How to delay motor to start

[GoldDigger]

What is the point of delaying the motors that are on on VFDs?

They may not present a starting load, but you might want to hold them off until the across the line start motors are running.
More significant to me, in light of some of the questions and suggestions, is whether you want the delay from start signal to startup because you expect all of them to try to restart when the power come up after the transition? If so you might want to delay all of them from generator start rather than delaying the start signal of each one even if it happens long after the generator has started. But that will allow some other external event to cause all of them to try to start at once from generator power. Different fixed delays will not work if the start signals happen to be staggered wrong in time.
It really comes down to a need to prevent certain undesirable simultaneous start conditions when the generator is on, rather than imposing different fixed delays. Which suggests that the performance would be best when run by a small PLC.
The bad side effects of one simultaneous start bringing down the generator may well be costly enough to justify a PLC.

 

[Jraef]

If you want to go retro, you can use a cam timer switch to sequence the starting of the motors.

That IS retro!

 

[ptonsparky]

That IS retro!

How would a cam timer switch compare in price to the lowest priced, capable, AB plc?

 

[ATSman]

A lot of commercial transferswitches have auxiliary contacts that change when switch position changes, this can also be used to trigger the time delay relays previously mentioned.

Also, most modern day ATSs have this feature built in to their controllers. As with the case with ABB-Zenith on their MX250 controllers they call it Universal Motor Disconnect (UMD.) It also has the elevator pre-transfer feature that post #31 mentioned that will work also. It would help if the OP provided the manufacturer and model# of the ATS.

 

[hillbilly1]

Also, most modern day ATSs have this feature built in to their controllers. As with the case with ABB-Zenith on their MX250 controllers they call it Universal Motor Disconnect (UMD.) It also has the elevator pre-transfer feature that post #31 mentioned that will work also. It would help if the OP provided the manufacturer and model# of the ATS.

None of our customers have those options installed, but then most of them do not have elevators either. Most of the options they get are for energy management. Switch position, source available. None have load shedding options installed. They can do that through EMS control. Most use Kohler or Asco switches with a few GE scattered in there.

 

[Russs57]

All depends on the details. Could be as simple as an 8 buck ICM 2 terminal time delay relay in series with one side of the coil on the motor starter. The VFD should be dealt with via programming, either in the drive or whatever is giving the run command..

Sure we can get a lot more elegant, but the above may be all he needs. Plus it is simple, cheap to institute, and to understand. If a delay to restart can be tolerated upon transfer to emergency I would think it could be tolerated on re-transfer to normal and/or power blinks. For the four loads you would only need about minute from loss of power for all loads to be on-line. Perhaps as low as 15 seconds depending on types of loads and your VFD controls.

 

[ptonsparky]

All depends on the details. Could be as simple as an 8 buck ICM 2 terminal time delay relay in series with one side of the coil on the motor starter. The VFD should be dealt with via programming, either in the drive or whatever is giving the run command..

Sure we can get a lot more elegant, but the above may be all he needs. Plus it is simple, cheap to institute, and to understand. If a delay to restart can be tolerated upon transfer to emergency I would think it could be tolerated on re-transfer to normal and/or power blinks. For the four loads you would only need about minute from loss of power for all loads to be on-line. Perhaps as low as 15 seconds depending on types of loads and your VFD controls.

Yes, those little details none of know.