How to delay motor to start

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petersonra said:
What is the point of delaying the motors that are on on VFDs?
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To keep generator at reasonable rating, even with VFDs, if all motors started same time, the gen set size will be huge, can we program VFD to delay motor start?
 
Josh111 said:
I assume what is wanted here is actually to have each motor have its own delay and not a general delay for all motors. Also you didn’t specify but I’m assuming that you intend to start all the motors as soon as possible when the generator switches over as opposed to randomly starting motors as needed. Thus, each motor would need to have its own delay relay, most likely, unless you have an overall controller of some sort.

In addition to time delay relays or use of any such functions in the VFD, you probably need to come up with a trigger that causes those time delays to only be in the circuit when the ATS is on generator. Does your ATS have auxiliary dry contacts for use on things like this?

Lastly, how much of an inconvenience would it be if you just simplified your design by having those delays in your system at all times regardless of whether the generator or the utility was supplying?
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Well said, all motors can start same time but have to be after non-motor loads. Same thing when the normal power restores.
 
The subject is delayed motor start. Does it really need any kind of VFD?
 
ptonsparky said:
The VFDs are existing on some of the motors.
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Yes, I readily accept that. Most of my professional live was in variable speed drives. Just that the motor starter my not require it in many cases. maybe most.
 
How you implement the staggered start will depend on how your motors are controlled. If you simply use 3 wire control, when the power drops out, someone has to go and hit the Start button again, which effectively adds that staggered start. If it’s all 2 wire controls that are being turned on by a PLC, you can just add the delay into the PLC program. If it is 2 wire control with some other automated device calling for the Start, and that device remains maintained after a power loss, then that’s where you add a time delay relay. So whatever is doing the On-Off control, that device is now used to energize the timer coil, then the timer contacts energize the starter coil.

I would not worry about the VFDs, they will ramp up no matter what and most will current limit anyway. But if you want, all of the above techniques can apply to the VFD Run command circuit instead of the motor starter coil.
 
anbm said:
To keep generator at reasonable rating, even with VFDs, if all motors started same time, the gen set size will be huge, can we program VFD to delay motor start?
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The current required by the VFDs to run the motors will be much lower than the full load current of the motor when it starts up because the VFD will ramp the motor up to full speed
 
petersonra said:
The current required by the VFDs to run the motors will be much lower than the full load current of the motor when it starts up because the VFD will ramp the motor up to full speed
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Simply not true at all in any way. You are confusing power and current. Plus it depends on how the VFD is set up. You definitely won’t see licked rotor current but above FLA Edie silly during acceleration is normal.
 
I would do this all with a PLC because it is so flexible. But before going there…

As mentioned VFDs can significantly reduce current. If it’s a centrifugal pump ir fan you can current limit at FLA if you don’t mind the longer startup times and simply ignore any load management.

With starters the current can be significant. It’s application specific but an electronic soft start can significantly reduce current, increase motor life (and bypassed soft starts outlast VFDs) and at a reasonable price and much better running efficiency compared to a VFD (same as a starter).

With a PLC it’s easy to trigger an on delay timer that interlocks with a start command to inhibit it whenever one of the other loads starts. With 4 motors you end up with 4 timers tied to each motor. Plus you could potentially send the signals via PLC network so there Is only a network cable (or even wireless) going to each cabinet. In practice use normally closed interlocks so if something fails it doesn’t lock out the load,
 
hillbilly1 said:
Unless ordered with them, most ATS’s do not have elevator recall contacts. Switch position contacts are a more common option.
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Six of one, half a dozen of the other I suppose. Around here they always have recalls. I had a trane chiller have all 6 compressors do this exact same thing and that’s how I fixed it a 2 wire off the ats contacts to the Plc in the Trane a few lines of code and wahla no more tripped breakers
 
anbm said:
Four existing motors + some non-motor loads are fed from the same electrical panel. The panel is fed from an ATS (normal source gets power from main service panel and emergency source is fed from standby generator).

When the ATS connects to generator power, we want to start each motors at different time (delay to start), what can be added/modify in field to make this delay starting happen? Among those 4 motors, 2 has VFD controls and 2 via motor starters.

Below article said something about time delay relays, is this type of relay what I need to add and make it work?
Assuming this relay will "talk" to the ATS to know when ATS is on generator power?

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Also another thing to check is how close to in
Phase it transfers power the farther out the higher the inrush the closer the longer it takes to transfer 5degrees is usually good
 
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