Blinking Lights

[markstg]

Power Co Response

Power Co Response

Below and Attached are the POCO's response to my blinking lights inquiry:

I have attached part of your power quality recording. The Red & Purple lines are your voltage. The Green & Blue are current. As you can see, when your equipment starts up, the Green & Blue lines spike as expected. Your voltage is pulled down with each motor start. This is the cause for the flickering lights you are experiencing.

Please let me know if you need any additional information.



Any advise on what to discuss (argue) with POCO on the voltage drop in there service feeder? Looks like a voltage drop of 3-4 Volts.

 

[don_resqcapt19]

....
Any advise on what to discuss (argue) with POCO on the voltage drop in there service feeder? Looks like a voltage drop of 3-4 Volts.

I would expect a drop of a lot more than 3 or 4 volts would be well within the voltage standards set by your state utility commission.

 

[gar]

140709-1714 EDT

markstg:

Since current and voltage overlap on the plot I can not really see the amount of voltage drop, but it looks about 2 V. Also motors other than yours are causing voltage down spikes of about the same magnitude. Whether a relatively instantaneous drop of 2 V is to be expected or not I can not judge. Do you know what the averaging period is for the measurements?

When I look at my home's voltage and current based on a 1 second average measurement the down spikes are not nearly as significant as yours. This is at the main panel. The drop is greater within the house.

Your power company is not likely to do anything because the voltage drop is relatively small.

.

 

[mgookin]

Below and Attached are the POCO's response to my blinking lights inquiry:

I have attached part of your power quality recording. The Red & Purple lines are your voltage. The Green & Blue are current. As you can see, when your equipment starts up, the Green & Blue lines spike as expected. Your voltage is pulled down with each motor start. This is the cause for the flickering lights you are experiencing.

Please let me know if you need any additional information.



Any advise on what to discuss (argue) with POCO on the voltage drop in there service feeder? Looks like a voltage drop of 3-4 Volts.

That looks like real good power quality.

Go buy 120V lamps.

 

[kwired]

Below and Attached are the POCO's response to my blinking lights inquiry:

I have attached part of your power quality recording. The Red & Purple lines are your voltage. The Green & Blue are current. As you can see, when your equipment starts up, the Green & Blue lines spike as expected. Your voltage is pulled down with each motor start. This is the cause for the flickering lights you are experiencing.

Please let me know if you need any additional information.



Any advise on what to discuss (argue) with POCO on the voltage drop in there service feeder? Looks like a voltage drop of 3-4 Volts.

Also need to know what kind of time a change needs to occur for it to be recorded. If the voltage actually drops say 10 volts in just a few milliseconds, some recording equipment may not record that change, or at least not all of the change, but it still may be enough to cause noticeable change in lighting supplied by the same voltage source.

 

[PetrosA]

Two things are working against you - 130V incandescent lamps running on less that 125V and the dimmers that control them. I'm guessing that whatever lights you have that aren't on dimmers don't show such a noticeable dip in output as the dimmer controlled ones do. If these are relatively new dimmers, they probably never output the full 124V that you have to the lamps, so it's likely they're running at closer to 115-118V on full.

The important argument with most POCOs is tariff voltage, as measured at the main panel or meter socket. With one local POCO, tariff voltage is 232V minimum, so until you can show that your voltage is going below that, they won't budge. I was able to show that we were getting less than tariff in our last house, and it turned out that the POCO had undersized primaries down to our little village. Once they upgraded them, we were fine. It was a battle, though. Find out what your POCO considers tariff voltage and work from there. You might need to rent some data logging tools to prove it.

 

[don_resqcapt19]

Peter,
Our "tariff voltage" does not apply to short sags, dips or spikes as the poster is having trouble with. Not sure how it is in other states.

Illinois Commerce Commission Section 410.300 Voltage Regulation

a) Standard voltage. Each entity supplying electrical energy for general use shall adopt a standard service voltage of 120 volts (when measured phase to neutral) and shall maintain the service voltage within the allowable variations from that value at all times.

b) Allowable voltage variations. For service rendered at the standard service voltage, voltage variations as measured at any customer's point of delivery shall not exceed a maximum of 127 volts nor fall below a minimum of 113 volts for periods longer than two minutes in each instance. For service rendered at voltages other than the standard voltage value, voltage variations as measured at any customer's point of delivery shall not exceed 10% above or below the service voltage for a longer period than two minutes in each instance.

c) Variations of voltage in excess of those specified above shall not be considered a violation of this Section if caused:

1) by operations of a retail customer in violation of an agreement with or the rules of the entity;

2) by the operation of apparatus on a retail customer's premises that results in large inrush currents;

3) by infrequent and unavoidable fluctuations of short duration due to system operation; or

4) by acts of nature or other situations beyond the entity's control.

