This document discusses overvoltage protection for data concentrators used in smart grid applications. It describes the different network levels in smart grids - core, distribution and access networks. For the access network, which provides last mile connectivity between hardware and smart meters, technologies used include power line communication and various wireless standards. Outdoor data concentrator hardware is susceptible to lightning strikes and surges. The document then discusses lightning protection zones and the electrical parameters for surge protection devices used to protect communications ports and power inputs for such outdoor hardware from transient overvoltages.

1. The following paper was presented at the 2011 IEEE Innovative Smart
Grid Conference in Anaheim, CA January 18, 2011.
Overvoltage Protection of Data Concentrators used in
Smart Grid Applications
Transient Protection for Pole-Mounted Data Concentrator Hardware
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2. Overvoltage Protection of Data Concentrators used in
Smart Grid Applications
Transient Protection for Pole-Mounted Data Concentrator Hardware
James Schroeder, BSEE, MBA, PE, IEEE Senior
Member
Schroeder Consulting Services
249 Lyndel Dr.
Palmyra, PA 17078
Edward Doherty, BSEE, MBA, IEEE Member
Mike Nager, BSEE, Senior Member IEEE
Phoenix Contact
P.O. Box 4100
Harrisburg, PA 17111
Abstract—“Smart Grid” is a term used to define several phases of
activities within the utility industry: from providing
communications, monitoring and control capabilities for the
energy infrastructure at the macro scale to controlling the energy
usage of home appliances at the micro scale. This paper will
address the segment of the Smart Grid activity that distributes
data during last-mile connectivity between the data concentrator
and the end user (home) level. Specifically, this paper will discuss
the products and methodology required to protect outdoor link
layer hardware from lightning strikes and current surges.
Keywords-lightning protection, Smart Grid communication
networks, transient overvoltages
I. INTRODUCTION
Data flow within the Smart Grid network takes place at
three levels of connectivity: the core, distribution, and access
networks [1]. Below is a summary of each network’s function
and the technologies used for that function:
A. Core Network
The core network provides connectivity between
substations and utilities head offices. Technologies used for
core network connectivity include:
• Wired technology – fiber, BPL (broadband over power
lines)
• Wireless technologies – WiMAX, license-exempt
broadband wireless
B. Distribution Network
The distribution network provides broadband connectivity
between data collected by Smart Grid link layer hardware and
distribution devices (e.g., monitors, sensors, SCADA systems)
located on the grid and their related databases and analytical
servers, which are located at headquarters. Technologies used
for distribution network implementation include:
• Wired technology – fiber, BPL (broadband over power
lines)
• Wireless technology – WiMAX, GSM, license-
exempt broadband wireless
C. Access Network
The access network provides last-mile connectivity
between Smart Grid link layer hardware (routers, data hubs,
etc.) and smart meters located on the edge of the Smart Grid
(at homes, offices, and municipal facilities). Technologies
used for access network implementation include:
• Wired technology – PLC (power line communication)
• Wireless technologies – ZigBee (IEEE 802.15.4), Wi-
Fi (IEEE 802.11), WiMAX ( IEEE 802.16), GSM,
license-exempt broadband wireless.
Several types of Smart Grid link layer hardware are
available in the marketplace. They include:
• Silver Spring Network’s eBridge and Access Points
• SmartSync’s Grid Router
• Cisco’s Integrated Services Routers
• Alvarion’s BreezeMAX PRO Outdoor units
• Trilliant’s SecureMesh Collector
These examples of link layer hardware share several
characteristics. They can all be used in multiple functions
within the network, including neighborhood area networks
(NAN), business area networks (BAN) and home area
networks (HAN). Additionally, they all require
communications and power inputs to function and use pole-
mounted hardware. All link layer hardware mounted outdoors
is susceptible to lightning strikes and power surges.
II. DISCUSSION
As mentioned above, link layer hardware requires a power
input cable and a communications cable (antenna). This power
input cable typically requires 120 V AC or 240 V AC. The
communications cable port will operate in the frequency
ranges specified by the communications standard being used:
typically 915 MHz, 1.9, 2.15, or 2.4 GHz for wireless
technologies referenced above. Surge protection devices
(SPDs) are available to protect both the power and
communication lines of the data link layer hardware.

