I'm working on a new building with an elevator. During elevator startup, the motor is not able to ramp up to full acceleration, it won't get past the starting inrush. It starts up fine using temporary generator power. 208V-3PH, 60HP traction, with soft start (300% FLA). Stated voltage drop limitations from the elevator manufacturer are 5% running, 10% starting. Calculated drop is less than 2% running, 6% starting. Actual recorded drop during starting inrush is within the 10% limit. The upstream overcurrent device (400A breaker) isn't tripping. Any ideas?
Elevator not starting on building power
- Thread starter msteiner
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mayanees
Senior Member
- Location
- Westminster, MD
- Occupation
- Electrical Engineer and Master Electrician
bizarre
bizarre
Hey Matt! The only reason I'm responding to this is that I see it's you. I don't have an answer.
It appears that the generator is a more stiff source than the Utility.
What size is the gen?
I assume "won't start" means that the soft-start trips out? What trip indications do you get? Is the soft-start adjustable?
Have you considered across-the-line? or is the soft-start part of the elevator offering?
John
bizarre
Hey Matt! The only reason I'm responding to this is that I see it's you. I don't have an answer.
It appears that the generator is a more stiff source than the Utility.
What size is the gen?
I assume "won't start" means that the soft-start trips out? What trip indications do you get? Is the soft-start adjustable?
Have you considered across-the-line? or is the soft-start part of the elevator offering?
John
Thanks John!! I had the same thought about the stiffness of the source. I don't know what is actually happening when they try to start (posting this for a colleague who is the EE on the project). They brought in a 150kW generator to start it up. I asked about the adjustability of the soft start, waiting for a response. Utility source is a 4000A swbd, fed from a utility transformer.
A 4000 A service (>1 mva) won't start it but 200 kva will?
how long and what size is the run to the elev controller?
where do you hook the genset in to test? Does this shorten the run?
when run off the service is there other bldg load?
when run off the genset is it the only load?
need the error/fault codes from the drive
we just had a similar issue, we increased the allowable ol time on the controller
how long and what size is the run to the elev controller?
where do you hook the genset in to test? Does this shorten the run?
when run off the service is there other bldg load?
when run off the genset is it the only load?
need the error/fault codes from the drive
we just had a similar issue, we increased the allowable ol time on the controller
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Most likely one of two things:
- You have a bad connection somewhere when connected to the utility power and it only rears its head when you are starting, meaning you have a severe voltage drop on only one phase and you are not measuring that phase so you don't see it.
- Your soft starter is too small for the load and the starting current never drops to a low enough level because the starter is current limiting all the time. But on the generator, the load causes the generator to slow down, dropping the frequency and allowing the limited current to create more torque (like what a VFD does) so it can accelerate.
Belevolk
Member
- Location
- Southern Arizona
Soft start settings
Soft start settings
There are usually a bunch of SS settings that are available. GUESSING here cause you do not say TRIPPING, If it is coming out of the electronics and is failing at the transition/run. The following should be looked at
Ramp up time, usually given by the mfg of the equipment not of the starter Might want to extend this a bit, 1-2 seconds
Torque boost, % and time extend the time 1 sec and boost 5%
Then there is the dumb stuff that you have already done. Checked connections, meggered cables, verified settings are correct for your load.
I will look about to see if I can find my old CH-Eaton soft start Excel spread sheet. You can put settings in and see the curve.
If I can find it I will post it.
D
Soft start settings
There are usually a bunch of SS settings that are available. GUESSING here cause you do not say TRIPPING, If it is coming out of the electronics and is failing at the transition/run. The following should be looked at
Ramp up time, usually given by the mfg of the equipment not of the starter Might want to extend this a bit, 1-2 seconds
Torque boost, % and time extend the time 1 sec and boost 5%
Then there is the dumb stuff that you have already done. Checked connections, meggered cables, verified settings are correct for your load.
I will look about to see if I can find my old CH-Eaton soft start Excel spread sheet. You can put settings in and see the curve.
If I can find it I will post it.
D
Updating with some more information... The soft start is provided by the elevator manufacturer. It's not tripping, because they're not letting it run for more than a few seconds for fear of burning out the controller or motor (already replaced one motor). So I don't have any error codes to report.
