Transcript Caroline_Stormx - The University of Texas at Arlington

The effects of Smart Meters on GFCI Outlets
Caroline Storm, Simon Donahue, David Wetz, Advisor
Department of Electrical Engineering, The University of Texas at Arlington, Arlington, Texas 76019
Abstract
Smart Meters have recently been deployed on a wide scale. These devices has proven to be
successful, but there is still much that is unknown about how they impact the devices around
them. One such device, is a ground fault circuit interrupter, or GFCI. A GFCI is a residualcurrent device that disconnects itself from an applied load when it detects in an imbalance of
current. Typically, GFCIs are required in electrical installation where water may interfere with
electronics. Under the construction pole setup conditions electrical contractors in North
Texas have been experiencing repeated and uncontrollable GFCI tripping events, absent of
the presence of water or leakage current, which were believed to be caused by interference
with the RF transmissions from the Smart Meter located in very close proximity, typically
within 0.5 m, to the GFCI. The goal of this research was to find out if the was actually the
case and if so how to prevent it.
Results
Test 1: Source of energy
The first test was to discover whether the energy was being radiated and then
pick-up by the hot and neutral lines versus being conducted from the sense
board. This was done by reading the voltage across the differential transformer
in two different set ups:
1. The GFCIs’ power was supplied directly from the Smart
Meter
2. The GFCIs’ power was supplied from a uninterrupted
power supply (UPS), effectively isolating them from the
Smart Meter
Test 2: How to mitigate the effects
2.1 Distance
Knowing that the problem came from radiated energy, rather then conducted
through the transmission lines, we wanted to see if the problem could be
solved by moving the Smart Meter father away. Given the construction pole
set up the Smart Meter and GFCIs could not be moved more then 15 inches
away. We took measurements over 1 inch intervals and found very little
difference.
Differential voltage-no trip conditions
Introduction
Smart Meters use wireless RF to transmit data to the main HUB. It has been observed within
the laboratory and at construction sites, that these transmissions interfere with GFCI outlets,
producing problems for those using these two devices in close proximity. There have been no
reported causes of this interference in homes where the Smart Meters are located a
considerable distance away from the GFCI outlets. Instead the concern comes from
installations on construction poles where the proximity between the meter and the GFCI is
within 0.5 m. There are three likely sources of interference between the GFCI and the smart
meter. First, direct coupling with the differential transformers inside the GFCI. Second,
radiative coupling in the hot or neutral line to the GFCI. Thirdly, conductively interference
into the GFCI’s electronic sense board from the Smart Meter PCP. The goal of this research is
to establish the reason for the faulty trips and to find a cheap and easily implementable
solution to mitigating them.
Figure 5. GFCI transformer voltage during a no trip conditions. Spike around
702 mV
Figure 2. GFCI differential transformer Voltage under no trip conditions. It
spikes around 900 mV
Summary and conclusions
One of the more important things to note is that the
power line going from the smart meter to the GFCI
outlet box is acting as an antenna. This means the
orientation of the wire has a profound effect on the
frequency of tripping. However, due to the difficulty in
finding an orientation to stop the tripping, and keeping
the wire in that orientation, a better solution needed to
be found. We propose the use of ferrite beads on the
GFCI end of the power line. By effectively suppressing all
the energy form the Smart Meter RF communications
the extra functional tripping is eliminated. A test was run
for 56 hours and found that this measure effectively
stopped the tripping. It is an easy, cheap solution which
can be implemented on already installed construction
pole set ups.
Literature cited
‘Smart meter deployments continue to rise,’ U.S. Energy
Information Administration, July 7, 2013.
Z. Zhang, W-J. Lee, D.A. Wetz, B. Shrestha, J. Shi, A.
Jackson, H. Honang and J. Fielder, ‘Evaluation of the
Switching Surges Generated during the Installation of
Legacy and ‘Smart’ Electric Metering Equipment,’
Proceedings of the 48th Industrial & Commercial Power
Systems Technical Conference, Louisville, Kentucky, May
20 – 24, 2012.
Powered off Smart Meter-trip conditions
Materials and methods
For all our tests we used a combination of the following equipment.
Agilent 4403B spectrum analyzer
G. Mezei " An Investigation of Radiofrequency Fields
Associated with the Itron Smart Meter " Electric Power
Research Institute, 2010 Technical Report, Dec. 2010
LeCroy Wavesurfer 24Xs Oscilloscope, with the probes hooked up to the differential
transformers
APC Smart-UPS 1500VA
B-field probe
Figure 6. GFCI at 12 inches during trip event. Spike around 704 mV. Enough to
cause the GFCI to trip.
Modified and unmodified GFCIs
Figure 3. GFCI differential transformer connected directly to the Smart Meter
during a trip event. Spiking around 1.25 V
W.D. Ford and R.G. McCormack, ‘Investigation of Ground
Fault Circuit Interrupter,’ Technical Report E92,
September 1976, Construction Engineering Research
Laboratory.
Powered off UPS-trip conditions
Acknowledgments
Figure 3. Test set up. The oscilloscope and spectrum analyzer are out of the picture
Figure 7. GFCI at 15 inches during trip event. Spike around 703 mV. Still enough
to cause the GFCI to trip.
Background
Eaton has been doing similar work and found that isolating the hot and neutral lines
from the field was enough to control, and stop, the tripping events. Effectively
showing the tripping was not being caused by direct coupling with the transformers.
Figure 4. GFCI connected to a UPS during a trip event. Spiking around 1.60 V
These graphs demonstrate that given the 15 inch constraint of the
construction power poles the problem cannot be solved by physical separation
of the Smart Meter from the GFCIs.
We thank David Wetz for technical support. Simon Donahue
was the masters student whom worked with me on this
project. He provided much of the technical knowledge and
instruction
NSF Grant EEC-1156801
For further information
Please contact [email protected]