Thread: Interesting 3P motor

So Bob,

If you did install the motor would you use a pair of VFDs to enable the fan the run at its intended speed and the main motor at variable speeds? There have been a number of discussions regarding simultaneous running of two motors on a single VFD but in the case of this motor, I imagine there would be no advantage of its use over any other motor if a single VFD was used.

Bob.

Originally Posted by Anorak Bob

So Bob,

If you did install the motor would you use a pair of VFDs to enable the fan the run at its intended speed and the main motor at variable speeds? There have been a number of discussions regarding simultaneous running of two motors on a single VFD but in the case of this motor, I imagine there would be no advantage of its use over any other motor if a single VFD was used.

Bob.

Hi BT,

I suspect that the fan is a 2 pole motor, while the main motor is a 4 pole, so even if they both ran from the one vfd, the fan will always be twice the motor speed.

Ray

Originally Posted by RayG

Hi BT,

I suspect that the fan is a 2 pole motor, while the main motor is a 4 pole, so even if they both ran from the one vfd, the fan will always be twice the motor speed.

Ray

I haven't tried it out yet but I also assume thats how it works.

Originally Posted by Anorak Bob

So Bob,

If you did install the motor would you use a pair of VFDs to enable the fan the run at its intended speed and the main motor at variable speeds? There have been a number of discussions regarding simultaneous running of two motors on a single VFD but in the case of this motor, I imagine there would be no advantage of its use over any other motor if a single VFD was used.

Bob.

No, that is not how these are used. Only the motor is run by the VFD. The fan runs directly from 50Hz line frequency. It is supposed to provide constant cooling, no matter how slow the motor is running.

Originally Posted by cba_melbourne

No, that is not how these are used. Only the motor is run by the VFD. The fan runs directly from 50Hz line frequency. It is supposed to provide constant cooling, no matter how slow the motor is running.

I think that was the point AB was making. You need to run 2 VFD's if you want the fan to run at 50Hz *and* you don't have mains supplied 3 phase 415V power.....

PDW

There is only one cable gland into the terminal box so I think the twice as fast theory wins.
(Before someone suggests running two sets of supply down one conduit, I suspect that would be considered bad (and unsafe) practice)

Michael

Originally Posted by Michael G

There is only one cable gland into the terminal box so I think the twice as fast theory wins.
(Before someone suggests running two sets of supply down one conduit, I suspect that would be considered bad (and unsafe) practice)

Michael

Michael, it only takes 2 minutes to drill a hole for a second gland. And its a perfectly safe practice.

That said, that particular motor in its previous live was probably not used with a variable speed drive. The additional fan was installed to improve cooling, probably because the motor was used in an environment with elevated ambient temperature. If you look at that fan, you see that it is an axial fan. Unlike the centrifugal fan type that is normally used in TEFC motors. It likely provides a greatly increased airflow over the stock centrifugal fan, without taking up much more space.

Originally Posted by cba_melbourne

Michael, it only takes 2 minutes to drill a hole for a second gland. And its a perfectly safe practice..

There was a couple of feet of old wiring still attached to the motor and there were definitely 2 sets of 3P power (one to the fan and one to the motor) in there

That said, that particular motor in its previous live was probably not used with a variable speed drive. The additional fan was installed to improve cooling, probably because the motor was used in an environment with elevated ambient temperature. If you look at that fan, you see that it is an axial fan. Unlike the centrifugal fan type that is normally used in TEFC motors. It likely provides a greatly increased airflow over the stock centrifugal fan, without taking up much more space.

As I said in my OP there were two toothed pulleys attached to this and on just about every motor the seller had.
The seller was the electrical fitter that pulled the machine down and he said one pulley was to drive something and the other was to a mechanical type tacho which fed back to the VFD. He had a bunch of the old tacos with the corresponding toothed pulleys, and the original VFDs there and they look big and clunky. Very interesting to see all this and I'm glad he rescued it as the gear had never been switched on and was in very good condition

Originally Posted by cba_melbourne

Michael, it only takes 2 minutes to drill a hole for a second gland. And its a perfectly safe practice

Not suggesting that it is not safe practice to mount a second cable gland. I was pointing out that there was only gland into the terminal box as pictured, so it was likely that only one supply was run to the motor. Looking at the terminal block photo again, it looks as if there are jumper cables between the two sets of terminals further supporting the idea.
The reason that I suggested running two sets of cables in one conduit could possibly be considered bad practice was that it could give rise to confusion as to which conductor is in which set - if one set is made safe are you sure the other set has too, and that there has not been any cross wiring. While it has probably been done, I can't see regulators liking it.

Michael

Originally Posted by Michael G

Not suggesting that it is not safe practice to mount a second cable gland. I was pointing out that there was only gland into the terminal box as pictured, so it was likely that only one supply was run to the motor. Looking at the terminal block photo again, it looks as if there are jumper cables between the two sets of terminals further supporting the idea.
The reason that I suggested running two sets of cables in one conduit could possibly be considered bad practice was that it could give rise to confusion as to which conductor is in which set - if one set is made safe are you sure the other set has too, and that there has not been any cross wiring. While it has probably been done, I can't see regulators liking it.

Michael

Slightly off the topic, but I commissioned a multiple pump control system a few years back, and the electrician had run the cables, he ran the normal red, white, blue orange circ. there were three pumps, so he did three runs of cable.. and at the other end he connected all the red wires to pump 1, the white was pump 2 and the blue was pump 3... I don't think he had much experience with 3 phase stuff.. I complained, but he refused to change it...

The question Bob asked was do you need 2 vfd's, I'm not sure we got enough information for a definitive answer..

Ray

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Originally Posted by DavidG

We strongly advise contacting a Licensed Tradeperson for all electrical work.

To be honest, I'd pay more attention to this statement if they spelled "licenced" correctly, that is, the Australian way, as opposed the the American spelling they've chosen to use.

Although that might explain all that American-inspired flag-waving stuff they do around Australia Day.

Originally Posted by RustyArc

To be honest, I'd pay more attention to this statement if they spelled "licenced" correctly, that is, the Australian way, as opposed the the American spelling they've chosen to use.

Licenced is not a word that exists in the Macquarie (Aussie) dictionary
In the the Macquarie, "Licence" is the noun, "License" is a verb, and "Licensed" is either a verb or adjective.
In the case in question the electrician is being described so it's the latter.

Rusty - A licensed trades person has a licence to do the work.