Delta 3 Phase and VFD problems
Delta 3 Phase and VFD problems
(OP)
We have had problems with VFD’s and spindle drives with our 240V Delta three phase. The new Baldor drive required Y three phase only. Searching only provided thread237-106308
Our incoming power has a wild leg that is 210V to ground.
Some systems work, Fanuc, and Haas, but not Allen Bradley, or Benshaw.
Any Ideas?
Our incoming power has a wild leg that is 210V to ground.
Some systems work, Fanuc, and Haas, but not Allen Bradley, or Benshaw.
Any Ideas?





RE: Delta 3 Phase and VFD problems
The solution is either to provide an isolation transformer with grounded wye secondary (preferred) or turn off all of the drive protections for ground and short-circuit faults and then hope the leakage currents aren't larger than the drive input fuses. If they are larger than the fuses, your only remaining choice is the transformer.
Aren't floating delta supplies just wonderful!! Just so you can keep running with a ground fault! I will oppose those systems as long as I am able, if for no other reason than the hazards they present to operating and maintenance personnel.
RE: Delta 3 Phase and VFD problems
What kind of problems?
"240V Delta three phase..."
What are your voltage measurements? This denotes only the "nominal" voltage.
"The new Baldor drive required Y three phase only..."
What series of Baldor drive? I see that the H2 Series recommends having a balanced voltage with respect to ground, but does not technically "require" it. If they did, they would sell very few 240V VFDs in the US, because 240V Wye does not even exist here. Did you actually contact Baldor and ask them? Sometimes they put this stuff into manuals just to cover the rare problems, not the general use. BTW, I have never seen this issue with Allen Bradley nor Benshaw either.
You may have some other pertinent problems with your incoming line, such as a severe voltage imbalance, but just being a Delta system is not the sole cause. 240V "red-leg" Delta as it appears you have, is a low cost way of having 3 phase main power with a small amount of 120V for lighting and such by connecting to a center tap on one winding of the transformer. That is why you read 210V to ground on one leg, it is the one NOT common to that center tap. The down side with this arrangement is that those 1 phase 120V loads represent an immediate imbalance in current, which creates an imbalance in voltage. The original intent, that of a "small amount" of 1 phase loads tapped off, is often lost on the 2nd, 3rd or 4th owner/tenant and they keep adding on to the system without realizing the consequences. One day, your 3 phase voltage imbalance is so bad that your 3 phase equipment starts giving you trouble.
Bottom line, more investigation is warranted.
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Delta 3 Phase and VFD problems
We burnt up 2 Allen Bradley spindle drives and one Benshaw VFD This has been very expensive for a small company.
The incoming power is from our power company in rural western Washington.
The between leg voltage is 240V and we do use the other 2 legs for 120V and 240V single phase. There is a neutral provide for the 120V and 240V single phase. The power company has monitored the system as have we and there are no imbalances that should cause problems.
We did install an isolation transformer on the new Baldor drive, but the Fanuc and Haas do not have an isolation transformer do not seem affected. We may have had a similar problem with another VMC that the dealer and factory could not make work correctly, so they took the machine back.
Are there internal design differences that can make one system work and the other not?
RE: Delta 3 Phase and VFD problems
Consider what happens to the voltage of the DC bus as each rectifier diode (or thyristor - I guess diode for this application) conducts: when the device conducts, that pole of the DC bus is connected to the line voltage less a diode forward volt-drop. On a rectifier fed from a balanced Y system the DC bus voltage is roughly split in half relative to ground, and this value doesn't vary enormously as one device commutates to the next. With a grounded delta the bus voltage relative to ground jumps from near zero to full line voltage as the rectifiers commutate, causing a high dv/dt between the DC bus and ground.
I agree with DickDV's comments regarding the G/F detection and the possibility of the detection circuitry misbehaving as a result.
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Sometimes I only open my mouth to swap feet...
RE: Delta 3 Phase and VFD problems
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One of solutions would be to install a isolation tranforerm with Wye secondary as suggested before. I would suspect an ungrounded delta system would work too, but you need the ground the center tap for 120V.
RE: Delta 3 Phase and VFD problems
Does this make sense??