The elevator feeder has two splices in it. It starts as 2 sets of #3/0 Cu, transitions to 1 set of 750 Al for an underground run, then back to 2 sets #3/0 Cu. I suspected a bad splice, but they've been recording voltage drop on all three phases, and they're all within spec.
EC wants to drop out the other building load and try to start it. On temp generator, there was no other load on the gen.
The elevator feeder has two splices in it. It starts as 2 sets of #3/0 Cu, transitions to 1 set of 750 Al for an underground run, then back to 2 sets #3/0 Cu. I suspected a bad splice, but they've been recording voltage drop on all three phases, and they're all within spec.
EC wants to drop out the other building load and try to start it. On temp generator, there was no other load on the gen.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
If supplied by the elevator mfr, there's a 90% chance it is a Siemens 72G Elevator Soft Starter, it's specially designed for that industry. It does not have most of the typical setting found in a lot of COTS soft starters.
If they burned up another motor in the past, it likely had nothing to do with it being soft started. Either that, or they did not properly set the OL trip current in the soft starter. A LOT of people do this totally wrong. They read article 430 and see that you are "allowed" to have the OL trip at 125% of the motor FLA, so that's how they set a programmable setting. But what they are doing wrong is that in the soft starter electronics, the 125% is ALREADY accounted for in the way the OL circuit works. So when the manual says "set it to motor FLA", that's exactly what you must do. If you set it to 125% of motor FLA, you are in effect setting it to 125% of 125% (156%), so the motor burns up if overloaded.
Honestly, it's probably just needing longer to accelerate the motor than they are giving it... 2-3 seconds is probably too short of a time, it can take up to 30 seconds. The 72G soft starter has no "Ramp Time" settings, only Starting Current. The factory default is set for 425% of the UNIT rating (not the motor rating). It's the job of the elevator technician to make sure this setting is adequate to start the motor before it trips on OL. So if they set it to 300% of the motor FLA, it might take 10-20 seconds to start, but there is absolutely nothing wrong with that.
If they burned up another motor in the past, it likely had nothing to do with it being soft started. Either that, or they did not properly set the OL trip current in the soft starter. A LOT of people do this totally wrong. They read article 430 and see that you are "allowed" to have the OL trip at 125% of the motor FLA, so that's how they set a programmable setting. But what they are doing wrong is that in the soft starter electronics, the 125% is ALREADY accounted for in the way the OL circuit works. So when the manual says "set it to motor FLA", that's exactly what you must do. If you set it to 125% of motor FLA, you are in effect setting it to 125% of 125% (156%), so the motor burns up if overloaded.
I assume a traction with gear type counterweighted machine
what is rated capacity? Rated speed?
are the brakes releasing properly? I assume so since it picks with the genset
will it run unloaded?
is it stalling with rated load in it?
I would start unloaded and add weight until it won't
2-3 sec is not enough
most can run at 300% for 20 sec or so
60 sec at 150%
the drive mfg/pn would help
what is rated capacity? Rated speed?
are the brakes releasing properly? I assume so since it picks with the genset
will it run unloaded?
is it stalling with rated load in it?
I would start unloaded and add weight until it won't
2-3 sec is not enough
most can run at 300% for 20 sec or so
60 sec at 150%
the drive mfg/pn would help
Manual for drive mentioned above
http://www.aesupply.com/pdf/Class72G_Instruction Guide1_01_21_20053-3.pdf
looks like it can be used on an electric or hydraulic machine?
has ph rotation been checked?
perhaps elev and genset are opposite?
http://www.aesupply.com/pdf/Class72G_Instruction Guide1_01_21_20053-3.pdf
looks like it can be used on an electric or hydraulic machine?
has ph rotation been checked?
perhaps elev and genset are opposite?
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- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Ooooh... EXCELLENT point! The Soft Starter will accept either, but only one at a time. So if the two sources are different, it may help to explain why it works when on the generator!
something doesn't add up
it can pick with the genset which has a starting kva of 450 or so with 35% v drop
the motor needs 300% or ~ 165 kva, so drop should be very small
genset 150 kw / 185 kva
but it can't start with 1 mva xfmr ? Which if even 50% load can provide as much or more?
plus he measured drop and it is within limits
be nice to know the actual drive model
this one is rated at 200 vac so a 4% drop from 208 would be moot
operating spec: -15%/+10% 200-460 VAC
imo v drop is not the issue
where was the genset connected to the ckt?
