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

[Jraef]

I screwed up using the term "transient reactance", that's something different. I couldn't think of the word and put that in as I typed as a placeholder, then forgot to go back to it after looking up the term. I still can't find the term I was looking for. Sorry...

It relates to the transformer impedance and if the impedance is low, as in 1-2%, the effect on the output voltage from motor starting is more immediate. But most service transformers are 3-5% Z or more, which means the transformer holds up better to a sudden change in load without having the output voltage collapse immediately. So yes, I also inappropriately said "any" transformer, when I should have said "most service transformers".

 

[Sahib]

jraef: if impedance i.e % impedance is more, internal V/D of transformer is also more unlìke what you state. But that is not issue here. See post#19.

 

[topgone]

jraef: if impedance i.e % impedance is more, internal V/D of transformer is also more unlìke what you state. But that is not issue here. See post#19.

The OP clearly said "globally", and we think it's not just inside the building where the elevator is located. CBEMA has a standard on this problem.
It's either the service wires were sized small or the transformer is, assuming all other factors are good.

 

[e57]

If this is say an "Otis" install - THEY should be handling this - messing with that drive could be messin with the operation of the elevator... If someone is on record for maint of it - they should be on it... JM2C

PG&E (POCO) would have likely wanted $.25M for a new transformer if this were a NEW service these days... But that boat sailed for them, and now your problem if within tolerance for VD on inrush. I keep having elevator sales guys selling "faster" elevators - only for PG&E to trigger 3 phase and a new transformer.... Or pay big money for a new transformer it should have gotten up front - or when they added load to it on the buildings next door....

Would it not suck if they put in a newer larger vault, and it still happened... Or worse never found an issue to 100% point to and went through sever months or years of this - only to find something like a bad breaker or $5 terminal...

So I'm going to ask some KISS method questions....

Now - assume you calc'ed the building and the service and conductors not undersized?

Have you considered a data logger? (Not PG&E - one inside at say the main...) I say that because the "Other" load causing this is the building itself - and the neighbor for that matter... But knowing how this elevator reacts at varied loads on the rest of the building could be an indicator of other problems before this elevator... At the service, panels or out to the street... Do a day or 2 at a few points. The whole circuit upstream... And more often than not - the problem they are complaining about is much worse when you are not there.... The larger the load - the larger the current, and larger voltage drop due to that current. That larger load is not likely occurring between 730AM and 4PM M-F. Its 830 saturday night... (PG&E is not going to share what they find out if they are logging...)

*(BTW you can rent a data logger to get a much better picture of current and voltage in a much more precise way for this, than a clamp meter or averaging meter - There used to be a guy who rented them at the bottom of Potrero - but there are inexpensive places on the internet now...)

And the next item - is an IR thermometer... With a moderate load on the building - send this elevator up and down a bunch of times... See if anything gets hot... This is a great way to hunt down a resistive connection or termination up stream at the feeders and main - Id even suggest you contact the POCO for it to be done before the main as well... A "Hot" resistive connection will manifest itself under load, and be a point where voltage drop is created - and by doing so drive current up - driving voltage down even more. Even raise voltage of other phases... I can not count how many times an IR thermometer has found something I would have walked by 20 times. For situations like this - I would even start with it! A little bit of phase loss on one leg can be spotted with an IR thermometer... Easy to use, and not expensive. Get an "ambient temp" in each panel then follow all of the terminations and breakers.... If you don't have one - get one you wont be sorry anyway even if it doesn't help this situation - it will be handy at some point trust me...
http://en-us.fluke.com/products/thermometers/

 

[e57]

jraef: if impedance i.e % impedance is more, internal V/D of transformer is also more unlìke what you state. But that is not issue here. See post#19.

Not knowing the building and issue first hand, but not uncommon for there to be a single transformer serving a single building. In fact it can be common for certain areas to have single family homes on a single transformer... Granted those homes are 14000sq'.... :huh: A multi family here would often end up with its own - especially with an elevator.

That said - could be anywhere upstream - and looks like we agree on a poss. loose connection....

