Blinking Lights 2

[markstg]

At my house I have a 5 ton, 2 stage scroll compressor condensing unit, and my house lights blink on the unit starting.
Specs are 118 LRA, 230V, 23 FLA.

Lamps are incandescent 130 V.
Service size is 200A, 120/240V, single phase
Measurements at the unit disconnect switch are:
Normal Voltage 246 V
Starting Voltage: 231 V
Starting Amps: 121 A
Running Amps: 10 A (Low Stage)
Starting time: 1 second.
Start is on Low stage.

This is on a 1 year old house and has done this since installed.
There is no issue when the compressor goes from low stage to high stage.

Neutrals have all been checked, Meter, Panelboard, and are all tight.

Power compnay service is: 50KVA transformer, 7 Houses on overhead lateral, my service drop from lateral tap to service is 80ft., lateral distance tap to transformer is 120ft. POCO conductors are aluminum don't know size. POCO not interested in my blinking lights with such small voltage drop.

Attached is the Power company recording of Voltage and Current at my service.

I was thinking placing a capacitor at my service may mitigate the dimming lights. Any thoughts.

 

[markstg]

I obtained 2 - 100 ufd run capacitors and connected them in parallel to my service.

The blinking lights are not noticeable with the capacitors in the circuit when the compressor starts.
I did 10 test and unless you are looking directly at the lights the blinking is not perceivable.


My test was flawed, and the lights do still blink with the capacitor in the circuit, for what appears to be a lesser duration.

Back to the drawing board.

 

[ScottyUK]

Get some proper test equipment and present some measurements of what is happening.

 

[electricpete]

If the caps remain connected to the motor side of interupting device when the motor is switched off (normally or abnormally), you need to be careful that you have not overcorrected. If overcorrected, the LC resonant frequency of motor/caps is below line frequency, and the motor residual voltage will excite that resonance during coastdown, potentially causing large overvoltage.

=====================================
(2B)+(2B)' ?

 

[markstg]

ScottyUK (Electrical)
27 Jul 14 12:08
Get some proper test equipment and present some measurements of what is happening.

All I have is a digital voltmeter and ampmeter. They have min and max functions, but only tell what is expected from a steady state view. I don't have access to transient type recorders.

 

[markstg]

I installed a hard start kit (100 microF Cap and voltage relay) on the AC compressor and my clampon read 23A on compressor start, and lights still blink.

 

[Mobius44]

That's unfortunate, but since the hard start didn't help you then try to locate and attempt to reduce the voltage drop occurring during the compressor start. Since you've checked for loose connections and found nothing, perhaps instead the wiring is undersized, nicked, or corroded? The voltage drop might be internal to the breaker panel, or even in the main breaker itself.

Since you don't have an oscilloscope or similar equipment to help track down the problem, perhaps use a couple of the blinking lamps? If you can find an upstream wiring connection that doesn't dim the lamps, then you can pinpoint if the voltage drop is mostly coming from one connection or device. However if you get all the way to the service entrance and the lamps still blink, then you'll have to talk with your utility, and after much discussion they might replace your service run or transformer. However some fights aren't worth the effort, you'll have to decide if it's worth the time and energy. As others have noted you may also want to consider switching from incandescent lamps, some alternatives aren't as sensitive to voltage variations and offer a good payback via energy savings and longer lamp life.

Best of luck!
Sean

 

[squeeky]

Dear David and Skoggs,

I will accept what you say and wait for the next opportunity. We will soon be looking at a project where the manager does not want a PF controller but a correctly sized capacitor connected to the motor to correct to 0.95pf. Our standard practice would be to use the N/O auxillary contact on the contactor to bring in the capacitor contactor. If the job goes ahead and we have time during the commissioning, I will bridge the N/O and see what happens. I am very fortunate to have access to a Power Quality analyser and if I can book it for the commissioning I should get some good scans. All going well I should be in a position to post something and hopefully upload the results where everyone can see them. I will be very interested to see the results and may have to consume humble pie. It will have 5 x 45kW motors, 4 pole, 400v, B3, foot mount, IE2 motors. Project due for installation in November / December this year. Hold thumbs.

 

[Skogsgurra]

http://gke.org/presentationer/files/PFC and Motor Protection 1.pdf

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[squeeky]

Dear Gunnar and David, Purhaps the problem lies in the sizing of the capacitor for pfc or stopping blinking. As I now see it the cap has to supply sufficent voltage/ power during the start up duration to prevent the blink. Sizing calculation would be interesting. I found this, see inserted file. Does this mean that we should only correct for the no load? It seems that we would have to correct for the voltage drop and duration as it seems to be an energy problem not voltage as the cap is at the point of utilization.

 

[markstg]

I made more readings of compressor starting amps with the Hard Start Kit and captured 111A starting current.

The power factor correction problem can be analyzed using steady state methods (motor nameplate values, steady state rated power values and phasor arithmetic).

The Blinking light problem is a transient analysis problem and it appears the blinking lights cannot be 100% mitigated, see attached paper.

I believe the only practical solution for my blinking lights is for the power company to install a larger transformer that has less internal impedance and can supply more short circuit current.

