Load reactor

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ptonsparky

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NE (9.06 miles @5.9 Degrees from Winged Horses)
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Electrical Contractor
Customer has a 30hp 480v Fuji drive that we would like to use on a 7.5 hp pump. Instruction manual strongly suggests inserting a filter to prevent motor damage. Question is will a filter for a 30 hp motor, sized for the VFD, help with a 7.5 hp motor or should I size it for the 7.5?

Reason the vfd was in their storage was because of its past history of burning out motors. No filters were used at that time.
 

beanland

Senior Member
Location
Vancouver, WA
Reactor

Reactor

The reactor needs to have a value appropriate for the current. The correct Henrys is needed. A larger reactor will have bigger wire for the larger VFD rating but the actual current will be for the motor. You have the option of 3% and 5% reactors. If the VFD has a "history" then maybe a reactor with a higher impedance may be helpful.

All the reactor does is "smooth" the voltage waveform so that voltage spikes created in the BFD do not damage the insulation in the motor. That is what generally runis the motor. Unless, the motor cannot take the added heating caused by the harmonic content from the VFD. That is why purchasing motors rated for VFD use is important.
 

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
By the way, if the VFD was in storage for more than a year, you should go through what is called a "reforming procedure" on the capacitors. Otherwise they will likely pop soon after being just energized, load or no load. If you Google that term (along with VFD) you will find some articles on how to do it. But most of the time, if you don't have the right equipment, it's usually less expensive to just buy a new 7-1/2HP VFD.
 

mull982

Senior Member
.

All the reactor does is "smooth" the voltage waveform so that voltage spikes created in the BFD do not damage the insulation in the motor. That is what generally runis the motor. Unless, the motor cannot take the added heating caused by the harmonic content from the VFD. That is why purchasing motors rated for VFD use is important.
Can you explain how the reactor smooths the voltage waveform. I always thought that the reactor created a larger impedence to these voltage spikes and therefore limited the resulting current from them. Also it was always my understanding that reactors were used to limit current and not voltage.

How is the reactor used to smooth the voltage waveform.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
By the way, if the VFD was in storage for more than a year, you should go through what is called a "reforming procedure" on the capacitors. Otherwise they will likely pop soon after being just energized, load or no load. If you Google that term (along with VFD) you will find some articles on how to do it. But most of the time, if you don't have the right equipment, it's usually less expensive to just buy a new 7-1/2HP VFD.
From what I read, this could be a fun process or I just hook one of the drives up to a spare motor, stand back & turn the power on. :grin:.
 

Jraef

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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
Can you explain how the reactor smooths the voltage waveform. I always thought that the reactor created a larger impedence to these voltage spikes and therefore limited the resulting current from them. Also it was always my understanding that reactors were used to limit current and not voltage.

How is the reactor used to smooth the voltage waveform.
Google the term "inductive time constant". But the condensed "Readers Digest" version is that current through an inductor can only change state at a certain predictable rate, so adding inductance slows down the rise time of any anomalies in the current waveform.
 

JWCELECTRIC

Senior Member
Location
Massachusetts
IMO I would not run the 30HP rated VFD on a 7.5 motor, typically you can go down to half the HP on the motor for that size vfd, otherwise the drive is not efficent due to the losses
 

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
IMO I would not run the 30HP rated VFD on a 7.5 motor, typically you can go down to half the HP on the motor for that size vfd, otherwise the drive is not efficient due to the losses
Switching losses are based on current, so that won't really matter. But there is a possible issue with regards to setting the OL protection in the VFD, which in some cases does not go below 50% of the max. amp rating of the drive. So in that case you would be correct. A 30HP drive may not adjust the OL protection low enough to accommodate a 7-1/2HP motor.
 

Besoeker

Senior Member
Location
UK
Customer has a 30hp 480v Fuji drive that we would like to use on a 7.5 hp pump. Instruction manual strongly suggests inserting a filter to prevent motor damage. Question is will a filter for a 30 hp motor, sized for the VFD, help with a 7.5 hp motor or should I size it for the 7.5?

Reason the vfd was in their storage was because of its past history of burning out motors. No filters were used at that time.
Do you mean input or output filters?
 

Besoeker

Senior Member
Location
UK
IMO I would not run the 30HP rated VFD on a 7.5 motor, typically you can go down to half the HP on the motor for that size vfd, otherwise the drive is not efficent due to the losses
Jraef is right. Switching and conduction losses reduce with current. A 7.5 HP drive on a 7.5 HP motor will run the input rectifier and inverter IGBTs at or about their rated capacity. They get hot. By contrast, use a 30HP inverter at a quarter of its rating all will be cool.

Think about it this way. If you install a cable that is four tines the current rating it need be, it will have lower losses than if you installed one just capable of the duty.
 

mull982

Senior Member
Google the term "inductive time constant". But the condensed "Readers Digest" version is that current through an inductor can only change state at a certain predictable rate, so adding inductance slows down the rise time of any anomalies in the current waveform.
I understand the inductive time constant and the fact that current cannot change instantaneously through an inductor, and that the current will increase based on the time constant.

I dont understand how this will effect the voltage waveform though since current is a result of the voltage. I know there will be a voltage drop across the inductor that will be out of phase with the line voltage, however I dont understand how this would smooth the voltage waveform.
 
Customer has a 30hp 480v Fuji drive that we would like to use on a 7.5 hp pump. Instruction manual strongly suggests inserting a filter to prevent motor damage. Question is will a filter for a 30 hp motor, sized for the VFD, help with a 7.5 hp motor or should I size it for the 7.5?

Reason the vfd was in their storage was because of its past history of burning out motors. No filters were used at that time.
Modern drives used with inverter grade motors do not normally require reactors unless that motor feeders are too long. The drive instructions should detail this.

I have installed hundreds of drives without reactors and no service problem was experienced. I like the Eaton wave traps better on long leads because it does take care of the problem right at the motor. Carrier frequency has also a major effect, the lower it is the longer leads can you use.
 
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