 

[Haji]

It's either the service wires were sized small or the transformer is, assuming all other factors are good.

No, because

that setup has been" in commission" since 2009

 

[topgone]

No, because

the dots don't connect, IMHO.:lol:

 

[Haji]

the dots don't connect, IMHO.:lol:

Really?:huh:

 

[iceworm]

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 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.

I screwed up using the term "transient reactance", that's something different. I couldn't think of the word and put that in as I typed as a placeholder, then forgot to go back to it after looking up the term. I still can't find the term I was looking for. Sorry...

It relates to the transformer impedance and if the impedance is low, as in 1-2%, the effect on the output voltage from motor starting is more immediate. But most service transformers are 3-5% Z or more, which means the transformer holds up better to a sudden change in load without having the output voltage collapse immediately. So yes, I also inappropriately said "any" transformer, when I should have said "most service transformers".

I also looked up "transformer surge capacity" and "transient reactance capacity". I didn't do any better than GD did. However, as you said, "trc" is not a good term. I don't know where else to look.

I don't know of any physics that support the idea, "which means the transformer holds up better to a sudden change in load without having the output voltage collapse immediately".

You have knowledge about a phenomena that leaves me baffled. Please share. I'm not asking you do do research for me, just explain the physics as known to you.

ice

 

[GoldDigger]

If you are talking entirely about the reaction of the transformer to sudden surge or inrush loads within a sub-cycle time frame, I can see some possibilities here. But anything more than one cycle and the transformer output energy will be coming entirely from the energy input on the primary and the transformer cannot make things any better if the primary is not stiff.
My opinion as a former physicist.

 

[wyreman]

If this is say an "Otis" install - THEY should be handling this - messing with that drive could be messin with the operation of the elevator... If someone is on record for maint of it - they should be on it...
###EXACTLY, but they say "not my problem"' and I don't want to open up their enclosure to check for miswired high voltage leads [wired for 460 and supplied w 208]

PG&E (POCO) would have likely wanted $.25M for a new transformer if this were a NEW service these days... But that boat sailed for them, and now your problem if within tolerance for VD on inrush. I keep having elevator sales guys selling "faster" elevators - only for PG&E to trigger 3 phase and a new transformer.... Or pay big money for a new transformer it should have gotten up front - or when they added load to it on the buildings next door....
###DOING LOAD CALCS ON MY BLDG NOW. PGE DOESNT SEE IT AS A PROBLEM

Would it not suck if they put in a newer larger vault, and it still happened... Or worse never found an issue to 100% point to and went through sever months or years of this - only to find something like a bad breaker or $5 terminal...
###SORRY WHAT IS $5 TERMINAL :/

So I'm going to ask some KISS method questions....

Now - assume you calc'ed the building and the service and conductors not undersized?

Have you considered a data logger? (Not PG&E - one inside at say the main...) I say that because the "Other" load causing this is the building itself - and the neighbor for that matter... But knowing how this elevator reacts at varied loads on the rest of the building could be an indicator of other problems before this elevator... At the service, panels or out to the street... Do a day or 2 at a few points. The whole circuit upstream... And more often than not - the problem they are complaining about is much worse when you are not there.... The larger the load - the larger the current, and larger voltage drop due to that current. That larger load is not likely occurring between 730AM and 4PM M-F. Its 830 saturday night... (PG&E is not going to share what they find out if they are logging...)
###PGE USED TO HAVE THESE AT THE LENDING LIBRARY BY MOSCONE

*(BTW you can rent a data logger to get a much better picture of current and voltage in a much more precise way for this, than a clamp meter or averaging meter - There used to be a guy who rented them at the bottom of Potrero - but there are inexpensive places on the internet now...)

