30kw EOT Crane Motor Taking 235A Agaisnt FLC of 49A??

Is the no load current normal? Is the gear train free? Run only the motor, & check current.

Please do not take this the wrong way....

If you are not an expert on cranes and how they function, do not... I repeat... DO NOT work on this equipment, 65 tonnes falling from any height is not something you want to see happen.

Seriously... this type of equipment should only be serviced by someone who is an expert in its inner workings. Caution is called for!

Probably tend to agree with this, but the chances of a 65T crane coming down are very slim.

Need to know what type of motor starter is being used. What is the make of the hoist motor? My first gues is that the hoist brake is not releasing.

30kW Motor tested on No Load having no-load current as per Motor data sheet (17-18A) Normal.

We have checked gear train are free.

Hoist break are free and only worked at a time of stopping the motor for holding the load. Also we have tried by loosing the break but eventhough not gettting any clue....

Motor are with DOL starting.

when started with full load...load getting pulled up some 6 inch...but motor getting started drawing more current approx. 235A and gets tremendiously hot..... while measuring winding resistance just after the load test try.... winding resistance reading are '0'.... but after some time winding resistance getting around 0.12mohm/phase.

we have checked for single phasing also.... when trying for load testing we have measured load current for all phases... and same way at a time of no load ..we have measured for all phases... alll are showing same...

Plz help.... we have called manufacturers senior engineer..... but he is also not finding any solution.... he is also fail to understand what is the problem.

Regards,

T.D.

Check to see if there is any volt drop across the DOL contactor no-load and load. What make of motor is this?

Phase to Phase IR sounds low 120K! How are you able to measure this excessive current, surely the overload or fuses would trip it out almost immediately.

Is motor current normal under no-load conditions?

Also diconnect phases from motor and check to see if you are getting full voltage at the cable ends. Don't electrocute yourself when you do this.

How is supply getting to motor from contactor - cables, busbar or is contactor on crab with the hoist?

If you have tested the motor on No-Load and have checked that the brake is releasing properly etc including the gear train, then:

- How did you check the Gear Train? Visually? This will not be enough.

- If any maintenance work or repair to the gear train or cabling has been done recently, then check that there was no mistakes in re-assembling and threading the cables!

Reason: The 235A draw means that the motor is not able to reach its full speed or running rpm: ~5 times the nominal nameplate current. I would think that the lift speed for 65T with 30kW motor would be max at 5cm/s which means that 6inch would take >3 seconds.(that is if you really tested at full load of 65T).

Normally, the motor would draw > 6 times 49A and quickly drop to 3 times and then to 49A (or less) within few seconds. If the current remains at 235A for 3 sec., then the motor is OVERLOADED and can't reach its normal running rpm.

Anyway, This is One possible reason for drawing that much current and still be OK when tested under no load. Otherwise, your motor would already have been damaged and would not even perform at no load. I also presume that you are switching OFF manually, before the O/Load devices come ON. If not, then you are running without any motor protection. Which would reinforce my deduction that this crane has had some work done to it recently ....

Plz help.... we have called manufacturers senior engineer..... but he is also not finding any solution.... he is also fail to understand what is the problem.

Pardon my ranting, but a "senior engineer", upon seeing the no-load cable speed, without even taking out a stop watch, can perceive that it is several times too fast. (For a brand new engineer, this would not be obvious, but a senior engineer should have some familiarity with the equipment he's selling.) Having seen it running too fast, he could then pull out a stop watch , and see that the speed is about five times too high. Thus, under full load, you'd expect the current to be 5 times too high (because the gear ratio is wrong). How long would this take? 10 seconds to make the first observation. 30 seconds to pull out a cell phone and time 10 seconds of cable pull. 10 seconds to measure the distance.

About a minute for someone with a clue.

It sounds as though the overload protection equipment has been bypassed and that the installation is one step away from suffering a cable fire!

• Isolate the supply to the crane. Lock it off.
• Call the crane vendor and arrange for its technical support to call by and service the equipment as a matter of priority.

Yep. Doesn't sound too good, does it?

I agree. It scares me to think of the number of times I have had to stop owners and operator's from doing this type of work, when they have no clue what or how to do it. I guess thats why there are so many lawyers.

Has the crane worked properly in the past and has developed a fault, or is it a new installation?

