xfmr stiff enough... Elevator soft starts - lights dim

[wyreman]

Is the poco xfmr sized big enough or is the otis soft start not soft enough?

POCO came out with a RVM for a week and says they are good, there is no problem, this is never more than 5% drop.
When the elevator starts, and only when the elevator starts, and always when the elevator starts.... the lights dim globally at the 6 unit apt bldg

owners want to fix it.

Seems to me either the motor is drawing more than the poco xfmr can handle - altho poco says the 5% is ok - I have clamped 7-8% instantaneously on my old fluke and me new klein
either the motor needs a softer start or the poco xfmr is not stiff enough

the elevator is rated 156A
50hp at 230v 156amps
there's even a note in the can that says adjust overload relay to a "must trip" on 156a Max
I clamp 275a!
6 unit bldg has a 600a main

I measured at the mains and at the disco - always the same
at either end of the wire
giant inrush of 250/275a and 5%+ sag in voltage.

Elevator says they have a soft start on there, but I dont want to really go into the menu and see how they have it dialed in.
POCO says they are within tolerance.
I am just supposed to find the fault.

I would like to see proof of the soft start - is starting as soft as possible for this motor.
I would like to see the RVM readings that show it never dips below 5%
I didn't see any loose connections at the covers I did pull off. Impedance was pretty good generally at nearby outlets i did measure

Questions:
1. is it a stiffness question for the poco - but they wont admit it seems like
2. Would a properly co-ordinated soft start still have a 256a inrush on a 156a load?
3. If there were load calcs including the 156a elevator on this 6 unit apt bldg - it seems like half the capacity of the main is devoted to the elevator [all 6 units have small elec baseboard htrs, gas range, common dryer and 80a feeds]
Is there any chance the main was under sized to the poco and they connected up a load to big for their xfmr? Still a poco thing

I guess the load calcs are next

 

[wyreman]

i wanted to upload more photos but they wont go

 

[iwire]

Is there really anyone at fault? A 5% dip can easily be seen by the human eye.

 

[wyreman]

But I clamp up to 7-8% and owners want to correct it.
Looks like its more likely to get a better tuned soft start than a bigger xfmr.

How to prove the soft start is optimal for that motor? btw thx for response!

and most apts dont have that where the lights dim when your wife is coming up the elevator!

and there is that "must trip" overload relay note in the can
and the little 600a mains...

 

[GoldDigger]

The FLA rating on the nameplate is for 230V. What is the actual voltage at the terminals of the soft start when the motor is running?
What is the running current after the surge has leveled off?
A lower voltage than 230 before starting will result is a lower surge but a higher running amperage.
Less than a factor of two between surge and run is actually pretty good. Without the soft start it could be as bad as a factor of 10, and that could drop the voltage well below what the motor would start well on.
To get better than that would require a full VFD on a three phase motor rather than just a soft start. And you would have to find one compatible with the elevator controls and suitably rated for elevator use.

The voltage drop across the wiring from main to motor will not directly affect the dip seen in the lights, but it could affect the current drawn by the motor, as noted at the beginning of the post.

 

[wyreman]

211v to start typical
down to 194 typical
its running at about 206/207v after the surge

but there is a nameplate in the can that says the motor should run on 200v
but a hand written note says the machine is set for 208v
thats shown on the photo of the metal otis cover on the hydraulics -photo here-

but that is extremely observant...

 

[kingpb]

You have not said what the service voltage is. Regardless, have the utility put the transformer taps on the -5% setting. This will increase your voltage by 5%. You should not have to worry about over voltage on your main bus as long as at no-load ( or lightly loaded) its not measuring over 10% rated. If so, use the -2.5% tap.

 

[Jraef]

To address your other concerns.

That IS indeed a soft starter, specifically designed for elevators.

