Overvoltage fault.

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ptonsparky

ptonsparky

Tom
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EC - retired
Sahib said:
I think one of harmonics generated by VFD is causing resonance thereby high input voltage to the drive. Conduct a harmonic analysis, check adequacy of existing line reactor and replace same with suitable one, if found necessary.
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I think the owners will jump on the band wagon for a harmonic analysis. I'll need to give them a cost analysis first. How much?
 
Jraef

Jraef

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ptonsparky said:
I do wonder why the two small drives located within 25' were not affected or at best did not show a fault. I'm not taking the time to check the parameters. AB & CH drives
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I doubt this was harmonics, that would have showed up right away, not a year later (unless someone added caps somewhere). Most likely it was that little .33HP motor, but not the motor itself, the contactor for it. When contacts open, they create what is essentially a capacitor as the surfaces separate, and the arc jumping across it increases the voltage, quite a bit actually. That's why you see a "blue flash" when a contact opens; the arc has to be extinguished by the dielectric of the air around it, which means the contact separation must be enough and the arc must be "quenched" via an "arc chute" in the contactor. Regardless of the efforts to extinguish that arc, and stop the voltage build-up, it takes time to happen. If the contactor is chattering, there is insufficient time, so the arc never fully extinguishes and the votlage becomes a nasty series of successive spikes. That can cause all kinds of havoc, not the least of which can be over charging of a DC bus in a drive. The line reactor SLOWS DOWN the voltage change, and that usually helps when it is ONE spike, but a chattering contactor is not the same. I saw this once before where these spikes (from a chattering air compressor starter) were causing a Soft Starter to fire its SCRs on on their own, damaging them, so I can see it charging up a DC bus on a drive.

Small drives often come with Dynamic Braking transistors built-in, so people sometimes simply hook up a little resistor to that which will act to shunt excess voltage off as heat, whether for braking or OV from some other source. The circuit doesn't care why the DC bus voltage is high, it just triggers the braking transistor when it is. In some cases really small drives will even use the Pre-Charge resistor as a form of braking resistor too, although that's risky because if you burn it out, the whole drive is toast.

Once you get above 10HP (15HP for A-B), you have to add the DB transistor, either up front when you order it or as an external module. No matter which way you do it, you pay extra so people don't bother if they don't need it for actual braking.
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Sahib said:
Why not just put appropriate SPD at FHP motor location as it is not too costly proposal ?
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We solved the problem by fixing the erratic switch operation that caused the starter to chatter. A 7/16 inch wrench, two paper clips, a rubber band and an hours worth of time to find parts and make adjustments. How much is the SPD?

add: An operator had removed a return spring that was too strong but a spring is required to open the switch. The band was a quick temp fix and they know it needs to be replaced
 
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Sahib

Sahib

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Location
India
ptonsparky said:
We solved the problem by fixing the erratic switch operation that caused the starter to chatter. A 7/16 inch wrench, two paper clips, a rubber band and an hours worth of time to find parts and make adjustments. How much is the SPD?
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Does the VFD drive problem still exist ? As for SPD price, it is a few hundred dollars. You may get a quote from local dealers. Can't you?:cool:
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Braking resistors

Braking resistors

I had warned them my fix was good only until it quit. Tail light warranty.

They bought a new micro switch and replaced the rubber band with the proper spring and still notice the sewing machine starter chatter at the make of the micro is the major problem. While they were watching they noticed another related belt starter chatter. (The one we thought it was back in the OP) Instant overvoltage.

So we have at least two starters giving us grief along with the possible interlocking aux contacts of a third. These starters are 40-50 years old. Not much doubt in my mind now that they have been chattering for some time with no obvious ill affects, until we put the VFD in. Nothing else cared.

I can attempt to fix them all or try a method that masks the problem.

I see the braking resistor for this unit has a jumper that moves to select the voltage range at which it starts working. There will be no regenerative affects due to ramp at stop. It is set to coast and no coasting occurs. Do I pick a range and see how things work, then drop it again if needed? T&E method or is there a better method? I could measure the DC bus voltage during normal operation and pick a range above that.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
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ptonsparky said:
I had warned them my fix was good only until it quit. Tail light warranty.

They bought a new micro switch and replaced the rubber band with the proper spring and still notice the sewing machine starter chatter at the make of the micro is the major problem. While they were watching they noticed another related belt starter chatter. (The one we thought it was back in the OP) Instant overvoltage.

So we have at least two starters giving us grief along with the possible interlocking aux contacts of a third. These starters are 40-50 years old. Not much doubt in my mind now that they have been chattering for some time with no obvious ill affects, until we put the VFD in. Nothing else cared.

I can attempt to fix them all or try a method that masks the problem.

I see the braking resistor for this unit has a jumper that moves to select the voltage range at which it starts working. There will be no regenerative affects due to ramp at stop. It is set to coast and no coasting occurs. Do I pick a range and see how things work, then drop it again if needed? T&E method or is there a better method? I could measure the DC bus voltage during normal operation and pick a range above that.
Click to expand...
You don't want the DB resistor being turned on needlessly nor for long periods of time, otherwise it burns out and/or damages the transistor that controls it. Even if set for Cost to Stop, speed changes that take place as it is running can still create regen. If the info is available, I would find out the Over Voltage trigger level and set this up for the resistor to be triggered slightly below that. What brand of VFD is it?
 
Saturn_Europa

Saturn_Europa

Senior Member
Location
Fishing Industry
Occupation
Electrician Limited License NC
ptonsparky said:
I had warned them my fix was good only until it quit. Tail light warranty.

They bought a new micro switch and replaced the rubber band with the proper spring and still notice the sewing machine starter chatter at the make of the micro is the major problem. While they were watching they noticed another related belt starter chatter. (The one we thought it was back in the OP) Instant overvoltage.

So we have at least two starters giving us grief along with the possible interlocking aux contacts of a third. These starters are 40-50 years old. Not much doubt in my mind now that they have been chattering for some time with no obvious ill affects, until we put the VFD in. Nothing else cared.

I can attempt to fix them all or try a method that masks the problem.

I see the braking resistor for this unit has a jumper that moves to select the voltage range at which it starts working. There will be no regenerative affects due to ramp at stop. It is set to coast and no coasting occurs. Do I pick a range and see how things work, then drop it again if needed? T&E method or is there a better method? I could measure the DC bus voltage during normal operation and pick a range above that.
Click to expand...

Have you thought about replacing those 40-50 year old starters? Maybe it will help, maybe it won't but they are at the end of thier life anyway.

When you put them in Hand do they chatter?
 
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Jraef said:
You don't want the DB resistor being turned on needlessly nor for long periods of time, otherwise it burns out and/or damages the transistor that controls it. Even if set for Cost to Stop, speed changes that take place as it is running can still create regen. If the info is available, I would find out the Over Voltage trigger level and set this up for the resistor to be triggered slightly below that. What brand of VFD is it?
Click to expand...

Automation Direct GS3-4010
 
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