With the sound and rapid overheating I would suspect open circuit rotor bars in the squirrel cage. Unfortunately the only way to check this is to strip the motor. A motor of this type IE heavy duty high starting torque it is likely to have either a double cage or a deep taper slot.

Unfortunately there are no external checks that can be done to detect this fault, it requires a visual inspection.

Deep taper

Double cage

Recently.... approx 2 hours back...

we have tested ;

Voltage at Isolator Terminal reading 408 Voltage phase to phase

Measured at Motor Main Contactor terminal 408 Voltage phase to phase

Measured at Motor terminal 408 Voltage phase to phase

Motor connection checked - delta connected (6 terminals)

per phase resistance checked again 0.3-4mohm

Megger value checked again phase to phase = >1Gohm, phase to earth = >1Gohm.

Voltage measured at stator contactor-1 (forward running) R-Y-B = 408 Voltage phase to phase,

Voltage measured at stator contactor-2 (Reverse running) B-Y-R = 408 Voltage phase to phase,

Connection from Sator Contactors to Motor terminal through 3 core cable.

when tested on No-Load motor runs fine...drawing no load current of 18-19A...breaks getting released smooth operation....

the same crane having a micro motor for 200mm/min. speed having rating of 3.7kW with 6amp of FLC working fine lifting entire 65T of load.

while subject 30kW motor with FLC of 49A are main motor for 2mtr/min. speed of load lifting.

EOT crane are brand new , company fitting, we are doing first time field installation & commissioning testing.

main motor (30kW) starting time 1 sec. at 100% voltage and 2 sec. at 80% voltage.

Starting current

(1) 600% of FLC at 100% voltage,

(2) 500% of FLC at 80% voltage,

(3) 100% of FLC at 1sec at 100% voltage

(4) 400% of FLC at 1sec at 80% voltage &

(5) 100% of FLC at 2 sec at 80% voltage.

Motor RPM 980 rpm, 6 poles.

we have O/L relay set at 63A, but we are switching off the motor manually when as soon as its current reads approx. 235A with overload sound.

we have called Suppliers engineer who is at site currently ..saying he has done so many EOT commissioned ....they are facing this type of problem first time with No-Clue at all...what is happening......

plzz help ..........

Regards,

T.D.

Personally I would be asking them to supply a new motor. If it's still in the commissioning stage of the supply contract it's their problem not yours.

"the same crane having a micro motor for 200mm/min. speed having rating of 3.7kW with 6amp of FLC working fine lifting entire 65T of load."

If the above motor is satisfactorily lifting same load, then obviously, 30kW motor is defective.

It looks like you have measured three different phase-to-phase resistances. The fact that you measured 0 ohms when the motor was hot suggests a short that shows up from the distortion of hot windings.

The vendor should be handling this, (quickly and efficiently) both for their security and yours, and to get the next sale.

This is peculiar motor problem. Which make is crane and motor?. Is it slip ring type motor with resistance box and master controller?. Crane motors are supposed to be suitable for crane duty with high starting torque and suitable for frequent reversing. Are the brakes electro hydraulic thruster type?. Have you received test certificate for the motor?.

Unless you work for the company that supplied this equipment, I suggest that you step back and let the vendor deal with it. You are putting yourself and tour employer in the position where you may void your warranty.

As stated previously it is not your problem.

Ask the engineer to uncouple the motor from the hoist gearbox and see what happens then. Check the input coupling to the gearbox to make sure it turns freely, otherwise the rotor id f**cked

Have you double checked your motor connections? If you have connected the motor in Delta instead of Star, you could be saturating it so much that it immediately stalls under load, but uncoupled it would look fine and nothing would show up in off line tests.

Mr. JRaef

We have double checked the motor winding connection as per design/manufacturers data sheet which is showing delta connection......and actual connection are of Delta only.

If the gearbox used in the crane is as you described in your other thread, then your answer is obvious. To lift 66T, you would expect to draw about 5 times nameplate current. That makes the crane useless, and further means that the crane was not engineered in any meaningful sense. It should not be operated, because there are many possibilities for failure that could injure or kill people.

No changes in motor power, gearing etc should be attempted, because there is no way of knowing what will fail next. A crane must be engineered as a system, and if the vendor is off by a factor of 5 or more on the motor, then other parts of the crane may be badly undersized, too.

