asd or vfd questions

[puckman]

I like to ask some people who have work with asd or vfd for some help with these drives.
My company seems to make changes to equipment without any though to engineering their equipment. They have replaced across the line control with asd or vfd without changing the motors or wiring. These motors are mostly for pumps above ground and some for submersables.

Should these types of changes be made as a complete unit , correct type of asd , inverter duty motors and vfd type wire ?
There has been asd's replaced for atleast 4 different motors all between 5 - 10 hp for a start . The asd last 2-3 years and then need replacing do to damage. They operate at about 40 hz.

Should submersables 40- 75 hp use wire rated higher then 600v if on a asd ? ASD techs say units have filters built in drives.
Thanks for any information with the installation or troubleshooting process you can advise will be use and helpful.

 

[kwired]

I like to ask some people who have work with asd or vfd for some help with these drives.
My company seems to make changes to equipment without any though to engineering their equipment. They have replaced across the line control with asd or vfd without changing the motors or wiring. These motors are mostly for pumps above ground and some for submersables.

Should these types of changes be made as a complete unit , correct type of asd , inverter duty motors and vfd type wire ?
There has been asd's replaced for atleast 4 different motors all between 5 - 10 hp for a start . The asd last 2-3 years and then need replacing do to damage. They operate at about 40 hz.

Should submersables 40- 75 hp use wire rated higher then 600v if on a asd ? ASD techs say units have filters built in drives.
Thanks for any information with the installation or troubleshooting process you can advise will be use and helpful.

In general you should have a motor designed for use with the drive. You said the drive only lasts 2-3 years. I have had more trouble with motor not lasting if it is not designed for use with the drive. This is usually a bigger problem with motors operating on 480 volts than it is for 230 volts. This is partly because VFD's send voltage spikes to the motor that can be over 750 volts on a 480 volt circuit. This eventually destroys motor insulation - and is compounded by excessive length from drive to motor. I am not real good with all the details of this - search for IGTB reflected wave and you will find a lot of information on it better than what I can explain.

The other problem with motors is cooling. If running at lower speed and not designed for such purpose it may not be cooled as well as it is at normal speed. At 40 Hz this is likely not too much trouble in most cases.

Does your drive have good ventilation - free of dust. Is is subject to surges - lightning.

Frequent starting, stopping or reversing can be a situation where the drive needs derated or this extra duty will be hard on the drive.

 

[mike_kilroy]

vfd on any motor

vfd on any motor

as last post pointed out, vfds should be used on motors capable of having them; ie., specifically identified as "inverter duty," - or any other motor that can withstand the vfd

if the motor was built since probably 1960, and is 230v model, it will generally be fine on a 230v vfd. Ditto for a 480v motor & vfd. Mix and match motor and vfd is fine as long as you do not try to run a 230v non vfd motor on a 480v vfd (thinking you can just turn down the output and limit it to 0-230v).

If u run a 230v non inverter duty motor on a 480v input vfd drive the motor will likely last from 2-6 minutes before shorting out due to the standard 1200v spikes that exist at each IGBT shut off (600v on 230 drives). Potentially 50% higher if long lead lengths (typically over 50-ish feet).

And running at 40hz is NO issue to motor cooling; the general duty motor with internal shaft mounted fan will cool fine at full nameplate rated torque down to 1/4 base speed easy; should be ok down to 1/6 w/o issue but you gotta start watching the heat to verify no issue; should be able to take a 1800rpm motor down to full torque output to 200-300rpm but I would verify a specific motor by watching it the first few times to be sure.

I would be interested in feedback on what manufacture drives you see only lasting 2-3 years. Your description of what your employer has done in itself should not be a bad thing at all - in fact, it should be a good thing to help those motors last longer since they are now running at less speed, and in some cases maybe less load (assuming the pumps load goes down by the cube of the speed), and I would have expected a 10+ yr life on these drives - unless there is more info like environment, lots of starts/stops, bad power source, etc, that you did not share.

 

[Besoeker]

I like to ask some people who have work with asd or vfd for some help with these drives.
My company seems to make changes to equipment without any though to engineering their equipment. They have replaced across the line control with asd or vfd without changing the motors or wiring. These motors are mostly for pumps above ground and some for submersables.

Should these types of changes be made as a complete unit , correct type of asd , inverter duty motors and vfd type wire ?
There has been asd's replaced for atleast 4 different motors all between 5 - 10 hp for a start . The asd last 2-3 years and then need replacing do to damage. They operate at about 40 hz.

Should submersables 40- 75 hp use wire rated higher then 600v if on a asd ? ASD techs say units have filters built in drives.
Thanks for any information with the installation or troubleshooting process you can advise will be use and helpful.

