VSD(VFD) motor connections Star or Delta

Not a PLC question

Got called out to a plc problem but turned out to be issues with a VSD keeps going over voltage intermittently. All parameters in VSD match data plate of motor and VSD is the correct size. Motor is a 7.5kw 3 phase 400-415v.

On examination of the motor connection from VSD I noticed motor was wired up for Delta, been a while since I worked on a VSD driven motor but I always thought the preferred connection for this was Star.

Can anyone recommend the correct connection?

Cheers

What voltage does the motor nameplate say for the 2 types of connections?

Alan

From memory there was a few stated on motor data plate, at either 50 or 60 Hz but 415v Delta was listed.

holyhobgoblin said:

From memory there was a few stated on motor data plate, at either 50 or 60 Hz but 415v Delta was listed.

Click to expand...

what model drive is it and what voltage are you running into the drive?

Drive is a Delta VDF-F Series, not used these before. I prefer ABB range of drives.

Measured voltage between phases was 430v on the input.

Now I've typed that think I need to recheck parameters in drive, will have to download full manual.

You need to check what type of over voltage alarm you are getting.

If it is a supply over voltage then obviously you need to be looking at the supply rather than the motor. I have had systems running on generators where the AVR was near its limit, and so we got occasional over volts. Otherwise it can be from voltage spikes caused by big bits of kits starting and stopping.

If it is a DC bus over volts then you can again be looking at a supply problem or you may be getting the motor creating a voltage as it decelerates. You might need to increase deceleration time so that the motor is driven to a stop rather than coasting to a stop. This applies to higher inertia loads.

Another possibility is as you say, the settings in the drive may be wrong. Depending on the drive software/interface this can be easy, or a nightmare of searching the manual and pressing many buttons.

Finally you could have a drive with an occasional fault. I find tends to be the least likely, but if you have a spare drive it can be worth swapping out to see if the problem goes away.

If the drive has been working fine for a while, and no settings (decel time) hwv been changed, and nothing has changed mechanically (like lubing it and killing system friction), then the bus capacitors in the drive may be getting weak (worn out).

Just like Bryon said above, the DC bus may be seeing overvoltage from regeneration. There are many ways to work with such an issue, but first determine if something has changed on the rest of the system which upset the balance!

Check on the motor nameplate which type of connection (delta or star) is required for 415V. A few days ago I had to replace ABB motor 460V which had to be connected in star type for 460V, so I agree with you that star would be required for your 415v motor.

Is it possible that motor is connected/working on 230V (or so) and that's why delta type of connection has been used? Check the voltage on the motor.

About the VFD keeps going overvoltage:
If non of the parameters have been changed and everything had been working fine before the error started then I would say that something's going on with the VFD. Try to replace the VFD with another one if you have.
What type/model of VFD is that motor connected to?

holyhobgoblin said:

Drive is a Delta VDF-F Series, not used these before. I prefer ABB range of drives.

Measured voltage between phases was 430v on the input.

Now I've typed that think I need to recheck parameters in drive, will have to download full manual.

Click to expand...

Looking at the quick start manual the drive can accept anything from 342-528 V, so it is not your input voltage. so this means either your braking resistor is open if installed, or you are decelerating the motor faster than the drive can bleed the back current back into the line,..... providing that the bus voltage monitoring circuit is functional. If you are skilled at repairing DC drives, kill power, wait until DC bus is dead, and check all screws in the rectifier, bus circuit, and output circuit. A loose screw can cause the problem. Bad Caps would cause "low Voltage" alarms in my experience, although I guess a high voltage alarm may be possible if the voltage monitoring circuit was quick enough.... let me know what you find

contact the motor manufacturer - I have been told rule of thumb is motors that are greater than 5Kw should be delta connected and those less should be Star.
as far as the "OVER" voltage fault (not certain with Delta) this is caused by the power being shut off to the motor before the VFD has been stopped so the VFD sees the motor Back EMF and reads that as an error.
If the system has a "safety Relay" attached - this can cause that fault.
it turns off the power to the VFD before the unit is told to stop.
Commonly I use a timed Safety relay firstly it stops the VFD then it drops the power.
VFD's as with servo's are able to stop motors extremely fast.
But, If you cut power they 'Freewheel' when brakes are not fitted.

This drive may have a large input voltage range but it may be one of those where you have to enter the actual input voltage as a parameter. If, for example, it has been entered as 400VAC or even 415VAC, an actual input voltage of 430VAC may well cause the fault.

Check the IM for a parameter that identifies input voltage.

iant said:

If the system has a "safety Relay" attached - this can cause that fault.
it turns off the power to the VFD before the unit is told to stop.
Commonly I use a timed Safety relay firstly it stops the VFD then it drops the power.

Click to expand...

No, the safety circuit will cause the VFD to stop but then the VFD would show "under voltage" alarm. When the safety circuit is activated then the power is cut off from VFD. Anyway, the VFD would shut off completely and then become fully functional after the safety circuit is reset.

i think your right with the Under Voltage.
But there are some cheap and nasty drives i have seen out in the field
knuck foes
the safety ccts you refer to are not in the older vfds

There are a few parameters which can cause over voltage (Refer to the manual)

Monitor parameter 00-06 and 02-09
01: U displays DC-Bus voltage of AC drive

Here is what the manual says​

Over voltage
​

​

​

The DC bus voltage
has exceeded its
maximum allowable
value.​

Corrective actions
1. Check whether the input voltage falls within the rated AC drive input voltage.
2. Check for possible voltage transients.
3. Bus over-voltage may also be caused by motor regeneration.
Either increase the decel time or add an optional brake resistor.​

4. Check whether the required brake power is within the specified limits.

i hate to say it
but point 3.
[FONT=&quot]Bus over-voltage may also be caused by motor regeneration
can happen if the supply is cut when the motor is still running
If the motor is running a load like a flywheel


[/FONT]