This all seems pretty stunning. I gather you are a plant electrical maintenance guy, so you would not have checked the basic engineering of the crane first, and reasonably assumed that there might be something wrong with the motor or wiring.

But clearly, the crane motor is overloaded by a factor of 5. Under no load, the cable should retract at 11.8 meters per minute, per the gear ratio and drum diameter from your other thread. (This is about 5 times as fast as your company was expecting.) One HP is 33,000 ft lb per minute (a figure that I find easy to remember, without having to look it up.) 11.8 meters per minute is roughly 40 feet per minute. 66T is about 145,000 lb. So the required HP (to lift 66T at 11.8 Meters/minute) is 175. That's a lot more than the roughly 40 hp provided by a 30 kW motor.

When things are this far off re grade-school-level basic calculations, you can reasonably assume that the vendor knows nothing about cranes. Given the many obvious hazards (loads dropping and smashing people, cables snapping and decapitating people) cranes are ordinarily very carefully engineered with large safety margins. It would be unsafe to assume that the gearbox "just" needs to be changed for one of the correct ratio, because if the vendor cannot understand the basics, who knows what else will fail? (Typically, for example, the cable that lifts 66T will not actually fail under test until about 250T, so a 66T test tells you nothing about the engineering of the crane. The cable on your crane might part at 100T, making it woefully undersized per ordinary engineering standards.)

You need a new crane vendor. Their "senior engineer" should have been able to figure this out in a couple seconds, but more obviously, the crane should not have been delivered. You have a 10 T crane, maybe. Whether the cabling, gearboxes, framework, etc is sized for 10 T or 66T is anyone's guess. Have the effects of load acceleration (cable jerk, etc) been taken into account? Anyone's guess.

Kudos to you for delving into the basics, as you have in your torque/gear ratio threads. It makes this all crystal clear.

Mr. K_Fry

Motor rating are 30kW (40HP)

Motor shaft conencted directly to grearbox having ratio of 166.7 : 1

Output of gearbox connected to rope drum having 652 p.c.d. x 3600 lg. with lifting hook connected though pully block.

Now, caculation of requried HP/KW for lifting the load,

145504.9 lb(=66000kg) * 6.562 ft (2 mtr/min of req. lifting speed) / 33000 * (0.8 eff. assumed) result coming 36.17HP / 26.98 kW which is well below than motor rating of 30kW provided.

Plz correct my Cal. if i'm wrong.....

Waiting for your further guidance....

Regards,

T.D.

Your calc is OK as it stands, but I understand from K Fry's post that with the gearbox ratio, drum dia etc installed the lifting speed is not 2 m/min, more like 12 m/min. I haven't gone through it myself, but on that basis power needed is 6 x higher.

Has this crane been modified in some way, perhaps by reducing the number of falls of rope, to increase the lift speed by a factor of 5 (#10↑ remains unanswered at this time)? If so then the rope may even be well overloaded!

Here's an experiment to try. Start a manual transmission car on a steep hill in fifth gear. Can't be done. Is the "problem" that there is not enough available HP? No. The problem is in the gear ratio, so there is not enough tractive force (which relates directly to wheel torque).

Unless you are leaving something out, your crane is not geared for 2 mtr/minute, given the 980 rpm of the motor. Because the cable speed is too high, the cable force is too low (per motor amp). Thus the motor appears overloaded but the problem is in the gearing (and who knows what else).

My numbers above were based upon the hook being attached directly to the cable. If the hook is on a pulley with a 2:1 cable run, then the hook speed is half of the previously calculated figure -- still much too high.

A crane engineer should look at your installation.

I concur with PW Slack -- Lock out the crane until it's design and construction has been verified.

Thanks.

Which brings me back to my post #2, If you are not an expert on these systems. You had best have nothing to do with it. Ooppss... when working on these things are not good.

This, to me, at least sounds like a home made job. Stated that the crane vendor is on site and it sounded like they had purchased this unit. Now we find site personnel are doing the engineering calculations.

Methinks there is something rotten in the state of Denmark...someone deperately trying to save his job. I really don't want to see the headlines "Many killed and injured as hand made 66t crane falls from the sky"

Leave it alone before someone gets hurt. Sheesh!

