vfd over current tripping issue
- Thread starter leslyaj007
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ATSman
ATSman
- Location
- San Francisco Bay Area
- Occupation
- Electrical Engineer/ Electrical Testing & Controls
I enjoy reading all comments and certainly learn a lot from these forums.
I am by no means a VFD guy so bear with me. I worked on (4) MV Benshaw Soft Starters(SS) that were part of a large conveyor system (several domed bldgs) that loaded product on to vessels for export. This was 20yrs ago and was during the startup phase (new equipment) of the plant. It was for sure a learning experience for all personnel involved and required a fine tuning of the settings on the SS controllers (which were bringing in OC fault codes) before the systems were operating properly. The terms motor FLA, CT ratios, initial current, maximum current, ramp time, full speed, decel enable/disable all come to mind.
I may have missed it but I do not remember the OP saying that this was startup on new equipment and am surprised that this was not brought up in any of the posts.
On another note, I was always under the impression a SS operated like a VFD up until the time the bypass contactor closed with motor up to full RPM(and across the line.) Whereas a VFD is constantly controlling the
motor. Is this correct? Any comments?
I am by no means a VFD guy so bear with me. I worked on (4) MV Benshaw Soft Starters(SS) that were part of a large conveyor system (several domed bldgs) that loaded product on to vessels for export. This was 20yrs ago and was during the startup phase (new equipment) of the plant. It was for sure a learning experience for all personnel involved and required a fine tuning of the settings on the SS controllers (which were bringing in OC fault codes) before the systems were operating properly. The terms motor FLA, CT ratios, initial current, maximum current, ramp time, full speed, decel enable/disable all come to mind.
I may have missed it but I do not remember the OP saying that this was startup on new equipment and am surprised that this was not brought up in any of the posts.
On another note, I was always under the impression a SS operated like a VFD up until the time the bypass contactor closed with motor up to full RPM(and across the line.) Whereas a VFD is constantly controlling the
motor. Is this correct? Any comments?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
ATSMan,
Correct, he never mentioned exactly when his fault occurred. Unless he comes back, we may never know.
On your second question, not exactly. A Soft Starter is only ramping or controlling the VOLTAGE, frequency remains the same. Whereas a VFD is controlling voltage and frequency together. With voltage control only, the motor torque varies by the square of the applied voltage, so at 50% voltage, the motor can only develop 25% of rated torque. Because the VFD maintains the motors design V/Hz ratio, it can make the motor develop rated torque at any speed. That makes a big difference in starting a load. So comparatively, at 50% speed, you would be at 50% voltage, but 100% torque is available from that motor.
Correct, he never mentioned exactly when his fault occurred. Unless he comes back, we may never know.
On your second question, not exactly. A Soft Starter is only ramping or controlling the VOLTAGE, frequency remains the same. Whereas a VFD is controlling voltage and frequency together. With voltage control only, the motor torque varies by the square of the applied voltage, so at 50% voltage, the motor can only develop 25% of rated torque. Because the VFD maintains the motors design V/Hz ratio, it can make the motor develop rated torque at any speed. That makes a big difference in starting a load. So comparatively, at 50% speed, you would be at 50% voltage, but 100% torque is available from that motor.
ATSman
ATSman
- Location
- San Francisco Bay Area
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- Electrical Engineer/ Electrical Testing & Controls
Thanks Jraef for clearing that up. Always enjoy your posts.
rlundsrud
Senior Member
- Location
- chicago, il, USA
I call this the Cassandra complex. I occasionally get asked a question by someone working on a DIY project. If my response conflicts with what they wanted to do they just disregard it and do what they had originally planned. It is incredibly frustrating.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Yes it is...
Nicely put. I'm going to use that... For me it's not just DIY people. I get it all the time with industrials, especially bean counters who don't want to cough up the money it will take to avoid a catastrophic failure. It's frustrating, but at the same time can be lucrative because when the failure I warned about DOES happen, the price tag to get them back on line is ALWAYS a lot more than the original proposal. I just went through this back in December; quoted the spare parts for a project, they didn't buy them, then 3 years later a major component took a hit and failed, it took a week to get them back on line. Lots and lots of OT, air freight etc., PLUS they suffered over $10k/day in production losses. Oh well...