 

[gar]

140710-1026 EDT

There needs to be some controlled experiments performed.

Some rough tests I have performed are:

A GE dimmable CFL 26 W is moderately insensitive to sine wave voltage variation down to somewhere around 100 V. This does not means the intensity does not change, but not as much as an incandescent or LED. On the other hand a standard CFL or LED is moderately sensitive to sine wave voltage variation.

Some non-instrumented experiments this morning using a 1/3 HP motor with no mechanical load on my workbench. Supply impedance to bench is poorer than at main panel. A 10 A load produces about 5 V drop. Using a Fluke 27 in MIN/MAX the voltage change from the 1/3 HP motor starting is about 4.5 V. I don't know the averaging time on the Fluke for the MIN/MAX measurement. I would expect a larger short time voltage drop from the motor.

Comparison of bulbs:
100 W incandescent very noticable flicker from motor start.
26 W GE dimmable CFL has very little flicker.
Standard CFL and CREE 10 W LED are intermediate in flicker.

Changing color temperature of incandescent, mean voltage, does not visually change noticeableness of flicker.

An inertia load on the motor would probably increase the apparent flicker on all but the GE dimmable CFL.

I might expect a lower wattage incandescent to show more variation than a high wattage because of the thinner filament, less thermal mass. But this I can not determine without instrumentation.

.

 

[markstg]

What if I put a 300 microfarad capacitor at my main panel? This would provide 27A leading current. Maybe enough to lessen the voltage drop. I could wire it to a spare breaker in my panel.

 

[GoldDigger]

What if I put a 300 microfarad capacitor at my main panel? This would provide 27A leading current. Maybe enough to lessen the voltage drop. I could wire it to a spare breaker in my panel.

The starting surge current (unlike the connection surge in a transformer) will be close to unity power factor. It is the running current (and the later stages of acceleration) that will potentially have its power factor mitigated by the capacitor. And to do that, it really should be located at and switched with the motor, rather than being constantly connected at the main panel.

 

[gar]

140710-2242 EDT

markstg:

Why do you think a capacitor across the line will prevent or reduce light flicker?

Try the experiment.

For a non-valid comparison --- what is the reactance of 300 ufd at 60 Hz? It is about 9 ohms. How does this compare with about 231/121 = 1.9 ohms. Even if the capacitor had some effect it would be insignificant. Any contribution would be turn on phase dependent, but there is not enough energy to do much at any turn phase angle.

.

 

[markstg]

140710-2242 EDT

markstg:

Why do you think a capacitor across the line will prevent or reduce light flicker?

Current that doesn't have to be supplied in the line to the meter will reduce the voltage drop at the meter.

Here's my analysis:

With a 300MFD capacitor, impedance 9 ohms, at 240V gives a capacitive current of 27A

Assume motor starting power factor of .3, ILine = Ic + Im
Im = 120*.3 + j120*.954
Ic = -j27
ILine = 120*.3 +j(120*.954 - 27)
ILine = 36 + j86.88
ILine = 94 amps

The line current has been reduced from 120A to 94A.

Is my analyis flawed or is it that the amp reduction will not provide enough voltage drop relief to make a significant difference.

 

[kwired]

Current that doesn't have to be supplied in the line to the meter will reduce the voltage drop at the meter.

Here's my analysis:

With a 300MFD capacitor, impedance 9 ohms, at 240V gives a capacitive current of 27A

Assume motor starting power factor of .3, ILine = Ic + Im
Im = 120*.3 + j120*.954
Ic = -j27
ILine = 120*.3 +j(120*.954 - 27)
ILine = 36 + j86.88
ILine = 94 amps

The line current has been reduced from 120A to 94A.

Is my analyis flawed or is it that the amp reduction will not provide enough voltage drop relief to make a significant difference.

All you are doing is reducing apparent power (correcting power factor). The power factor during starting which is causing the most significant drop in voltage is very likely higher power factor then the running power factor.

