentage points, where as the real world calculation methods vary by tens of percentages, and the real world can vary by much, more depending on the specifics of the conveyor design and products used. You will not find all the answers in a book.

I suggest MSW take a more cautious approach.

LKN

Conveyor Dynamics, Inc. ■

Hello msw,

Further to my earlier message, I add following clarification although the same already implies in my message .

One needs to find out the maximum positive power and maximum negative power among varied operational conditions (parameters), as listed in my message.

The motor alongwith the electrical system should be capable to suit max positive power and also max negative power demand, as may occur during conveyor operation. Accordingly, motor size will correspond to | kW at motor |. (the symbol || means modulus).

I have presumed that your mentioned – 60 kW is maximum modulus | kW |

The varied value of conveying friction coefficient also implies likely variation in magnitude of various frictional resistances.

The aforesaid motor kW may need marginal revision / increase, in accordance with the specific electrical system being considered for stopping. All the varied intricate situation cannot be taken care in such reply, without actual example, while deciding the optimum solution.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyor.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

If I understand you correctly, using the ISO power calculation procedures and you use:

1. f= 0.012 for the downhill analysis and obtain power = -60 kW

2. f=0.030 for empty belt and obtain power = 26 kW

Belt is only downhill with no near flat or incline sections.

Then I advise to select a 75 kW drive for the reasons previously stated. It is not adviseable to select the motor size at the demand leaving nothing in reserve to cover unknown design or oerating conditions.

Lawrence Nordell ■

MSW,

I do not know the profile. If it is only down hill, then to get better REGENERATIVE BRAKING normally one size higher motor is selected ignoring the positive power in addition to other type of electrical braking.I did conveyor system in BAILADILA MINES in INDIA considering the same.All conveyor are running well with out over speeding.So you can take 75KW motor as already stated by MR.Nordell.

Regards.

A.Banerjee ■

HI MSW

Mr nordell have given valuable sugessions. Down hill conveyor design is really a challage .

it is better in case you go for dynamic symulation of this conveyor by reputed consultants who have done the same in past.

As explained earlier you pl consider every aspect of loading, smooth starting and smooth stopping.

you also consider mechnism of stopping conveyor in case of power failure.

Drive should be suitable for delevering retarding torque below syncronous speed under all loading / oprating conditions.

Type of drive is also very important best but expensive option is 4 quardant control vfd drive .

you also ensure tension in the system should be high limiting to belt allowable tension,

A R SINGH ■

Dear Mr Khalid

None of the sugession seems to be good Engineering Practice.

In case of large downhill conveyor it may not be feasible to induce frictional forces to make power positive. problem is not so simple as you are thinking Designers are working for long on this subject.

A R SINGH ■

Dear Khalid

I suggest you calculate the cost of ownership for the client. A downhill conveyor will cost the owner much less to transport his product from mine to plant. Obviously, you have not made such a computation. ■

Dear Mr Khalid..

I am amazed that such a simple re-gen conveyor has sparked so many deviations from the normal simple solution.

Your expensive and horrendously cost and maintenance intensive attempts to absorb power are beyond me. Why waste the power when you can put it back?

I would comment as follows, based on numerous working examples, the most economic solution is:

- For -60kW Abs use 75kW installed (beware a flooded belt)

- Use f=.012

- Use squirrel cage 4 pole single speed motor

- Fit high speed brake for initial action

- Fit low speed brake as well to bring to halt and as back up

- Usually put drive at tail, TU at head

LSL Tekpro ■

Mr Khalid

In reply to your seemingly heated but nevertheless amusing rhetorical questions, I answer as follows:

1.0 Just about all of the down hills re-generate power here in South Africa, and all the down hills that I have done certainly do. Pretty much everywhere else too, judging by the ones I have seen all around the world.

2.0 No one needs to pay a million Ruppee for the design. Its old simple technology (but if anyone is stupid enough to pay me a million Ruppees for the design I probably would not say no!)

3.0 You have to have brakes on a downhill conveyor anyway in case it trips out!

4.0 A squirrel cage is automatically re-generative on overspeed, as one of my learned colleages (Mulani) has already indicated to you. Power nearly for free!

5.0 I do not wish to waste time commenting on your strange selection of equipment, , long belt damaging skirts, ridiculously small roll diameters, extra unecessary trippers with all their maintenance, bush bearings and the like...that is complete nonsense ... Keep it simple and correct....as always.

We are here to transport material as efficiently and economically as possible, not to deliberately create problems.

LSL Tekpro ■

Dear Khalid,

You may believe that by introducing enough rolling friction to counter the downhill gravity force is justified. Have you calculated the amount of power and component expenses to operate the same conveyor and its high rolling friction when it is empty?

You will find the power and component needs will be greater than having an efficient rolling friction design.

With your concept, the empty belt will require all your full load rolling losses plus the empty belt losses. This will sum to more than the full belt losses.

Where as, with the efficient rolling loss design, the full belt component selections (motor, belt, etc) are rated for full belt losses minus empty belt losses. Empty belt losses are just empty belt losses. ■

this is also one of the ways to know about the subject.

regards, anil seth ■

Dear Mr Khald

it is up to you to agree or disagree with expert advise of forum members. And in case cost factor is involved for running a smooth down hill conveyor same is to be borne by end user of the conveyor not by forum members.

