PQ Scope Picture & Question

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100312-1700 EST

iwire:

First it looks like a very stiff supply. However, there is slight rounding off of the voltage peaks. This rounding might be from other loads external to your customer.

Whatever is causing the disturbance is line synchronized, and maybe to phase A because the high frequency oscillation stops at phase A's current zero crossing. The start of the oscillation might relate to an SCR turning on on phase A.

Phase A's current starts to drop from the expected sine wave at about 60 deg from the phase A voltage zero crossing. This deviation in current shows up as the low frequency rise in the neutral current, somewhat centered but lagging the phase A peak voltage. This same current anomaly shows up on the other two phase currents synchronized with their voltages. But B and C's currents do not seem to have the same effect on the neutral.

It looks like phase A is the source of the oscillation.

I believe there are two different causes of the waveform distortion, but might originate in the same equipment.

Do the compressor motors have some type of power control?

Is the power distribution wiring such that it would be easy to put your monitor in a more localized position to search for causes?

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100312-1727 EST

iwire:

Suppose the anomaly has nothing to do with the change in energy usage.

A large part of a supermaket load is lighting. If the power company raised the supply voltage then this could be a factor.

Experiment on an 8' Slimline.

Volts Pwr VA PF

100 103 114 0.91
110 112 120 0.92
120 120 129 0.94

Consider that there are slight errors because my line voltage varies slightly during each test, and the measurements are made in sequence.

The measuring instrument was a Kill-A-Watt.

Over this range there is approximately a linear correlation of power vs voltage. If we assume that the fluorescent is like a constant current load, then the result is to be expected. In a separate experiment the current went from about 1.09 to 0.99 . This was a decrease in current, but the PF changed a little.

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No doubt that could do it, the power company did replace the pad mount but I do not know if that consider with the increase or what the voltage was before the change.

We have actually installed voltage regulators in a couple of stores to drop the voltage to 114 volts to save money.

For what it's worth the lighting in the store is almost entirely F32/T8 with electronic ballasts.
 
iwire said:
I can sleep fine with the anomaly but I will look like a hero if I can figure out why they are using more KWH. :)
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Well, since you have been called to check out a 4 percent rise in a bill, I'll bet the owner is pinching pennies.

Are all the coolers and freezers full? They are designed to be most efficient when full of product. It has to do with the airflow. Last year we did a large supermarket and there were tests to the controller (Einstein) that could only be done when the coolers were full of product.

Also, has anything been changed that may affect the wash out of the coolers? Could it be that some changes were made to the heating system's air direction to save money by making people feel warmer that could now be washing out the coolers?

What type of historical data do you have? Is there an exact point where the increase occurred, or has it been gradual?

When was the last time the lighting system was re-lamped? Penny pinchers won't do it until they burn out. Some of the rise may be due to old lamps.

Good luck on this. There may be no electrical problem at all, just an owner problem.
 
K8MHZ said:
Well, since you have been called to check out a 4 percent rise in a bill, I'll bet the owner is pinching pennies.
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I would not call 4% pennies on this bill. They use about 237,000 Kwh per month. 4% is about 10,000Kwh



Are all the coolers and freezers full? They are designed to be most efficient when full of product. It has to do with the airflow. Last year we did a large supermarket and there were tests to the controller (Einstein) that could only be done when the coolers were full of product.
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This is no Mom and Pop shop, this chain caters to affluent neighborhoods, every thing is full, it is part of the 'look'

Also, has anything been changed that may affect the wash out of the coolers? Could it be that some changes were made to the heating system's air direction to save money by making people feel warmer that could now be washing out the coolers?
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Great point, I had not thought of that even though I have seen it happen first hand.

What type of historical data do you have? Is there an exact point where the increase occurred, or has it been gradual?
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Next to nothing yet, I was asked to swing by and see if I could help them out.

When was the last time the lighting system was re-lamped? Penny pinchers won't do it until they burn out. Some of the rise may be due to old lamps.
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The entire store was remolded 2 years ago, all new lighting fixtures and they change lamps as they look bad.


Good luck on this. There may be no electrical problem at all, just an owner problem.
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Thanks, I plan on keeping an open mind about the problem, I just was hoping someone would see that sine wave and say 'Yeah that is the problem and you can fix it like this...' :)
 
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100312-1922 EST

iwire:

I have a cheap 4' fixture from Home Depot that has an input power curve that rises faster than voltage. Also starts to fail around 105 V.

Is there a spare light fixture with which you can experiment and see how power is related to voltage?

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100313-0727 EST

iwire:

When did the power company change the transformers? What did the bills look like for 12 months before and 12 months after the change?

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mivey said:
Thanks for the link, I found the comments interesting. The second picture is really noisy. I also noticed the currents were slightly higher.
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The second picture was from another site of the same type about 8 months ago.

Are you sure the meter is OK?
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I have no reason to think otherwise, it is fairly new equipment.



Have you been able to read higher currents (say above 480 or 490 amps)
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Yes.

ever get a clean signal with those CTs?.
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Imposable for me to say, both pictures may indicate a clean signal from the CTs but from a dirty source.
 
Interesting reading and brings back some memories.

I will throw this out there as it may be related or not. I came across a similar sine wave signature years ago but only on one current phase.

Our RPM PQ analyzer was attached at the service entrance to an office building. According to them they were experiencing many brownouts.

I ignored this distortion and figured it was instrument noise. When returning to pick up the recorder, I evaluated the 2 weeks of data and noticed many sustaining dips in the voltage throughout the two week survey.

In scope mode the distortion was still present, I quickly swapped the CT's and it was still present.

The report was forwarded to the utility company by the customer and we were told they would follow up.

About two months later, we were called to the same location to follow up with an infrared survey, visual inspection, etc.

The customer had mentioned to the team that his utility bill has also been increasing. The guys were able to access the CT cabinet (tag no padlock) and documented the secondary current from the utility Co CT's and compared the ratio current to actual and found 3X more current on the B phase CT than A and C.

We instructed the customer to contact the power company with this information. Unfortunately this internet company went out of business shortly thereafter and we never found out what happened.

This got me thinking that perhaps the distortion on the B phase may have been noise contributed by the failed revenue CT or was it a coincidence?

While reading these posts it got me thinking. Anyone think this is possible?
 
100313-1319 EST

iwire:

At the shop we have two American Fluorescent 4' T8 fixture with which we are experimenting for lighting the CNC machines. The idea is to go to more localized lighting and eliminate the general lighting from 8 foot units.

The model number is 234SLESW and made in China.

This has a much better electronic ballast than the unit I previously mentioned. This will operate to below 60 V input. The Kill-A-Watt I am using for the measurements only works down to 100 V.

Results:

V ... I ... P. VA . PF . Foot-candles

100 0.82 48 82 0.57 41
110 0.80 50 89 0.56 43
120 0.82 55 99 0.57 44
130 0.82 61 106 0.58 45

Note the PF values are read from the Kill-A-Watt.

For a 30% change in voltage
The light output changed 10%
The power changed 27%
The VA change was 29%

The change in power consumption at the supermarket could easily have resulted from the transformer change.

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