Mr.philphy

I appreciate your deep concern about the safetly..... and we are also considering the same our first proiority....

We are not doing any load test further after getting a reading of 235A at 66T first try ... and once of 19-20A at a time lifitng 10T second time...

We are only doing No-Load test there after just to acertain some parametere .. like no load current, voltage at various places etc.

And yes u r rightly said this is a do or die like situation.....huge pressure for commissoing the same.... lots of equipments installation are on hold due to none-working of the subject EOT crane....

I request all top electrical engineering experts here including you to help in sorting out the poblem... or identifying the problem.. whatever it may.......

Regards,

T.D.

TD You stated before that there was pony motor. I assume this is a creep or slow speed hoist. Have you tried lifting the load using the slow speed only?

Mr. philphy

Yes we have tried to lift the 66T load using micro hoist motor having speed of 0.2mtr/min. and motor rating of 3.7kW which is connected to the same shaft with main motor of 30kW.

We have lifeted the entire load (66T) using micro motor approx. 1.2 mtr. height but not tried any horizontal movement with this load....

lifitng eith mirco motor (3.7kW) is working fine...

Regards,

T.D.

OK now the next question. Is the pony motor directly coupled to the main motor. That is when the pony is running it also mechanically turns the main motor rotor which in turn inputs to the gearbox and rotates the drum. If this is the case then the pony motor does the main breaking as well. How is the pony motor coupled to the main motor? and how is it disconnected when the main motor runs? Dos the pony motor remain running when the main hoist motor is energised?

Micro(pony) motor shaft is coupled with main motor shaft through two numebrs of Full Gear Coupling (101) with Planetary unit (10:1 ratio) and EHT thrustor in between.

When Main motor runs Micro(pony) motor diconnected electrically but stay running mechanically due to the coupling of shaft with main hoist motor.

Regards,

T.D.

Since the kW output of the motor is proportional to the current drawn, and you have stated that the motor was taking ~20A when lifting 10T:

A simple rule of 3 will give you: 65 x 20 / 10T = 130A required to lift the 65T, which is ~ 79kW !

(Not taking in consideration the magnetising current and no load current. But even if you take it in as being somwhere like 20%, then the value will be: 20-49*0.2 = 10.2A, then 10.2A*65T/10T = 66.3A + 8.2(no load etc) = 74.5A which is ~46 kW)

In both estimates, your motor seems under-rated for the 65T crane. At such overload, the P.F. will drop very low and the current drawn will go high, much higher than the 75A estimated, or the 130A. 235A will suggest a p.f. of 0.2 !

As k-Fry said: the cable being drawn, at the DRUM, it's speed is directly related to the lift speed. You need to check the number of pulleys involved with the cable-hook to know the actual lift speed on the load: 2m/min is 3.33cm/sec while the 6inchif per sec will make it ~5 times more ==> 10m/min !! at worst, 5 m/min if it took 2 sec for you to stop the overloaded motor !!! ?? lots of questions and doubts here. You must study the crane cabling and the motor speed to reach a clearer picture (4poles motor? 1450rpm on nameplate?).

Sorry, I forgot that the previous thread mentions 980 rpm!

But this does not change the opinion that the motor is still grossly overloaded.

...and the wiring too. #7↑.

but 18-19A is a no-load current... and while lifting 10T is taking arround 20A .....which is too close to no laod ... ..... then actual current drawen for lifting 10T weight is hardly 1-2A ....

I don't know whether this rule of 3 works....

Can u guide how to calculate rope wraping speed on rope drum.... ? what is the formula.. ???

Regards,

T.D.

What I said about calculating the total A from your 10T trial is only an indication or a quick approach to have a rough idea on the values involves.

The motor has an initial Magnetising current which is added to all the fictions due to the motor bearings and all the gearbox + pulleys + ropes etc. Your no-load measured current is the addition of all these. It will be difficult for me to know the whole setup and all these values. The only thing is a rule of thumb on the magnetising current at about 10% of the nameplate A (just a wide guess), =~5A.

