Blinking Lights
Blinking Lights
(OP)
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.
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.





RE: Blinking Lights
The samples are taken with minutes between them and cannot show anything about flicker.
Make the utility do a correct recording. Then you (and they) will see what is going on.
It is obious that the starting current makes the lights flicker. And there are usually limits as to how much flicker one shall tolerate. At least, there is in the EU.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
The utility is not likely to help unless your neighbors start complaining. Your compressor is likely meeting standards although with a 6% voltage drop you are technically limited to a few starts a day max. Have you thought replacing your bulbs with LED? The are less voltage sensitive.
RE: Blinking Lights
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Blinking Lights
LED's are not an option since they will not work with my dimmer switches.
I changed a room of lights to 120V, and could not notice any difference in the dimming on compressor start from the other rooms that are 130V.
RE: Blinking Lights
RE: Blinking Lights
RE: Blinking Lights
RE: Blinking Lights
RE: Blinking Lights
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.
RE: Blinking Lights
I say proposed because these starting schemes have not been widely implemented. (I have read the paper but I have never seen this scheme used in the field.)
Enough capacity to supply the locked rotor VARs is too much for continuous use and may lead to over voltage and other issues.
You seem to have found a sweet spot with enough capacity to mitigate the lamp dimming.
It would be interesting to know if your voltage rises when the capacitors are turned on, and the current drawn by the capacitors.
You may get better results if the capacitors are connected at the motor end of the motor feeder. Maybe not. There are some offsetting factors which are hard to estimate.
VARs supplied at the motor terminals will result in less voltage drop in the feeder and so more starting current, but a higher voltage will result in more VARs from the capacitors, tending to reduce the current. Then the retio of the cable impedances from the transformer to the service and the service to the motor will be a factor. Given the high reactive component of the starting current the cable reactances are also a factor.
If you are happy with the results, I would not move the capacitors.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Blinking Lights
RE: Blinking Lights
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Blinking Lights
Then you state that you wish to use capacitors. Yes they will lift the voltage if you install them at the DB. This will help when starting but not enough. Yes the 2% rise is fine, you should not even see the difference and the shortening of life span won't be that great.
If you put the capictors on the motor terminals you really will have a problem. There will be an inrush due to the motor starting and charging of the caps. In my view the dimming will get more pronouced due to the even greater current draw.
What about star delta starting or a soft starter to limit the current draw.
Then finally it may be the voltdrop on your Utility's side or loose terminals on the transformer, LV and MV.
RE: Blinking Lights
RE: Blinking Lights
As davidbeach says.
It is true that there is a capacitor charging when switching on, but that charging is over in a few hundred microseconds and does not make light flicker at all.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
RE: Blinking Lights
The switching of the capacitor is not a problem in a system where impedance is as high as it is here. It is not about switching huge PFC capacitors at the PCC, where Isc is huge. It is about connecting a motor/capacitor to a grid that is quite weak (with a substantial X in the transformer) and therefore limits the charging current. I see no reason to worry about the contactor.
I dare say that davidbeach has a lot of practical (and an immense theoretical) knowledge. And, if may say so, so have I.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
RE: Blinking Lights
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Blinking Lights
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.
RE: Blinking Lights
RE: Blinking Lights
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(2B)+(2B)' ?
RE: Blinking Lights
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.
RE: Blinking Lights
RE: Blinking Lights
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
RE: Blinking Lights
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.
RE: Blinking Lights
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
RE: Blinking Lights
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.
RE: Blinking Lights
RE: Blinking Lights
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
RE: Blinking Lights
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
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
"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"
RE: Blinking Lights
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.
RE: Blinking Lights
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
OK i'll bite, What is a KUSA start?
RE: Blinking Lights
"Will work for (the memory of) salami"
RE: Blinking Lights
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
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
Keith Cress
kcress - http://www.flaminsystems.com
RE: Blinking Lights
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
RE: Blinking Lights
RE: Blinking Lights
Are you sure - or just pretty sure?
I wasn't aware that it could be a single phase motor. Sounds awfully impractical. Why does one do that?
OK, I have visited the US many times and everytime I've seen poles bending over from transformers with 4160 V in and single phase out. But very often there are three "buckets" - so three-phase seems to be available.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
Thanks to all who have parcipated in this post, I have learned alot.
RE: Blinking Lights
This is a single phase motor. This is a residential area and single phase is all that is available on the pole.
RE: Blinking Lights
Based on what?
