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Old 03-29-2010, 08:06 PM   #1
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Default Line Reactor/Load Reactor

I've heard these terms when speaking about VFDs. I realize that a line reactor is meant to smooth out the incoming sine wave using inductors. Is the same true about load reactors?

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Old 03-30-2010, 10:11 AM   #2
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I have only ever used line reactors, like you described. Have never even heard of a load reactor so I am kinda curious now myself.

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Old 03-30-2010, 12:34 PM   #3
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If you apply a line reactor, I'm not sure if there is a "load reactor", none the less if you apply a line reactor at the motor side, motors and reactors are made of the same materials, reactors applied in front of motors become sacrificial lambs. They eventually fail due to the same voltage-induced stresses.
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Old 03-30-2010, 09:22 PM   #4
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We place line and load reactors with every drive we set. We use them as protection for the drive. It's cheaper and easier to replace a line or load reactor than it is to replace a drive. They are basically a 1 to 1 transformer and they fry before the drive fries. So if there is a problem on the line side that burns, and if it's on the load side that one burns...

Where I work every motor in the whole plant has a drive, no questions asked it has a drive. So as you can imagine we change out reactors all the time, and almost never change out drives.

Last edited by knomore; 03-31-2010 at 09:21 AM.
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Old 03-30-2010, 11:32 PM   #5
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Here's my take on line/load reactors;

A line reactor is basically a current-limiting type of reactor. It'll cut back on the inrush current when the VFD is first energized. Most manufacturers recommend them it the transformer feeding the VFD is anywhere from 10 to 100 times the rating of the drive. This varies greatly because of different designs in the AC to DC conversion part of the drive.

A load reactor is used to smooth out spikes created by reflected power in long runs between the VFD and the motor. Usually, if the run is less than 200', they are not needed. This figure also varies by different manufacturers.

Older motors that do not have spike resistant windings should always have a load reactor.

Most VFD manufacturers will give recommendations as to the use of either of these reactors.

Rob
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Old 03-31-2010, 01:29 PM   #6
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Quote:
Originally Posted by knomore View Post
We place line and load reactors with every drive we set. We use them as protection for the drive. It's cheaper and easier to replace a line or load reactor than it is to replace a drive. They are basically a 1 to 1 transformer and they fry before the drive fries. So if there is a problem on the line side that burns, and if it's on the load side that one burns...

Where I work every motor in the whole plant has a drive, no questions asked it has a drive. So as you can imagine we change out reactors all the time, and almost never change out drives.
Line reactors do nothing to protect the drive. They are there for one reason and one reason only, Power Conditioning. Get out your scope and see.
If you are installing line reactors to prevent damage to the drive, you are wasting your time.
There is no protection available from any transformer.
I do like your SOP though. Every drive gets one.

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Originally Posted by micromind View Post
Here's my take on line/load reactors;

A line reactor is basically a current-limiting type of reactor. It'll cut back on the inrush current when the VFD is first energized. Most manufacturers recommend them it the transformer feeding the VFD is anywhere from 10 to 100 times the rating of the drive. This varies greatly because of different designs in the AC to DC conversion part of the drive.

A load reactor is used to smooth out spikes created by reflected power in long runs between the VFD and the motor. Usually, if the run is less than 200', they are not needed. This figure also varies by different manufacturers.

Older motors that do not have spike resistant windings should always have a load reactor.

Most VFD manufacturers will give recommendations as to the use of either of these reactors.

Rob
Great post as usual from Rob.
I would like to add that load and line reactors are usually exactly the same thing. The same part number for line or load unless you are dealing with a power conditioning manufacturer. They do differentiate between the two and have specs to show how they do their jobs.

Always install the load reactor as close to the source (drive) as possible. And always install load reactors when motors exceed 100' from controller.
Put a scope on the output of the control without the reactor and then with the reactor. Observe the conditioning properties of the reactor as the drive operates. Its like night and day. Once you see this picture, you might just use one (load reactor) all the time like knomore does.

