Hitachi J300 VFD (22Amps) 2

[rasberry]

Hi Guys,
I'm having a spot of bother with a J300 VFD.

It's application is to control a 7.5 kW motor, driving a vibrating plate.

This motor is driven @ the base frequency of 50 Hz only, and in reality, this application, approximates a soft starter. Its operation is that it starts and stops, every 15 Seconds.

I set it up and it ran perfectly for two days, but the owner required me to reduce the acceleration time.

This I did, but since then, it runs for two operations only, upon the third, it justs sits there, with an indication of 26Amps, showing on the monitor. This with the plate unloaded

It would appear that the unit is going out on current limit,
but for the life of me, I cant see why.

Ive examined the trip register and its history, but there is no indication as to a possible fault.

I restored the parameters to their original settings, ???
(I think) but the problem persists.

Does anyone have any ideas ??

Thanks guys,

Rasberry

 

[ozmosis]

Rasberry
what is your accel time? When you say you reset the parameters back to their original settings, is this the factory default or the original settings when you had it running for 2 days? I guess you have tried increasing the accel time.

 

[DickDV]

Instead of waiting for it to fault, why not observe the output current when accelerating and shorten the accel time until the current reaches the rating of the drive. That way you are essentially giving your customer the shortest accel time the drive is capable of.

Actually, the drive is capable of a bit more if it is a variable torque (normal duty) drive because you can use a little of the overcurrent capacity. If it is a constant torque (heavy duty) drive, you could use even more of the overcurrent capacity since the rating is 150% for 1 minute in 10 minutes.

Either way, you will know right where you stand with respect to drive capacity and not have to wonder.

 

[rasberry]

Hi Guys,

Many thanks for your help.

Things have since developed since last post.

The machine operates under two modes, Manual & Automatic.

In the manual mode, the motor in question is started in DOL.
Whilst the machine was run in automatic, it started to play up, in that it would trip the o/load, very occasionally. It would trip and then run OK for a week for a week or more. all the usual tests revealed nothing, but of late we have been experiencing supply Authority problems which further obscured the matter. Anyway to cut a long story short, I took the motor out of service, and dismantled it. Whilst the NDE bearing was quite ok, the landing beneath the bearing had given way.

This goes quite a long way to explaining the problems weve experienced under Automatic (VFD) control.

The motor is under repair but when it goes back in, we'll start all over.

Thanks again,

Rasberry.

 

[rasberry]

Guys,
regarding My Last post, I mentioned that I was getting O/Load problems whilst in auto, that was in error, the problem was ocurring whilst in DOL, Manual!

Ras

 

[ozmosis]

rasberry
I'm not 100% clear now if all the problems you have described are only occuring when in DOL. If the original post you made is indicating that it also had problems when operating with the VFD then I would double check the settings within the J300 as this should at least detect any over-current situation with an alarm or push it into current limit whereby it will automatically reduce the output frequency to try and reduce the current but should still indicate an alarm. Eventually, if in a constant current limit situation, it would/should trip on over-current.
I have in recent years analysed the Hitachi drives (and many others) in detail as part of my job, and their build quality and performance are very good but you will only achieve the protection if the settings match the motor and application.(this is true for all VFD's)

 

[waross]

Do I understand correctly.
4 starts a minute.
A VFD was installed and correctly configured to reduce overheating of the motor.
The owner insisted on an operating cycle that was more than the motor protection would allow.
When the VFD would not allow the motor to be abused the owner went back to DOL starting. In a short time, the duty cycle overheats the motor and the overload protection operates to prevent a motor burn out.

Sounds like a basic design flaw. Try a continually running motor with an eddy current clutch.
A hydraulic drive vibrator would be good.
I think that you are very fortunate that the overload protection has prevented motor burnouts.
Sounds like a need for tact, diplomacy and more dollars.
respectfully

 

[DickDV]

Before you give up on AC drives, why not try a motor of the same hp or kw but of a lower base speed (more poles). Then take the motor over base speed (50 or 60hz) to get the original speed back. Motor has more starting torque, cools better, and operates somewhat unloaded when accelerating and decelerating. Use the same drive, just a different motor.