From here, taking that the 10T would require: 10000 kg x 9.81 x 2/60 m/s = 3270 N.m/s or Watt which gives I(A) = 3270/(400V x 1.73 x 0.8) =5.9A or 6A

You cannot escape the fact that the 10T at 2m/s will take ~6A. The balance 20-6 = 14A is required to drive the rest(Theoretically)

For 66T you will need 39.6A, therefore, +14 = 53.6 or 54A Already overloaded in my opinion.

The best way arround this is to run at 10T ONLY and check the speed of the lifting of the said load, in m/min (Time it for a distance H ). This will give a definite answer about the real speed of moving the load (Whichever), vertically. If that speed is more than 2m/min, as suspected by Fry, then stop and send it back to the supplier for him to sort the cable train etc... If exactly 2m/min, then the motor is too small.

The best way arround this is to run at 10T ONLY and check the speed of the lifting of the said load, in m/min (Time it for a distance H ). This will give a definite answer about the real speed of moving the load (Whichever), vertically.

Doing this test would make sense. In the OP's other thread he writes :- Gearbox output shaft connected to rope drum of 652 PCD. x 3600 LG. and the rope end connected with the huck for lifting the 66000kg weight.

I assume huck is a typo for hook. Perhaps he did not mean a direct connection, however. Perhaps the connection is through several sheaves. Maybe during testing someone unfamiliar with the effect of the block and tackle left it out? A picture could be worth 1000 words.

Mr.LAA_Lucke

Measuring of lifting speed on No-Load will be ok????

B'coz we don't want to take a risk of lifting even 10T to measure lifting speed.

Plz suggest...

Regards,

T.D.

Yes, you could run without Load, as long as the hook and cables etc are hanging down vertically. There is enough tension produced by the weight of the hook (65T Lifting Hook must be substantial!).

OK will try measuring on No-load and let you know the results....

Isolate it and lock it off before someone gets hurt/killed! Do not re-energise it without both the equipment vendor and the Engineer/Surveyor for the company providing indemnity protection and loss insurance present!

The rate of increase of potential energy of the load cannot exceed the rating of the motor, otherwise the motor will burn out.

66000kg x 9.81m²s^-1 = 6.5e5N to suspend the load.

Motor power divided by load force ↑ gives a maximum of about 46mm/sec lifting rate, not allowing for losses in the motor, gearbox, rope and any pulleys. In practice it won't be much more than about half this figure.

Is this crane trying to lift faster than this?

With the information to hand this crane is a disaster waiting to happen. Do make sure that all CR4 readers are standing well back when it either catches fire, collapses, or the rope breaks.

As per IS : 3177, I had calculated min. power requirement as per below ;

Required kW = 66T x 2 mtr/sec x 0.67 (Service Factor for Vertical Motion of AC Motor) x 1.5 (duty factor for Class M5 Crane) / 6.12 (constant) * 0.8 (Combined Gears & Sheaves Eff.) * Derating factor for req. ambinet temp. (40 deg.C.)

kW = 66T x 0.67 x 1.5 / 6.12*0.8*1 = 27.10 kW Required Power.

Motor Supply Power = 30kW.

Motor Power Supply is more than min. required power to lift 66T of load.

Plz guide further.....

Regards,

T.D.

#38↑ remains unanswered.

Where is the crane vendor in all this? What on-site assistance has been sought and provided? Why has the motor overcurrent trip not operated at 235/49 of its correct setting?

Over-current is operated on set value of 63A, it's working fine.

The FLC of the motor is 49A, though. Why does the motor take 235A without the overcurrent trip disconnecting it?

Mr. PWSlack

It is a measured current 235A just before trip by O/L on 63A (bimetallic relay).

Regards,

T.D.

It is apparent, that he is the vendor. You don't have to go far, looking for him.

Hi Tigerdon,

Are from India?. Please let me know the mfr. of the crane. There some small scale operators who dont have design facility and make site fabrication of the crane at dirt cheap rates.

I fear that you are starting to drive us all crazy.

You wrote:

kW = 66T x 0.67 x 1.5 / 6.12*0.8*1 = 27.10 kW Required Power.

If one does the math, 66 x .67 x 1.5 / 6.12 x .8 = 8.67. (A figure obviously too low for this crane.)

You can verify that by simply copying the line into Google, and it will do the math for you.

Is there some reason that you left out the lift speed? Does this not seem critical to you?

