Transfer a motor onload from vfd to mains 2

[amitkumarnain]

Hello,

I need to transfer motor once it reaches 50Hz i.e 100% speed on vfd to mains .The same needs to carried out for FC102 , ACS850 , ACS550 , ACS800 . I hear the synchronous transfer option exists for ACS800 . Danfoss has agreed to offer synchronous card (which is still in R&D ) .My going through various forums here and others i understand following solution exists :
1.) Use Synchronous transfer cards. But these are available only for Danfoss FC102 and ACS800 . What do i do about ACS550 / ACS850 loads?
2.) I can ramp up the motor to say 52.5Hz instead of 50Hz and bring vfd out of loop , use phase sensing relay . When this relay senses phase angle from back emf being generated by motor is same as mains power supply switch on the bypass contactor .

I see option 2 is more like hit and miss .

Also what will happen if i just bring vfd out of circuit and switch on DOL without any sensing of phase or use any Sync cards.

For ACS800 Sync Card is RSYC-01 . Can this or any other card be used for ACS850/550?

Thnks
Akn

 

[itsmoked]

Also what will happen if i just bring vfd out of circuit and switch on DOL without any sensing of phase or use any Sync cards.

Very very bad things can happen. The motor switches to be a generator the moment you disconnect it. A generator no longer sync'd to the local power grid. Then you close a contactor to that power grid and connect an unsync'd generator to it. Things can explode. What's being spun can fail from the impulse.

The arc generated when you interrupt the drive current from the VFD can also damage its output stage.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Unless you have an Active Front End (AFE) VFD, option 2 is really the only thing you get. Option 1 in non-AFE drives is really option 2, just using a canned subroutine embedded in the card with a line monitor to determine the phase angle of the source and the ability to take full control of the isolation and bypass contactors, instead of you doing it on your own outside of the drive. Some drives have option option 1 built-in to the VFD hardware and firmware.

"Will work for (the memory of) salami"

 

[squeeky]

May I enquire why you would want to do this?

 

[DFordPE]

If all you want to do is bring it up to speed, why not use an SSRV starter. They come with bypass contactors built in.

 

[jraef]

Because sometimes you need variable speed, and sometimes you don't? Or because sometimes the restrictions on starting power are so great, a solid state soft starter cannot work?

We have that latter issue going on a lot now here in central California. Farmers are having to get water from deeper and deeper in the ground as the aquifer drops due to our prolonged drought, so that means larger and larger deep well pumps. At the same time, farmers in far flung areas can no longer use diesel powered pumps because of air quality restrictions. So they apply for the utility to run distribution lines for 400-600HP pumps out to farms where there was no electrical service previously. Yet the utility lines are already stretched thin because of the NIMBY syndrome, so the services are very weak and the resultant heavy restrictions on starting kVA are not allowing deep well pumps to start with soft starters now. I just worked on one where the utility allowed them 600kVA maximum to start a 500HP pump! The solution is the use a VFD as a "glorified soft starter" because it can accelerate the pump to full speed without exceeding FLC, no matter how long it takes. But once they are at full speed, the VFDs would require cooling to keep running for very long and rather than do that, they want to bypass them across-the-line.

"Will work for (the memory of) salami"

 

[amitkumarnain]

The customer has limitation on main 11kv/430V transformer on capacity . Now if he keeps all his 415V vfds online he is having harmonic and the load on vfd is also runs full speed . So we wanted to transfer to mains on the fly from VFD .The benefit is lower harmonics at PCC , additional capacity as site effect of lower harmonics, higher efficiency once vfd offline .

 

[squeeky]

For amitkumarnain, having asked around the efficiency answer came up the most often but to avoid other efficeny losses pfc would have to be added. I must say I have enjoyed this discussion and having approached several manuafacturers of VFDs I find that they can all do it but it requires a special add on card. I did not know this and would have probably "given it a go" had I not read this.

The other use that came up was running multiple pivots from many pumps. The basic system would have a pressure transducer which would control the speed according to the pressure. More demand, more flow, lower pressure, increase the speed. Now the first motor / pump cannot supply the demand as more pivots are started so it starts the second pump. The VFD now drops the speed as low as it can go and while the second pump supplies base load, the first does the "top up". Then the next pump and then next until all are running. Highly energy efficient. The problem with this is that one pump runs with the VFD and the last one hardley ever runs.

WEG (and I suppose others) have a built in program within the VFD PLC which allows you to run all motors / pumps with equal running hours and thus requires the change over contactors and the special card to be added. All wonderful modern, energy saving machines.

Thank you for this posting.

 

[DFordPE]

Why not just install a filter ahead of the VFD?

 

[LionelHutz]

You have 3 options.
- use the synchronous transfer option on the VFD.
- overspeed and then open transition with a phase relay.
- install a harmonic filter ahead of the VFD.

It would likely be simpler to just place some of the VFDs, especially the smaller ones and ones without line sync capabilities, onto passive filters.

I've tested different passive harmonic filters. The MTE Matrix was the best performing and the Mirus Lineator was a close second. The MTE will lower your current harmonic distortion to 5%. The "secret" seems to be in the single figure 8 core of the filter. I also tested some simple trap type passive filters that had multiple inductors, some with taps, and they were all useless junk. One filter was 10X the cost of a 5% reactor and had worse performance.