Hot line reactor 3

[Batfastard]

I recently installed four VFD's for four air handlers. These are 208v 3 ph motors from 10-20 hp. Three of four drives are running well. Motor currents and temperatures are good at 60 hz.
A 15 hp drive has a line reactor which is excessively hot at 60 hz. It does vibrate quite a bit as well.
I have tried two different reactors with the same result.
Motor currents are normal and the electronic drive does not appear to be having any problems. The system is working normally except for the hot reactor. Reactor current is about 75% of full load.
The supply conductors are about 125 feet long and oversized at #2 rw90.
The motor is original and not designed for invertor duty.
I performed a harmonic study on these systems as well as the building service. Although intrepreting the results are a little bit over my head, I am on the understanding there are no immediate problems with the results. THVD on this drive is about 1.6% and THID 55%.
I ran a separate ground wire #6 back to the station bus.
Any ideas?
Batfastard

 

[davidbeach]

Define hot. If the other drives don't have the reactors, what is your reference for hot? What is the temperature rating of the reactor and how close are you coming to that rating.

 

[jraef]

Bingo.
Reactors add impedance, i.e. 1-1/2%, 3%, 5% etc. etc. Since that impedance isn't creating electromotive force as a motor does (except vibration to a certain extent), it is dissipated as heat. As davidbeach alluded, your interpretation of heat may be well below the design tolerance of the reactor.

As to excessive vibration, first off realize that just like heat, there is always going to be some vibration, it is a magnetic device. It shouldn't be more than what you would expect from a transformer hum however. Excessive noise is usually a bad installation, bad manufacturing, bad design or a combination of any of the above. I have run across several installations where I had an excessively noisy one, replaced it with another of the same brand and saw no difference, then replaced it with a different brand and the problem went away. Most of the time however it has to do with the installation, a mechanical harmonic in the reactor vibration spectrum that interacts with something peculiar to that location. You can also try relocating it and making sure you have vibration isolation of some sort.

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[DickDV]

The above posts are right to the point. If it ends up that the reactor is too hot for its rating, try reducing the drive carrier frequency to the lowest possible setting and see if the heating is reduced to acceptable levels.

If not, its time for a new properly spec'ed reactor.

 

[Batfastard]

In defining hot, this reactor has a temp. rise of 115 C Surface temp was measured at 142 F. The rated ambient temp is 40 C.Ambient temperature in this panel is close to 40 C due to the heat.

The temperature in this reactor appears to be within limits.
What my concern is, there are similar reactors in other drives which are carrying more current (% of full load) and not near as hot as this one.
Could this be a symptom of something else not right in the system or just a case of not everything is created equal.

 

[electricpete]

"I performed a harmonic study on these systems as well as the building service. Although intrepreting the results are a little bit over my head, I am on the understanding there are no immediate problems with the results. THVD on this drive is about 1.6% and THID 55%."

Isn't 55% a little high?

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[Batfastard]

Yes, the research I have done suggests 55% THID is very high. The design of the drive cabinet is from a third party. I have forwarded my study results to the design engineers and not heard back from them. (About two months ago). I am the installer. I provided the power for these units.
I am on the understanding if these THID values are not causing problems elsewhere in the building, (phantom trips etc.) then maybe we can live with it. Please correct me if I am wrong.
I do not think it is the harmonics that is causing the line reactor to heat up like that as another drive installed at the same time has higher current harmonics, yet its reactor is not as hot.
Perhaps these reactors are spec'd wrong?
Please advise

 

[jraef]

You may have a point, but you would need to post the specs on the reactor and the VFD if you want that kind of assessment. It might prove enlightening.

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[CJCPE]

Although 55% THID would be high for a distribution system current, it is about what could be expected for an individual drive operating at 3/4 load with 3% total source impedance. The total source impedance could consist of a 3% reactor with no internal drive reactor and a huge transformer(s) providing 208V to the drive. It is more likely a smaller reactor and a more typical power distribution system.

The drive with higher THID and a cooler running reactor must have a lower impedance reactor. Perhaps it is that one that is wrong. The "hot" reactor seems to be well within its temperature rating. Perhaps all of the others are oversized (lower impedance and higher current rating).

 

[bacon4life]

"Surface temp was measured at 142 F."
Did you mean C, or is it only a 21 C rise on a device rated for a 115 C rise?

 

[Batfastard]

I meant surface temperarure of the reactor 142F or 61C. The internal temperatue is probably higher. I do not think it is over the temperature rating of 115C or 239F.
The reactor is a TCI KDRD24L, 208/240v 15 hp 46.2a with a watt loss of 85. I believe it is 3%, but I do not know the inductance.

 

[electricuwe]

jraef,

regarding your post dated July 9th:

If that would be the reason for an reactor to get hot, then what is the difference between an reactor and a resistor ?

 

[jraef]

Well electricuwe,
Now that I re-read it I guess I edited that too many times and ended up oversimplifying it too much. The point I wanted to make was that reactors are never pure inductance, there is always resistance in the circuit so they will always be hot to some extent. In addition, as the reactor doesn't pass higher frequencies, those are converted to heat. So the more harmonics that are present, especially in the higher bandwidths, the hotter the reactor will get.

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