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- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I've seen it happen. When on the genset, the load burdens then slows the generator, which lowers the frequency as the voltage drops. So that actually is what a VFD does too, meaning you will actually get MORE torque per unit of current than if the frequency was correct. Then the generator brings the motor up to speed with it as it recovers from the step change in load. The first time I had this happen was at the Ford Island Bridge in Pearl Harbor, the drawbridge you go on to get to the USS Arizona memorial. When running on the backup generator, the starters worked to power up the hydraulic power units but when connected to the utility power, they tripped on OL before they could accelerate the motors. I got a free trip to Hawaii on that one. I tweaked the settings on the Soft Starters in about 10 minutes, but didn't tell anyone for 3 days...
The tricky part is that the Soft Starter must be tolerant of the frequency drop and continue functioning. Some are, most are not. So MOST of the time, the soft starter will trip on Under Frequency and nobody knows that it MIGHT have worked if it had not tripped first. But Nordic Soft Starters (and A-B and Motortronics who I worked for) use a somewhat unique firing circuit, so they are (were) insensitive to frequency drift. Nordic was part of Furnas who was bought by Siemens and is now gone, the only remaining product that Siemens sells that is made from that older technology is the 72G, because getting approvals on elevator controls is a logistical nightmare and incredibly expensive. So Siemens wisely left that product alone, selling it exclusively to elevator OEMs.
The tricky part is that the Soft Starter must be tolerant of the frequency drop and continue functioning. Some are, most are not. So MOST of the time, the soft starter will trip on Under Frequency and nobody knows that it MIGHT have worked if it had not tripped first. But Nordic Soft Starters (and A-B and Motortronics who I worked for) use a somewhat unique firing circuit, so they are (were) insensitive to frequency drift. Nordic was part of Furnas who was bought by Siemens and is now gone, the only remaining product that Siemens sells that is made from that older technology is the 72G, because getting approvals on elevator controls is a logistical nightmare and incredibly expensive. So Siemens wisely left that product alone, selling it exclusively to elevator OEMs.
May be the remote possibility that utility has a much higher harmonic distortion than that of generator so that actual power input to the motor through soft starter during starting is lower on utility supply than on generator supply and hence longer time to ramp up. A comparison of harmonic distortion of utility and generator supply may reveal it.
Electric-Light
Senior Member
Does the direction of travel affect the behavior? Cable elevators are counter-balanced. I believe at half the rated lb rating.
It's usually not doing real work when its just one or two people going up but it is working at full load going down to hoist up the couterweights.
It's usually not doing real work when its just one or two people going up but it is working at full load going down to hoist up the couterweights.
elevator motor wont go
elevator motor wont go
jraef,
Looks like everyone is headed in the same direction, I thought your answer was written exceptionally well. I do a ton of elevator motors, dc, mostly, but I remember winding old OTIS AC two speeds. What I don't get around [ yet ] is the new AC traction motors. I get the freq lowering the strain and it all makes sense but 20-30 seconds seems forever, in the 30 seconds is it accelerating?
I can see the lower current via lower freq and you know that controller, but it just seems forever to eat 30 seconds, hell I see these elevator guys get beat up if someone has to wait 30 seconds, for the only car that goes to the 40th floor, very interesting, and again very well written
elevator motor wont go
jraef,
Looks like everyone is headed in the same direction, I thought your answer was written exceptionally well. I do a ton of elevator motors, dc, mostly, but I remember winding old OTIS AC two speeds. What I don't get around [ yet ] is the new AC traction motors. I get the freq lowering the strain and it all makes sense but 20-30 seconds seems forever, in the 30 seconds is it accelerating?
I can see the lower current via lower freq and you know that controller, but it just seems forever to eat 30 seconds, hell I see these elevator guys get beat up if someone has to wait 30 seconds, for the only car that goes to the 40th floor, very interesting, and again very well written
counter weight = car wt + over wt
over wt is typically 40-50% of rated capacity
Electric-Light
Senior Member
Yeah. Meaning that the horsepower draw is at the lowest when cab loading is at about 50% of rated load. So, this means the full hoisting effort is roughly half the rated poundage. Therefore, the maximum power draw is raising the cab at full load, or lowering the cab empty. Why is this important? If it comes down fine empty, then it shouldn't have problem stating up fully loaded.
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