I'm with kwired on this. I've come across problems but mostly with the motors not being suitable for variable frequency inverter duty. The output from the inverter is a series of pulses with a sharp rising edge that give motor insulation a much harder time than when directly connected to the supply.
If your drives have output filters the drive supplier may have taken into account that these are retro-fit applications that might have had standard motors.

Difficult to speculate on what's causing the drives to have such a short life. Are they in a hot and/or dirty location? Is the supply voltage reasonably stable?
Got any information on the nature of the failures?

 

[kwired]

Mix and match motor and vfd is fine as long as you do not try to run a 230v non vfd motor on a 480v vfd (thinking you can just turn down the output and limit it to 0-230v).

If you just turn down the output you will likely only have 30 Hz when voltage is 230. You can set the V/F so that you only have 230 volts at 60Hz and the motor will be happy with that. The drive may need derated to do this though.

If u run a 230v non inverter duty motor on a 480v input vfd drive the motor will likely last from 2-6 minutes before shorting out due to the standard 1200v spikes that exist at each IGBT shut off (600v on 230 drives).

I have connected many non inverter duty motors to drives. Some have failed - no suprise but they all had hundreds of hours of use not 2-6 minutes.

 

[puckman]

These asd are cutler hammers and their tech service says that there is no other protection to add to the units since they have built in reactors . We are using 480 volt motors 1800 rpm non inverter duty . They are mounted inside enclosures for inviorment protection, xfans have been added to remove the heat inside enclosures. Some of the motors do stop and start a few times an hour. All repairs or replacements are made to the asd.

I have seen our submirsables pump/motors in the 40-75 hp changed from soft starters to asd and the cables [ built with motor] to the motor appears to be non vfd cables. Is that a standard retrofit ?

 

[Besoeker]

All repairs or replacements are made to the asd.

Maybe time to change drive supplier?

I have seen our submirsables pump/motors in the 40-75 hp changed from soft starters to asd and the cables [ built with motor] to the motor appears to be non vfd cables. Is that a standard retrofit ?

For some decades, I've been dealing with variable speed drives ranging from a few kW to several MW and on various applications including submersible pump sets.
In that time we have not used cables that were particularly designed for variable speed drives. That said, we do take care to avoid, as far as possible, running signal cables with power cables.

I'm from UK and cabling practices here are often quite different to what you might be accustomed to. The power cable from drive to motor is (almost*) always steel wired armoured three core with a separate earth (ground) conductor. Conduit isn't used very much. In fact, one of the largest UK distributors has just three sizes and offers only two if you want metallic.

 

[Jraef]

My take on this is that I usually tell users that if the machine is not critical, i.e. There is redundancy or the process is not essential to the continued operation of a larger process, then you may as well use the motor you have until it dies, no need to prophylactically change it out. But if the loss of the motor will cause down time, which is money in most applications, then change the motor out when you install the drive, it will cost you less in the long run. If you do reuse an old motor, put in LOAD reactors at the very least.

Tangent issue:

If you just turn down the output you will likely only have 30 Hz when voltage is 230. You can set the V/F so that you only have 230 volts at 60Hz and the motor will be happy with that. ...

I think what Mike was referring to (if I may), is that if you reprogram a 480V drive, run from a 480V source, to operate a 230V motor, the problem is that the peak voltage of the PWM pulses will still GE based on the DC bus voltage of the 480V. The RMS voltage can be adjusted down but the insulation in an older 230V motor likely cannot handle it.

Most 480V drives will not operate on a 230V input, their internal power supply for powering the electronics themselves will not go that low.

 

[Jraef]

These asd are cutler hammers and their tech service says that there is no other protection to add to the units since they have built in reactors . We are using 480 volt motors 1800 rpm non inverter duty . They are mounted inside enclosures for inviorment protection, xfans have been added to remove the heat inside enclosures. Some of the motors do stop and start a few times an hour. All repairs or replacements are made to the asd.

I have seen our submirsables pump/motors in the 40-75 hp changed from soft starters to asd and the cables [ built with motor] to the motor appears to be non vfd cables. Is that a standard retrofit ?

I do not know of any drive that Eaton sells which has built-in LOAD reactors as standard, but they may have built-in LINE reactors. Line reactors do nothing for the motor side. Unless these were custom built drives where someone added LOAD reactors. You really should check it out yourself and not just blindly accept what the Eaton guy tells you. There are a lot of salesmen out there who have no clue about the differences, they just see the word "reactor" and say everything is fine. There are also a number of drive mfrs who claim that the output of their drive is "cleaner" than others so they don't need load reactors. It may be true with regards to ONE problem, but read below. That feature does nothing if this is your issue.

