Rewiring a 415V 3 phase motor for a VFD

[Ch4iS]

So I snagged a 415V 1.1KW motor on ebay and hoping it was 240V compatible it looks like it is, 6 wires coming from the motor and the wiring for star and delta on the back of the cover. :2tsup:

I was just wondering but dont these motors run with 2 actives and a neutral where the cheap chinese HY VFD's run 3 actives? am I missing something? or do you guys who have added a VFD to your 3 phase machinery use a different VFD?

[jhovel]

Oh dear... no no no.... "three phase" means "three actives - 120 deg out of synch with each other". Then there is a neutral which is the geometric and electrical centre of those three phases connected in star configuration to a 3-phase motor. Sometimes its connected to ground, in Australia usually not.

In some rural areas there used to be (and may still be) "two phase" supplies which was more like a 480V supply with a centre tapping on the pole transformer, to allow users to run 240 equipment and big 480V motors that didn't draw MASSIVE currents requiring REALLY thick supply cables. Those "two phases" are actually not out of synch.

Maybe that's what you were thinking about?

Joe

[.RC.]

Sometimes its connected to ground, in Australia usuall not.



I thought all neutrals (in three and sinlge phase) are connected to ground back at the switchboard...

[Ch4iS]

Maybe that's what you were thinking about?

Joe

Thanks joe. :doh:

It's something I remember reading some time ago when discussing the 3 phase chinese spindles someone saying they were different to normal 3-phase equipment having 2 actives and a neutral. Maybe he meant something else :? it just got me thinking after I had bought the motor.

[RayG]

Hi Chris,

You should find a diagram showing the connections for star and delta on the motor nameplate.
What you want to do is to wire it up as delta. (it will most likely be wired as star if it's been running on 415)

Then you will have three terminals that are the 3 actives Joe referred to. They go to the U V W connections in the drive. You should also run a ground to the motor from the drive. So the cable from the drive to the motor is 3 core plus earth. Ask for orange circular 3 core plus earth at your local electrical distributor.

Regards
Ray

[Ch4iS]

Cheers for the replies fellas, it's just me getting confused at some bad/mis-interpreted information.

[Vernonv]

Those "two phases" are actually not out of synch.Just to clarify ... for a 480V supply they are actually 180º out of phase (sync).

[jhovel]

Just to clarify ... for a 480V supply they are actually 180º out of phase (sync).

Are they? You learn something every day. So the 'neutral' tap on the transformer is actually a centre tap on the secondary?
That would mean then that there are 2 240V 'phases' and the 480V is NOT relative to ground?

Joe

[ian]

Are they? You learn something every day. So the 'neutral' tap on the transformer is actually a centre tap on the secondary?
That would mean then that there are 2 240V 'phases' and the 480V is NOT relative to ground?

Joedredging teh memory bank from 30+ years ago, I recall talk of "earth (or wasit ground?) return" circuits -- supply 240V to a remote property by running 1 wire
you might be able to do the same with 2 wires and get 2 x the amps?

[BRADFORD]

dredging teh memory bank from 30+ years ago, I recall talk of "earth (or wasit ground?) return" circuits -- supply 240V to a remote property by running 1 wire
you might be able to do the same with 2 wires and get 2 x the amps?

This is called the SWER (single wire earth return) system.
It works as the name suggests, with a transformer at each property supplied.
Some of these transformers are centre tapped giving 240volts from each side to the centre neutral, and 480 volts accross the actives.
This is quite common in more remote areas, in fact the supply to my house is as described above.

[Vernonv]

So the 'neutral' tap on the transformer is actually a centre tap on the secondary?Yes, the centre tap is the neutral and it is earthed at the switch board (MEN link) and possibly at the transformer.


That would mean then that there are 2 240V 'phases' and the 480V is NOT relative to ground?Yes and yes ... so when you measure across your three wires (2 x active, 1 x neutral) you get 2 x 240V phase/active to neutral, and 480 phase/active to phase/active.

This is what feeds our small rural property, but it is NOT a SWER system, because we have 2 wires feeding the local transformer and the transformer feeds multiple properties.