Even if you were able to correct to exact unity power factor at all times, that starting inrush is still going to pull down voltage because of impedance in the source and/or the conductors between the source and load. To prevent the voltage drop you need to either reduce impedance of the source/conductors, somehow introduce more power (a capacitor isn't really a storage device when used in an AC circuit, especially in high power factor circuits), or lower the starting current of the offending load.

You would be better off spending money on soft starting methods then applying capacitors.

 

[gar]

140711-1647 EDT

markstg:

What is the time constant of an RC circuit of 300 ufd and 1.7 ohms?

It is 300*1.7/1,000,000 seconds, or 510 microseconds, or 0.51 milliseconds. One half of a 60 Hz cycle is 8.3 milliseconds.

Do you really think that a 300 ufd capacitor will have any significant effect on flicker? If so, then spend a few hundred dollars and run the experiment.

.

 

[markstg]

All you are doing is reducing apparent power (correcting power factor). The power factor during starting which is causing the most significant drop in voltage is very likely higher power factor then the running power factor.

Yes would be reducing apparent power. The starting power factor is low (.3) not higher then running (.6 or .7)

 

[markstg]

The 120V, 65W rated lamp has a lumens of 630

I'm going to get a few 120V lamps and check out if the dimmimg is less perceptable.

I changed a room of 130V lamps to 120V lamps and there is no perceptible difference in the Lamp Blink.

Not the most scientific test but I'm looking for results not minor effects.

 

[kwired]

Yes would be reducing apparent power. The starting power factor is low (.3) not higher then running (.6 or .7)

Ok but your motor is still pulling maybe 6 times full load current even if only a few fractions of a second, when you first hit it with full voltage. If the source has too high of impedance to maintain voltage it is going to drop, then rapidly recover as motor accelerates and current goes back down.

A capacitor is a storage device - but what it stores is released as DC current, in an AC circuit it is an impedance, but it is that release of stored energy as DC current each cycle that is what corrects power factor, it is supplying the additional "apparent power" the inductive component of the motor is looking for. your capacitor is only going to correct power factor, not store any usable energy that can be put back out as AC current. The motor is still going to draw more "true power" when it is accelerating and will drop off and level off when it reaches speed. The source still needs to provide this power, if it can't provide what is demanded, the main symptom is voltage drop.

 

[markstg]

Ok but your motor is still pulling maybe 6 times full load current even if only a few fractions of a second, when you first hit it with full voltage. If the source has too high of impedance to maintain voltage it is going to drop, then rapidly recover as motor accelerates and current goes back down.

A capacitor is a storage device - but what it stores is released as DC current, in an AC circuit it is an impedance, but it is that release of stored energy as DC current each cycle that is what corrects power factor, it is supplying the additional "apparent power" the inductive component of the motor is looking for. your capacitor is only going to correct power factor, not store any usable energy that can be put back out as AC current. The motor is still going to draw more "true power" when it is accelerating and will drop off and level off when it reaches speed. The source still needs to provide this power, if it can't provide what is demanded, the main symptom is voltage drop.

The motor will always pull the same amps (both real and reactive) without or with the capacitor in the circuit. With the capacitor in the circuit it provides reactive power (amps ) that the source doesn't have to.

 

[kwired]

The motor will always pull the same amps (both real and reactive) without or with the capacitor in the circuit. With the capacitor in the circuit it provides reactive power (amps ) that the source doesn't have to.

I agree, but the motor is still going to pull more real power while accelerating, and nearly instantaneously will pull locked rotor power when first hit with full voltage, this will drag voltage of the source down if it doesn't have enough capacity to deliver what is being demanded, which is why the lights connected to the same source are dimming when the motor starts, voltage drop on conductors also is a contributing factor.

Add: you will get some relief from the amount of reactive power the source doesn't need to supply even during startup, but the amount of real power is still high at startup.

 

[gar]

140712-1946 EDT

markstg:

I believe you are using a flawed analysis by using a steady state linear load analysis on a transient event with a time varying non-linear load.

If I supply an incandescent lamp from a Sola constant voltage transformer, then under signal known exactly conditions there is nearly an undetectable flicker when starting my test motor. Probably not noticeable under non-signal known exactly conditions. You would not want to use this approach because of the cost and low power efficiency.

There is no way and no analysis of the use of a shunt capacitor across your main supply or load point that will eliminate the lamp flicker. Use a 10,000 W bulb and you may not see flicker. I have already suggested that you try a GE dimmable CFL and see if the small flicker is acceptable.

.