# Linear reactor question



## subelect (Nov 25, 2007)

We had a VFD burn up on a 50 hp, 480 volt motor. When I was removing the damaged components, I find out that the phases come off the fused disconnect, (#14 control power wires feed the control ckt), thru a manual starter, then a 3 phase linear reactor and into the VFD.
1. Why would a large inductive load like a 50 hp motor need a linear reactor? This was not part of the VFD, in fact it is a different brand name than the damaged VFD. What good does it do besides providing a space heater in the pump panel?
2. Why would the engineer call for a manual starter between the fused disco and the linear reactors? If you wanted to test the control ckt, just disconnect the phase wires. Plus, how often do you need to test the control ckt?
Have you ever seen this before? It failed when the VFD tanked, so it will need to be replaced, if there is a reason for it to be there. 

By the way, I ran the motor on a temporary piece of 6/3 SO. Ran fine for 5 minutes; meggered out good and phase resistances are balanced. Still no idea why the VFD died.

Thanks,
Rick


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## mattsilkwood (Sep 21, 2008)

Fairly short read. http://ecmweb.com/mag/electric_line_reactors_vfds/


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## eric7379 (Jan 5, 2010)

subelect said:


> We had a VFD burn up on a 50 hp, 480 volt motor. When I was removing the damaged components, I find out that the phases come off the fused disconnect, (#14 control power wires feed the control ckt), thru a manual starter, then a 3 phase linear reactor and into the VFD.
> 1. Why would a large inductive load like a 50 hp motor need a linear reactor? This was not part of the VFD, in fact it is a different brand name than the damaged VFD. What good does it do besides providing a space heater in the pump panel?
> 2. Why would the engineer call for a manual starter between the fused disco and the linear reactors? If you wanted to test the control ckt, just disconnect the phase wires. Plus, how often do you need to test the control ckt?
> Have you ever seen this before? It failed when the VFD tanked, so it will need to be replaced, if there is a reason for it to be there.
> ...


I'm not a religious person by any means, but whenever I am asked a question about why something stopped working for no apparent reason, I simply reply "God's will". 95% of the time there is a definite reason why something failed, but sometimes things just fail.


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## John Valdes (May 17, 2007)

Do you mean "line reactor". If yes, there are several good reasons it exists. One good reason is anyone that sells drives or orders drives usually buys a line reactor if they have good sense. Two, most drive manufacturers sell the reactor at 1/2 price if you buy one with a drive. They trust in "line reactors".
Line reactors are filters/chokes for voltage spikes, and do wonders for nuisance tripping. Line reactors are built by the drive manufacturers and other specialty process manufactures. Transcoil is a good example.
Drive cabinets should be sized with the reactor considered. ( I would always mount the reactor outside of the drive enclosure) in its own enclosure.

The disconnect is all that was required. The manual starter between the disco and the drive is a waste of material and serves no purpose that I can think of.

Not sure why the drive tanked either. But switching the manual starter cannot do the drive any good at all. I would remove the manual starter asap. An operator messing with this starter might have something to do with it.

Lastly drives do fail, just like everything else does. Line reactors are the smart way to go and you should be glad you have one in place. It might just save your ass one night about 3:00am. Save you that trip.


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## Hunter1151 (Nov 4, 2010)

Was the starter in series with the line reactor? Then VFD? If this is correct, then did the starter fail removing line power to the VFD, this will fail the drive. The motor can generate a back feed signal, now this is dumped right on drive, typically this is controlled with ramping the drive and breaking resistors. If power is to immediately removed from motor, put starter on load side.


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## Thedroid (Dec 6, 2010)

There shouldn't be any starter opening or closing on either side of the drive. The manual starter shouldn't be used to stop the motor. This is a 50hp drive, and probably wasn't cheap. Controls should have an Start relay closing the drives run circuit. Stop should stop the motor but not the drive. I imagine this is similar to your app, and doubt any engineer would choose to shut off a 50hp drive/motor by opening either line or load.


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## JRaef (Mar 23, 2009)

In Europe, what we call a "Manual Motor Starter" is called a "Circuit Breaker". They use them interchangeably over there, but we cannot because we are not allowed to have adjustable thermal trips on anything except motor circuits. The feed to a reactor and a VFD would not qualify as such, we would have had to use a regular Molded Case Circuit Breaker.