Al members of the forum are expert in there field and giving free sincere advise

You may be satisfied with your theory but no one from the forum members have accepted the same.

I sincerly advice you to make use of avalable technology insstead of -------------

A R SINGH ■

I am fully agree by the statement given by MR. A. R. SINGH and the hon. members of this forum.

anil seth ■

Gents

Perhaps the moderator should step in and refresh us all with the purpose and rules of the forums.

All CAPS is email lingo for yelling and screaming at the top of yr voice - something that should be avoided and discouraged from contributors.

Some with lower english skills do need to try and ensure that their tone is well conveyed and well meaning as there does appear to be some examples of perceived rudeness coming through either not intentioned or just bad manners.

I look forward to the positive atmosphere of all future forum posts.

It is nice to watch the membership numbers continue to climb.

This forum is one of the better ones.

Cheers

James M ■

Mr. Graham,

You have suggested two brakes to be used in down hill conveyor.

-high speed brake

- low speed brake

Can you explain little bit about those type & its design criteria.

Also how it is operated with speed sensor& I request you give single line diagram to understand.

A.Banerjee ■

Good day Mr Banerjee..

I usually use 2 brakes on downhill conveyors for the following reasons:

- If one brake fails, the conveyor is still safe and you avoid catastrophies (no hold backs here)

- use the high speed one first, and use the low speed after the conveyor stops as a parking brake

- If you have to remove the drive with the belt full of material, the low speed one will hold the load

- The high speed brake is cheap and therefore you pay little extra for a perfect system

LSL Tekpro ■

Two brakes systems on a 60 kw downhill?

I do not believe you guys are serious.

1. Many brake systems throughout the world relied on one brake system until about 15 years ago. Certain large systems had problems with belt to pulley hydroplaning and with lagging failure. (Morence 3200 kW regenerative) Many designers were privileged to the details of the lagging failures and hydroplaning. We opted for added wrap by applying another pulley. This is now becoming a norm. THis probelm also occurs with uphills such as Palabora (7150kW incline) due to belt washdown when loaded with worn lagging. Upon restart, and aborted stop, Alesvaloran! (sic)

2. The power pack does not need redundancy as the brake cycle is fail-safe based on the same hydraulic feed. This is so unless distance dictates otherwise. Usually there are two calipers to balance the bending moment - both can't fail simutaneiously.

3. There are other ways to deal with big systems (> 2000kw downhill) that are superior to the use of two brake systems. but this should be the topic of another thread.

We have said enough about a 60 kW downhill. ■

As always Larry..

The proof of the pudding is in the eating as they say.

I have had such consistent success with the 2 brake system for such a range of powers for so many years that I will not be swayed on this one.

I especially reccommend it for manriding decline conveyors, where safety is a big issue these days. (We are just not allowed to kill people like we could in the old days)

Enjoy you hydroplaning!

LSL Tekpro ■

Dear Spriggs

what type of brake you generally use in case of power failure do you use any machanical brake also

A R SINGH ■

Hello Arsingh..

I use spring applied, with power to release (failsafe) disc brakes for both high speed and low speed applications.

Cheers

LSL Tekpro ■

Dear Graham Spriggs

in case of power failure your both brakes applied symultanously or you provide some additional precaution

A R SINGH ■

Arsingh...The high speed brake is applied fairly quickly.

The low speed one is applied quite slowly, such that the conveyor is normally at a standstill before it comes meaningfully in.

This is independant of whether there is a power failure or not.

The idea as you pointed out is never to have both brakes acting at the same time.

This is especially important on manriding conveyors underground, as the last thing you want is an excessive braking effect. Underground is often wet, and miners wear plastic waterproof clothing which gets slippery when on the wet rubber of the belt.

There has been a case here where the men on the belt have slid down the conveyor in wet conditions, and have broken the bones of the mine captain manriding further down the conveyor.

Hope this helps you..

LSL Tekpro ■

Dear Mr. Singh,

Down hill conveyor is provided with a) Electrical bracking & b) mechanical braking.

Electrical braking is used when there is over speed of conveyor(automatically) & also for normal stopage.

Two nos. mechanical brakes are used along with speed sensor to stop the conveyor when in need.Each brake is designed to stop the conveyor during individual application( 100% capacity).

Then question comes why two?Electrical braking is applied first to slow down the conveyor &both the mechanical is applied to come to dead stop. Application of brake is simulated by speed sensor being set at pre-determining speed.We follow the above design practise.

In case of power failure, both will work & can shear 50% torque during braking.

Mr. Singh I thing I am clear to you now.

Regards.

A.Banerjee ■

Dear Mr. Singh,

Now-a-days, we are going for BUBENZER disc brake. Servo control system is used to control the braking torque so that constant reterdation is achieved.But we are Diverting the main topic.

Regards.

A.Banerjee ■

Dear Mr Banerjee..

We have a saying:

"Why make it easy? when you can make it complicated!"

LSL Tekpro ■