Both line and load reactors are money well spent. Just make sure you put them in applications where they are needed. Line reactors IMO should be used all the time. Load reactors not all the time.
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Old 04-07-2010, 12:58 AM   #7
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Quote:
Originally Posted by micromind View Post
Here's my take on line/load reactors;

A line reactor is basically a current-limiting type of reactor. It'll cut back on the inrush current when the VFD is first energized.
VFD is basically a SMPS. A computer power supply does not, but a larger server supplies often have a set of resistors in series with the line for this purpose. When its first energized, it is operated through the resistors, then after a few seconds, relays or triacs jumper the resistors. Sometimes these triacs fail closed causing the SMPS to start across the line and occasionally activating the magnetic trip breaker.

Most manufacturers recommend them it the transformer feeding the VFD is anywhere from 10 to 100 times the rating of the drive. This varies greatly because of different designs in the AC to DC conversion part of the drive.

Line reactors protect the line upstream and reduces RFI. By putting as close as possible to the drive, the length of wires carrying harmonics is reduced. (which act as radiating antenna). They also reduce harmonics current. Harmonics cause transformers and generators to overheat.
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Old 04-26-2010, 06:26 PM   #8
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I wouldnt see any reason for a load reactor. I have never messed with a load reactor but as long as the VFD is setup properly for a motor then you shouldn't have any problems. I guess I could see where you would need one if you had a very expensive drive, then you will need to take all the precautions you could.

Only time I have used a line reactor is when the input voltage going to the drive was a little too high.
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Old 05-05-2010, 07:26 AM   #9
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Quote:
Originally Posted by Seth View Post
I wouldnt see any reason for a load reactor. I have never messed with a load reactor but as long as the VFD is setup properly for a motor then you shouldn't have any problems. I guess I could see where you would need one if you had a very expensive drive, then you will need to take all the precautions you could.

Only time I have used a line reactor is when the input voltage going to the drive was a little too high.
The load reactor will decrease the dv/dt(voltage rise rate) of the pulses generated by the output of the vsd. It will reduce the voltage spikes on the motor windings. Also helps reduce leakage currents when long motor cables are used.
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Old 05-05-2010, 12:17 PM   #10
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Quote:
Originally Posted by Seth View Post
I wouldnt see any reason for a load reactor. I have never messed with a load reactor but as long as the VFD is setup properly for a motor then you shouldn't have any problems. I guess I could see where you would need one if you had a very expensive drive, then you will need to take all the precautions you could.

Only time I have used a line reactor is when the input voltage going to the drive was a little too high.
You have little experience with drives from your statement. Professionals setting up VFD's use line and load reactors all the time. Line reactors are a simple 1:-1: ratio transformer. They do not change voltage. They condition voltage. They prevent nuisance tripping, and adjust impedance. They are listed by their impedance value in all manufacturers catalogs.

Load reactors suppress spikes associated with VFD PWM. These spikes at 460 can be as high as 1500 volts. The load reactor does a good job of reducing these spikes to where they are not apparent visually on the scope. These spikes if not controlled will cause pin hole imperfections in motor windings, and eventual motor failure. That is why most all motor manufacturers use a special coated magnet wire. Baldor Electric trademarks theirs as "Spike Resistant".
If you are using a motor not designed for inverter duty, the load reactor may just be the answer. So, the load reactor is a very important option.
Distance from control to motor may require the addition of a load reactor.
It is fairly standard throughout industry that distances of more than 100' require a load reactor. Long distances produce a phenomenum call "Ring Up Voltage" This is an audible whining sound that can be very irritating in office or hospital settings and can overheat the motor.
The addition of the new VFD output cables are helping greatly in this regard.

Finally. Line reactors are good insurance. So good, that many manufacturers will sell the line reactor for 1/2 price when ordering a control and motor. (Baldor). They are inexpensive and could save you many headaches in the future. I recommend line reactors on all drive inputs.
Load reactors should be considered and implemented when distance and noise is an issue.


Last edited by John Valdes; 05-05-2010 at 12:25 PM.
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