But if the entire VFD package was built by an IEC manufacturer and they somehow UL listed the entire assembly like that, then from an NEC issue the use of that device as a circuit disconnect becomes irrelevant. Most likely they got away with something though because a UL inspector would have bounced it too, but they are not in all places at all times. It could also be that the assembly was never UL listed and where you are, that wasn't a requirement for installation.

But having a disconnecting device in the line side of a VFD is not only fine, it's a requirement. There is no problem opening an up-stream device, but down stream is sometimes a problem. I seriously doubt this had anything to do with your VFD failure. 

If I had to guess, I'd say the fact that this drive was built to IEC standards and not US standards means someone bought something that was not really designed to be connected here and it just took this long for the magic smoke to escape.


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## Thedroid (Dec 6, 2010)

I recall seeing in several different manuals that starting and stopping the motor by applying and removing power to the drive can damage the drive. I do understand that faults may open an upstream device and remove power from the drive while its running, but this wouldn't be an everyday event. I have seen a 3hp well pump that uses a contactor upstream of the drive to start and stop the motor. Its been in service for about a year so far without any trouble, but I wouldn't do the same thing on a 50hp pump. Your assumption is probably right on the terminology error, and we still don't know the details of the controls.


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## John Valdes (May 17, 2007)

JRaef said:


> In Europe, what we call a "Manual Motor Starter" is called a "Circuit Breaker". They use them interchangeably over there, but we cannot because we are not allowed to have adjustable thermal trips on anything except motor circuits. The feed to a reactor and a VFD would not qualify as such, we would have had to use a regular Molded Case Circuit Breaker.
> 
> But if the entire VFD package was built by an IEC manufacturer and they somehow UL listed the entire assembly like that, then from an NEC issue the use of that device as a circuit disconnect becomes irrelevant. Most likely they got away with something though because a UL inspector would have bounced it too, but they are not in all places at all times. It could also be that the assembly was never UL listed and where you are, that wasn't a requirement for installation.
> 
> ...


I understand very little of your post. IEC standards? What does this have to do with a drive failing in the field. I use IEC controls all the time here in the US. I use IEC more than I do NEMA in fact.
The NEC covers this installation as it is installed in the US and is a simple drive with a nameplate.
The extra disconnect (manual switch) regardless of what its called was not required. It also could be the reason for the failure. I agree contactors opening and closing on the load side are strictly prohibited. Line side switches when used correctly are not an issue. Just like you said.
But installing a switch in addition to a disconnect could invite on/off repetitions by production personnel and may have been a part of the failure. I would not want my drive cycled on and off at the will of the production people. The drive takes a few seconds to start itself up. That is why you never use "power down" as the means of stopping the control. You use the available I/O to control.




Thedroid said:


> I recall seeing in several different manuals that starting and stopping the motor by applying and removing power to the drive can damage the drive. I do understand that faults may open an upstream device and remove power from the drive while its running, but this wouldn't be an everyday event. I have seen a 3hp well pump that uses a contactor upstream of the drive to start and stop the motor. Its been in service for about a year so far without any trouble, but I wouldn't do the same thing on a 50hp pump. Your assumption is probably right on the terminology error, and we still don't know the details of the controls.


Starting and stopping the drive as your control method is stupid. Installing contactors on the load side is also asking for trouble.
But I do agree that someone cycling this drive on and off from the manual starter could be the source of the failure.


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## Thedroid (Dec 6, 2010)

Which one of "my" methods was the stupid one? Just trying to throw out some ideas.


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## Wirenuting (Sep 12, 2010)

An upstream disconnect should be no problem on a VFD. A downstream disconnect,,, outside of the drive unit,, will cause big problems if opened or closed. It creates a wave that bounces between the local disconnect and the drive unit and will 
A) blow the drive 
Or
B) blow a pinhole in the motors windings. 
We understand that an insight disconnecting means shall be provided, but a control circuit break must be installed in the local disconnect to drop the drive command before opening the disconnect blades. 

A disconnect installed, just because, is a bad design. If the drive unit can be locked out then a local disconnect is not required.


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## John Valdes (May 17, 2007)

Thedroid said:


> Which one of "my" methods was the stupid one? Just trying to throw out some ideas.


None. I was not directing stupid to anything you said. I agreed with you. :thumbsup:


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## Jlarson (Jun 28, 2009)

I've had nothing but problems with line and load side contractors and disconnects. I won't install them unless it's absolutely unavoidable. 

Just the other day a tech from a utility asked me if I had any ideas why they would be having drives go out randomly for no reason. When I asked how they where started and stopped he said operators would just use the disconnects on the line side. Once this practice was stopped they had no more random failures.


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