#205907 - 04/23/12 04:36 AM
Re: ComEd voltage dispute
Broom Pusher and
Loc: Anaheim, CA. USA
I will begin this Post with a quote from the "Good Book" of ANSI C84.1:
C84.1 Table 1: Standard Nominal System Voltage and Voltage Ranges - 60 Hz.
Voltage Class = Low Voltage (</= 1KV)
Nominal System = 120/240V Three Wire (1 Phase 3 Wire)
MAXIMUM Utilization & Service Voltage: 126/252V
MINIMUM Service Voltage: 114/228V
MINIMUM Utilization Voltage: 110/220V
MAXIMUM Utilization & Service Voltage: 127/254V
MINIMUM Service Voltage: 110/220V
MINIMUM Utilization Voltage: 106/212V
Range "B" is typical for Power Utility Providers in my areas, and appears to be referenced by the Utility servicing the O.P.
Looking past C84.1 and directly at Nominal Voltage Ratings of given Appliances, Equipment and Lighting Fixtures, the Design specific Working Voltage limits might be "XXX Volts, +/- 10% Maximum Tolerances".
For a given piece of Equipment rated at 120VAC 60 Hz; +/- 10%, this equates to a Maximum Line Input Voltage of 132V, and a Minimum Voltage of 108V.
If the Equipment has an Input Voltage rated at 110VAC; +/- 10%, the Maximum Line Input would be 121V, and the Minimum Line Input Voltage would be 99V
Now for the relevant rated Voltage!
If the Equipment has an Input Voltage rated at 115VAC; +/- 10%, the Maximum Line Input Voltage would be 126.5V, and the Minimum Line Input Voltage would be 103.5V
So far, it appears the Line Conditioners are rated for 115VAC L-N Input Voltage - with 10% Tolerance.
-- Now to look at the Low Voltage Secondary Distribution Feeders --
It is entirely possible, and otherwise normal, for the L-N Voltages observed on the Customer's Side of the KWH Meter / Service Disconnect, to be higher than the L-N Voltage measured at the Transformer's Secondary Bushings (Terminals).
Most common reasons are AC Induction Motors running with very minimal Shaft Load, or no load at all ("Idling").
The Rotors of Unloaded & Lightly loaded Induction Motors will Rotate at or above the Synchronous Frequency of the connected System.
The results of this are a Leading Power Factor, and the Load becomes one of Capacitive Reactance (XC); whereas with a Lagging Power Factor, the Load is one of Inductive Reactance (XL).
Higher XL, or Lagging Power Factors have a resulting increase in Current per the increased level of offset.
Higher XC, or Leading Power Factors have a resulting increase in Voltage per the increased level of offset.
Other culprits responsible for increased Customer Voltage include "Loosely regulated" Electronic Ballasts, Electronic Ballasts not matching the driven Lamps characteristics ("Variety Pack" of various Fluorescent Lamps driven by a certain Ballast), "Noisy" SMPS (Switch Mode Power Supplies) pushing Harmonic VARs back against the Transformer, and similar Non- Linear AC Load Equipment.
A Transient Effect normally occurs when starting an L-N PSC Fan / Blower Motor - except the "Side" of the Secondary which sees the increased Voltage is the "Opposite Side" of the Winding.
A PSC Motor is connected between the "Left End Of The Winding" (refer to as "Line A") and the Center Tapped Neutral. When the Motor is started, the Voltage between the "Right End Of The Winding" (refer to as "Line B") and the Center Tapped Neutral will be slightly elevated.
The increased Voltage will taper down as the Motor increases speed, and balances out when the Motor reaches a stable speed (slipping behind the closest synchronous speed available, allowing the required VA draw to "carry" the needed True Power ((Wattage)) from the Generating Device, in to the Motor's Rotor, and eventually developing a measurable output Horse Power at the Shaft...).
Incandescent Lamp Failures...
Premature failure of Incandescent Lamps is not always an Over Voltage issue...
Excessive Heat, excessive vibration, and "El' Cheapo" Lamps are equivalent Tungsten Filament Killers as well.