3. Fig. 1 Speed versus energy characteristics for surge protection devices
A. Basic Principles of Surge Protection
SPDs can be characterized as high-speed, voltage-triggered
switches that close during an overvoltage event. This action
diverts energy away from the protected devices and to
electrical ground, while limiting potentially h
armful voltage differences between the lines being
protected. Effective operation depends on a low impedance
ground path.
The four major types of SPDs are the suppressor diode
(also known as silicon avalanche diode or SAD), metal oxide
varistor (MOV), gas tube (gas discharge tube or GDT), and the
spark gap. For a given application, they can be used either
alone or in combination to provide the necessary protection
and response time. Fig. 1 shows component characteristics in
terms of energy handling capability versus speed of response.
As indicated in Fig. 1, the energy versus response spectrum
is bounded by the fast response, low energy capabilities of the
suppressor diode on one end of the spectrum to the slow
response, high energy characteristics of the spark gap at the
other end of the spectrum.
In order to evaluate the protection of pole-mounted
hardware, we will discuss lightning strike information and the
concepts associated with Lightning Protection Zones (LPZs).
B. Lightning Strike Information
It has been documented that the current magnitude
associated with lightning strikes can vary from approximately
2.0 kA to 200.0 kA or higher. This magnitude variation is a
function of several factors beyond the scope of this paper.
Various agencies have done studies on the frequency of
lightning strikes that occur worldwide and on a country-by-
country basis.
Fig. 2 – Source Vaisala-GAI [2]
The map in Fig. 2 documents the findings from the
National Lightning Detection Network. It shows the cloud-to-
ground strikes over a ten-year period within the United States.
Note the increased susceptibility to lightning strikes in the
southeastern and Midwestern portion of the country, which
can experience more than 14 flashes per square kilometer per
year. Current magnitude and frequency of lightning strikes are
two main parameters to consider when designing a surge
protection device system. Other factors include potential
unplanned maintenance cost, replacement equipment cost and
availability, as well as system downtime consequences.
C. Lightning Protection Zone Definitions
A primary tool used in the surge protection device industry
for the quantification of SPD requirements for pole-mounted
link layer hardware is IEC 62305-4. This standard defines
protection zones for electrical and electronic systems against
lightning. The protection zones are established using the
“rolling sphere” concept as shown in Figure 3. [3]
Lightning Protection Zones (LPZs) for pole-mounted link
layer hardware typically include zones LPZ 0B and LPZ 1
shown in Table I.
Fig. 3 – Lightning Protection Zone applied to a pole-mounted hardware
TABLE I
DEFINITION OF LIGHTNING PROTECTION ZONES (LPZ)
Zone Definition
LPZ 0A Zone where a direct lightning flash and electromagnetic
hit is possible. The internal equipment may be subjected
to full lightning surge current. Lightning current test
pulse of first stroke 10/350 µs.
LPZ 0B Zone protected against direct hit, but unattenuated
electromagnetic field is present. This zone is determined
by an external lightning protection system consisting of
air termination, down conductor and earth termination
system. Current test pulse of first stroke 10/350 µs.
LPZ 1 Zone where a direct hit is not possible and the currents in
conductive components are lower than in LPZ 0A and
LPZ 0B. Surge current is limited by current sharing and
by SPDs at the boundary. Spatial shielding may attenuate
the lightning electromagnetic field.
LPZ 2 Zone where the surge current may be further limited by
additional SPDs at the boundary and current sharing.
Additional spatial shielding may be use to provide
additional attenuation to the lightning electromagnetic
field.

4. TABLE II
ELECTRICAL PARAMETERS FOR SPD USED IN COMMUNICATIONS EQUIPMENT
AT LPZ BOUNDARIES LPZ 0B - 1
Parameter Symbol Rating
Maximum Continuous Operating Voltage UC 60 V
Nominal Operating Current IN ≤ 1.5 A
Nominal Surge Current (8/20µs) line-line I SN 100 A
Nominal Surge Current (8/20µs) line-PE I SNT 2 KA/sig. pr.
