operating a 150 horse power 480 volt motor with VFD

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jim gage

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I am looking a drawing for a dust collector system and in the 1 line they spec a 225 kva 208 delta to 480 wye transformer feeding the VFD for the system
Does anyone know any reason why this could pose a problem in this situation? The tech that is ramrodding the job thinks this will cause problems with the VFD
due to inrush
I thought with a VFD set at a minute 20 seconds ramp time there would be little if any inrush?
He said it would cause the coil to collapse?
Can anyone give me some feed back on this topic
The transformer will be constantly energized and only the VFD will be operated on and off I guess I am confused and he couldn't explain why he had concerns
 
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jim gage said:
I am looking a drawing for a dust collector system and in the 1 line they spec a 225 kva 208 delta to 480 wye transformer feeding the VFD for the system
Does anyone know any reason why this could pose a problem in this situation? The tech that is ramrodding the job thinks this will cause problems with the VFD
due to inrush
I thought with a VFD set at a minute 20 seconds ramp time there would be little if any inrush?
He said it would cause the coil to collapse?
Can anyone give me some feed back on this topic
The transformer will be constantly energized and only the VFD will be operated on and off I guess I am confused and he couldn't explain why he had concerns
Click to expand...
You are correct.
VFDs don't generally have an inrush problem.
The usual configuration is a rectifier to convert AC to DC, a large smoothing capacitor bank on the DC, and the IGBT inverter stage to convert the fixed DC voltage to variable voltage, variable frequency AC to control the motor speed.

It starts at low voltage and frequency and ramps up to required speed. That keeps the current to a controlled level.
 
Besoeker said:
You are correct.
VFDs don't generally have an inrush problem.
The usual configuration is a rectifier to convert AC to DC, a large smoothing capacitor bank on the DC, and the IGBT inverter stage to convert the fixed DC voltage to variable voltage, variable frequency AC to control the motor speed.

It starts at low voltage and frequency and ramps up to required speed. That keeps the current to a controlled level.
Click to expand...
Correct. Inrush is not an issue here, whomever said that to you is undoubtedly unfamiliar with how VFDs function.

What WILL however be an issue is in how you connect that transformer secondary, the 480V side in this case. If you are planning on using a standard off-the-shelf transformer and back-feeding it, that 480V side will most likely be Delta, and that is NOT good for VFDs. VFDs are all made to expect a solidly grounded Y service, so all of the internal components are designed around the fact that the maximum line to ground voltage reference will be 58% of the line to line voltage. In a Delta system, L-G can be the same as L-L. If you corner ground it, you still have that problem on two of the 3 phases, so although that gets you through the NEC requirements for a Delta sevice, it's still bad for the VFD. What you really need is a 208V Delta to 480Y277V transformer, and you will ground the XO on the 480V side. Anything else and you will be voiding the warranty on the VFD in most cases. The problem is, that's going to be a custom would transformer.

If you can't wait for a custom transformer like that, option 2 would be to add another transformer in between that is 480D to 480/277Y, they are called "drive isolation transformers" and are usually readily available. That's not going to be cheap though.
 
jim gage said:
I will be using a 208 delta/ 480 wye XFMR and I will be bonding on the secondary
So I guess I need to find out more why he thinks it will be a problem.
Click to expand...

You sort of have the same thing if you were feeding directly from service that was supplied by 480/277 wye system, so I don't have a clue as to what he is concerned about either.
 
jim gage said:
I will be using a 208 delta/ 480 wye XFMR and I will be bonding on the secondary
So I guess I need to find out more why he thinks it will be a problem.
Click to expand...
You are good to go.

A possible issue he may be thinking of. In using some older COTS step-down transformers as step-up, the configuration of the windings is such that when going the opposite direction, the LV winding, normally expected to be the SECONDARY, is physically wound on the outside of the HV (formerly primary) winding. That then causes the core magnetizing current to have to pass THROUGH the HV windings to get to the core, which increases the inrush on the LV side. That is why, in the 2014 Code, they began requiring that if using a transformer for step-up, you must be able to demonstrate, via the nameplate or manufacturer's literature, that the transformer is designed to be used this way (450.11.B). Most new transformers are now designed to be connected either way because of this. it just means that both sets of windings are next to the core.

