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480V VFD problem
2

480V VFD problem

480V VFD problem

(OP)
In one of our projects, we have a bunch of 480V VFDs in LV MCCs, which have not been used for the past 6 years. What are the steps required to ensure that these VFDs can be made operational? I understand that there are some issues regarding the DC capacitors. Please advise, if you have experience of a similar situation. Thanks.

RE: 480V VFD problem

(OP)
Looking at high labor rates, and time for shipping equipment for testing and installation at site, won't it be more prudent to replace the capacitors right away? Please share your thoughts. One issue may be the certification of the equipment.

RE: 480V VFD problem

It all depends on the situation. If you are in an industry with an operational electrical department, the cost for forming the capacitors will be low.

If you need to hire people to do the job and send them across the globe, it will cost a lot more.

Replacing the capacitors is not a simple task. Most modern VFDs are compact builds and it is usually a lot easier to reform than change capacitors.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V VFD problem

(OP)
Unfortunately, the LV MCC lineup has been phased out by the manufacturer (though not the VFD itself). We may have to ship the sections to a third party inspecting firm, who can be contracted to reform the capacitors. If these are irreversibly damaged., we may then opt for replacement of the capacitors as a last resort. Rest of the VFD section will need to be checked too.

RE: 480V VFD problem

480 V - sounds like USA. Where are you?
There are a few guys available "locally" in other parts of the world that have the equipment and knowledge to do this. It is not rocket science.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V VFD problem

I cannot imagine anyone who has phased out an MCC but not the VFDs inside. The product life cycle of a modern VFD is a fraction of the product life cycle of an MCC.

My point is, if you have an obsolete MCC and the supplier is telling you the VFD is still valid, it's highly likely that it is only a technicality and the VFD is long in the tooth as well, so even if you reform them and re-use them, they will be very very expensive to maintain in short order. Might be worth considering selling it off as surplus and starting fresh with modern product to take advantage of modern options.

"Will work for (the memory of) salami"

RE: 480V VFD problem

Are these new MCCs that have not yet been installed or is this a plant that was in use, mothballed for six years, and is now being re-commissioned?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 480V VFD problem

Depending on the size of the VFD's, it might be cheapest and simplest to just power them up and replace any that fail.

An alternative you could attempt is trying around a 1500ohm, 500W resistor in series with each phase of the AC source. Temporarily replace the cables between the disconnect and the VFD with these resistors and turn-on power until either the drive DC bus reaches >600VDC or it doesn't charge and is proven to have failed. Almost any electrician could handle doing this.

RE: 480V VFD problem

cherryg,
This isn't by chance in Las Vegas is it?

"Will work for (the memory of) salami"

RE: 480V VFD problem

(OP)
waross...this was a newly (then) procured equipment, which was never used. The project was shelved and all the equipment went into preservation.
jraef...this is at FT McMurray..Alberta....
Luckily the equipment vendor is providing us full support on the VFD lineup....the only new fabrication will be the Incomer, since the present MCC had MLO................

RE: 480V VFD problem

About 17 miles north of Ft Mac??

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 480V VFD problem

I have almost the exact same scenario taking place in Las Vegas right now too, except that the MCC is not obsolete. Interesting. A weirdly indirect sign of the economy recovering perhaps?

"Will work for (the memory of) salami"

RE: 480V VFD problem

Hi Jeff;
Can you give us a description of your reforming procedure?
Thanks.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 480V VFD problem

/hijack Now you have my curiosity up Bill.. What is that place?? Staring at it I can't begin to figure it out. Looks like a sand based oil field? /hijack

Keith Cress
kcress - http://www.flaminsystems.com

RE: 480V VFD problem

If you are in Google Earth, search Tar Island AB. You should see Highway 63 to the west. Find the interchange leading to Tar Island. On the west side of the interchange is the Voyageur site. This was to be an 11 Billion dollar heavy oil up-grader project that was started and then was aborted and finally cancelled. It may not be this site, a number of projects were impacted by the economic slowdown.
While you're there, go 5.8 miles North-West of Tar Island and zoom in on Mildred Lake. Zoom in close until you see four photo icons just west near the highway. Three of the icons have photos of the old red/orange drag-line. I was on the commissioning crew when drag-line was brand new and started for the first time back in the '70s. The machine was supplied with a 25,000 Volt trailing cable. Four 3000 HP motors drove the 20 large DC generators that supplied the motors.
The bucket was around 80 yards and hung from a 400 foot long boom that reached 212 feet in the air.
The motor line-up was 10 x 1050 HP DC motors and 10 x 1300 HP DC motors.
It was an awesome sight when the factory tech made a mistake and eight of those generators flashed over with a "ring of fire" around the commutator.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 480V VFD problem

Tar island is the Suncor base-plant site.
Mildred lake is the Syncrude base-plant site.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 480V VFD problem

Quote (Waross)

Hi Jeff;
Can you give us a description of your reforming procedure?
Thanks.
Bill
--------------------
Officially, we tell everyone to disconnect the control boards (usually ribbon cables) so that nothing turns on, then apply DC at the rated voltage, ramped up or increased in 4 steps, over at least 2 hours. But for 460V drives it's hard to get hold of a DC power supply that can handle 635VDC (or more if it's a 575V drive). So you can use a Variac applied to two of the AC terminals, but it must be ramped very slowly starting from zero over the course of 4-6 hours, no steps (or many many small steps) because the ripple current (since you essentially do not yet HAVE caps), can damage the caps. I have seen some instructions that just say to use a transformer to drop the AC input in one step for 2 hours, but I would not use that method on something un-powered for more than 2 years. I have seen it kill caps too, ripple current is a killer.

If you have access to the Rockwell Knowledge Base (or are willing to register for free) it is in article 18015, at least the part about the DC. The AC option is from my previous experience / mistakes...

"Will work for (the memory of) salami"

RE: 480V VFD problem

A much easier way of doing it is to hook up a resistor (can be one or more incandescent lamps) and an overvoltage relay whose "coil" is connected to the DC link (possible via a voltage divider) and whose output contact is wired in series with the resistor and opens when the set voltage is reached.

The resistor will limit current (both direct current and ripple current, so no sweat) and the voltage will grow slowly (RC time constant) until the contact opens. Start with the relay set to 30-40%, then increase to 60-70% after a few hours and finally increase the setting to full DC link voltage and let the system stay there for a few hours. The capacitors will discharge when the relay opens. The relay then closes and cycles on/off to keep capacitor voltage fairly constant.

The beauty with this method is that you are alway current limiting and that not much bad can happen. Also, if there is a bad capacitor, you will notice that the relay doesn't operate at all. And, best of all, you can go fishing while you are waiting for the process to finish!

This Resistor/Relay method was built inte all of the earlier Siemens VFDs. They later used an SCR bridge+resistor and now, I don't know how it is made.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: 480V VFD problem

In my opinion you can power up the VFDs with certain precautions. Capacitor replacement can come later.In any case, for the VFDs it is recommended to replace the capacitors after a period of around 7 years.
However before you power up ensure that the insides of the VFDs are thoroughly cleaned .Clear all residual dust or moisture inside . Otherwise some of the control cards are likely to fail. Also for the capacitors, initially you can raise the voltage gradually through a 3-phase variac.
There is no way to check whether the VFDs shall be operational or not without powering it up. Once it is powered up, if any problem persists, you would get to see the error codes and you'll have to act accordingly as per the OEM troubleshooting chart.

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