Help with Lead Lag Standby?

[IlluminEyeTrickz]

Hello all,
I have a triplex pump skid, which they want up to 2 pumps to operate and the other to be on standby. I am kind of racking my brain on figuring out the standby part.

Does anyone have an example of a similar setup that I could look at?

I realize that Rockwell has a P_LLS lead lag standby plantpax module, but the manual is very unclear and from what I can tell it only works with the P_Motor AOI and I am using powerflex 525 drives.

Thank you kindly for any help in advance!

 

[drbitboy]

search for [lead lag standby] on this forum, see the [Search the forum using Google] text box above, you might get some ideas from that.

 

[cardosocea]

The P_LLS instruction can be used with VFDs. I had one configured with PF753 drives.

This document has logic explaining how to interface the motor to the P_LLS.

https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/syslib-rm054_-en-p.pdf

You may need to use different named bits to achieve the result since P_MOTOR has something like Run command and the drives have RunForward or something like this.

 

[Ken Moore]

What triggers the standby pump to start? Low Flow? Low Pressure? Running pump failure?
VFD output?

 

[cardosocea]

What triggers the standby pump to start? Low Flow? Low Pressure? Running pump failure?
VFD output?

This is a very good question. The LLS block gets a number of pumps that should be running and sticks to that if one fails by starting another one. However, you have to create external logic for the P_LLS to cycle the pumps (there's a command for it) and you'd have to create separate logic to determine whether the number of pumps to be running should be increased.

It works ok for 2 or 3 pumps, but anymore and it's not as nice as it doesn't have a priority or selection scheme to decide which pump to run next (whether to equalize running hours or not).

 

[IlluminEyeTrickz]

What triggers the standby pump to start? Low Flow? Low Pressure? Running pump failure?
VFD output?

The standby pump will start in the event of a high high level, if the other two cannot keep up with the level.

 

[dmroeder]

Google

Above and beyond.

 

[drbitboy]

Above and beyond.

Heh, thanks, but it was copy paste; I was surprised it worked !