Dear Mukesh,

If you really need 140% nominal torque during starting, then use a squirrel cage electric motor with a saddle torque of 155% ( to be sure that there always will be speed acceleration) and start Direct On Line.

Whether there are VFD drives that can increase the voltage, I do not know.

If such a motor does not exist, oversize the drive motor.

I do not know whether a hydraulic torque converter can do the starting up as well.

Your question is best asked to a supplier.

Let us know your findings, please

Success

Teus ■

Originally Posted by mukesh.sanghani1

starting torque require through VFD drive for Conveyor

Dear Sir

We require % starting torque (100 %, 120 % or 140 %)of full load toruqe for Motor during fully loaded conveyor start through VVFC drive.

(Convyor Full load torque 1150 KG-M)

Mukesh

Yes, you require that, OK, so that's the question?

Just tell your drive supplier these are the characteristics you require and let him select the components accordingly.

We regularly tell our drive suppliers that we need 2 x FLT at startup with variable frequency drives. ■

Most VFD's can provide your higher nominated starting torque than motor nameplate if the inverter has the rated commutating capacity.

Short term higher torques is common and depends on the duration. So, you need to define the duration and check against inverter specification.

When you turn down the motor hertz, via the inverter, you shift the breakdown torque curve toward the initial starting RPM. Ask the inverter supplier for details.

We tested, with the mfgr., an inverter to see how much starting torque could be developed for La Caridad in 1976. It developed sufficient lock rotor torque to snap the 250 hp motor shaft. This was > 250% of motor nameplate. ■

In the early days of VFD's we had an experience where a client supplied VFD wouldn't start a loaded conveyor. "Sorry" said the supplier, "it will only allow 80% of full load torque at startup." ■

Originally Posted by mukesh.sanghani1

Dear sir

During starting (near Zero speed - low hertz) how much torque required ? (% of name plate torque)

VVFD drive : ABB(ACS 800 ) / Siemens sinamis

Mukesh

If you are designing the conveyor you must tell the drive supplier what torque you need. ■

Hi there..

When we put electrical VSD drives on our belt feeders, we need high torque for initial break away.

We get 160% FLT

Cheers

LSL Tekpro ■

Designer,

Maybe you could share the mfgr who told you the inverter could not produce more than 80%. I find the statement to be rubbish.

The natural physics, of most, if not all inverters can be altered to control the volts to hertz ration and general voltage boost. Problems can arise when the motor is placed some distance from the inverter. The line losses (line size) need to be compensated for, else you get too much voltage drop and no torque. Also, if you pass the output power through a boost transformer (380 volts to 4160 volts, etc) the transformer can have problems with the frequency at the low end. ■

Originally Posted by nordell

Maybe you could share the mfgr who told you the inverter could not produce more than 80%. I find the statement to be rubbish.

It was a long time ago, I'm guessing early 1970's and it was our first experience with an inverter. My memory isn't that good but I think it was Danfoss (no disrespect to modern Danfoss inverters). We supplied the conveyor, the user supplied the inverter. It started empty OK, it ran full OK, it wouldn't re-start when fully loaded. I think it also had a worm gearbox which might not have helped, a lot of our machines had worm gear units at this time. The user had to fit a larger inverter to overcome the problem. It was in a chemical plant in the north west. ■

One thing to remember is that this application calls for a constant torque constant speed to be activated. Out of the box 99.9% of all VFD's are configured with variable speed and torque if you do not tell the mfg not to do that resulting in the drive not being able to start and in some really bad cases throwing belts etc. ■

Conveyors are variable torque (load, speed, and temperature) and variable speed ( from rest to nominated speed - sometimes selectable).

As I said in a prior posting, most inverters are volts (torque) and Hertz(Speed) regulated. At low speeds (3-10 Hz) the voltage can be boosted, and often is for a number of reasons, well above the nameplate demand. At steady-state, the inverter is rated to its nameplate. At starting, it is ofter rated about 125-150% for 100-150 seconds, depending on designer preference. Above this threshold, the inverter need to be rated for a higher commutation level.

Inverters are not all the same. Some practice "Flux Vector" or similar control which conserves energy by capturing the potential electrical losses such as power factor, et al. Thus, they are more efficient at any speed and can operate at lower speeds for a longer period. ■

Originally Posted by mukesh.sanghani1

Dear sir

During starting (near Zero speed - low hertz) how much torque required ? (% of name plate torque)

VVFD drive : ABB(ACS 800 ) / Siemens sinamis

Mukesh

ABB ACS800 is a high performance drive series. You'll have lot of different options to build a complete part number like ACS800-U1-0004-5-P901. That is 3HP, 5A drive. ■