In your case this is going to be a custom wound transformer and is unlikely to be made that way anyway...
 
operating a 150 horse power 480 volt motor with VFD tech response to my question

operating a 150 horse power 480 volt motor with VFD tech response to my question

jim gage said:
I am looking a drawing for a dust collector system and in the 1 line they spec a 225 kva 208 delta to 480 wye transformer feeding the VFD for the system
Does anyone know any reason why this could pose a problem in this situation? The tech that is ramrodding the job thinks this will cause problems with the VFD
due to inrush
I thought with a VFD set at a minute 20 seconds ramp time there would be little if any inrush?
He said it would cause the coil to collapse?
Can anyone give me some feed back on this topic
The transformer will be constantly energized and only the VFD will be operated on and off I guess I am confused and he couldn't explain why he had concerns
Click to expand...

These are the techs exact words when he responded to my questions

" Because we have had issues with vfd's and the long ramp time and the transformers browning out.

The vfd will pull a sustained load until the motor gets to about 40hz.

That will be somewhere around 260 amps for 30 to 40 seconds.

What we have seen on these is a electromagnetic induction field collapse and a large secondary voltage drop that causes the vfd to error out on start up.

He said he talked to John the engineer at Nederman the manufacture of the system and he is working the numbers to get the best solution.
I hope the best solution is necessary and not just an additional cost to my customer."
 
jim gage said:
These are the techs exact words when he responded to my questions

" Because we have had issues with vfd's and the long ramp time and the transformers browning out.

The vfd will pull a sustained load until the motor gets to about 40hz.

That will be somewhere around 260 amps for 30 to 40 seconds.

What we have seen on these is a electromagnetic induction field collapse and a large secondary voltage drop that causes the vfd to error out on start up.

He said he talked to John the engineer at Nederman the manufacture of the system and he is working the numbers to get the best solution.
I hope the best solution is necessary and not just an additional cost to my customer."
Click to expand...
I'd be inclined to file that advice - in the trash can.
 
jim gage said:
These are the techs exact words when he responded to my questions

" Because we have had issues with vfd's and the long ramp time and the transformers browning out.

The vfd will pull a sustained load until the motor gets to about 40hz.

That will be somewhere around 260 amps for 30 to 40 seconds.

What we have seen on these is a electromagnetic induction field collapse and a large secondary voltage drop that causes the vfd to error out on start up.

He said he talked to John the engineer at Nederman the manufacture of the system and he is working the numbers to get the best solution.
I hope the best solution is necessary and not just an additional cost to my customer."
Click to expand...
Under sized transformer may cause problems, but unless you are running straight from the source generator, there is usually several transformers between your load and the source:?

260 amps for 150 hp motor @ 480 volts is pretty high current. Unless you are accelerating a high inertia load I doubt you would ever see that high of current for more then a few cycles let alone 30 to 40 seconds. If he is talking 208 volt primary current of the transformer that sounds more expected level of current but that should be easy for a 225 kVA transformer to handle.
 
kwired said:
Under sized transformer may cause problems, but unless you are running straight from the source generator, there is usually several transformers between your load and the source:?

260 amps for 150 hp motor @ 480 volts is pretty high current. Unless you are accelerating a high inertia load I doubt you would ever see that high of current for more then a few cycles let alone 30 to 40 seconds. If he is talking 208 volt primary current of the transformer that sounds more expected level of current but that should be easy for a 225 kVA transformer to handle.
Click to expand...

This is a blower motor for a dust collector it will be high inertia to get that thing rolling but I still don't think that will be a problem. Guess I don't want to sell my customer a bill of goods unless he needs it. ??
 
jim gage said:
This is a blower motor for a dust collector it will be high inertia to get that thing rolling but I still don't think that will be a problem. Guess I don't want to sell my customer a bill of goods unless he needs it. ??
Click to expand...
And variable torque.
From standstill the input current to the VSD will be very low and build up as the motor accelerates. The output current to the motor will probably be limited by your relatively long ramp time but, in any case, will not exceed the VSD current limit setting.
 