I was in the soft starter business directly for 15 years, and in fact I was responsible for that Siemens product at some major elevator OEMs. I've had a LOT of specific experience with this. 256A on a motor with 156A FLC is actually lower than I would expect. The minimum current you could possibly get that would allow that motor to accelerate is 200% FLC, even then only if the motor is completely unloaded. It's just a law of physics. I suspect that what is happening is that the low setting is effectively stalling the motor, then the ramp time expires and it goes across the line, but because the motor was already partially accelerated, the current surge when it does is too fast for your meter to see it. But by then, the transformer feeding this service was already maxed out, so the transient when that current surges causes it to saturate and drop voltage, briefly. So in essence, having it set so low is actually CAUSING the lights dimming.

Turn UP the current limit setting on that soft starter, or SHORTEN the ramp time. I know it sounds counter-intuitive, but trust me, that's the problem. Every transformer can supply a brief surge current transient, and recover quickly with no noticeable voltage drop. What's happening here is that the low setting on the soft starter is consuming that transformer's transient reactance capacity before the motor can accelerate to 80% speed, so when the soft starter goes into bypass, the transformer can't take it any more. Accelerating that motor faster will allow the transformer to react to it better.

 

[topgone]

How big are your service conductors and how far is the PoCo transformer from your load center?

 

[wyreman]

It was just green tagged about 5 yrs ago so the 600a Srvc should be sized right
It's a 120/208 3p 4w

Waiting for poco log of brown outs and will ask mapping Dist to Xfmr
The voltage is steady except for each and every time elevator starts Going up

 

[Jraef]

So I was just now able to view your video for the first time. Something is not right here.

At first it looked more clear to me that what I described is what is happening. The Soft Starter is limiting the current to 106A for quite a while, which on a motor rated at 156A would NOT be enough to allow it to accelerate. That's why you get that secondary surge after a few seconds; that's the end of the soft starter ramp time. So when the ramp time expires, the starter goes across the line and the current re-surges, this time even higher because the motor was not at even close to full speed.

But here's the rub:
That starter is only rated for 156A if you wire it "Inside the Delta", which is complicated to describe if you've never seen it, but means they are taking advantage of the motor being capable of Wye-Delta starting and using that wiring configuration to place the soft starter inside of the delta wiring. What that does is reduce the current that the soft starter sees to 58% of the motor current (because it's divided by the sq. rt. of 3), so the soft starter is smaller and cheaper. I personally hate that concept because it's very very confusing to people who have never seen it. But the elevator OEMs do it to save money and then figure that only their trained technicians will ever see it. The world doesn't work that way however...

So anyway... on a motor rated 156A, the starting current SHOULD be about 936A (600%). then because the soft starter is inside of the delta, it is going to only see 58% of that, so 524A max. That soft starter can allow the current limit setting to be from 116% to 425% of the motor current, so on that motor, it means 181 to 663A. But in your video, it was only drawing 106A! The soft starter is not limiting that current to 106A, it can't. Something else is wrong.

My new suspicion is that the motor is wired for 460V. That's the only way the current could be that low. So it's making that problem I described above even WORSE, because even when the soft starter is done, the motor is not getting full voltage. It's looking for 460V, you are giving it 211V when the soft starter is done, which is STILL not enough, so it is pulling high amps trying to make the elevator run, which is saturating your transformer and causing it to drop voltage.

 

[wyreman]

Only thing is that setup has been" in commission" since 2009
Could the motor go 4 years miss wired like that without dogging out?


I'll go back next week
I could inspect if they used the "wong "hi voltage leads on original install
But I don't want to void any warranty

 

[rlundsrud]

So I was just now able to view your video for the first time. Something is not right here.

At first it looked more clear to me that what I described is what is happening. The Soft Starter is limiting the current to 106A for quite a while, which on a motor rated at 156A would NOT be enough to allow it to accelerate. That's why you get that secondary surge after a few seconds; that's the end of the soft starter ramp time. So when the ramp time expires, the starter goes across the line and the current re-surges, this time even higher because the motor was not at even close to full speed.