If, in your retrofit application, there are multiple sets of motor leads run in the same conduit or tray, as is often the case when originally run for Across-the-Line or even soft starter control, then that can be a BIG problem for the VFDs. Mutual inductance on the conductors is not an issue if everything is at the same supply frequency together, but when you have VFDs, every set of motor leads is at a different frequency or at the very least, unsychronized with respect to each other. That's where mutual inductance begins to add to your problems and can cause spikes that will take out the transistors in the drives. At the very least LOAD reactors will attenuate the spikes, better yet is to replace the cables with shielded INVERTER RATED cables to prevent the mutual inductance and cross talk noise. Best practice is both.

 

[Besoeker]

I do not know of any drive that Eaton sells which has built-in LOAD reactors as standard, but they may have built-in LINE reactors.

That's what was behind my comment:
"If your drives have output filters..."

If, in your retrofit application, there are multiple sets of motor leads run in the same conduit or tray, as is often the case when originally run for Across-the-Line or even soft starter control, then that can be a BIG problem for the VFDs. Mutual inductance on the conductors is not an issue if everything is at the same supply frequency together, but when you have VFDs, every set of motor leads is at a different frequency or at the very least, unsychronized with respect to each other. That's where mutual inductance begins to add to your problems and can cause spikes that will take out the transistors in the drives.

The very idea of running multiple single core motor power cables in a conduit in a common conduit just wouldn't be considered here.Wouldn't even get to the starting blocks, far less get out of them!

On a slightly different issue, the transistors have inverse diodes and, usually, a bl00dy great capacitor bank close coupled on the DC link. That ought to absorb any spikes. After all, the diodes are to allow inductive current to continue to flow after a transistor leg is switched off.

 

[Jraef]

...
The very idea of running multiple single core motor power cables in a conduit in a common conduit just wouldn't be considered here.Wouldn't even get to the starting blocks, far less get out of them!

That's why I mentioned the retrofit issue. It's fairly common to run everything together when NOT controlled by a VFD, then when upgraded, people often overlook that issue and cause themselves problems.

On a slightly different issue, the transistors have inverse diodes and, usually, a bl00dy great capacitor bank close coupled on the DC link. That ought to absorb any spikes. After all, the diodes are to allow inductive current to continue to flow after a transistor leg is switched off.

Up to the limits of the devices. I have seen 2000V spikes on the output side when you have multiple output conductors in the same raceway. Not all drives are built the same, some don't take the issue as seriously as others.

It's all still speculation thoughbat this point, because wevreally don't know what is in the circuit.

 

[mike_kilroy]

If you just turn down the output you will likely only have 30 Hz when voltage is 230. You can set the V/F so that you only have 230 volts at 60Hz and the motor will be happy with that. The drive may need derated to do this though.


I have connected many non inverter duty motors to drives. Some have failed - no suprise but they all had hundreds of hours of use not 2-6 minutes.

Thank you Jraef for explaining what I said so why the motor failure would be very short

We sometimes DO run old 230 volt motors on retrofits on 480v drives but we use 2:1 transformers on the output - cuts the 1200-1500v spikes in 1/2 along with the fundamentai output voltage, doubles the output current, and provides inductance similar to adding an OUTPUT inductor....

 

[mike_kilroy]

These asd are cutler hammers.... They are mounted inside enclosures for inviorment protection, xfans have been added to remove the heat inside enclosures. .....

have u actually MEASURED the inside cabinet temp after running a long time? Might the cooling not be sufficient and u really are overheating the asd's to point of failure?

 

[puckman]

One thing i would say is that all drives are rated 480v and the motors are 480volt .
There is alot of things for us to check out and things to change from the information you all have given to us . Reading all your responses shows me how much I don't know, never realized how much there is to installing a vfd.
Thank you all for the help with this situation.

 

[Besoeker]

That's why I mentioned the retrofit issue. It's fairly common to run everything together when NOT controlled by a VFD, then when upgraded, people often overlook that issue and cause themselves problems.

I worded that badly. We don't do conduit for power cables period and very little for anything else. One of our largest national distributors stocks up to 30mm (<1 14 inch) diameter.
Almost all power cabling for motors, whether fixed or variable speed, is steel wire armoured multicore.

Up to the limits of the devices. I have seen 2000V spikes on the output side when you have multiple output conductors in the same raceway. Not all drives are built the same, some don't take the issue as seriously as others.

I've also seen spikes but at the motor end rather than the drive:

Typical motor voltage:

Typical drive terminal voltage:

Horizontal axis for P1 is zero to 20us. Note the much steeper dv/dt but lack of overshoot. That capacitor bank is a quite effective snubber.

I

t's all still speculation thoughbat this point, because wevreally don't know what is in the circuit.