In this line: Required kW = 66T x 2 mtr/sec x 0.67 (Servi... you have 2 mtr/sec as the lift speed. Is this intentional? That is a very fast crane.

If we inserted the 2 then the kW would still be ludicrously low for a crane capable of lifting at such an incredibly high rate of speed. It would also not match your 27.10 kW answer.

At one point, (in your other thread) you said that the cable went directly to the hook. Is this incorrect? If this is incorrect, what its the real pulley ratio?

What are the thoughts of the senior engineer from the vendor. Why have they deserted you? Why are you left to do the calculations?

Your measurement of the no load speed of the hook is awaited.

An analysis of the thread will answer as to who is the vendor. It is written in uppercase, bold all over the wall. It's HIM.

He meant 66T x 2 x 0.67 x 1.5 /(6.12 x 0.8 x 1.0) =27.09 kW

He needs to learn how to write his formula ...

And still it is faulty from any point of view!

Mr.LAA_Lucke

I accept my typo error....

but yes u r right and i mean to say that only..

CORRETED FORMULA :

He meant 66T x 2 x 0.67 x 1.5 /(6.12 x 0.8 x 1.0) =27.09 kW

Regards,

T.D.

I appreciate your reply..

I accept typo error in my calculation correct calculation is as per below, however answer remains same:

kW = 66T x 2 x 0.67 x 1.5 / 6.12*0.8*1 = 27.10 kW Required Power

Senior engineer said we have tested in presence of your inspector on no-load, on full load & on over load, and it's working fine there…that's it….

They are telling your input DG supply is a problem…and not in a crane motor….

In addition to that, they are telling that we don't recommend to do full load test on DG supply.

But I don't think it has anything to do with DG input supply…. B'coz entire construction power supply which covers highly inductive welding receptacles are running on the same DG…. It has a enough power capacity to supply the load of crane…..

Regards,

T.D.

Looking at the formula you posted, I can see that you have written 2 mtr/sec !!!!!!!!!!!

Also, I don't know where you got this formula from, but maybe it is miss-printed somewhere in some documentation, OR from a design book like Engineering formulas(?).

In any case, 2 m/sec lift speed is enormous and no matter what are the service factors or duty factors etc provided, we usually go FIRST on the sound theories and then apply factors to either increase or reduce the final values, depending on the subject being designed. in this objective, the straight forward formula is:

Power in kW required = 66T x 9.81(g) x h (in metres, lift speed per SECOND)= 66 x 9.81 x (2/60) where 2 is 2m/minute which gives 21.5 kW

If you want to have a safety factor which takes care of all the friction losses in addition to the cable and hook weights + safety, let us say 1.5 times the calculated theoretical requirement, then the Motor kW = 21.5 * 1.5 = 32.4 kW THIS IS FOR 2 m/minute which is 2/60 = 0.0333 = ~ 3.4 cm/sec

For 2 mtr/sec, well then you will need an enormous leap:1290 kW before any safety factor!(don't forget the size of the cables and the HOOK!!!

From the electrical side, Motor Power P(in Watt)= U(volts) x Amps x 1.73 x 0.8 here: 32400 = 400 x A x 1.73 x 0.8 ==> A = 32400 /(400 x 1.73 x 0.8) =58.5 A typical full load for 32.4 kW motor.

Will wait to see the result of your no load vertical travelling speed.

From this you can deduct the Amps required by the motor.

I hot this formula for min. power requirement calculation from IS : 3177..

Regards,

T.D.

I have been in the overhead crane industry for many years and I must admit it has been about 5 years since I worked on one. However, 2m/sec, 120m/min sounds a bit excessive and i don't think I would feel comfortable working with that. I was thinking of the strain if the operator went straight into fast speed with full load on the hook.

Anothr question how many falls of rope does this beast have?

Mr. philphy

It's is 2mtr./min and not 2mtr./sec...

Regards,

T.D.

Required kW = 66T x 2 mtr/sec x 0.67 (Service Factor for Vertical Motion of AC Motor) x 1.5 (duty factor for Class M5 Crane) / 6.12 (constant) * 0.8 (Combined Gears & Sheaves Eff.) * Derating factor for req. ambinet temp. (40 deg.C.)

"ERROR CORRECT"

kW = 66T x 2 x 0.67 x 1.5 / 6.12*0.8*1 = 27.10 kW Required Power.

