Quantcast

3 phase motor torque/power with delta or Y wiring

UKworkshop.co.uk

Help Support UKworkshop.co.uk:

minilathe22

Established Member
Joined
31 Jan 2016
Messages
213
Reaction score
0
Location
Stevenage, UK
Ok so there are many posts about how to wire a 3 phase motor one way or the other. However one topic I cannot seem to find any information on, is if you have the choice between running the motor at 380V on a Y wiring setup, or using 240V with delta setup, does either option make the motor perform any differently, in terms of useable power/torque when using the lathe? I ask because I need to upgrade my VFD, I have found it keeps cutting out from getting too hot. The motor is a 6 pole 1.1kW motor, but the VFD is rated only 0.75kW for constant torque applications. I like to turn large bowls, so often find myself using the VFD at low RPM settings for extended periods.

Currently the motor is set to delta wiring for the 240V VFD. Would there by an advantage to look out for a 380V (output) VFD and change the wiring to Y setup? As its an extra cost to get a VFD that produces the higher voltage. Just curios whether I would notice any difference.
 

Inspector

Nyuck, Nyuck, Nyuck!
Joined
18 Jun 2006
Messages
1,598
Reaction score
68
Location
Saskatoon, SK., Canada
To the best of my knowledge you can't run 380V from a 220V single phase VFD. If you have 380V mains then I think there are VFD's that will do 380V to 380V variable. But don't hold me to that. You need to stay with the 220V Delta if you only have single phase input.

Pete
 

CHJ

Established Member
Joined
31 Dec 2004
Messages
20,072
Reaction score
36
Location
Cotswolds UK
Using a VFD, either a modified 240 volt output version or one designed to produce the voltage increase in the first instance, (sort of voltage doubling) is unlikely to result in any increased power availability.

By their very nature VFD's are producing an approximation of a true sine waveform , I can't envision one also multiplying the output voltage being any more efficient.

I'm surprise a 1.5HP 650 rpm motor is stalling regularly on a 7.5KW VFD. is the VFD fitted, or can it be fitted with a Heat sink, have you tried fitting an associated cooling fan.
 

minilathe22

Established Member
Joined
31 Jan 2016
Messages
213
Reaction score
0
Location
Stevenage, UK
I believe the higher voltage is offset by the change in wiring, the only advantage being for long cable runs the high voltage runs at a lower current, so for the power company they can use thinner wires. As I would be producing the higher voltage at the same location as the lathe I don't think the benefits appt to my situation.
 

Inspector

Nyuck, Nyuck, Nyuck!
Joined
18 Jun 2006
Messages
1,598
Reaction score
68
Location
Saskatoon, SK., Canada
Your VFD is too small and needs to be at least a 1.5K and to have variable speed the motor would need to be Delta wound.

Pete
 

minilathe22

Established Member
Joined
31 Jan 2016
Messages
213
Reaction score
0
Location
Stevenage, UK
After a bit of headscratching I ran the VFD and set it to show me the amps being used, to turn just the spindle without any woodturning taking place is using over 2 amps, reaching 4amps at high rpm. It seems my recently replaced bearings a quite stiff and consuming alot of current just to turn the spindle. So I think I need to run them in first.

With the belt slackened turning the spindle by hand feels a bit too difficult for my liking. They are sealed bearings with rubber contacting seals.

But yes in the long term I will look out for a higher rated VFD.
 

BertD

Established Member
Joined
7 Jan 2017
Messages
22
Reaction score
0
Location
Calgary Canada
At risk of over simplifying, Y connected ; more amps = more torque. Delta wound ; same running hp with less amps but less torque on starting or low speed. Volts x amps being the same hp rating. In industry some applications use switchgear to "Y start, Delta run" for applications that require very high torque to get turning then switches to delta for continuous running. Amps creates heat so short start time, no problem, but when continuous run in Y means more heat for same horsepower. With lathes it is good to know that the cooling fan on the motor is running slower moving less air at slow speed, combine that with the higher current required at low speed high torque it's like a double whammy for the motor with regard to heat buildup. Mixing and matching may work rotationally however the heating function may not be easily noticed until it trips out or fails.
 

guineafowl21

Established Member
Joined
28 Oct 2015
Messages
267
Reaction score
24
Location
Inverness
BertD":eajcqmfv said:
At risk of over simplifying, Y connected ; more amps = more torque. Delta wound ; same running hp with less amps but less torque on starting or low speed. Volts x amps being the same hp rating. In industry some applications use switchgear to "Y start, Delta run" for applications that require very high torque to get turning then switches to delta for continuous running. Amps creates heat so short start time, no problem, but when continuous run in Y means more heat for same horsepower. With lathes it is good to know that the cooling fan on the motor is running slower moving less air at slow speed, combine that with the higher current required at low speed high torque it's like a double whammy for the motor with regard to heat buildup. Mixing and matching may work rotationally however the heating function may not be easily noticed until it trips out or fails.
Sorry, Bert but that isn’t right. Y connection results in lower current, delta higher (for a given voltage). If you swap 400V Y for 230V delta, the current should be about the same.

The point of star-delta starters is not to increase starting torque, but to limit the inrush current on start-up (star draws lower current, as above). This is to stop breakers tripping and lights dimming when starting up a heavy rotating mass.

Once the motor is up to star speed, you change to delta for full power.
 

Sideways

Established Member
Joined
26 Dec 2017
Messages
949
Reaction score
16
Location
United Kingdom
minilathe22":30f7r59f said:
I ask because I need to upgrade my VFD, I have found it keeps cutting out from getting too hot. The motor is a 6 pole 1.1kW motor, but the VFD is rated only 0.75kW for constant torque applications. I like to turn large bowls, so often find myself using the VFD at low RPM settings for extended periods.
That did make me smile. A perfect example of how not to do it...
(i) expecting a significantly undersized VDF to drive a motor that's 50% larger than it's designed for
(ii) applying heavy loads while running the whole thing at low rpm where the motor isn't capable of delivering anywhere near it's rated power.
One of the advantages of a VFD solution fortunately is that while they can't do the impossible, at least the electronics can help protect users from themselves :D
 

guineafowl21

Established Member
Joined
28 Oct 2015
Messages
267
Reaction score
24
Location
Inverness
“HowTo: How to get Maximum Torque at Low Speed from a Simple VxF Inverter

A simple VxF Inverter will perform well at low speed when the ‘Boost’ parameter is set correctly. The method of setting this is as follows:-

- Remove the final drive to the machine, so the motor is completely free of load.
- Run the Inverter at 50Hz.
- Find the motor current in the drive diagnostic and make a note of it.
- Run the inverter at 5Hz.
- Adjust the Boost parameter until the drive diagnostic of current shows the same value you noted for 50Hz.
- Save the parameter, if this is a function of the drive.

The motor will be correctly fluxed and give maximum torque down to very low speed. Typically 5Hz or less. If the Inverter has ‘Auto-boost’ to be set manually as a value. Take 50% of the value above and load it into ‘Manual- Boost’ and enter 50% into ‘Auto-boost’. This will make maximum torque when the motor and drive sees maximum load at low speed.”

Copied from inverterdrive.com. They have a good section on how to size and use VFDs correctly.
 
Top