RE: Delta 3 Phase and VFD problems
Rbulsara,
The link shows one design that would not work with delta power. (thank you)
Is it possible to connect all the DC together and solve the imbalance?
RE: Delta 3 Phase and VFD problems
RE: Delta 3 Phase and VFD problems
I am afraid not. It is most likey what davidbeach and I are suspecting. You need to talk to the manufacurers to give you their reasoning.
RE: Delta 3 Phase and VFD problems
RE: Delta 3 Phase and VFD problems
Then again, to some bean counters those few cents may mean the world. The strange thing is that this just shifts the costs to the end user, in fact INCREASES cost substantially if they have Delta system, and as I mentioned, I have never heard of a 240V Y system in the US! 208/120 Y for certain, but not 240/138V Y. Ludicrous if you ask me.
Unless the issue is the potential voltage IMBALANCE that can occur in red leg delta system. Then again, how does one explain the fact that most 240V VFDs 3HP and under can operate on 1 phase input? You can't get any more of an imbalance that having one phase completely missing.
I do agree with DickDVs thoughts on the GF issue however. I have seen this a lot. We have quite a few 480V ungrounded Delta systems in the US, this has always been problematic with respect to GF tripping.
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Delta 3 Phase and VFD problems
GF tripping would not burn up drives...or would it? A higher than rated voltage would, I think. Trust me, I do not pretend to be an expert in VFD manufacturing.
As for bin counters...lets not get started...
RE: Delta 3 Phase and VFD problems
Are you saying that 230V 3ph power in North America is almost always delta source, ie, floating with no neutral?
I'm learning some things in this post too.
RE: Delta 3 Phase and VFD problems
Loss of a phase, for correctly sized devices in a rectifier, will not cause them to get damaged either. They may or may not work but will not burn up.
RE: Delta 3 Phase and VFD problems
There may be some corner grounded 230V delta and some ungrounded 230V delta somewhere, but not common like the 230V 3phase 4 wire center tapped delta. Many power companies are replacing these as transmission lines are upgraded and all 3 phases are available for a wye transformer bank. Our REA power company recently upgraded the line adding the 3rd phase, but they just moved all the residential and single phase on to the new phase. Ok by me, I'm not ready for a shakeup, voltage wise.
RE: Delta 3 Phase and VFD problems
I didn't think GF would necessarily damage the drive, I was just agreeing that if can be a problem, i.e. nuisance tripping. EdDanzer never said the Baldor drives burned up, in fact he never said what his problems were, just that they didn't work. He did say that AB and Benshaw VFDs burned up though, and that bothers me. I completely agree that if properly sized, the semiconductor devices should be fine under these circumstances, but the point you and ScottyUK raised is that maybe some manufacturers are skimping on components and subjecting users to this kind of risk. I have installed and commissioned a lot of 240V drives on Delta systems before, this has never been a problem. Admittedly though, I can say I have never done so with a Baldor, AB or Benshaw drive, so maybe there is something to this! Still conjecture for all of us at this point however.
DickDV, ccjersey's post answers your question quite well, that is my experience too. I know that overseas there is 380Y220 or 400Y230 or 415Y240, but here we have either 480Y277 or 208Y120. 240V is always delta in one way or another, the most common being the type with a spit winding and a grounded neutral to provide 120V. Here is a transformer connection book. Figures 11 and 15 are the most common connections for 240V 3 phase systems.
EdDanzer,
My experience having lived in Western Washington for 12 years is that there is a lot of the Open Delta version (figure 15) being used in legacy systems. It works fine, until, as I said, the user connects too much 120V load, then it gets severely unbalanced. It could very well be that the day your Utility came out to measure, you were not using as much as other times. It could also be as you suspect, some drives may not be capable of being hooked up without that grounded Y secondary transformer in front of them.
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Delta 3 Phase and VFD problems
We monitored the power for about 5 days several years ago, and adjusted the 120V balance, and continue to monitor it when changing machinery mix or other loads.
Both the AB and Benshaw drives blew diodes and IGBT’s on the input or front side.
I should be getting a call from Benshaw with a more complete explanation later this week.
What I don’t understand is how converting the AC to DC should care about voltage to ground. This may change the DC buss voltage some?
Several years ago I designed and built 3ea. 100 amp DC power supply for some servo amplifiers and did not have voltage imbalance problems.
