New to the AB PowerFlex 750

Hi everyone,
I have a new project that is going to use a AB PowerFlex 750 VFD Drive. I have worked with VFD's before, but someone else always did the programming. I understand how they work but am way lacking on the details.
Here is what I am doing:
Drive: AB PowerFlex 750 Model #20G1AND125AN0NNNNN
Motor: 75HP mounted to a 6x8-13 pump
Controller: Controllogix (exact Model to be determined based on I/O needed)

Here is what I am doing. I have a single pump that is rated for 1800 GPM at full speed. It is supplying Oil to load up to 3 rail cars at 600 GPM each. The Electronic Presets will control flow via FCV's and send a DO to the PLC for pump request. A Analog Output can be added to send a flow rate to the PLC if needed.

What I want to do is this:
1. When a pump request is sent I want to start the pump slowly to avoid shock to the system and the pump.
2. If there is only 1 pump request, run the Motor at 33%.
3. If there are 2 pump requests, run the Motor at 66%.
4. If there are 3 pump requests, run the Motor at 100%.
5. As pump request drop off set the motor to the proper % for # of requests.

Given that what do you guys recommend?
Would you use the AO from the Loading Computers to determine what speed to set the motor?
Would you use Ethernet to send the info from the PLC to the Drive? Or is hardwired I/O the way to go.

I just need some ideas on where to start. Thanks for any help you can provide.

the easiest and possibly cheapest solution would be to buy a Powerflex 755 drive and use Ethernet. You have to buy additional cards to be able to use hardwired I/O and setup for hardwired I/O isn't as simple as the 40 or even 700 series. IMO, ethernet is easier, more reliable, and gives you lots of extra control and information you may need in the future.

Some tips. If you are going ethernet (Best Method)get a 755 over a 753 as the ethernet is onbaord in a 755 and a add on card in a 753 and the price is not much difference plus you get a lot of useful maintenance parameters in the 755 also.

Program the drive through Logix or Drive executive if possible as the HIM is a real PITA.

What PLC do you have?

The PLC will be a CompactLogix maybe a L33. I haven't selected the PLC yet as the I/O requirements are not clear yet.

We are building the pump skid and I asked the customer about the PLC/VFD they planning on using and I got the "Blink...Blink" what MCC? You mean your skid doesn't come with a starter?

So now I am involved with the VFD and will most likely be doing the PLC work too. Which I am pretty happy about as I really like the PLC work. A chance to do something different.

I have been thinking about this. Am I over engineering this? We dont normally use VFD's but most of our pumps only have 24 or 30 HP motors. With a 75HP motor I what thinking it would be better in the long run to use a VFD. I figured it would help with energy cost and would keep the ware and tear on the pump and motor at a minimum. Could I get the same results by using a Soft Starter?

What do you guys think? How would you approach this application?

Sounds like you might be over-engineering it. Do you just need to control a single pump and that is it?

It sounds like the FCV valves are being controlled by something else, you get a request from that system to "turn on the pump". To me it seems quite simple. Hard wired, relay and yes to a Soft Start. You won't be able to do your speed presents but you'll limit the initial shock of starting up the pump.

Adding a CompactLogix, VFD w/Ethernet and your programming time seem like an unnecessary expense. But, you've talked with your customer about it now it may be an expectation.

What did your proposal say you'll provide??

Bullzi said:

I have been thinking about this. Am I over engineering this? We dont normally use VFD's but most of our pumps only have 24 or 30 HP motors. With a 75HP motor I what thinking it would be better in the long run to use a VFD. I figured it would help with energy cost and would keep the ware and tear on the pump and motor at a minimum. Could I get the same results by using a Soft Starter?

What do you guys think? How would you approach this application?

Click to expand...

Depends on the application. We would need more detailed info but normally a 75 HP with VFD in most aplications would not yield enough energy savings to wow management enough to cover the costs.

That's been my experience anyway YMMV.

Paully, The original design called for all the parts to be shipped for field assembly. We didn't have a starter in the original. They changed up later and wanted a turn key skid assembly. I didn't do the quote and there was no starter on the "skid" quote.

Anyway I talked to the customer today and he likes the idea of a VFD and the price didn't scare him off. In the oil business it is hard to scare anyone with price. But I keep trying

Since you are loading rail car that implies temporary fittings and or hose. VFD to allow slow ramp up of pressure and flow will keep surging to minimum thus in theory no blown hoses. You seem to be doing petroleum - spills on this stuff are big hysteria and expensive. If it were vegetable oil well - almost - who cares - biodegradable ??

No mention of what type pump so cannot do any more crystal ball stuff.
Either way big mess and downtime.

Dan Bentler

The Pump is a Centrifugal. It has a max pressure of about 80 PSI. I am not too worried about pressure.

I was more worried about a situation where only one position is loading. The minimum flow for this pump is 800 GPM. One position only loads at 600 GPM. I could put a return line with a PRV back to the tank but that also creates its own cost and problems.

I was doing some research on the AB site. I can across a video talking about CIP Motion . In the video the commentators talked about using a Quality of Service (QoS) Ethernet Switch with the PF755 Drives. I am not doing any motion so do I need a QoS switch to make the PF755 work as a standard VFD?

Qos is used when you have lots of devices on ethernet and you need to give important items like drives and I/O the priority of traffic flow and Bandwidth.

If you had a Historian for example that polled the plc for data once every hour you would give it a lower priority than your I/O and Drive for example.

Nothing you need to worry about with the application you have described.

CIP Sync won't apply either as you said.

Reduced suction and or a valve could control your pump flow but the drive is more idiot proof. With a valve Bubba may come by and decide that "This thing richt heer` needs to be open all the way to make it work right Cletus"

Bullzi said:

The Pump is a Centrifugal. It has a max pressure of about 80 PSI. I am not too worried about pressure.

I was more worried about a situation where only one position is loading. The minimum flow for this pump is 800 GPM. One position only loads at 600 GPM. I could put a return line with a PRV back to the tank but that also creates its own cost and problems.

I was doing some research on the AB site. I can across a video talking about CIP Motion . In the video the commentators talked about using a Quality of Service (QoS) Ethernet Switch with the PF755 Drives. I am not doing any motion so do I need a QoS switch to make the PF755 work as a standard VFD?

Click to expand...

Min 800 gpm at what pump RPM?. What is max flow and at what RPM. The pump must move fluid to keep impeller and shaft seals cool. THe drive motor depending on type must run fast enough for the enclosed fan to keep motor cool.

Centrifugal pumps must have net positive suction head (NPSH) to avoid cavitation and wear on impeller. Throttle the discharge all you want but NEVER throttle the suction.

I'd be talking to the pump maker and looking real hard at the curves for the pump.

I think you need to consider the basics of your equipment before you start altering it. You cannot overcome poor equipment design or selection with programming and fancy black boxes. I would consider a smaller pump when filling only one tank. Yes it is going to cost but you now have redundancy.

Dan Bentler