But here's the rub:
That starter is only rated for 156A if you wire it "Inside the Delta", which is complicated to describe if you've never seen it, but means they are taking advantage of the motor being capable of Wye-Delta starting and using that wiring configuration to place the soft starter inside of the delta wiring. What that does is reduce the current that the soft starter sees to 58% of the motor current (because it's divided by the sq. rt. of 3), so the soft starter is smaller and cheaper. I personally hate that concept because it's very very confusing to people who have never seen it. But the elevator OEMs do it to save money and then figure that only their trained technicians will ever see it. The world doesn't work that way however...

So anyway... on a motor rated 156A, the starting current SHOULD be about 936A (600%). then because the soft starter is inside of the delta, it is going to only see 58% of that, so 524A max. That soft starter can allow the current limit setting to be from 116% to 425% of the motor current, so on that motor, it means 181 to 663A. But in your video, it was only drawing 106A! The soft starter is not limiting that current to 106A, it can't. Something else is wrong.

My new suspicion is that the motor is wired for 460V. That's the only way the current could be that low. So it's making that problem I described above even WORSE, because even when the soft starter is done, the motor is not getting full voltage. It's looking for 460V, you are giving it 211V when the soft starter is done, which is STILL not enough, so it is pulling high amps trying to make the elevator run, which is saturating your transformer and causing it to drop voltage.

I like to think that I am reasonably intelligent and it often amazes me how a large percentage of the population seems to be, well, not so bright. I just can't imagine how the world must look to you, I feel like a complete moron when I see some of your insights (or at least try to comprehend them). I only hope that someday I can have enough cognitive function and knowledge that when you read one of my posts you won't wonder how many attempts it took me to get past the third grade. And while this may appear to be a paid political announcement, or just plain a$$ kissing, I really am just trying to give voice to how much I appreciate having you and this forum as a resource and knowledge base. Kudos to you sir!!

 

[Ultrafault]

I think you missed the decimal. That is 10.6 amps. I assumed the motor was not running at that time.

 

[Phil Corso]

WyreMan...

1) Have you measured the three line-currents during operation?

2) Are you able to "Clamp-On" the three conductors together?

Regards, Phil Corso

 

[iceworm]

... Every transformer can supply a brief surge current transient, and recover quickly with no noticeable voltage drop. What's happening here is that the low setting on the soft starter is consuming that transformer's transient reactance capacity before the motor can accelerate to 80% speed, so when the soft starter goes into bypass, the transformer can't take it any more. Accelerating that motor faster will allow the transformer to react to it better.

I did not know that - really interesting physics. Do you have a reference that shows the model you are using to support this conclusion? I would be very interested is seeing that.

ice

 

[iceworm]

... Every transformer can supply a brief surge current transient, and recover quickly with no noticeable voltage drop.

I did not know that - really interesting physics. Do you have a reference that shows the model you are using to support this conclusion? I would be very interested is seeing that.

J -
I truely am very interested in this. If you have any evidence or reference - please share.

I have to go the work - got somebody paying for my time. I'll check back later.

ice

 

[Jraef]

J -
I truely am very interested in this. If you have any evidence or reference - please share.

I have to go the work - got somebody paying for my time. I'll check back later.

ice

Look up "transformer surge capacity".

 

[Sahib]

wyreman: no problem with poco as no light dimming in any adjacent buildings reported. Thorough check for loose connections.

 

[GoldDigger]

Look up "transformer surge capacity".

I looked it up and all I found were references to the thermal surge capacity of transformers, where the power beyond rated power could be tolerated for some period of time before the windings reached a critical temperature.
Absolutely nothing that suggested that some magical reactive power storage in the transformer could reduce the effects of voltage drop in the primary feeders to the transformer.
If such a capability exists it would be limited to sub-cycle time periods unless dealing with a tuned resonant CVT.

It is certainly allowable to put a short term load on a transformer well beyond its steady state capacity, but the motor will still see a corresponding voltage drop in secondary wires, the transformer itself and primary wires.

It may not have been what you intended to say but your words conveyed the impression that the surge capacity of the transformer would reduce overall VD to the motor. Analogous to the way a capacitor bank can reduce the VD to a low PF load.