RE: Delta 3 Phase and VFD problems
An unbalanced voltage however is a problem in that the difference between phases can increase the ripple on the DC bus and if not able to be absorbed by the capacitors, can cause stress and possibly damage to the IGBTs. By the way, the balance between the 120V loads is somewhat irrelevant, the culprit would be the ratio of 1 phase to 3 phase loading on the transformers.
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Delta 3 Phase and VFD problems
How would you check the ration between phases?
RE: Delta 3 Phase and VFD problems
This could, I suppose, cause unequal heating among the rectifiers and failure, especially if the heat sink was designed with little or no excess cooling capacity.
RE: Delta 3 Phase and VFD problems
EdDanzer, what size VFDs are we talking about here, i.e. 3HP and under, or larger than 3HP? Also Series number of the drives? The reason I ask is that both companies sell a wide range of drive offerings and the Series may have very different topologies between them. I heard back from my freind at LS in Korea, and he says that their drives do NOT stipulate that the incoming line is Y or Delta, they don't really care, which means they are using devices rated as high as necessary in case it is a delta supply. He also pointed out that LS is not the only supplier of VFDs to Benshaw, so the ones you tried may have been different.
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Delta 3 Phase and VFD problems
RE: Delta 3 Phase and VFD problems
I found your comments on single phase loading on open delta systems interesting. I grew up in western Canada, and the open delta systems that I remember were installed for large single phase loads and small 3phase loads. The most common was a single large 3 phase pump in a rural or agricultural area. It was common to see a 50KVA or 75 KVA transformer paired with a &.5 KVA, 10 KVA or a 15 KVA to supply the 3 phase.
I still see legacy full delta systems, but for 40 years or so, wye connections have been used here for larger systems.
Different strokes eh?
respectfully
RE: Delta 3 Phase and VFD problems
When operating a drive off an asymetrically grounded 3-phase system such as corner grounded or 4-wire delta, the extra ripple that shows up on the direct current buses really only affects how much power line frequency current flows through the motor winding capacitance to ground and the capacitance of the wiring between the drive and the motor. This current can also couple to the rotor and then damage the bearings. Usually, you need to worry more about zero sequence current at the carrier frequency of the drive because this goes right through winding and wiring capacitance. You may need an inductance between the drive and the motor to decouple the capacitance from the drive even if the power source is solidly grounded wye. Also, XHHW-2 and EPR (RHW-2) wire insulation has less capacitance to ground than THWN and in fact a VFD circuit that is running more than 10 feet using THWN wire will ot work when wet. Water increases the capacitance of allegedly waterproof insulation because the water acts as a big capacitor plate that is in intimate contact with the surface of the insulation. The thinner THWN insulation really acts up when wet - essentially less waterproof than XHHW.
What you also need is an inductance between the branch circuit breaker and the drive, a drive isolating transformer which also acts as an inductance, or a unversal harmonic filter or a long enough branch circuit that the resistance alleviates commutation notching. As each input diode switches off the incoming diode creates a momentary short circuit because the outgoing diode does not trun off instantaeously. If you do not have an inductance, resistance, or unversal harmonic filter in each branch circuit this momentary short circuit chews up the diodes. It is also know now that when 2 3-phase rectifiers both operate from the same bus with no decoupling inductance or resistance the voltage uncertainty from 21 rectifier's commutation cn cause the other rectifier to fail to commutate, resulting in a blown drive.
You can get a unversal harmonic filter from Mirus International that provides both the input decoupling inductance and correct the harmonic current distortion to that of an 18 pulse rectifier which helps a lot on weak power systems. They also make a version of this filter that also does single phase to 3 phase conversion so as to operate 3-phase input drives off of single phase power.
Mike Cole
RE: Delta 3 Phase and VFD problems
132Y230 volts is a standard drive isolation transformer secondary here is the U.S. Depending on how you connect the primary taps you can get 138Y240 or 127Y220 out of it. A standard 12-lead standby generator can also be wired to produce this voltage. You cannot get utility supplied 138Y240 but you can get it as a separately derived system where the customer supplies the transformer or generator.
