# A/B 753 VFD & Generator.



## JRaef (Mar 23, 2009)

The drive will only support the motor for 15msec, after which the power output will be turned off and reset the pre-charge circuit. So it's only a potential issue if the power transfer time is less than 15msec, which is all but impossible. For transients shorter than that, you will want the line reactor. But just to warn you, if your transfer switch "bounces" in and out successively, you CAN indeed blow the pre-charge resistor, so just make sure there is a de-bounce timer enabled in the transfer switch. Different suppliers call it different things, but you get the drift.

If you don't want the control board to shut down and have to re-boot, which can take upward of 15 seconds to finish its self check routine, you can buy a 24VDC aux power board for that drive and feed it with a 24VDC UPS. That will keep the control board active, but will not affect the pre-charge circuit.


----------



## frenchelectrican (Mar 15, 2007)

I am on simauir page as JRaef mention about the translation time between line and generator source.

What I did with our city wells is that I did put in a small 24 volt battery on some units and other units I just tied to the generator starting battery system so that way it will cut down the start up of self checking time. 

so keep in your mind to use that option if you need to do that.


----------



## micromind (Aug 11, 2007)

Thanks, guys. 

I didn't know about using a 24DC source to keep the control board alive, I'll file that info for future use. In this application, it doesn't matter if the pump stops for a few minutes. 

One thing I'll likely try is to see if the transfer switch controller has a 'elevator disconnect' feature. If so, I'll use it to allow for the VFD to ramp down before a transfer back to utility. Even though the system has a surge tank, ramping down would be better that a sudden stop.


----------



## JRaef (Mar 23, 2009)

micromind said:


> ... One thing I'll likely try is to see if the transfer switch controller has a 'elevator disconnect' feature. If so, I'll use it to allow for the VFD to ramp down before a transfer back to utility. Even though the system has a surge tank, ramping down would be better that a sudden stop.


Not a bad plan at all.

Another thing to consider is that the 753 (and many other VFDs) have what's called a "Flying Restart" feature (parameter 356) that allows a drive to catch a motor that is already spinning and re-ramp it without causing harm to the drive or motor. So if for example your drive does just turn off and then come back on after the generator is stable, but the motor is still spinning down, when you re-initialize the VFD it will look at the back EMF coming from the motor, synchronize it's output frequency to match it, then re-accelerate it from there.

The only down side of Flying Restart is that if the VFD was off but when you give it a Run command, the motor is slowly *back*-spinning due to back flow, Flying Restart will sometimes get fooled by that and begin ramping the motor in the wrong direction for a second or two before it sees what's happening. It will correct itself, but that first second or two freaks people out when it happens. So if you are going to use it, make sure there is back flow prevention, i.e. a check valve in a pump or an air shutter in a fan.


----------



## Jlarson (Jun 28, 2009)

Be careful with flying restart on well pumps.


----------



## micromind (Aug 11, 2007)

This motor has a ratchet so it can't turn backward. It also has a cla-valve between the pump and the tank, static pressure is about 60 PSI. 

Since the bearings are continuously water lubed, I'm going to start with a 60 second ramp and see how it reacts when the air bleed closes. Even though there's a surge tank, I'd rather have a fairly slow flow when the water column hits the cla-valve. 

The static level in the well is about 120'.


----------



## Cow (Jan 16, 2008)

micromind said:


> This motor has a ratchet so it can't turn backward. It also has a cla-valve between the pump and the tank, static pressure is about 60 PSI.
> 
> Since the bearings are continuously water lubed, I'm going to start with a 60 second ramp and see how it reacts when the air bleed closes. Even though there's a surge tank, I'd rather have a fairly slow flow when the water column hits the cla-valve.
> 
> The static level in the well is about 120'.


I just did a 150HP Yaskawa on a submersible well pump this week. I haven't installed a 753 yet, but the Yaskawa IQPump's we've just started using have a precharge circuit where you can set the speed and time the drive initially runs at when given a run command until it sees a certain amount of pressure at the transducer, which is an adjustable setpoint. As soon as it hits that setpoint, it ramps to the speed you want it to run at normally. It worked great on this pump, the pipe used to shake and the air bleeder would slam shut when that full 60HZ pump speed eventually got water to the surface. Love the precharge settings!! It also has a thrust mode for submersibles when they're first started to keep the bearings lubed properly. Without that thrust mode, if you instead stretch the accel time out for a long time to avoid water hammer it could be to the detriment of the bearings, or so I'm told.


----------

