Invertor Problem

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I have just fitted a 4kW invertor to a 3Kw three phase motor which runs a conveyer. All settings are as it always use to be when it was DOL with a running speed at 50hZ.
All was fine for half a day, and now the invertor is tripping out on overload about once an hour. The conveyer only runs for about 5 mins every 20 mins. The Thermal overload (set to 6.6A as FLC on motor plate says) also is tripping occasionally. All paramaters on the invertor are correct. Is there anyway running the motor through the invertor could cause the motor to be underpowered/draw more current? I am heading back tomorrow morning to take a look, but just wanted some ideas first.
 
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Hmmmm ... the inverter itself needs power to work. Also, the current into the inverter won't be a sinewave, it will take big gulps of current towards the peaks so the thermal overload will not 'see' the kind of current its designed to.

IMHO the thermal overload tripping is a red herring & it should be removed - that functionality is built into the inverter.

How smart is the inverter? Can you see what current it trips on? - maybe from a log? Can it be programmed for different overload profiles? If so, have you set the best-fit for your application??
 
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Hmmmm ... the inverter itself needs power to work. Also, the current into the inverter won't be a sinewave, it will take big gulps of current towards the peaks so the thermal overload will not 'see' the kind of current its designed to.

IMHO the thermal overload tripping is a red herring & it should be removed - that functionality is built into the inverter.

How smart is the inverter? Can you see what current it trips on? - maybe from a log? Can it be programmed for different overload profiles? If so, have you set the best-fit for your application??
True about the thermal overload, I left it in as the manual says too. It is the Invertek E3 invertor. You can set the type of load, there is fan and pump, or standard. As this is a conveyor, I have left it on standard.
I had them monitor the current drawn this evening, (on the display) and it was aroud 6.3A - and all was ok - that was running for about 4 mins.. But at other times it will trip. The load on the motor doesn't really ever change (very insignificantly anyway)
Will check logs (if it has them) tomorrow on what current has been drawn.
 
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True about the thermal overload, I left it in as the manual says too. It is the Invertek E3 invertor. You can set the type of load, there is fan and pump, or standard. As this is a conveyor, I have left it on standard.
I had them monitor the current drawn this evening, (on the display) and it was aroud 6.3A - and all was ok - that was running for about 4 mins.. But at other times it will trip. The load on the motor doesn't really ever change (very insignificantly anyway)
Will check logs (if it has them) tomorrow on what current has been drawn.

Just had a look at a manual for an Invertek E3 drive, and it suggests gG fuses or MCBs in the supply. No mention of using a thermal overload, and I've never seen it done, and I've seen and set up hundreds of drives. It's not relevant to your problem though, the fusing is only to protect the supply cable.

Did it auto tune ok? Are you operating it in vector control or V/F control? Does it just run at a fixed frequency?
 
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Have you allowed for the motor inrush current?
Have you checked the motor windings?

Just because it was running ok before doesn't meant it hasn't developed a fault.
 
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Conveyor belts have a lot of inertia / static friction to overcome when starting from stationary, especially if loaded with product.

If the invertor is tripping when the belt is starting to move then either a slower ramp up to speed or a more powerful invertor to cope with the load due to belt inertia
 
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Have you allowed for the motor inrush current?
Have you checked the motor windings?

Just because it was running ok before doesn't meant it hasn't developed a fault.

This drive can supply all the current this motor needs to start and run.

Your point about the motor windings is valid though. If it's an old motor, the winding insulation may not be strong enough for vfd operation.
 
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Sorry for the delay in updating you all. So I went there on Friday morning to have a look. It turns out that they have increased the amount of product being put onto the belt. So instead of say 200kg being on it at any one time, there is probably double that now. If only all this information was given to me on the phone at the time. We are now going to be changing the motor and gearbox to keep up with the additional load they want.
 
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Hmmmm ... the inverter itself needs power to work. Also, the current into the inverter won't be a sinewave, it will take big gulps of current towards the peaks so the thermal overload will not 'see' the kind of current its designed to.
Any VFD's I've worked on simply rectify the i/c supply with some very good LC filtering so I would imagine the supply current should be fairly well smoothed out.
It's certainly a very common thing to leave the original contactor and overload in circuit as the VFD is often simply added adjacent to the existing local isolator without any modification to the control panel/starter.
 

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