And the next item - is an IR thermometer... With a moderate load on the building - send this elevator up and down a bunch of times... See if anything gets hot... This is a great way to hunt down a resistive connection or termination up stream at the feeders and main - Id even suggest you contact the POCO for it to be done before the main as well... A "Hot" resistive connection will manifest itself under load, and be a point where voltage drop is created - and by doing so drive current up - driving voltage down even more. Even raise voltage of other phases... I can not count how many times an IR thermometer has found something I would have walked by 20 times. For situations like this - I would even start with it! A little bit of phase loss on one leg can be spotted with an IR thermometer... Easy to use, and not expensive. Get an "ambient temp" in each panel then follow all of the terminations and breakers.... If you don't have one - get one you wont be sorry anyway even if it doesn't help this situation - it will be handy at some point trust me...
http://en-us.fluke.com/products/thermometers/

### STILL HAVENT CLAMPED ALL THREE LEGS AT THE SAME TIME TO SEE IF VD IS UNIFORM

 

[wyreman]

I labored over the numbers and came up with 562A for the service allowing 150*1.25 for the 50horse elevator.
8 units gas dryers at 1150ft^2
2 small space htrs per unit

The only thing is that those service conductors should either be much bigger or in parallel as I get 1250mcm for the service conductors.
Nothing printed onthem
look more like 750s to me
then they should be a pair!

Don't look that big as ,,, they bend

we had a high voltage maintenance at my old job and
he told me about heating process
for a foundry where those big wires bend just like spaghetti

 

[wyreman]

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

I ran the calcs and I get 1250mcm single conductors, but these look way too small.
If this passed w a green tag from the city
and POCO hooked up to it
and the conductors are too small... I wonder who's fault it all is? :/

https://www.dropbox.com/photos/shared_space/iLU5ldAOkzi1Tam

really looks like I'm missing the other parallel conductor here!

 

[e57]

I ran the calcs and I get 1250mcm single conductors, but these look way too small.
If this passed w a green tag from the city
and POCO hooked up to it
and the conductors are too small... I wonder who's fault it all is? :/

https://www.dropbox.com/photos/shared_space/iLU5ldAOkzi1Tam

really looks like I'm missing the other parallel conductor here!

The Green Tag and Permission to connect letter that SFDBI EID is only an inspection of the equipment on the load side of the point of service. SFDBI EID is not responsible for or does it inspect the utility connection....

That said, the size of the conductors and quantity is determined by PG&Es Greenbook - not the NEC.

If if this is in between the POS and main disco - it would be the contractor who built it... Inspected by SFDBI EID... However SFDBI EID is not "quality control" for all things.... For the most part spot check, not spot check EVERYTHING... If that the case inspections would be all day long and you would pay a lot more for permits. And it is the owner who got screwed - and correction would be the contractor EC who did it.

If on the PGE side, that is fully PGEs issue and problem to solve.

 

[topgone]

I ran the calcs and I get 1250mcm single conductors, but these look way too small.
If this passed w a green tag from the city
and POCO hooked up to it
and the conductors are too small... I wonder who's fault it all is? :/

https://www.dropbox.com/photos/shared_space/iLU5ldAOkzi1Tam

really looks like I'm missing the other parallel conductor here!

Egads! My hunch was correct!
It's not a problem anymore to know who screwed up that install, IMHO. Either you upgrade your lines or ask PoCo for possible, cheaper solutions.

 

[wyreman]

Questions:startup thru soft start allow WHAT VALUE would be appropriate?

Questions:startup thru soft start allow WHAT VALUE would be appropriate?

I havent been back yet but I need clarity on
Questions:soft start allowances WHAT VALUE would be appropriate?
Confirm with calibrated instruments


i

• instrument verify
• Calcs:
• motor rated 156A across the line
• the starting current SHOULD be about 936A (600%).
• Across the soft starter
• then because the soft starter is inside of the delta, it is going to only see 58% of that, so 524A max across the starter
• 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.

[*]What we would expect
[*]Check the current limit setting in the Parameter menu. This should not be set below 200%.
[*]Verify that the overload setting is correct.
[*]Verify the starting current limit is set to at least 200% of the motor FLA.
[*]The overload setting should be set to the FLA of the motor.