Just got vendor's motor sizing caculation as below :

KW = (M x V x Cv x Cdf ) / (6.12 x E C amb)

Values ;

Where M = Mass of the rated load on the hook 66 + Wt of hook block and the wire rope in tonnes 2

= Total Load on Hook 68

V = Hoisting speed in 2mtr/min

Cv = Service factor for vertical motion for AC Motors 0.67

E = Combined efficiency for gears and pinions

= (0.95) n x (0.99) m for antifriction bearings

n = number of pair of gears 3

m = number of rotating sheaves between drum and equalizer for 12 falls. 5

Therefore E = 0.815355

Cdf = duty factor for M5 vertical motion as per Table 2 of IS:3177 = 1.5

KW Calculated as per above Formula is = 27.39093

Ambient temp derating factor for 40 o C amb = 1

Therefore Required KW = KW/Camb 27.39093

1 No. Squirrel cage 30KW, 6 Pole 40% CDF, 150 Starts/Hr Class F insulation, IP 55, Flame Proof

S4 duty cycle motor supplied. IEC Frame E225M

Kindly reply if any error in vendor's sizing calculation... plz....

Regard,

T.D.

There's nothing much wrong with the calculation. I haven't really kept up with this, but I gather from various posts the velocity is not 2 m/min, it's about 5 x higher. That's why it needs more power.

I based my 5 times too fast statement on the OP's other thread, in which he wrote that the cable attached directly to the hook. Per info in this calculation, it actually goes through a 12 fall block and tackle -- so the speed should actually be lower than the spec speed.

Let's see, if I recall, the drum is 652 mm dia. That means 2.05m per drum revolution. The drum is driven at 980/167 = 5.86 rpm. So, 12.0 m/min cable speed at the drum. With a 12 fall tackle, the lift speed would be 1 m/min.

Curious. It will be interesting to see what the actual no-load lift speed is.

Even more curious: the difference between 10T amperage and no load amperage is very slight -- just an amp or two, IIRC.

Mr.K_Fry

Can u plz explain what is meaning of 12 fall pully block?

Regards,

T.D.

In a "block and tackle" (which many cranes have to multiply lifting force while reducing lifting speed by the same factor) the "falls" are the parts of cable between pulleys.

(The nomenclature may get confusing here. In the US, "block" has essentially the same meaning as "pulley". Tackle means the rope used with blocks. Sheeves are the actual grooved rotating parts in a block on which the cable (rope) rides.)

In a simple block and tackle, one can get the lifting ratio by counting "falls" or "parts" between blocks (excluding the part leading directly to the pulling mechanism).

In a simple block and tackle there are generally 11 sheeves rotating for a 12:1 ratio. Perhaps the tackle on your machine is compound, where 5 or 6 sheeves would be rotating.

If these are put together wrong, (with one rope rubbing on another) a lot of friction can develop. Also 99% maybe too high efficiency for each sheeve, because cable does not bend all that easily -- but this is a small effect. (Suppose each turn of rope is 98% efficient... then 12 turns would be only 78% efficient.)

http://en.wikipedia.org/wiki/Block_and_tackle

Have you measured the lifting speed under no load yet? That is critical information that tells what the actual overall ratio is.

Thank your very mch mr. K Fry,

I reffered mechanical crane drawing of subject EOT, it is showing following :

Bottom Moving Block have 6 rope pully 500 dia. and top fixed Block have 4 pully 500 dia. and Equalise Pully 320 dia.

Regards,

T.D.

K-Fry to correct if I am wrong, but thid drawing says that you have 6 falls each side, using two cables on the drum. Which means that the speed will be 12/6 = 2 m/min.

The configuration is using two lift cables, each rated for 1/2 the load. The Sepeed will be the same for both cables, with the equalising pulleys making sure the two sides are balanced, preventing any tilting on the bottom set of pulleys.

I agree, it's a 6:1 system. So, it is correctly geared for 2m/min.

Curious. 18 amps under "no load" seems fairly reasonable. It is on the high side of the usual range of no load/full load current, but I'm assuming that "no load" in this case is not really no load, but rather with no load on the hook, leaving the load of the cables, hook and friction.

