Power Quality

[new_pe]

Hello,

I have a few questions about conducting a Power Quality Analysis.

1) What are the Utility companies really required to provide? I am having trouble getting this information from the utility company. I have copied and pasted what they are telling me. I believe commercial/industrial fall into their +/- 7.5% voltage "rule." These are based on 5 min averages though and don't speak to transients of anything less than the 5 min average. Does this mean they can go 1000% as long it is less than a 5 min average? It seems to me the info they're giving me is not the whole story and that there must me a more detailed specification of what they promise to provide (or are required). I'm aware of IEEE std 519-1992/ANSI C.XX (still trying to get a hold of these) but I don't know where it says that the power company is required to uphold these standards and I'm sure different utilities probably play by different rules, unless there is a federal regulation or mandate that I'm unaware of. Here's what they gave me:

TERMS AND CONDITIONS
___________________

VII. VOLTAGE
A. The following definitions apply to terms used below:
Nominal Voltage
-
the reference level of service voltage.
Maximum Voltage
-
the greatest 5-minute mean or average voltage.
Minimum Voltage
-
the least 5-minute mean or average voltage
Urban Areas
-
areas of concentrated electric loads - generally, cities and towns having population of approximately 2500 or more are considered urban areas.
B. The Company will endeavor to maintain the voltages of Electric Delivery Service within the following limits:
1. For Electric Delivery Service to residential locations in urban areas, the variation from nominal voltage to minimum voltage at the Delivery Point will not be more than 5 percent of the nominal voltage, and the variation from nominal voltage to maximum voltage will not be more than 5 percent of the nominal voltage.
2. For Electric Delivery Service to residential locations in all other areas, the variation from nominal voltage to minimum voltage at the Delivery Point will not be more than 7.5 percent of nominal voltage, and the variation from nominal voltage to maximum voltage will not be more than 7.5 percent of the nominal voltage.
3. For Electric Delivery Service to other locations the variation from nominal voltage to minimum voltage at the Delivery Point will not exceed 7.5 percent of nominal voltage, and the variation from nominal voltage to maximum voltage will not exceed 7.5 percent of the nominal voltage.
C. Variations in voltage in excess of those specified arising from causes beyond the control of the Company shall not be considered a violation of this Section VII.


2) Does anyone have any experience with power quality meters? Any of them have software/hardware that is really top notch? If manufacturers names may not be mentioned this can be sent to me in a private message, if that is allowed.

3) I have some data, and having looked at it the rms voltage stays within the +/- 5% of 480V, however there was a few days time period (of the 30 days that data was taken) where the rms was regularly over 504V, but not by more than 10V, which would fall in the +/- 7.5%. I have also noticed a few dips, one very irregular, on one phase down to 300V rms but it only lasted a few cycles at most. I didn't see any of these transients in a high voltage spike or impulse. Since the rms voltage was only really over the 5% or 504V for a couple days I don't know whether its worth the utility investigating changing taps on the their transformer. Anyone care to chime in?

 

[jbelectric777]

Without all the hooplaw, the POCO is required by PUC to provide "sufficient" source voltage as to not cause the customer undo current problems because of poor system voltage. I take that as 110V and the FPN in the code (3% max loss) or 106.7V, anything less will not be in listed specifications and will increase the cost to use such an appliance.But thats just me, someone had posted a similar question last week and in some rural co op companies people dont know the source is actually too low, maybe they are at the end of the line. In my experience the POCO has been more than acommidating by checking their system and one time even installed a capacitor bank. This cant be stressed enough on a rural system where big inductive loads bring the source too low, its just an outdated system... That make any sense?

 

[mivey]

No real requirement other than the service rules and regs which can be overseen by the governing authority in the case of an IOU.

Generally, ANSI C84.1 can be used as a guide but it is not a requirement. For 480v, C84.1 says:
Application: Range A min, Range A max, Range B min, Range B max:
Utilization-Non Ltg: 432.0, 500.0, 416.0, 508.0
Utilization-w/ Ltg: 440.0, 500.0, 424.0, 508.0
Service: 456.0, 504.0, 440.0, 508.0

The explanation of ranges with some paraphrasing:

1.1 Scope
...
In defining maximum system voltage, voltage transients and temporary overvoltages caused by abnormal system conditions such as faults, load rejection, and the like are excluded. However, voltage transients and temporary overvoltages may effect equipment operating performance and are considered in equipment application.


5 Explanation of voltage ranges

...two ranges for service voltage and utilization voltage variations, designated as Range A and Range B, the limits of which are given in Table 1. These limits shall apply to sustained voltage levels and not to momentary voltage excursions that may result from such causes as switching operations, motor starting currents, and the like.

...{excursions outside range A should be infrequent and measures shall be taken within a reasonable time to improve the voltage to Range A requirements when excursions occur}...{Insofar as practicable (capable of being done), equipment shall give acceptable performance in Range B, although not necessarily as good as in Range A}

...{It should be recognized excursions outside range B will happen but should be infrequent and corrective measures shall be taken promptly when excursions occur}...{equipment may not operate satisfactorily outside Range B and protective devices may operate to protect the equipment}

You are supposed to protect your equipment from abnormal supply voltages. But, IMO, the utility should be willing to help you and/or investigate. The voltages you are describing are higher than what I would allow on a regular basis.