Drive question

[augie47]

I will get more detail today so at the moment this is somewhat of a generic question.
Yesterday I saw some what appeared to be VFDs, most likely foreign due to a C-E rating and a 400v input power (@104 amps).
The secondary on each of the drives supplied (4) manual motor starters (IEC) that apparently provided OCP and a disconnecting means for individual motors.
Before I dig more deeply, is there any problem with this set up as far as the manual starters providing the OCP on the load side of the drive ? Secondly, there drives are connected to 480v.
On the surface it would appear to be a violation of 110.4, however, my guess is the 400v rating is based on 50Hz although it does not state. Is it a violation and/or unsafe to operate these drives with a 480v 60Hz input ?

 

[gar]

150113-0910 EST

My guess is that the input circuitry of the VFD is a rectifier followed by a large capacitor. This means the DC bus voltage will be proportional to the AC applied voltage. Probably not wise to run the bus 20% above its nominal value. There might even be overvoltage detection and/or limitation. 60 vs 50 Hz should not be a problem unless there was some sort of tuned input. DC bus ripple will be less with 60 Hz.

If my guess is correct, then you need a step down auto-transformer, and with various taps so the DC bus can be adjusted to its optimum voltage.

.

 

[kwired]

I will get more detail today so at the moment this is somewhat of a generic question.
Yesterday I saw some what appeared to be VFDs, most likely foreign due to a C-E rating and a 400v input power (@104 amps).
The secondary on each of the drives supplied (4) manual motor starters (IEC) that apparently provided OCP and a disconnecting means for individual motors.
Before I dig more deeply, is there any problem with this set up as far as the manual starters providing the OCP on the load side of the drive ? Secondly, there drives are connected to 480v.
On the surface it would appear to be a violation of 110.4, however, my guess is the 400v rating is based on 50Hz although it does not state. Is it a violation and/or unsafe to operate these drives with a 480v 60Hz input ?

Though I believe it is generally preferred to have such an overload device control an input to the drive instead of directly opening the load, I don't think it is all that hard on most drives to open circuit the output, or part of the output, but it not a good idea to suddenly add additional load when the output is operating, so these overloads are probably not much trouble if their only intention is to provide overload protection.

400 v 50 hz vs 480 v 60 hz is in the right v/hz ratio but you probably still need to refer to drive documentation to see if it is designed to accept 480 v input, my guess is it probably will work, but may have a shorter life if not designed for it.

 

[petersonra]

many such drives have dual ratings so it may be quite acceptable for 480V input. sometimes it is not on the nameplate though.

I don't have a problem with the setup in general.

 

[gar]

150113-1023 EST

kwired:

What does the voltage to frequency ratio have to do with thre operation of a rectifier and capacitor input filter?

.

 

[kwired]

150113-1023 EST

kwired:

What does the voltage to frequency ratio have to do with thre operation of a rectifier and capacitor input filter?

.

:slaphead:Never mind that comment.

 

[augie47]

many such drives have dual ratings so it may be quite acceptable for 480V input. sometimes it is not on the nameplate though.

I don't have a problem with the setup in general.

I found additional data which showed the drive to be rated at 480v.
Thanks for the input on the output side.
Now all that is lacking is determining the withstand rating. I have an inquiry to the manufacturer.
FYI the Drive is Yaskawa.

 

[Jraef]

In most VFD mfrs stable of products, there are 3-4 "classes" of voltage ratings, all with a +- 10% input range minimum;
200V class drives cover 200-240V input
400V class drives cover 380-480V input, and
690V class covers 550-690V input
Then some, who are marginal at 480V input on their 400V class, will offer a "500V class" that really only addresses our 480V input.

So although it is LIKELY that your 400V class drive will cover 480V +10%, the only way to make sure is to attain a manual and check (calling US reps for foreign mfrs lately has become almost useless I have found). If it is one of the major players, like Yaskawa, Mitsubishi, Toshiba, ABB, Siemens, Scheider etc, that is most likely the case. If its some brand you have never heard of, then be cautious. If there is no name, or you see the name Huanyang, throw it out now and save yourself the trouble of throwing it out a month from now. They are the worst...