Actually, UNGROUNDED 3-wire 3-phase has more than its fair share of motor and power electronics damage due to silent or invisible lighting during rainstorms. I have experience with both 277Y480 solidly grounded and 480 volts ungrounded and there is no comparison in the rate of motor damage. I also worked at a small factory complex that had 6 480 volt systems, 1 solidly grounded, 3 definitely ungrounded, 1 where the grounding method was unknown, and 1 padmount transformer that was no longer connected to a service. All of the 277Y480 volt solidly gtounded systems had NO surge arrestors and had zero lighting damage to motors, drives, and soft starts.
I have also figured out that there is a 200 volt to 800 volt gap between the 30 minute voltage withstand rating of a motor and the clamping level of surge arrestors that are UL listed for ungrounded and resistance grounded systems. This means that the surge arrestor WILL NOT protect the motors from a 30 minute Saint Elmo's Fire incident unless bleeder resistors are connected phase to ground. The recommendation of an old Audel electrical book was to connect 1 megOhm 5 Watt resistors from each phase to ground. What you can get are 240,000 Ohm 3 Watt metal film resistors that have a 750 volt peak rating. You would connect these in series strings as follows:
3 resistors 240 volts ungrounded
4 resistors 480 volts ungrounded
5 resistors 600 volts ungrounded
The peak voltage rating of these series strings should coordinate with most surge arrestors.
By the way, when a motor controller is in the off state, the motor circuit downstream of the controller is UNGROUNDED! This means that if you are using PVC conduit, unshielded tray cable or UF cable or service entrance cable or whatever, the motor could suffer static electricity damage during rainstorms if bleeder resistors are not connected to the output of the motor controller and a surge arrestor installed at the motor terminals. This explains how a spare pump motor in a sewage plant can blow up the first of second time that it is needed! Also, I would not depend on the antikick diodes in a variable frequency drives to pass output static charge buildup back to a grounded power source. Theoretically, the drive does pass statice electricity back to a grounded source when energized but would you really want the antikick diodes to be doing that?
Mike Cole
RE: Delta 3 Phase and VFD problems
For an MCG model 160MXT-480D arrestor the clamping level at the surge protector is 2,000 volts and at the end of the 2 foot connecting cable is 2,050 volts. This means that static electricity can cook the motor insulation unless there are bleeder resistors. For that matter, static electricity can cook the surge protector unless bleeder resistors are installed.
Mike Cole
RE: Delta 3 Phase and VFD problems
It may be prudent to check any drive for delta compatability.
RE: Delta 3 Phase and VFD problems
That is very interesting. As a result of this thread, I did an informal scan of 230V drive manuals I have laying around. Of them all, ONLY the Baldor manual makes reference to recommending use on grounded Y systems. Nobody else mentions it at all. Those small Benshaw drives are actually made by LS Industrial (used to be LG, the big Korean electronics mfr.), and of the 3 other brands that drive is available under, not one of them mentions this issue in their manuals. I also had a long relationship with Teco, and posed that question to one of my inside engineering contacts, they didn't actually seem to understand the question! I had to explain it in detail, then they came back only with the old "It hasn't come up as an issue before" response.
Maybe they don't know? I wonder if the concept of a 230V pure delta system is so foreign to them that they never considered it in their design. If the devices were selected so as to not matter, then it has never been an issue, i.e. the Teco response.
I did find this in an ABB manual however:
So another "maybe" is that this is only an issue for drives with built-in EMC filters, those without them don't care and those with them who have never thought of the issue don't realize it (yet).
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
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RE: Delta 3 Phase and VFD problems
It is often good practice to fit an output choke when this is done to minimise the effects of a ground fault if this were to occur.
RE: Delta 3 Phase and VFD problems
RE: Delta 3 Phase and VFD problems
JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> FAQ731-376
RE: Delta 3 Phase and VFD problems
not all drives have a grounded internal Y cap and so in theory may not fall into this problem area. I notice the new Danfoss drives FC102 have a statement:
"Do not connect 400 V frequency converters with RFI-filters to mains supplies with a voltage between phase and earth of more than 440 V. For IT mains and delta earth (grounded leg), mains voltage may exceed 440 V between phase and earth."
RE: Delta 3 Phase and VFD problems
RE: Delta 3 Phase and VFD problems
I doubt that any of the drives you mention would be happy on a corner grounded source or a floating source with significant, balanced leakage to ground.