Increased current creates additional voltage drop in the transformer and conductors. If the voltage drop is great enough there will be perceptible flicker. In theory, the voltage drop could be reduced to levels that are not noticeable by installing much larger conductors and a larger service transformer. In practice, a "200 A" utility service means you have a 200 A main breaker. It does not tell you the size of the utility's transformer, the transformer loading, or the impedance of the system up to your service panel. For virtually any standard residential service, an impact load of 120 A is going to create some flicker.
RE: Blinking Lights
Increased current creates additional voltage drop in the transformer and conductors. If the voltage drop is great enough there will be perceptible flicker. In theory, the voltage drop could be reduced to levels that are not noticeable by installing much larger conductors and a larger service transformer.
Agreed
Quote
In practice, a "200 A" utility service means you have a 200 A main breaker. It does not tell you the size of the utility's transformer, the transformer loading, or the impedance of the system up to your service panel.
Agreed
Quote
For virtually any standard residential service, an impact load of 120 A is going to create some flicker.
Key words, "any standard residential service". I specifically submitted my load study to the Power Co. at the time of my service request showing my itemized loads steady state ( 167A )and the largest STARTING currrent load (AC #1 5 Ton, 120A.) Further the Power Company standards state Momentary start up loads up to 150A are acceptable. It appears the Power Company installed a "standard service".
But what this thread is really about was why capacitors added could or could not solve the transient voltage dip causing the blinking lights, and if they couldn't that the only solution is changes on the Power Company Side, as you describe.
RE: Blinking Lights
Keith Cress
kcress - http://www.flaminsystems.com
RE: Blinking Lights
Flicker is a problem because it bothers people, not because it represents a safety issue or causes any damage to equipment.
I'm not sure that the Power company is going to do much if you are only one complaining, since you are the one creating the flicker. Not unless you are willing to pay for the solution. I actually think the adjustable frequency drive and a three-phase motor is going to be the most cost-effective solution.
Also, FWIW, when a homeowner or contractor provides a load estimate to the utility, they will typically assume that the actual peak load will be about 50% of the calculated total, based on long experience. Utilties do not follow the NEC when sizing transformer or feeders.
Best of luck.
Dave
RE: Blinking Lights
RE: Blinking Lights
I have a three-phase 400 V 25 A incoming line. 230 V line-neutral. Quite happy with that.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Blinking Lights
The solutions i see are varied:
1) Reserve yourself to ignore it.
2) Install modern lighting instead of archaic flicker prone incandescents.
3) If a particular appliance is bothered by it get a UPS to run just it. (I once had a computer in a tannery that would reboot every time a leather scissor table's hydraulic motor pack started. Ultimately the solution was a small UPS for the computer. Every time the button was pushed on the table the UPS beeped and kept the comp happily running.)
4) As Skogs is checking, work up an inrush limiter KUSA that provides just barely enough resistance to the starting compressor as to minimize the flicker.
5) Put in an equal size unloaded motor to the compressor's motor that you start first. It will store kinetic energy locally (on the condenser unit's end of the supply line.) Then when the compressor starts the already spinning motor will 'generate' to supply energy into the voltage drop.
6) Switch the compressor out for a three phase unit. Use an oversized VFD to convert your single phase power into 3 phase power. This can eliminate ALL flicker.
Personally I'd probably go with #2. A buddy just dropped his power bill $20/month by switching all his incandescent bulbs out for LEDs.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Blinking Lights
If you're interested, there is quite a bit of information on line regarding flicker. Unfortunately even small levels of voltage fluctuation can cause noticeable flicker. Maybe the link below will be of use if you haven't done more reading than you want on flicker:
https://www.pacificpower.net/content/dam/pacific_p...
RE: Blinking Lights
Installed a room with LED lamps, and They Do Not Flicker.
If I ever get the wave forms from the Power Company I will post for general interest.
thanks.
RE: Blinking Lights
=====================================
(2B)+(2B)' ?
RE: Blinking Lights
Thanks I have learnt a lot. For me, cables and connections. There is a high impendance somewhere.
RE: Blinking Lights
It is a very long thread. I have just read some part of it.
For those who have followed the discussion I wonder if there is something in the thread about reducing flicker by just applying series capacitors.
The capacitive reactance of the series capacitor nullifies the inductive reactace of the feeder reducing the voltage drop due to the compressor operation at the point on which the lamp is connected. So the flicker will be reduced.
Best Regards,
Herivelto S. Bronzeado
Brasília, Brazil
http://www.linkedin.com/profile/view?id=46319837&a...
RE: Blinking Lights
I think that's the basis of the 'hard start kit' mentioned earlier, but didn't make much difference in this case.
RE: Blinking Lights
RE: Blinking Lights
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RE: Blinking Lights