As to the MMS units on the load side; this has been a common practice for years, and recommended by most VFD mfrs as the best practice, until very recently. In 2013 a study done by GAMBICA, an EU drives industry think tank, was investigating a lot of motor failures taking place in this type of installation, and found that bi-metal overload devices, such as those used in these IEC manual motor starters, are heating up disproportionately to the current flowing through them. That is causing nuisance tripping on motors that are marginally sized, meaning running at or near FLA and with the OL set at that level. That would not necessarilly be an automatic problem, except for the human response. Repeated overload trips, combined with an adjustable trip setting, tends to result in people turning up the dial to make the nuisance go away, which then eventually leads to premature winding failure. The trick to making the application work successfully then, is to be less stingy on motor sizing, and more stringent on not succumbing to the temptation to ratchet up the settings.

Other than that, as kwired said, it's not much of a problem to open the contacts down stream of a running VFD in an emergency such as an overload, but it is a problem to CLOSE contacts on a running VFD. So that then also becomes a procedural issue. In most cases an aux contact in each MMS is wired in series with all of them, then into the VFD to turn it off if any one of them trips. That means if you reset one, the VFD is off, then can re-start them all together as it should. If that was not done in your case, then you must somehow ensure that operators know not to reset a tripped unit while the VFD is running, or it will damage the VFD. You can get away with it a few times, and that often gives people a false sense of security, but the damage it causes to the transistors is incremental, so it's only a matter of time, but is unpredictable as to when the last straw happens.

 

[Besoeker]

I will get more detail today so at the moment this is somewhat of a generic question.
Yesterday I saw some what appeared to be VFDs, most likely foreign due to a C-E rating and a 400v input power (@104 amps).
The secondary on each of the drives supplied (4) manual motor starters (IEC) that apparently provided OCP and a disconnecting means for individual motors.
Before I dig more deeply, is there any problem with this set up as far as the manual starters providing the OCP on the load side of the drive ? Secondly, there drives are connected to 480v.
On the surface it would appear to be a violation of 110.4, however, my guess is the 400v rating is based on 50Hz although it does not state. Is it a violation and/or unsafe to operate these drives with a 480v 60Hz input ?

I mostly agree with what gar has said.
For the vast majority* of VFDs, there is a plain rectifier at the input and a DC link capacitor. One the more high spec. units there is often a DC link choke. This good for limiting ripple current in the capacitors and reducing the line side harmonics.

The information you have given on the VFD strongly suggests that it is a 55kW unit in which case it would almost certainly be 3-phase (in and out).
With a 400Vac input, the rectified voltage applied to the DC link capacitor is 540Vdc - the factor is 1.35.
So, for 480Vac, you would get 650Vdc. That's quite a big difference.

All the power circuit components would have to be rated for that additional voltage. Input rectifier diodes, the DC link capacitor, and the output IGBTs. Less obvious, but so would the internally generated electronic power supplies. These are often generated from the DC link using a DC-DC converter so that also has to be rated for the higher voltage.

I'm not trying to frighten you - honest guv!
Just trying to point out that it can't simply be taken for granted that you can run it on 480V.

Having said that, most of the VSD systems we supply are rated to cover that.

This is our spec for a couple of 55kW units (coincidentally similar to your rating) we'll ship this week.

Input voltage 380 -500 Vac 3 phase
Output voltage 0 ? Uin three phase
Input frequency 45 ? 66 Hz
Output frequency 0 ? 320 Hz
Output current rating 105A

So it meets your requirements for 480V/60Hz input.
But you MUST check with your supplier.

One final point, I really do not like the idea of manual motor starters on the output side of the VSD. If the OCP trips what does it do? If it opens the supply to that motor with the VSD on line, that's bad news. Many VFDs react badly to having the output opened while running. Even worse, if the OCP device is reset, will it bang that motor back on line like a direct on line starter would?

That really needs to be thought about.

As does my fee..............

 

[augie47]

Is anyone familiar with Yaskawa
I have attempted to get info from the mfg and ended up with little info other than SCCR is 100k when install per specs but I can't decipher the requirement in the 300 page install manual.

 

[Jraef]

Is anyone familiar with Yaskawa
I have attempted to get info from the mfg and ended up with little info other than SCCR is 100k when install per specs but I can't decipher the requirement in the 300 page install manual.