235 amps during starting is a reasonable value also, but this should only last for perhaps 3 seconds (I'm guessing here, based on memory of how a 30kW motor sounds during startup) If it takes three seconds to overcome mainly motor inertia, then the load acceleration is less than .1 G, not adding a lot to the static load.

I'm puzzled.

Maybe the 0 ohms resistance recorded with hot windings is telling. (Although it seems likely that it might have been measuring error, too.) Maybe under light load, the windings do not distort much, but under heavy low they distort enough to cause a short?

The OP says the micro motor is connected directly to the main motor shaft all the time through a 10:1 gearbox. This means the micro motor must be capable of being spun at 9800 rpm all the time -- 10 times its normal speed. Not impossible, but it would need to be the right motor. The fact that the micro motor seems to work well suggests that the main gearing, etc is apparently working OK.

I suppose tests at 20 and 40 tons would be revealing. I'd expect about 35 amps after startup at 40T. The OP would want to record lift speed, amps, and motor terminal volts in both cases (all done with great care for personal safety.)

Maybe a sheeve is jammed, and the effect is not noticeable until heavily loaded -- at a light load a cable could slip in its groove.

A 15kW and 30 kW motor can have the same frame size. Maybe the motor is mislabled?

This is peculiar motor problem. Which make is crane and motor?. Is it slip ring type motor with resistance box and master controller?. Crane motors are supposed to be suitable for crane duty with high starting torque and suitable for frequent reversing. Are the brakes electro hydraulic thruster type?. Have you received test certificate for the motor?.

PLEASE CONFIRM ABOVE. I SUSPECT IT IS ORDINARY MOTOR WHICH NOT HAVING HIGH STARTING TORQUE WHICH SHOULD BE MIN 150% OF NORMAL TORQUE AS PER I.S.

It seems that your lift will be in the region of 2m/min (from your description).

The Calculations are correct.

If you have confirmed that the actual lift speed is conforming with the 2m/min, then what is left is:

Either the DG is too small: The starting current of the motor on D.O.L will be at least 6 times the nameplate. Take it as 6 x 49 = 294 ~300A which translate to at least 200 kW (166, but take 200). Therefore, the DG must have 200 kW in reserve when the crane is loaded with 66T. If the DG is old or in not so good condition, take more reserve.

OR, as it has been suggested before, the motor is a standard unit while you need a high starting torque model (Wound rotor type like a shunt commutator type...or with auxiliary inbedded 2nd squirel cage etc)

OK I still to check lifitng speed on no- laod will confirm the results....

for DG is of a 1000kVA rating and a dedicated feeder of 250A provided for this crane.

and a Cable Connected from Isolator to Motor Contactor are of 3C x 16sq.mm size.

Regards,

T.D.

1000 kVA DG seems big enough. This will be 800 kW at p.f. of 0.8

Therefore, it should be loaded at a max of 640kW (80%) when the Crane Motor is lifting your 66T, so that it will have enough spare power to cover the required starting current. IF the DG is running at more than 700kW then you might have enough voltage dip to stall the motor or make it take too long to reach its full speed. This is the reason that the motor must be suitable for this kind of heavy duty.

Anyway, the test will at least confirm What the lift speed is.

The supplier's engineer (previous comments by you) cannot wash his hands on this issue as long as the crane has been erected to their specs and that there was no alterations SINCE the claim was that it run satisfactorily when tested at full load!

Go to this link and read about Induction motors with wound rotor and slip rings.

This is the type of motor you need for a crane: To produce high starting torque and prevent stalling and/or too long a starting period which will be drawing in the region of 5 to 6 time the nominal current.

http://www.lmphotonics.com/slipring.htm

If your motor is not a special high starting torque type (wound rotor or something with a double squirrel cage construction), you will keep having this problem when lifting the higher range of load.

Another thing: I am not very familiar with the way the micro-speed motor connects mechanically with the normal speed motor in cranes of this size. BUT, I think that there should be some kind of sequence and clutches to either start the microspeed motor first then engage the normal speed motor and unclutch+diconnect the microspeed motor, or Just disengage the micro-speed gear train when on normal speed. IF NOT Disengaged, the much higher gear ratio of the micro-speed will probably interfere with the running of the normal speed by putting a very high additional load !? (K-Fry can explain better this mechanisme?)