VFD Cabinet Design questions

Hi all,
I am working on a design for a VFD Cabinet and would like to run some ideas by everyone and get some opinions.

The VFD is a Powerflex 755 model 20G1AND125AN0NNNNN. It will be connected to a 75HP motor.
The Cabinet is a Hoffman WF75LP with an internal fan and vent system.

I have a 150 Amp Breaker on the incoming power. Next I have a Line Reactor (Transcoil model KDRULG3H). Then the Drive. I don't have a Load Reactor as the distance to the motor is short enough that my AB distributor did not recommend one. The motor is 300' from the VFD.

Now the questions:
1. Is it recommended to install fuses along with the CB on a system like this? I have seen systems that use both but I am not sure why you would want both. What is your opinion?
2. Given this set up are there any recomendations from your guys on how to improve the design?

Thanks for any help you can provide.

a CB is too slow for the electronics,however nowadays this safety is getting less important.

Some drives are only UL listed when protected by circuit breakers, because the UL testing and listing process is more rigorous and expensive. That is why you sometimes see VFDs that are always used with fuses ahead of them, it is necessary in order to apply their UL listing and get a reasonable SCCR rating. The PF755 however has been UL listed and tested without fuses, so the choice is yours.

Some people, propped up by the fuse industry anecdotal reports, feel that the high speed "semiconductor fuses" are going to protect the front-end components of the drives, the diodes in most cases, SCRs in some cases. Personally, I have NEVER seen a semiconductor fuse open fast enough to prevent that damage. Usually the device fails, THEN the fuse clears, so you have to replace BOTH of them...

If this is at 480volts, I think 300ft is a bit far for even an MG1 P31 motor without a reactor.

DickDV,
According to my AB guy and the manual he sent me I should be able to go 500' without a reactor. The manual he sent me was Drives-in001-en-p which is the Wiring and Grounding Guidelines for PWM AC Drives. In table A is were I found that.

Now that is what AB has said, doesn't mean it is correct, what would you recommend? I did a search on the site about reactors. I found a bunch of post by you and you seem to be a very knowledgeable guy. I am still confused as to when you use a reactor and when you don't. On the Line Side I think I understand why they are used. The Load Side is where it gets fuzzy. Could you or somebody enlighten me as to why a reactor is needed and when do you apply them??

Any help from you would be greatly appreciated!!

You need output protection to mitigate high voltage spikes and dv/dt as well as voltage and current harmonic distortions which will increase losses thus increasing heating in you motor.

The voltage spikes from reflected wave can reach in excess of 1500 volts peak to peak depending on several factors and also produces corona issues which will decrease the life of your motors insulation.

Depening on your cable routing thought should be given to EMI/RFI issues of VFD's which are magnified on long cable runs. VFD cable should be used to both mitigate the EMI/RFI issues and to increase the life of the cabling.

Many people make the mistake of using standard THHN or other wiring on long runs and the insulation is rated for 600 volts but you can have in excess of 1500 volts depending on length which can significantly reduce the life of your cabling also.

Although it is true that the fuses won't generally save the IGBT's if you have a serious fault, they will open much faster than the upstream CB's (a fraction of the time) and stop the fault from potentially doing more damage if it occurs on the top end of the drive. When IGBT's fail radically, it will be normal to lose one or two current limiting fuses, but the upsteam protective device should be just fine. For the length issues and using an output filter, my advice is Under 100', don't worry about it, but I am not good with the 500' length and I wouldn't accept that as "good" advice. At 300' I would use a Motor Terminal Protector which is essentially a passive wave trap connected to the motor leads at the peckerhead in parallel which will help with the high speed transients and reflected/standing waves.

The guidelines I have used successfully for many years for 480v, mg1 P31 motors and drive carrier frequency at 8khz or less are as follows:

100hp and over---- no additional protection below 250 Ft
10hp and smaller---- no additional protection below 60ft
Extrapolate linearly between those two hp levels

Motor not mg1 p31 cuts those lengths in half
Addition of a load reactor (3%) doubles those lengths
Use of a dv/dt filter quadruples those lengths

I am not fond of AB's terminators because (1) they leave the motor leads noisy and (2) they are placed at the motor end of the leads where there often is no safe place to mount them and the environment can be wet, cold, corrosive, or subject to mechanical damage.

Adding load reactors is relatively cheap so if there is any doubt in your mind I would add them. And I know of no downside to adding them. However, unless you are:
a) sitting in front of an o-scope looking at waveforms
or
b) have a group of test installations with the same motors and drives at varying cable lengths without protection

it is a little bit anecdotal to say "I have done (insert your solution here) and never had a problem". That is kind of like saying "I have always used a 10HP motor and drive in Application X and have never had a motor or drive failure". But Application X may only require a 3HP motor so it is little wonder you've never lost a motor or drive. But in the process you have spent alot more money than you really needed to.

If you are on the edges in the design, look at adding these components kind of like buying insurance. If it allows you to sleep better at night because you have the additional protection it is probably worth it.

Keith

Bullzi said:

DickDV,
According to my AB guy and the manual he sent me I should be able to go 500' without a reactor. The manual he sent me was Drives-in001-en-p which is the Wiring and Grounding Guidelines for PWM AC Drives. In table A is were I found that.

Click to expand...

The values in that table are actual tested values, not theoretical, both for reflected wave and Corona Inception Voltage issues. The reason they seem longer than others is because the 7 class PowerFlex drives have built-in features specifically to address those issues. If I told you what those measure were I'd have to kill you, but generally it has to do with lower rise time on the IGBT pulse leading edges and other things done help avoid capacitive coupling in the cables.

mostly nowdays inverter come with feature safety.probaly the fuse inside the panel or maybe nothing.

manufacture will say their inverter are follow the international standard(price different).

ok we feel confident with them.we use it.

on the next month, our insurance panel company make inspection they request to put fuse on incomming supply.

if not they will add + + + to our insurance montly payment.

and the end u need install a fuse.

additional cost/job ,request budget from boss.

boss - bla bla bla