I can probably help, I've done bunches of them over the years. Their manuals are less than desirable now that they sell under their own name. Years ago, Yaskawa only sold through other companies, like Saftronics, Magnetek, EMS, IDM, Omron etc. All of them except Magnetek used that same "Jinglish" (Japanese translated into English) manual that Yaskawa provided, and it sucked. Magnetek however were smart and re-wrote the manual for the US. They ended up kicking ass on all the other Yaskawa partners for years because of that. Some smart customers figured it out and when the internet came along, they would download Magnetek's manuals for free, then buy the same Yaskawa drive from whichever partner was willing to sell them cheaper. But that's all history, Yaskawa ended all of those relationships and took over marketing under their name only, and using only their Jinglish manuals.

Which series are you using? I have a manual for the E7 series here.

In general though, there is a chart usually in the Appendix at the back of the installation manual that gives you what you need to know. In that, they will have charts that say they are for "installing per the NEC" and another set of charts saying "Installations per UL". The charts for the NEC are, for the most part, useless, because they do NOT address the SCCR requirements, which are determined by UL. But they don't explain that clearly, you just have to know that I guess.

What you will see is that the "NEC" charts will list fuses or CBs, but the "UL" charts will only list semiconductor fuses. That's because that is the ONLY way those drives are UL listed and tested for SCCR.

 

[Jraef]

If it's an A1000 series, it's a little different, the charts are in the "Standards Compliance" section of the manual, then down to the "UL Standards" sub-section. There you will find this little blurb.

Drive Short Circuit Rating
The drive is suitable for use on a circuit capable of delivering not more than 100,000 RMS symmetrical Amperes, 240 Vac
maximum (200 V Class), 480 Vac maximum (400 V Class), and 600 Vac maximum (600 V Class) when protected by Bussmann
Type FWH or FWP fuses as specified in Factory Recommended Branch Circuit Protection on page 750.

Just so you know, it must be that specific Bussman fuse, not an equivalent of another brand.

 

[don_resqcapt19]

If it's an A1000 series, it's a little different, the charts are in the "Standards Compliance" section of the manual, then down to the "UL Standards" sub-section. There you will find this little blurb.
Just so you know, it must be that specific Bussman fuse, not an equivalent of another brand.

Is there a default SCCR if you don't use those fuses?

 

[augie47]

If it's an A1000 series, it's a little different, the charts are in the "Standards Compliance" section of the manual, then down to the "UL Standards" sub-section. There you will find this little blurb.



Just so you know, it must be that specific Bussman fuse, not an equivalent of another brand.

That is what I found and it did leave me with the impression that the only way the drive could be installed and still meet the UL listing was the Bussman FWP fuse even though the manual shows circuit breakers (no specific just an max ampere and some other fuses).
Bottom line it appears that for the install to be Code compliant and remain a listed product it will need the FWP fuses. Am I correct ?

 

[Jraef]

That is what I found and it did leave me with the impression that the only way the drive could be installed and still meet the UL listing was the Bussman FWP fuse even though the manual shows circuit breakers (no specific just an max ampere and some other fuses).
Bottom line it appears that for the install to be Code compliant and remain a listed product it will need the FWP fuses. Am I correct ?

Yes, that is correct. Even if you have a circuit breaker there for convenience, you still need the fuses, because they could only get the UL listing for the drives, with an SCCR, by testing it with those specific fuses. That's why the chart on that lists the circuit breakers is kind of bogus, because the NEC now requires having the SCCR and you cannot get the SCCR unless you use the fuses, because the SCCR is done by UL. As it was explained to me, they put chart with the breakers in there because "not everyone needs to worry about that UL listing issue"... Maybe true, but now everyone must abide by the SCCR requirement.

Don,
The default is like anything else that is untested, 5kA. Might be possible on a 240V system, it would be damned near impossible to get there at 480V. This issue has been kicking contractors in the butt all over around here lately, because the local AHJs have need educated on what to look for (must have attended a seminar), and they are nailing people on this right and left. It's hitting the HVAC guys particularly hard right now. I keep seeing Air Handling Units come in with the VFDs packaged with them, and the unit has a sticker on it that says 5kA SCCR. The mechanical contractor has no clue, then dumps the issue onto the EC, telling them "Supply a circuit not capable of more than 5,000A short circuit current" and walks away.

 

[augie47]

This will probably mean more to you (Jraef) than it did me but it was interesting.
After another day of phone calls and elusive answers, I was advised by UL that this drive was under UL 508-B and in order to be listed it would need a notation on the device as to the SCCR in relation to the corresponding OCP device to achieve that. Otherwise it would default to 10k.
The particular UL rep I spoke with has previously been 100% reliable.