Besoeker said:
And variable torque.
From standstill the input current to the VSD will be very low and build up as the motor accelerates. The output current to the motor will probably be limited by your relatively long ramp time but, in any case, will not exceed the VSD current limit setting.
Click to expand...
I agree, current will never exceed what the VSD is set to allow, and unless it is an oversized drive for whatever reasons, would almost never allow 260 amps for 30-40 seconds if it is only designed for a ~180 amp motor. Their settings still have limits that protect the drive itself, and even if you can go beyond some limits, when internal temp reaches a certain point they still trip on over temp fault.
 
Meh, 269A from a motor rated 180A is 144%, a CT rated drive should be able to deliver that for 60 seconds. So it’s possible.

But on a dust collection blower? Methinks something is amiss here, likely inexperience on the part of whomever is setting it up. For one, you only need high torque if you have no dampers to close off the air flow until it is accelerated. If there are no dampers or they were removed, that’s a poor design. For another thing, as Besoeker mentioned, any decent VFD can be set to limit the current, in which case it will override the acceleration time and take as long as it takes. If necessary, you can set the Current limit at 100% of FLA and that motor will eventually get to speed. That is likely a source of the real problem here, impatience. Someone it insisting on forcing this blower to accelerate faster than it needs to, resulting in having to use a CT rated drive on a VT load, and, in your case, over size the transformer to accommodate it.

The application is valid with the equipment specified, but may need management of expectations with the user.
 
Besoeker said:
Normally, a fan would be a variable torque application for a VFD.
Click to expand...

Agreed. But if someone had a transformer saturate because the VFD pulled 269A, that implies that the VFD was capable of it. A VT rated drive would have had to shut down to protect itself before it could pull that much current for that long, but a CT rated drive would be capable.

I have a number of customers who always buy CT rated drives even for VT loads. It makes them feel better I guess and who am I to argue with their wanting to spend more than necessary? I do the right thing and explain it to them, then take their money when they decide to overdo it.
 
Besoeker said:
The 269A is speculation by a tech who clearly doesn't know his onions.
Click to expand...
Well, in post #7 the reported statement by the other tech seems fairly definitive, not speculative. But whatever... we both agree it's wrong on several levels. I'm just saying his observation MAY have been true, BECAUSE they were doing it wrong and were using the wrong equipment. Had they not over sized the VFD, it never would have let that take place...
 
I have run into this kind of thing before and usually what it ends up being is the so called tech gave me numbers that did not match what was actually there. My inclination is to get first hand information rather than relying on numbers that don't make much sense.

One thing that might be possible is someone has set the V/Hz setting to something screwy so there is a lot more current at lower frequency than you might expect.
 
led recessed lighting

led recessed lighting

I was called to one of my customers building today because they had a string of 9 recessed cans all on the same circuit and all led
They had a recent power event in the building utility power and after the power came back up the led cans did not work.
I had no other lighting problems in the building even though all lighting is led and controlled in the same manner via OCs and switches
I went to trouble shoot the problem and turned the power off to that circuit and pulled the LED + and - off of the driver on the can so I could read the output to the LED in the fixture and had my apprentice turn the circuit back on then when it was re energized the entire string lite back up
What happened here to cause this to happen.
Original inspection of the problem by maintenance found 120 volts to the drivers but no working LED in the fixture
that is when they called me.
They are all working now but I need to know why
did removal of power reset a switch module or what?
 
jim gage said:
I was called to one of my customers building today because they had a string of 9 recessed cans all on the same circuit and all led
They had a recent power event in the building utility power and after the power came back up the led cans did not work.
I had no other lighting problems in the building even though all lighting is led and controlled in the same manner via OCs and switches
I went to trouble shoot the problem and turned the power off to that circuit and pulled the LED + and - off of the driver on the can so I could read the output to the LED in the fixture and had my apprentice turn the circuit back on then when it was re energized the entire string lite back up
What happened here to cause this to happen.
Original inspection of the problem by maintenance found 120 volts to the drivers but no working LED in the fixture
that is when they called me.
They are all working now but I need to know why
did removal of power reset a switch module or what?
Click to expand...

You might want to try starting a different thread. The jump from VFD to LED is a jump.
 
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