 

[topgone]

I havent been back yet but I need clarity on
Questions:soft start allowances WHAT VALUE would be appropriate?
Confirm with calibrated instruments


i

• instrument verify
• Calcs:
• motor rated 156A across the line
• the starting current SHOULD be about 936A (600%).
• Across the soft starter
• then because the soft starter is inside of the delta, it is going to only see 58% of that, so 524A max across the starter
• 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.

[*]What we would expect
[*]Check the current limit setting in the Parameter menu. This should not be set below 200%.
[*]Verify that the overload setting is correct.
[*]Verify the starting current limit is set to at least 200% of the motor FLA.
[*]The overload setting should be set to the FLA of the motor.

As far as I know, starting current limits for most softstarters are around 3-4 times the rated FLA(468A - 624A). Your specific soft starter prescribes no less than 2 times rated specifically because the unit might not be able to speed up the motor using settings below 2 x FLA. The softstarter set too low a current limit will do it by supplying your motor at a lower voltage to maintain that 2 x times limit. By the time the ramp time is over, the softstarter switches to "run" contactor, and it'll land on that starting curve where there will be current spikes. Set the ramping time to say, 10 seconds and monitor if the amps don't spike on change-over to "run" contactor. Increase your ramp time if motor current spikes when the run contactor is energized.

Better still, check thru calculation what current limit your system can allow without hitting flicker voltage, and check if the value you come up with is greater than the 2 x FLA.

 

[Haji]

By the time the ramp time is over, the soft starter switches to "run" contactor, and it'll land on that starting curve where there will be current spikes.

No tripping of soft starter?

 

[wyreman]

=Haji;1684458 No tripping of soft starter?

the soft starter has never tripped according to user report
- esp if that trip would require a service call to reset.

I thought of a possibilty, I'm not going back till Monday... I remember the feeder conductors for the elevator seemed small.
The motor nameplate says intermittent duty, but there are no mention of the number of minutes in the duty cycle, just 80 startsper hour!
Like a one min
If it's 156A sized at 125% those are 4/0 copper depending on the terminations at the controller might be 60^
could even size it at 140% but , going through it, I see it wouldn;t make any difference

as i read over at electrician talk:

I'll quote the NEC Handbook in that section:

"Branch circuit conductors for a motor with a rated horsepower used for 5-minute short-time duty service are permitted to be sized smaller than for the same motor with a 60-minute rating, due to the cooling intervals between operating periods."

It specifically says "short-time", but I think it applies to intermittent as well. It is probably just that in a 5 minute application the conductors won't heat to the point of insulation damage. But in varying or continuous duty, that motor may run for long enough, or be started numerous times in a short period (before the conductors can cool), to cause significant heating of the conductors.

A continuous-duty motor has circuit conductors rated for 125% because the inrush happens once in a great while, whereas a varying duty motor may start and stop frequently enough that the heating from the inrush current alone may be great enough to warrant a conductor sized to 140%.

InPhase277
Last edited by InPhase277; 02-08-2008 at 11:51 AM. Reason: afterthought

But if it is 85% he could've used 1/0 CU and that looks like what I did see there last week.


So if the feeder conductors are 1/0 Cu and the run is 80' one way and the start load is kept to 200% [312a] then the VD is still just 5% localized at the elevator. The bldg still should not sag.

Really seems that post #8 is closer to my experience that the starter is dogging for startup and taxing the xfmr, when it finally lets go across the line, there is no reserve and the building sags.
#this requires review of the soft start settings and lengthening the ramp time and or increasing the current limit until brownout reduced to acceptable level.

If this does not provide the remedy, then POCO will have to provide data on the XFMR capacity, size and length of service conductor run.
since I am concerned here as this 600a service is fed by single 4" conduit - where I would expect parallel feeders

 

[Haji]

I ran the calcs and I get 1250mcm single conductors, but these look way too small.

https://www.dropbox.com/photos/shared_space/iLU5ldAOkzi1Tam

You can easily check whether the voltage drop is not within limit and so the service conductors are too small (as a first guess, because loose connections upstream could also have similar effect) by measuring the voltage drop across the terminals shown in the above photo, while the elevator starts to move up.