1000 hp pumps (4160 volt each with itÆs own VFD) 1

[Andy32821]

We have three 1000 hp pumps (4160 volt each with it’s own VFD) to control the clear well level of a water discharge station. There is one PID level controller giving an output to the three pumps. The third pump is seldom used and the first two pumps have to run at 100% for ten minutes before the third pump is allow to start. The pumps are rotated monthly as to lead, lag 1, and lag 2.

The biggest concern is that the third pump not start unnecessarily to keep the month’s power demand as low as possible. None of the pumps will run below 50% because they can’t open the check valve against the head pressure at low RPM’s.

Most of the time it takes 1 ½ pumps to maintain setpoint.

My question is:

Is it better to let both pumps run all the time and ramp them between 50% and 100% or is better that the lead pump runs at 100% and lag 1 pump runs from “off” to 100% as needed (this results in the second pump shutting down completely about twice an hour)?

 

[jbartos]

Suggestion to jOmega (Electrical) Aug 25, 2003
JB:
Perhaps you will enlighten us as to what "bigger electrical and mechanical stresses" set 2 will experience, since Andy32821 stated that all three are on VFDs.
///The set 2 was obvious from the context to be:

"...or is better that the lead pump runs at 100% and lag 1 pump runs from “off” to 100% as needed (this results in the second pump shutting down completely about twice an hour)?"

Please, would you post for yourself in this Forum, namely, your request would read better as:
"Perhaps you will enlighten me (not us, who are those others?) as to what "bigger electrical and mechanical stresses" set 2 will experience, since Andy32821 stated that all three are on VFDs.\\


\\

 

[jOmega]

Well JB,
You made the statement about set 2 experiencing "bigger electrical and mechanical stresses".

You offered no support for your statement.

Your statement is contrary to general VFD Pump Application knowledge.

... and so, I asked, on behalf of all of us who read your posts, for you to provide us all with some proof or evidence or documentation that supports your statement.

I think you owe it to ALL of US... who read this forum to not make claims that cannot be substantiated.

Remember JB, the people who open these threads in this forum are seeking answers, knowledge, and truth.
Posting statements that are inaccurate, misleading, or unsubstantiable helps no one.

When you are challenged to support your claims, I think you owe all of us validation thereof.... or retraction thereof.

I hold myself to the same professional responsibility.

So, would you please advise us as to what "bigger electrical and mechanical stresses" set 2 would incur....
and be specific if you can