 

[squeeky]

Dear Markstg, Good paper. Only took 15 minutes to download Africa style. This puts a different slant on things. You bring the cap in first at the starter and then close the contactor, thus storing energy ready for the voltage dip. As I see it, it was the exact opposite of what I stated very early where the motor contactor came in and then the cap from the auxiliary of the motor contactor to prevent the inrush. At least I had the anti-recycle timer in. I see the dates are 1967 so the equipment would have still been around in Africa in the early 1980s when I became an appi. We go to tender on the pump station next week. I promise to give feedback in the starting if I go up to Malawi to commission. Thank you.

 

[itsmoked]

How can a capacitor possibly 'store' anything for an inrush issue? We're talking AC here. Many cycles are involved.

All a capacitor can do in this case is reduce a weee bit of voltage loss to the motor due to reduced power factor during starting.

Or am I missing something?

BTW: The brightness of an incandescent bulb varies by the more than the 3rd power of the voltage. A voltage drop of 6% results in about a 20% drop in light output.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

No Smoked - you are not missing anything.

I tried to tell squeeky about AC in another thread. But until he understands that it isn't about "smoothing" DC - he will probably not get it.

It will come to him. All we need is some patience - and hope that he doesn't try electrolytic capacitors...

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

Tangent alert:

"Capacitor assisted starting" of large AC motors was a well known (and thankfully dying) trick of industry in some circles. By "correcting" the poor PF at start-up in a source limited situation, technically more of the available current can be applied to creating torque. The problem is, for it to be effective the capacitors must be sized based on the no-load PF of the motor, often as low as .2-.3. That means that as soon as the motor gets to about 70-80% speed, you are now OVER correcting and can create massive other problems. So capacitor assisted starting has always been a challenge in that you must be capable of detecting motor acceleration and then disconnecting the start-assist caps before you create a voltage surge. That means an added contactor for the capacitors (with capacitor ratings), and some sort of speed detection on the motor shaft, then a control system to deal with it. All in all, compared to other less complicated methods of starting (because remember you STILL need a starter!), it just isn't worth it. I have seen several applications (whole log chippers for the paper industry) where people have attempted to do it on the cheap with timing alone. They all ended in damaged equipment, followed by removal of the caps and associated controls then replacement with something more conventional, such as a soft starter. So it ultimately cost them MORE than just doing it right the first time.

"Will work for (the memory of) salami"

 

[LionelHutz]

It's not only that the capacitor doesn't "store" anything, bringing the capacitor in first will cause a voltage rise. Say you add enough capacitor to correct a 10% voltage dip when the motor is started. Connecting the capacitor first would cause a 10% voltage rise and then the voltage would drop back to nominal when the motor was started. So, you still cause a voltage flicker because the voltage suddenly jumped by 5% or 10% instead of dipping by 5% or 10%.

Besides, the paper was misread anyways because it does not say to energize the capacitors first. In fact, the control scheme wiring they show uses an auxilary contact from the motor starter to energize the capacitors. Here is the quote from the paper.

"The second requirement for a Capstart installation is a control device to energize the capacitors the instant the motor begins to start and de-energize them once the motor reaches full speed."

Capacitor assist works quite well with a soft-starter. You can ramp the current and sequence the capacitor energizing to stay within a certain voltage window. A device to detect speed for dropping the capacitors out is required. But, the cost is very similar to a VFD, which mostly makes it pointless to do.

For this application I'd recommend trying a 1-phase soft-starter with a very short ramp time. It will remove the sudden transient so even though the voltage still dips, it dips over a longer period of time and I doubt anyone would notice it.

I suppose you could also try a zero-crossing solid-state relay. That might lower the flicker enough you can't see it.

 

[Skogsgurra]

While we are at it - why not try a KUSA start? It is simple and it *might* work. In fact, it works quite well in many instances. I will try that next in my "series of experiments".

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[markstg]

I found out the manufacturer and type of Power Quality Meter used by the Power Comapany, and their analysis software is free to download. So I requested the PQM file for my house and they said they need to check with the Legal Department to see if they can send me the file showing the PQ of the electricity I purchased. Geeeeeeez. Was hoping to share the waveforms with the group.

OK i'll bite, What is a KUSA start?

 

[jraef]

KUSA is a German acronym for Kurzschlussläufersanftanlauf-Schaltung. It's essentially a Primary Resistor starting scheme. A resistor is placed in series with the motor winding when first energized, then shorted out to get full power. A "poor man's" soft starter, but very simple. When I was with K-M, we built them with the resistor on just one phase of a 3 phase starter, it was VERY cheap compared to even a regular PR starter. Didn't always work though, the starting torque is very low and the 3 phase motor currents are very unbalanced, so you don't want to use it on anything that has a duty cycle of more than a few times per hour, or per day if it is a large motor.

"Will work for (the memory of) salami"

 

[Skogsgurra]

Yes, Jeff is right. I don't know if a scroll compressor has a large starting torque. If it has that, it will not work with a KUSA starter.

Why did I at all mention that? Mostly because this thread and its daughter threads have turned into a discussion that seems to cover every aspect on motor starting. But also because the KUSA start leaves one phase voltage more or less unaffected. If you put your lights on that phase, the pesky blinking may go away.

Still, I will do a small scale test. Curious myself...

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

A scroll compressor is probably the only compressor you might get away with that on. Why not use a double one so all phases remain balanced?

Keith Cress
kcress -

http://www.flaminsystems.com