I have an application where my 250 HP, 480V 18 pulse variable frequency drive keeps tripping on bus overvoltage. The electrical service feeding the mcc is from a 500 kVA transformer, 3 phase, 3 wire service comprised of 2 sets of (3-500kcmil, #2/0G) per phase. The VFD is fed from the MCC via a feeder breaker. The Utility put a meter on the secondary side of their 500 kVA transformer and noticed that for a split second the voltages in two phases become elevated and the third phase voltage drops, which is evident of an open neutral. What else could be causing this. The Utility did not seem to think it was their problem. What can be done to fix the problem?
Voltage Imbablance
- Thread starter jnh
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Re: Voltage Imbablance
Bus overvoltage is not necessarily due to incoming voltage. It is referring to the DC bus volts that is made and tapped off of for the varying DC voltage to the motor that provides the different frequencies. This over volts can be caused by many various things. First thing to do is check in the manual, it usually has a troubleshooting chart to tell you the most common problems. Do you have a breaking resistor on this motor drive? That gets a lot of over volt problems without it when you get that big. Is it instantaneous overvoltage? I had a drive for a large motor that had an instantaneous over volt just to keep it from running way to high on a spike. It was just catching it. We set it up just a little and it ran fine.
Again the bus overvoltage is to protect the DC bus which can get as high as 800 VDC. One other thing to check first, just like with overloads a lot of time. Do you really have an over volts condition. Check the voltage on the DC bus.
When does it trip on over volts. During speed changes? Just out of the blue? When you start or stop?
May need to change your decel time.
Bus overvoltage is not necessarily due to incoming voltage. It is referring to the DC bus volts that is made and tapped off of for the varying DC voltage to the motor that provides the different frequencies. This over volts can be caused by many various things. First thing to do is check in the manual, it usually has a troubleshooting chart to tell you the most common problems. Do you have a breaking resistor on this motor drive? That gets a lot of over volt problems without it when you get that big. Is it instantaneous overvoltage? I had a drive for a large motor that had an instantaneous over volt just to keep it from running way to high on a spike. It was just catching it. We set it up just a little and it ran fine.
Again the bus overvoltage is to protect the DC bus which can get as high as 800 VDC. One other thing to check first, just like with overloads a lot of time. Do you really have an over volts condition. Check the voltage on the DC bus.
When does it trip on over volts. During speed changes? Just out of the blue? When you start or stop?
May need to change your decel time.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Voltage Imbablance
I concur with the boss. Bus overvoltage has nothing to do with line voltage.
This is virtually always caused by regeneration. By that, I am refering to the motor acting as a generator and sending energy back to the VFD instead of using it.
This is often seen when decelerating a load - the kinetic energy of the moving motor and load has to go somewhere, and where it goes is back into the drive.
A brake resistor will often solve this type of problem. In severe cases, you could add a regen unit to the VFD and put the energy back to the line instead of heating up a resistor.
It is also possible that you have settings in the drive that are not appropriate for your application that could cause this type of trip.
I concur with the boss. Bus overvoltage has nothing to do with line voltage.
This is virtually always caused by regeneration. By that, I am refering to the motor acting as a generator and sending energy back to the VFD instead of using it.
This is often seen when decelerating a load - the kinetic energy of the moving motor and load has to go somewhere, and where it goes is back into the drive.
A brake resistor will often solve this type of problem. In severe cases, you could add a regen unit to the VFD and put the energy back to the line instead of heating up a resistor.
It is also possible that you have settings in the drive that are not appropriate for your application that could cause this type of trip.
Re: Voltage Imbablance
The VFD trips on dc bus overvoltage just out of the blue while it is running. It does not trip during accel or decel. At first I thought maybe the drive was acting in a regenerative mode, but would this cause two of the three phases to elevate and the third phase to lower simultaneously? What else could be causing this phenomena?
The VFD trips on dc bus overvoltage just out of the blue while it is running. It does not trip during accel or decel. At first I thought maybe the drive was acting in a regenerative mode, but would this cause two of the three phases to elevate and the third phase to lower simultaneously? What else could be causing this phenomena?
rcwilson
Senior Member
- Location
- Redmond, WA
Re: Voltage Imbablance
You said two voltages go up and one goes down? If these are phase to ground voltages (277V), it indicates your 3P3W system has a wandering neutral point. Putting a high resistance ground on the neutral might stabilize the voltages without creating too much of a path for harmonic currents from the drive. If a neutral is not available a zig-zag or wye-broken delta grounding transformer could be installed to stabilize the neutral.
If you are seeing two phase-phase voltages (480V) go up and one go down, I can't envision what is causing that.
