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VFD overvoltage fault ? 3

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nmark

Electrical
Mar 14, 2005
31
Hello,
I have (2) vfd's controlling 2 motors(conveyors) with a input voltage of 460 volts in real life I measure 494 volts at the input. The drive manufacturer says voltage input in good for +10%. 460*1.10=506
But over the past 2 weeks both drive's have faulted on a overvoltage fault numerous times.The fault has occured when the drive is running at a constant speed. I do not have a line reactors or chokes installed.
Both of the drives, motors are new . In addition to the new conveyor motors at the other end of the plant are 2 new 1000HP 4160 volt compressors DOL starting. We are going to monitor the voltage for spikes etc.. later this week.But while I wait any suggestions?
 
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Possibilities:
[ul][li]Regeneration: your conveyors are overhauling slightly at those times and since you are already close to the ragged edge of the voltage tolerance, it doesn't take much to cause a trip. Dynamic Braking resistors could help with that even if you are not planning on using them for braking. They just give any regenerative energy a place to go.[/li]
[li]In fact if the compressors are coming on and off DOL, they may be causing a voltage sag which causes the VFDs to slow down by lowering the output speed(if programmed that way), then when the line voltage returns it over charges the bus because the load is still regenerating. Seen that a number of times. Again, DB resistors and/or changing the programming of the VFD to react to line dips by coasting, rather than by lowering the output frequency[/li]
[li]Capacitor interaction. Do your compressors have PFC caps on them? Sometimes a resonance similar to a tank circuit can occur in the interaction of external capacitors and the VFD front-end to cause additional charging of the DC bus. Also make sure they are not using bulk pf correction because if so, when the compressors turn OFF, the pf will go high and that can cause over charging of the DC bus.[/li][/ul]
 
nmark
Nothing much more to add to what jraef has mentioned other than to measure (or monitor via a parameter)the DC link voltage rather than just the AC input.
Your steady state DC link voltage will be 690~710Vdc on this AC line voltage leaving little margin for the other effects as jraef describes.
The +/-10% mentioned by the VFD manufacturer will normally be for short durations rather than continuous duty. Most VFD's have their power devices (rectifiers, transistors) rated for the nominal DC voltage based on the AC supply voltage range specified. Some drives show a voltage range of 380~500Vac and this means the power devices are of a higher rating.
So if your drive has a nominal rating of 460Vac then you really are pushing the boundry by connecting to 494Vac as a nominal as this will not take into consideration any peaks.
 
You there too? Jeff?

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
I was there for ten years. Left in 1975...

My last job (this week-end) was for them. It is a long standing relation.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
I am their "Mädchen für Alles". Especially for things that others do not want to touch - or have forgotten about...

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
I didn't want to tempt fate by asking "which VFD?".
and Gunnar, I hope you mean "general dogsbody" rather than the other meaning I've heard in the beer halls of Hamburg... ;-)
 
The Romans might have called it a "PI IV"

Not that it is from Roman time. But nearly...

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
The drives are running for about 72 hours continuosly and a 2 hour down time roughly but it isn't set in stone and my drive parameters can't be changed on the fly.
I would like to lower transformer tap ahead of vfd's but that involves shutting down half the plant and that is not an option for about 8 weeks, So if anyone is still interested I might have more info at a later date.

Non Semper Erit Aestas.
 
nmark,
At the risk of embarrassment, what brand of VFD are they? There are a few out there which are really 415V designs that, unfortunately, some engineer was tasked with upgrading to handle "460V motors in the US", but did so without having investigated the fact that 460V is a utilization voltage, based upon a 480V distribution system. We have that discussion in this forum from time to time; a lot of people not from North America have a difficult time with that concept. I'm curious to know who made that design error.
 
How do you set the drive speed? I know you say it's constant speed but are you positive? If you're using an analog input for speed then there is always the possibility it's not and you are commanding it to slow down which is causing a regenerating condition that trips it.

The +10% should still be the operating range and the DB resistor operation and trip points should both be above that level. So, the drive should not be tripping if the input voltage reaches 506V. It should have to go another 5% to 10% over 506V to trip.

 
LionelHutz
I agree, the drive shouldn't trip within the +10% range of nominal but I was referring to continuous operation in the +10% range. This should be avoided as it will impact on the lifetime of the components within the drive and also limit any tolerance between the nominal DC link voltage and any AC surge or regenerated DC back onto the link.
If the drive nmark has is indicating 460Vac+10% then it is because lower voltage rated components are used compared to drives stating 480Vac or 500Vac +10%.
A typical trip limit of a "400Vac" drive will be 810~820Vdc and this is obviously beyond the +10% voltage range of the 460/480 or 500Vac nominal input.
 
At the risk of offending anyone I won't mention the brand specifically, but the name sounds similar to Yamaha.It does have a "stall" parameter where regardless of accel/decal times it will change speed as slow as necessary to compensate for regeneration.
The drive does not have a dynamic brake resistor.
It is controlled via a analog input but it consist of a HMI with a setpoint screen and the operator has to manually enter a speed as a percentage to increase or decrease and I am positive multiple overvoltage faults occured without operator changing speed.
The drive does not have a dynamic brake resistor.
From the drive I am able to get D.C.bus voltage and today it was running pretty close to 700v.
The input was at 500volts ac today.
And the drive is rated at 460v +10%, -15%. The manual says that it faults on a dc bus voltage exceeding 820.So far there has only been a voltage dip in the line momentarily -40 volt but no more faults.
 
nmark; you have never cleared up the issue of is there any possibility of the conveyors ever overrunning?

Is there commanded conveyor speed changes or do they just start up, get to speed, and sit there all day long, faulting occasionally?

Keith Cress
Flamin Systems, Inc.-
 
The operation is they get up to speed and literally sit there all day long unless the product changes. Or they have problems with the product then they need to change speeds but in the past 2 weeks they have been running the same product and have changed speed on average 1-2 times a day. But on Sunday the drives faulted 4 times I wasn't there but have been told product/speed had not been altered . It is possible that on some of the faults speed was changed but it would appear to be in the minority.
New information I have learned today is another drive controlling a fan (different manufacturer) has smoked.
 
Forgot to add compressor have not shut off yet tomorrow morning
they will be turned off and on while I am there.
 
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