Agreed.

 

[puckman]

I thought i was finished here with the asd but a couple of hours ago i was called into look at a asd right next to the one i had all the question about .
I got a call that the operators pump kept tripping out and he just reset it each time. I told the sup not to reset it any more but that fell on deft ears.
Anyway i checked the keypad which is used for seeing the speed of motor only , it is start by a remote s/s station and a pot.
Keypad said the unit was at 49c and the manual said asd operates at between 10c - 50c , went toget operator and unit quit [for good] while i left for 5 min. it would not reset . wired the motor / pump to a starter for them to run @ 60hz.
So i believe maybe it went out on high temp. Will have to find out how to find the recorded faults in keypad. They closed up for today.
This cabinet [asd inside] did not have a fan insde it like the last one did to take out the hot air.
running @ 32 hz
unit temp 49c
dc bus 662v
motor v. 248v
rpm 949
Thanks again.

 

[mbeatty]

Just a quick note on wire between drive and motor. Our runs are generally short (less than 10 feet) and we have experienced no problems using THHN in LFMC. We do keep all signal/control wires away from main supply wires. Also, all of our signal wires are shielded cable.

 

[Besoeker]

I thought i was finished here with the asd but a couple of hours ago i was called into look at a asd right next to the one i had all the question about .
I got a call that the operators pump kept tripping out and he just reset it each time. I told the sup not to reset it any more but that fell on deft ears.
Anyway i checked the keypad which is used for seeing the speed of motor only , it is start by a remote s/s station and a pot.
Keypad said the unit was at 49c and the manual said asd operates at between 10c - 50c , went toget operator and unit quit [for good] while i left for 5 min. it would not reset . wired the motor / pump to a starter for them to run @ 60hz.
So i believe maybe it went out on high temp. Will have to find out how to find the recorded faults in keypad. They closed up for today.
This cabinet [asd inside] did not have a fan insde it like the last one did to take out the hot air.
running @ 32 hz
unit temp 49c
dc bus 662v
motor v. 248v
rpm 949
Thanks again.

My experience is that insufficient air flow seems to be a more common problem than it ought to be.
If you care to drop me a PM with some details of drive rating and ambient conditions I can give you the air flow that I'd work with.

 

[kwired]

I thought i was finished here with the asd but a couple of hours ago i was called into look at a asd right next to the one i had all the question about .
I got a call that the operators pump kept tripping out and he just reset it each time. I told the sup not to reset it any more but that fell on deft ears.
Anyway i checked the keypad which is used for seeing the speed of motor only , it is start by a remote s/s station and a pot.
Keypad said the unit was at 49c and the manual said asd operates at between 10c - 50c , went toget operator and unit quit [for good] while i left for 5 min. it would not reset . wired the motor / pump to a starter for them to run @ 60hz.
So i believe maybe it went out on high temp. Will have to find out how to find the recorded faults in keypad. They closed up for today.
This cabinet [asd inside] did not have a fan insde it like the last one did to take out the hot air.
running @ 32 hz
unit temp 49c
dc bus 662v
motor v. 248v
rpm 949
Thanks again.

Continually resetting without finding out what the problem is does no good for almost any equipment. Production managers don't care - product needs to continue to move. If it is expensive enough equipment they destroy doing this they may get a good @@@ chewing. If it is not too expensive then it just gets fixed and on we go.

I have even seen this with magnetic starters. Got a call one time auger was tripping. When I got there they had a production employee sitting at the starter and pushing the reset about about as quick as it was tripping. The motor was hot enough to fry breakfast on. There was nothing wrong electrically - just happened to be high fat product running through the auger and enough was caked inside to load the thing down. Made them clean the auger and things were just fine.:slaphead:

 

[mike_kilroy]

have u actually MEASURED the inside cabinet temp after running a long time? Might the cooling not be sufficient and u really are overheating the asd's to point of failure?

ahem.... perhaps it is time for more than a spot check of temp - when it may not be the hottest..... can you get some kind of temp recorder and record actual temp over a few day period? As lots of us have said previously, these drives should run 10+ years, not short like you see..... u r doing something different than the rest of us to get such reduced life. ur job is to find what that is. perhaps it is temperature in those cabinets. a simple fan added may not be sufficient to dissipate the heat properly. have you added all the btus inside the cabinet and done cabinet size calculations?

we all know higher temp reduces electronic component life. for instance:

http://www.rfcafe.com/references/general/arrhenius-lifetime-acceleration.htm

or a rule of thumb that for every 10c rise you cut the life in 1/2.... so if we run 20c and you run 50c, my asd life may well be 6x longer than yours: hence I get 10+ years, you get 2.

record your temp over multiple days of running and see what you have.