Practically persuade customers to purchase OEM components for the future. Those who are hearing words of wisdome
, later, after a number of months or years, they make calls to say thank you or so. Those who are living on the principle "one day at a time", sometimes they are just lucky (fools sometimes are lucky), but mostly they have losses as was written above in the QUOTE. And then my phone is blowing up. "We are swear not to be fools anymore. We'll purchase all components from your list! Please, just figure out how to solve that issue right now!" Chelny
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ptonsparky
Tom
- Occupation
- EC - retired
I personally suffer from this ailment on occasion myself, most of us probably have. But why ‘Cassandra’? Because it sounds better than HUA?
RumRunner
Senior Member
- Location
- SCV Ca, USA
- Occupation
- Retired EE
I think it pays to understand that posters other than the US don't enjoy the luxury that we US consumers do.
A lot of places have very limited allotment of data in accessing the internet. And if they exceed their monthly allotment, they have to pay outrageous surcharge. They don't have free access like Starbucks.
When I was in Australia I had to watch the amount of data I used every time I sat in front of the computer. I always keep my host aware of how much I used every month.
These restrictions apply to all users even in University campuses.
What I'm saying is: Messages intended to posters outside the US must be concise for them to even consider reading the posts. That's one reason we don't hear from them after the first post.
Wow, this thread has continue...
Whom needs a cellular base station subsystem (gsm/3G tower) in a place of Australian desert where there's couple of living souls passing twice a month, but they are Dingos.
So I would say that every country has uninhabited areas where it's pointless to have café with free wi-fi or gsm tower.
P.S. The OP (or its people) just 'forgot' to connect dc brake with which were equipped gear motors, this caused a trip. Or he just turned over braking ring in case if it was equipped with mech brake. And he forgot already where and when he wrote here and what he wrote here.
I faced with such cases when el. installation was performed by customer's people.
Chelny
Whom needs a cellular base station subsystem (gsm/3G tower) in a place of Australian desert where there's couple of living souls passing twice a month, but they are Dingos.
So I would say that every country has uninhabited areas where it's pointless to have café with free wi-fi or gsm tower.
P.S. The OP (or its people) just 'forgot' to connect dc brake with which were equipped gear motors, this caused a trip. Or he just turned over braking ring in case if it was equipped with mech brake. And he forgot already where and when he wrote here and what he wrote here.
I faced with such cases when el. installation was performed by customer's people.
Chelny
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RumRunner
Senior Member
- Location
- SCV Ca, USA
- Occupation
- Retired EE
Wow, this thread has continue...
Whom needs a cellular base station subsystem (gsm/3G tower) in a place of Australian desert where there's couple of living souls passing twice a month, but they are Dingos.
So I would say that every country has uninhabited areas where it's pointless to have café with free wi-fi or gsm tower.
P.S. The OP (or its people) just 'forgot' to connect dc brake with which were equipped gear motors, this caused a trip. Or he just turned over braking ring in case if it was equipped with mech brake. And he forgot already where and when he wrote here and what he wrote here.
I faced with such cases when el. installation was performed by customer's people.
Chelny
--OP did not mention whether it is a gear head motor. It is a mundane assumption that DC brake is applied during startup.
Most gear head motors that are designed for driving machinery have brake-hold braking system especially when indexing is important.
OP's query is referring to VFD drive which is most likely dynamic braking--inherent to VFD drives.
By using kinetic energy of the driven machine, no dynamic braking exist to provide brake-holding capability.
Unlike electro-mechanical brake with springs or shoes, kinetic energy braking disappears when motor is de-energized.. . . no chances of interferring with start-ups that could cause current increase during starts.
As for internet access in the outback of the Australian desert, that's no longer a problem like it was ten to twenty years ago. Those aborigines have satellites internet access now.
Dingoes may not have access to the web but kangaroos do. Like deer in the midwest and southwest US, kangaroos are not grazers they are browsers. GOTCHA!
Spasibo
Khoroshego dnya
It's well-wishes—our Russian friend will translate.
As an aside: The linguist at the tip of my toes is poking me. The adjectival clause with the nominal function of "WHOM" sounds weird.
hmy:
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Since this appears to be descending into comments on other comments on other comments with no interaction with the OP, I’m going to close the thread.
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