Thread: More VSD/VFD problems.

Originally Posted by jhovel

Not sure if this is helpful: my view and understanding is that the powersupply can't increase the voltage. Therefore, the motor will draw whatever current it needs to run - up to its capacity - no matter what the nametag says.
Joe

Hi Joe,
Not quite.... with VFD's the current is controlled by how hard you drive the IGBT's, and this effectively changes the voltage. (no it can't increase the voltage, beyond what the DC bus will allow for)

In a simple V/F drive, the voltage varies with frequency, up to 50hz, and then flattens out at whatever the maximum is, so beyond 50Hz on a V/F drive torque starts dropping.
To help with starting at low Hz, VF drives increase the voltage at low Hz, called torque boost by most manufacturers..

On a vector drive (like the one Ironwood has) the VFD does calculations about what proportion of the current is doing various things, part of the current produces the magnetic field, (the magnetizing current) and 90 degrees out of phase with this, is the torque producing current. The magnetizing current drops away when you get above 50hz, a bit like the V/F drives do.

There are different types of vector drive.. this one, is a sensorless vector vfd, probably with a V/F core..

Sorry, getting carried away, I'll stop now....

Regards
Ray

I have had something come up unexpectedly, I cant see I'll get time to look at the lathe until the weekend.
Hopefully Saturday afternoon I'll do the reset to factory settings, and see what happens then.

Well I got some spare time sooner than I thought.
Had a spare hour or so today, so I did the reset to factory settings as per the manual.
After it did its thing I went through each parameter and checked to see it was the same as the factory setting in the manual, there were a few that didnt change back, so I did them manually.

I ran it up, the high current was still a problem, just wasnt cutting out. With all the belts on, and driving the spindle, it was getting up to 7 amps when turned up to 100 Hz.

I have a 1hp motor that I replaced with a single phase motor, out of a Durden Jointer, it is 2 pole so I changed the setting on the vfd to reflect this, I hooked it up in delta and hooked up the vfd to it.
It was drawing less than 2 amps with no load, I just put the sole of my boot on the pulley to provide a bit of load. When enough pressure was applied to start slowing down the motor, the amps started to rise, the current was getting up to 5 or 6 amps quite easily.

I dont know where to go with this next. Is it possible that the VFD is faulty ?

Originally Posted by Ironwood

I ran it up, the high current was still a problem, just wasnt cutting out. With all the belts on, and driving the spindle, it was getting up to 7 amps when turned up to 100 Hz.

dont know where to go with this next. Is it possible that the VFD is faulty ?

Hi Ironwood,
That sounds ok, I think it's only supposed to trip if it's overcurrent by 150% for 30 (or whatever F51 value is) seconds.

I thought the problem was it was tripping on overcurrent, now, the problem is it's not tripping? Or have I misunderstood something?

The motor should handle moderate overcurrent without problems. You could check the motor specs to see what the locked rotor current is, but I'm pretty sure it will be more than 7amps...

Regards
Ray

Originally Posted by RayG

Hi Ironwood,
That sounds ok, I think it's only supposed to trip if it's overcurrent by 150% for 30 (or whatever F51 value is) seconds.

I thought the problem was it was tripping on overcurrent, now, the problem is it's not tripping? Or have I misunderstood something?

The motor should handle moderate overcurrent without problems. You could check the motor specs to see what the locked rotor current is, but I'm pretty sure it will be more than 7amps...

Regards
Ray

LRA should be around 6-7 times FLA

LRA = Locked rotor amps
FLA = Full load amps

Well I have had a breakthrough today.
I hooked the 1.5hp motor back up to the Vfd, but I used a different piece of cable, I had thought a couple of times to try a different cable, but always dismissed it.
The old cable is the original one when the motor was driving a pump. Maybe has some broken strands or something internally .

Now I am getting about 2.8 to 3 amps at all Hz settings, it gets up to 5 amps briefly when accelerating up to speed ( 3 second acceleration time ).

Still maybe a bit high, but I am happy to at last have some light at the end of the tunnel.
Next step will be to do the autotuning over again, and see what happens this time when the Vector control is turned back on.

Hi Ironwood,

That's interesting, sounds like you are on the right track. Do you have any pictures of the two different cables?

Regards
Ray

Originally Posted by RayG

Hi Ironwood,

That's interesting, sounds like you are on the right track. Do you have any pictures of the two different cables?

Regards
Ray

I dont have any pics on hand, but I can take a couple tomorrow if you like.
There is not much to see really, the old cable is just a purpose made one, four wires fed through a piece of thick flexible conduit.
I will pull them out and inspect them now that I am not going to be using it.

The new cable is very temporary, it is a new piece of 3-core, with a single wire running beside it to make up the extra needed.
I will buy a new piece of 4 core cable tomorrow when I go in to town.

Hi Ironwood,

One other question, what sort of cable length are we talking about.

The reason I ask, is that the leakage capacitance would have to be pretty high to cause the sort of current increase you've been seeing.. which would usually mean long cables, and there are other issues that can occur with long cable runs on VFD's, pulse ringing and and sometimes overvoltage spikes which can damage motor insulation.

The shorter the better, under normal circumstances.

With the old cable I wonder if insulation breakdown at high voltage might be the problem with the old cables? A megger test might be interesting.

In any event, some 3 core plus earth orange circ is what you need to get

Regards
Ray

Ray, the old cable is just under 1.5 meters long, the new one is about 1 meter long.

The manual mentions 15 meters being too long.

To run from where I want to mount the VFD to the motor, I will need about 1.2 meters of cable.
Now that I know that its going to work, I can start to mount things in position and run some permanent wiring to switches etc.

Originally Posted by RayG

A megger test might be interesting.

you took the words out of mouth Ray

sounds like insulation breakdown between wires????

and who would have picked that ...ME...I mean I should have thought of it..I had this exact problem about 2 months ago..

The client said the pump was crook..(a 10hp motor mind you) its tripping the breaker...can you take it out and get it repaired...no problemos said I..rip it out (without checking) take it to motor rewinders who rang the next day and said...there's nothing wrong with except for the a noisy bearing...OK replace it...err them..????

...what is going on here...checked out the control circuit ..all ok ...contactor checked out ok..megger tested wiring to isolator..ok...what now mmm????, megger test wiring from isolator to motor...what!!!???? its 20 megohms?

I pulled the wires out of the old conduit last night when I got home.
I was expecting to see the insulation cracked or worn. It all looked good except for a couple of spots where they were rubbing together and formed small grooves in the insulation, but it doesnt go all the way through, I have bent the wires tightly on those spots to see if I could see the copper anywhere, but it all looks good.
Maybe the problem is too small to see by my poor eyes.

wonder if you may have had dust/dirt etc on the terminal plate of the motor which was causing some leakage?

Originally Posted by eskimo

wonder if you may have had dust/dirt etc on the terminal plate of the motor which was causing some leakage?

Well I wouldnt rule it out, but it looks pretty clean to me.

I hope to get into town today so I can get a short length of cable so I can start to make things a bit more permanent.
Everything is hooked up temporary at the moment, while I try and get to work satisfactorily.
Once I get the permanent wiring done, I will run the autotuning again.
Should be a better result this time hopefully.