Good luck
You said two voltages go up and one goes down? If these are phase to ground voltages (277V), it indicates your 3P3W system has a wandering neutral point. Putting a high resistance ground on the neutral might stabilize the voltages without creating too much of a path for harmonic currents from the drive. If a neutral is not available a zig-zag or wye-broken delta grounding transformer could be installed to stabilize the neutral.
If you are seeing two phase-phase voltages (480V) go up and one go down, I can't envision what is causing that.
Good luck
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Voltage Imbablance
How can they not think it is not there problem if the meter they used was right at there transformer?
charlie
Senior Member
- Location
- Indianapolis
Re: Voltage Imbablance
Wayne, they are linemen, not electricians or engineers. Do I have to explain more?
Wayne, they are linemen, not electricians or engineers. Do I have to explain more?
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Voltage Imbablance
Nope!
But if I was jnh I would be asking for there engineer, or there supervisor.
As I do feel it is a POCO problem.
Nope!
But if I was jnh I would be asking for there engineer, or there supervisor.
As I do feel it is a POCO problem.
charlie
Senior Member
- Location
- Indianapolis
Re: Voltage Imbablance
Wayne, I don't think I can disagree with you.
Wayne, I don't think I can disagree with you.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Voltage Imbablance
I think not.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Voltage Imbablance
I really do not see how a slight change in line voltage could cause a DC bus overvoltage. VFDs often have a low line voltage trip. Is the line voltage dropping down below this threshold? Maybe the wrong alarm message is being displayed.
I'd be inclined to put a recorder on the dc bus voltage and see if it really is exceeding its trip point.
What kind of application is this? It's quite possible there could be mechanical energy coming into the system somehow that is overloading your DC bus and causing the trip.
It's also entirely possible that you have some kind of malfunction with your drive.
Are you saying the DC bus overvoltage trip always occurs simultaneous to a change in the line voltage?
I really do not see how a slight change in line voltage could cause a DC bus overvoltage. VFDs often have a low line voltage trip. Is the line voltage dropping down below this threshold? Maybe the wrong alarm message is being displayed.
I'd be inclined to put a recorder on the dc bus voltage and see if it really is exceeding its trip point.
What kind of application is this? It's quite possible there could be mechanical energy coming into the system somehow that is overloading your DC bus and causing the trip.
It's also entirely possible that you have some kind of malfunction with your drive.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Voltage Imbablance
Next question would be does he have a VFD that needs a neutral?
You might have a delta and this grounding conductor is floating.
That's a good catch Charlie With all his referance to a neutral I was thinking he had a 480/277 service. But then what did the POCO test for?
Next question would be does he have a VFD that needs a neutral?
Are you trying to use this #2/0G as a neutral?
You might have a delta and this grounding conductor is floating.
Re: Voltage Imbablance
The mcc bus that the service is feeding is 3 phase, 3 wire. There is no neutral. I am just going by what the technician from the Utility told me over the phone. I have requested a print out of the snap shot to see exactly what was going on. I am confused by the whole deal. If a had a bad ground or something why would this scenario happen at certain times and not all the time? This scenario has happened when the drive has been running full speed and when the drive has been running half speed. I thought maybe regen was an issue, but I would nit think regen would cause two phases to go up and one phase to go down. Any thoughts?
The mcc bus that the service is feeding is 3 phase, 3 wire. There is no neutral. I am just going by what the technician from the Utility told me over the phone. I have requested a print out of the snap shot to see exactly what was going on. I am confused by the whole deal. If a had a bad ground or something why would this scenario happen at certain times and not all the time? This scenario has happened when the drive has been running full speed and when the drive has been running half speed. I thought maybe regen was an issue, but I would nit think regen would cause two phases to go up and one phase to go down. Any thoughts?
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Voltage Imbablance
If multiple transformers are connected in a "Y" secondary then it could have a loose connection at the center connection point? Other then that I'm at a loss?
If multiple transformers are connected in a "Y" secondary then it could have a loose connection at the center connection point? Other then that I'm at a loss?
MarkMcLain
Member
- Location
- Clarksville, TN
Re: Voltage Imbablance
you haven't said anything about the current/amps of those A/B, B/C, A/C secondaries of transformer during the over/under voltage events OR when the VFD drops from 'OverVoltage' on the DC side.
you haven't said anything about the current/amps of those A/B, B/C, A/C secondaries of transformer during the over/under voltage events OR when the VFD drops from 'OverVoltage' on the DC side.
