Inverter question

Hello guys!

I have a question regarding inverters.
We are running a lift with an 400V inverter Star conected to a
230/400 V 50Hz motor. we can run this motor up to 60Hz with full load without any problems. But if we change it to an 230V inverter delta conected it starts tu stall after 60Hz. I just cant understand this!
Does anyone have any ideas?

What drive are you using that you can use 400V input and still run the motor wired for 230vac or 400vac?

It is a Yaskawa drive and a 230/400V 50Hz motor.
If I use a 3-phase 400V drive star connected to motor there is no problems.
But if i run the motor with 1-phase 230V drive delta connected it starts to stall after 50Hz.

So its 2 different drives 1-phase and 3-phase but same power!

Need the exact part number of the drive.

Generally speaking, if your going to run a 400vac motor, you need a 400vac drive. If your going to run a 230vac motor, you need a 230vac drive. If you are feeding the drive with 400vac you probably have two problems. One is that your buss voltage is way too high for a 230vac wired motor, the other is that a 230vac motor of the same HP (kW) will need almost twice the current at 230vac as it would at 400vac, which a 400vac drive at that HP will not be designed to deliver.

There are some exceptions out there, but generally speaking a VFD works by taking your incoming voltage, rectifying it, creating a DC buss, and then PWM that buss voltage out to the motor. This means it doesn't really regulate the voltage out, but instead regulates the "average" voltage. Therefore it is normally important for your motor windings to match you line voltage.

They do have drives now days with voltage doublers and such, but generally still these drives are fixed in the sense that they usually expect a specific input range and a specific output range.

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Sorry..... I already typed this out before you edited your post.

meister- if I'm reading you correctly, you are running the motor delta connected off of single phase and you are running the Y connected motor off three phase.

Just about all drives have to be either derated or upsized when running off of single phase. Any where from 20-50%. So you would want to either run both off of the 3phase, or go to a larger drive for the 230V motor. Yaskawa probably has a formula or info on how much to derate.

Damien- Europeans use delta/wye to change the voltage of their motors when duel rated... generally have six leads coming out. Thus their motors are rate 400/230. where ours are 230/460.

So the OP is just trying to figure out why the same size motor(connected delta) with a 230V single phase drive want run the load that the 400V three phase drive will. It just about has to be the single phase aspect.

flowdam yes exactly.
I mean it should be the exact same voltage over the coils.

Let me also clarify
1st scenario (no problem)
Drive: 3x400V 2,2kW drive, output 3x400V (model Yaskawa VC4A007BAA)
Motor: 3x 230/400 50Hz
connection: Star
Running at 60Hz no problems

2nd scenario (problems)
Drive 1-phase 230V 2,2kW, ouptut 3x230V (model Yaskawa VCBA0012BAA) So the drive has only 1x230V input and 3x230V output!
same motor
connection Delta
Motor stalling near 60Hz

The motor should have the same voltage and current over the coils regardles of the drive.
the 230V drive has offcourse larger current ouput i mean the are both 3kW.

flowdam said:

Damien- Europeans use delta/wye to change the voltage of their motors when duel rated... generally have six leads coming out. Thus their motors are rate 400/230. where ours are 230/460.

So the OP is just trying to figure out why the same size motor(connected delta) with a 230V single phase drive want run the load that the 400V three phase drive will. It just about has to be the single phase aspect.

Click to expand...

Hi Flowdam,

I do realize that now, but that wasn't until after he edited his post which drastically changed the appearence of what he was doing. If the drive is rated at that HP(kw) with a single phase source that shouldn't have anything to do with it.

Although I am in the US, a large % of my drive/motor applications have been overseas, so I am actually more used to 380/220 50hz systems and ones much more weird than that than I am domestic applications.

Meister, It is a known phenomena that star connected motors have a slightly larger torque at lower speeds, and also a slightly lower torque at rated speed when the inverter is at max current. Sounds like the motor was sized without much margin.

Ok thanks, i did not know that.
you are probably right the motor was not sized with any margin.

Can you explain why it is that Star connected motor has different torque characteristics then Delta?

Do you think that this is the only explanation ,,?

When the 230V configured motor starts to slow down or "stall", try to determine if the drive has entered current limit. This is usually a programmable point. When the motor asks for current over that amount, the drive starts reducing the output frequency so the overcurrent condition will go away.

If you can display output frequency on the drive display, you should be able to see the frequency drop as the motor slows down.

If this occurs as I've described it, either the parameter for current limit needs to be raised or, if it can't be raised any further, then the drive is undersized and needs to be replaced.

DamianInRochester said:

Hi Flowdam,

I do realize that now, but that wasn't until after he edited his post which drastically changed the appearence of what he was doing. If the drive is rated at that HP(kw) with a single phase source that shouldn't have anything to do with it.

Although I am in the US, a large % of my drive/motor applications have been overseas, so I am actually more used to 380/220 50hz systems and ones much more weird than that than I am domestic applications.

Click to expand...

I gotcha. I guess I come into this after the edit.

Hi!

By 60 Hz with your single phase equipment, you might have been in the field weakening area for that vfd. That means torque loss. Here is a link to a basic VFD paper (from a previous thread): http://www.plctalk.net/qanda/showpost.php?p=406012&postcount=14

Kalle

Meister- I see your point on the drive ratings. You only have to derate when running a 3ph. rated drive on single phase voltage. I would play with the torque boost and current limit settings to see if it can get the delta connected motor over the stall condition, otherwise you should probably just pull the 400 3/ph to the area to get some commonality any way.

Good Luck.

Since torque boost only adds a little extra voltage to the V/Hz ratio at low frequencies, a high speed stall will not be helped by torque boost. Also, since this is a lift application, the drives are probably running in sensorless or flux vector mode where torque boost does not function even if you can select it.

But checking for a max possible setting on current limit and torque limit would be good. If there's nothing more to get there, the drive is simply too small.

This often happens when drives are sized based upon hp. It is better to size drives first on maximum continuous running amps and, second, on maximum short-term overload amps.