When the Incandescent Lamps are operating, how often do they flicker? What are their typical operation characteristics?
If a 130V rated Lamp is undesirable, how about lower Wattage or CFL Counterparts?
Dimmers would keep the initial startup surge issues down, if brought up from maximum dimming, then increased.
If the maximum level is kept below 100% (stop at 95% intensity, so the connected Voltage is less than the Lamp's rated Voltage), the Lamps will operate almost indefinitely.
The best method to determine a Voltage Issue is to find the System's Averaged Voltage, per instances.
A Charting Recorder is best here, as each "Event" may be recorded.
Simply stated, the Voltage at the Service Disconnect (KWH Meter) will be lower during peak usage, and higher during off-peak Hours.
The Charting (Recording) type Volt Meter will record Voltage Levels per Time of Day, whenever there is a Sag (decrease in Voltage), or Surge (Increase in Voltage).
When performing a local System analysis, verify the Voltage levels at the Service, while verifying the Voltage levels at a given Equipment Load.
(measure the Service Voltage _AND_ the Voltage at the Load at the same time).
Compare the two readings for verification, so as to determine where the Voltage increase is originating.
Power Quality issues may be generated from your House, your Neighbors, or both.
Power Quality issues on your Neighbors Service may create issues on your Service - and vice verse.
Lastly, "Load" the Circuit being tested prior to using Volt Meters with very high input Impedances.
Use a Linear Resistive device to Load the Circuit - such as a Quartz Halogen Lamp - between 100 and 300 Watts should be fine.
A Portable Heater will also work, but may load the circuit too much!
Simply plug the Lamp (or Heater) in to the same Receptacle being tested. i.e.: Testing a Duplex Receptacle: Plug the Lamp / Heater in to the lower Receptacle, and test through the upper Receptacle.
This should compensate for the Line Charging, which may be affecting a High Input Z Meter.
The Secondary Distribution Feeder Circuitry, of which my Service is connected to, has a total of (11) Customers connected to it.
The Transformer is 120/240V 1 Phase 3 Wire, 50 KVA, apx. 1.8% Z.
Judging from the way Incandescent Lamps react while Motors are Starting, the %Z should be less than 3% - the Flicker is very minimal, sag level is minimal, and duration is relatively short.
Transformer is 300 Feet away from our Service, and we are the last Service on the Secondary Feeder "String".
Conductors are #4 Copper-Clad Aluminum with type R Insulation.
Approximate Area (Square Footage) of the (11) Dwellings:
(2) at 5,200 Ft.˛ each,
(1) at 3,800 Ft.˛,
(4) at 3,000 Ft.˛ each,
(4) at 2,600 Ft.˛ each.
All have Swimming Pools, Split System Air Conditioning, Electric Cooking Appliances (Ranges and Ovens), Gas Space and Water Heating.
During peak usage periods, the L-N Voltage at our Computer Room used to sag down as low as 100V. L-L Voltage remained more stable, but ventured down as low as 215V.
Before the 50 KVA Transformer was installed (circa 2000), the previous Transformer was 37.5 KVA, with possibly 5% Z (Incandescent Lamps would have dramatic reactions to AC Motor starts).
Primary Fuse Links were blown at least 10 separate times before the Transformer had a Flash-Over Winding issue.(resulted in +15 Hour Outage!)
Power Quality was crappy before the Troubleshoot replacement of the Barbecued 37.5 KVA Transformer!
To combat this, I installed an Isolation Transformer at the Computer Room, to drive the sensitive Loads - such as Computers, Printers, Monitors, Audio & Video Equipment, as well as other specific Loads.
Transformer has a Tapped Primary Winding (3x 2% FCAN, 3x 2% FCBN), which is rated at 230VAC.
Secondary side contains Dual 120V Shielded Winding Coils, connected in Series and Center Tapped.
Transformer drives a Separate Panelboard, and the complete Assembly is an SDS (Separately Derived System).
BTW, There were a few other Power Quality issues to combat, besides the unstable Voltage from the Transformer.
Time to step down from the Soapbox!
-- Scott (EE)
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!