Running master/slave VFD

[adeebmostapha]

Hello guys,

i have questions about VFD. Can I runs 2 vfd simultaneously with one pressure transmitter? ok. let me illustrate the system that i want to implement.

There are 2 cycle

1st cycle:
VFD 1 : Master
VFD 2: Slave

after 1 hour (using timer)

2nd cycle:
VFD 1 : Slave
VFD 2 : Master

how to do wiring and commissioning for the system take in account im using Siemens V20.

 

[Dennis Alwon]

I cannot answer this question but others may be able to help however, we can only answer your first question of "can it be done." We cannot help with the wiring per forum rules.

 

[OldSparks]

Why would you do this?

If both drives are running all the time, what is gained by altering the “master” and “slave” functions?

Does the master run in variable speed, and the slave in constant?

If they are NOT both running simultaneously, and you are using a 4-20ma control loop, then the answer is a simple ‘yes’. The level transmitter can be connected to both drives at the same time. Only the drive that is in service will respond to the transmitter signal.

 

[Besoeker]

Hello guys,

i have questions about VFD. Can I runs 2 vfd simultaneously with one pressure transmitter? ok. let me illustrate the system that i want to implement.

There are 2 cycle

1st cycle:
VFD 1 : Master
VFD 2: Slave

after 1 hour (using timer)

2nd cycle:
VFD 1 : Slave
VFD 2 : Master

how to do wiring and commissioning for the system take in account im using Siemens V20.

Slave in what sense? Gets its speed reference from the master drive?

Maybe you need to frame the question differently.

 

[ActionDave]

I'm thinking that by master/slave he means lead/lag.

 

[Besoeker]

I'm thinking that by master/slave he means lead/lag.

The master/slave systems I've designed/been involved with had one drive in speed control and the other(s) in load share. But not swapable duties which is what the op is asking for. Maybe he/she will come back with better details but I won't be holding my breath.

 

[Jraef]

I'm thinking that by master/slave he means lead/lag.

That's what it sounds like to me too.

Assuming so, implementing it in a Step 7 programming for Siemens PLCs is beyond the focus of this forum. You may need specific training in how to develop programs in Step 7, usually a week long course at minimum. You can also contact Siemens and ask if they have a canned "pump alternation" subroutine they can share with you. It's a very very common application, I'm sure they do.

 

[ptonsparky]

I'm thinking that by master/slave he means lead/lag.

I hope that’s what he means. The only master/slave I’ve been involved with required outside help we’ll beyond me. Small detail in that it was only the second set of VFDs I had seen, let along worked on.

 

[petersonra]

Hello guys,

i have questions about VFD. Can I runs 2 vfd simultaneously with one pressure transmitter? ok. let me illustrate the system that i want to implement.

There are 2 cycle

1st cycle:
VFD 1 : Master
VFD 2: Slave

after 1 hour (using timer)

2nd cycle:
VFD 1 : Slave
VFD 2 : Master

how to do wiring and commissioning for the system take in account im using Siemens V20.

It is not clear to me either what you mean by master/slave.

If you mean lead/lag it is relatively easy to implement, depending on just what it is you are actually trying to accomplish.

If you are having trouble figuring out the wiring perhaps it would be best to get someone involved who has more experience with VFDs to help you.

 

[Besoeker]

It is not clear to me either what you mean by master/slave.

If you mean lead/lag it is relatively easy to implement, depending on just what it is you are actually trying to accomplish.

Lead/lag in what sense?

 

[ptonsparky]

Lead/lag in what sense?

During one cycle of operation VFD A operates first (Lead) to supply water with VFD B (Lag) starting after a predetermined time or continued pressure drop until pressure is satisfied.

The next cycle starts with VFD B taking Lead and A taking Lag duty. Purpose being to get similar run times for both. In reality, both pumps are worn out at about the same time.

Tracking the actual run times of each can tell you how well that particular pump is operating in comparison to the other IF someone is paying attention.

 

[Besoeker]

During one cycle of operation VFD A operates first (Lead) to supply water with VFD B (Lag) starting after a predetermined time or continued pressure drop until pressure is satisfied.

The next cycle starts with VFD B taking Lead and A taking Lag duty. Purpose being to get similar run times for both. In reality, both pumps are worn out at about the same time.

Tracking the actual run times of each can tell you how well that particular pump is operating in comparison to the other IF someone is paying attention.

Thank you kindly for that. It isn't what I would have termed master/slave but I understand the application.

For me, the master/slave arrangement, commonly used on paper making machines, would be two or more drives mechanically coupled via a "felt" or other material. The master controlled the speed. The slave(s) shared the load torque. Mostly used at the "wet end".

 

[ptonsparky]

Thank you kindly for that. It isn't what I would have termed master/slave but I understand the application.

For me, the master/slave arrangement, commonly used on paper making machines, would be two or more drives mechanically coupled via a "felt" or other material. The master controlled the speed. The slave(s) shared the load torque. Mostly used at the "wet end".

I described Lead/Lag as I would use it. Not Master/Slave.

The only M/S I was involved with was with plastic extrusion into sheets. 1/8" to 5/8" in thickness. I would guess in a similar fashion as to your paper making, although not near as critical.

 

[Jraef]

The OP used the term "master-slave" but the description of operation he offered appeared to be more along the lines of lead-lag, hence the comments to that effect. It's really incumbent upon the OP to clarify or at least tell us he got what he needed, rather than keep speculating ad nauseam.

 

[Besoeker]

I described Lead/Lag as I would use it. Not Master/Slave.

The only M/S I was involved with was with plastic extrusion into sheets. 1/8" to 5/8" in thickness. I would guess in a similar fashion as to your paper making, although not near as critical.

I've been around the block a few times, ridden hard, and put up wet. It gave me a wealth of opportunities that probably not many in our field get..
From the frozen Great Lakes to the Sahara Desert,
Paper, steel, water, plastics, anodising, petrochem, zinc mill in Turkey, Character building stuff I guess.

But drives for paper making were the most critical in terms of dynamic performance.
Although some of our machine tool drives eclipsed that by at least an order of magnitude - 10,000 rpm to zero within less than a second to within half a degree of position accuracy. To the eye it looked instantaneous.