Re: Voltage Imbablance
What type of process/motor load does this VFD drive? What is the typical supply voltage? Does this problem tend to occur at certain times of the day? Particularly with fairly high steady state voltage I have frequently seen VFD trips with this fault code caused by utility capcitor switching and the associated voltage transient. The cookbook solution for that type of problem is usually a line reactor in front of the drive.
What type of process/motor load does this VFD drive? What is the typical supply voltage? Does this problem tend to occur at certain times of the day? Particularly with fairly high steady state voltage I have frequently seen VFD trips with this fault code caused by utility capcitor switching and the associated voltage transient. The cookbook solution for that type of problem is usually a line reactor in front of the drive.
charlie tuna
Senior Member
- Location
- Florida
Re: Voltage Imbablance
jnh,
i have had this problem on a few different drives and as written above --- the bus d.c. vltage is produced by the drive and is no function of the supplied voltage value. the trip setpoint can be adjusted within the program of the drive. some static drives we installed required large regenative resistor banks to disapate the voltage on the d.c. bus during a shutdown. we found the actual shutdown signal was coming from the normal system control sequence but regeristering on the drive readout as a overvoltage fault. and we have had bad boards in new drives -- i would contact the factory and let them walk you through the problem. i have had them change design limitations via the drive's micoprocessor to solve field problems -- didn't like it but it worked! programming drives of different manufacturers is time consuming because they each seem to have their own percs! i have always made it a habit to copy the final program's parameters down and keep it in my copy of the drive instruction manual. many customers will get into this program and play with it prior to calling you on a problem that usually has nothing to do with the drive. this can cause a motor to become a "weapon on mass distruction", say on a printing press where the maximum rpm is doubled!! first thing i check is the original setpoints!!!
jnh,
i have had this problem on a few different drives and as written above --- the bus d.c. vltage is produced by the drive and is no function of the supplied voltage value. the trip setpoint can be adjusted within the program of the drive. some static drives we installed required large regenative resistor banks to disapate the voltage on the d.c. bus during a shutdown. we found the actual shutdown signal was coming from the normal system control sequence but regeristering on the drive readout as a overvoltage fault. and we have had bad boards in new drives -- i would contact the factory and let them walk you through the problem. i have had them change design limitations via the drive's micoprocessor to solve field problems -- didn't like it but it worked! programming drives of different manufacturers is time consuming because they each seem to have their own percs! i have always made it a habit to copy the final program's parameters down and keep it in my copy of the drive instruction manual. many customers will get into this program and play with it prior to calling you on a problem that usually has nothing to do with the drive. this can cause a motor to become a "weapon on mass distruction", say on a printing press where the maximum rpm is doubled!! first thing i check is the original setpoints!!!
Re: Voltage Imbablance
"the bus d.c. vltage is produced by the drive and is no function of the supplied voltage value."
sorry, Charlie but not so
As long as the drive has a passive front-end there is a direct link between AC supply voltage and DC bus voltage. The rectifier makes DC when the instant voltage of the AC cycle is greater than the DC bus voltage. For no-load the bus voltage will approach the AC peak voltage. Atload it will be slightly less and there will be current flow thru the rectifier trying to get back to peak voltage. When an overvoltage of the supply occurs it will cause more rapid flow due to the increased voltage difference and can rapidly overcharge the DC bus, particularly where the bus voltage is near max to start with. When this is due to transient overvoltage it can be prevented by increasing the source impedance (by installing a line reactor) which reduces the rate of flow and total charging which occurs over the period of the transient.
"the bus d.c. vltage is produced by the drive and is no function of the supplied voltage value."
sorry, Charlie but not so
As long as the drive has a passive front-end there is a direct link between AC supply voltage and DC bus voltage. The rectifier makes DC when the instant voltage of the AC cycle is greater than the DC bus voltage. For no-load the bus voltage will approach the AC peak voltage. Atload it will be slightly less and there will be current flow thru the rectifier trying to get back to peak voltage. When an overvoltage of the supply occurs it will cause more rapid flow due to the increased voltage difference and can rapidly overcharge the DC bus, particularly where the bus voltage is near max to start with. When this is due to transient overvoltage it can be prevented by increasing the source impedance (by installing a line reactor) which reduces the rate of flow and total charging which occurs over the period of the transient.
Re: Voltage Imbablance
jnh,
One sign that this might be due to a supply problem would be if the drive ever tripped off while energized but not running. If the drive is on but unloaded for long irregular periods during the day but does NOT trip unless running, then this is probably not a supply problem.
jnh,
One sign that this might be due to a supply problem would be if the drive ever tripped off while energized but not running. If the drive is on but unloaded for long irregular periods during the day but does NOT trip unless running, then this is probably not a supply problem.
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