Total Nominal Discharge Current
(8/20µs) line-line
I SNT 10 KA
Voltage protection level, line-line UP 9 V
Voltage protection level, line-PE UP 700 V
Voltage protection level line-line @
1KV/µs rate of rise
UP ≤85 V
Voltage protection level line-PE @
1KV/µs rate of rise
UP ≤700 V
Insertion loss @ 250 MHz ąE ≤2 db
Capacitance line-line C 12 pf @ 1
MHz
Capacitance Line-PE C 2 pf @ 1 MHz
Data Transmission Speed GBit ≤10 GBIT/s
Characteristic Impedance Zo 50 Ω
Category tested in accordance with IEC
61643-21:2000
C2
D. SPD Parameter Definitions
Key SPD parameters include surge current ratings,
voltage protection levels, and speed of operation for SPD
devices.
IEC standard 61643-21:2000 established specific electrical
parameters, performance requirements and testing methods for
SPDs connected to communications equipment. Table II shows
the electrical parameters for a typical SPD used in a
communications equipment application. The table also defines
parameters.
III. PRODUCT SELECTION CRITERIA DATA LINK LAYER
HARDWARE
A. Communications Port
Based on the definition of the LPZs and SPD performance
parameters discussed above, Table III shows typical rating for
SPDs used to protect ZigBee/Wi-Fi and GSM network
applications [5]. ZigBee and Wi-Fi communication ports
usually use an RJ45 connector with Category 5 or 6 cable,
while GSM modems typically use a coax connector and cable.
Where:
Uc = maximum voltage (d.c. or r.m.s. ), which may be continuously applied to
SPD terminals without causing any degradation in the transmission
characteristics of the SPD.
Up = parameter that characterizes the performance of the SPD in limiting the
voltage across its terminals. This value is greater than the highest measured
value of impulse-limiting voltage and is specified by the manufacturer.
In = Nominal current handling capability under normal operating conditions.
Is = The SPD must handle 100% of this surge current ( 8/20µS waveform)
without a significant change in protection level
8/20 µS Waveform = Surge current impulse waveform used to evaluate
nominal surge current ratings according to IEC 60060-1. Shown in Figure 4.
i
î
i
î
t
µs
t
µs
88
2020
1.01.0
0.90.9
0.50.5
0.10.1
0.0
Fig. 4 Surge current impulse waveform, 8/20 µS
TABLE III
ELECTRICAL PARAMETERS FOR SPDS USED IN DATA LINK LAYER HARDWARE
AT LPZ BOUNDARIES LPZ OB – 1 (IEC 61643-21:2000)
Parameter Symbol Rating ZigBee and
Wi-Fi
Networks
GSM
Networks
Maximum
Continuous
Operating Voltage
UC 60 V 60 V 10V
Nominal Operating
Current
IN ≤ 1.5 A ≤ 1.5 A 5.0 A
Nominal Surge
Current (8/20µs)
line-line
I SN 100 A 100 A 20 KA
Nominal Surge
Current (8/20µs)
line-PE
I SNT 2KA/sig.
pr.
2KA/sig. pr. 20 KA
Total Nominal
Discharge Current
(8/20µs) line-line
I SNT 10 KA 10 KA NA
Voltage protection
level, line-line
UP 9 V 9 V NA
Voltage protection
level, line-PE
UP 700 V 700 V ≤ 20V
Voltage protection
level line-line @
1KV/µs rate of rise
UP ≤85 V ≤85 V NA
Voltage protection
level line-PE @
1KV/µs rate of rise
UP ≤700 V ≤700 V ≤10 V
Insertion loss @ 250
MHz
ąE ≤2 db ≤1 db 0.2 dB
(1.7GHz
to
2.3GHz)
Capacitance line-line C 12 pf @ 1
MHz
Typ. 12 pf
@ 1 MHz
NA
Capacitance Line-PE C 2 pf @ 1
MHz
Typ. 2 pf @
1 MHz
<2 pf @ 1
MHz
Data Transmission
Speed
GBit ≤10
GBIT/s
≤10 GBIT/s ≥10
GBIT/s
Characteristic
Impedance
Zo 50 Ω ≥50 Ω 50 Ω
Category tested in
accordance with IEC
61643-21:2000
C2 C2

5. TABLE IV
ELECTRICAL PARAMETERS FOR TYPICAL TYPE 2 SPD USED IN POWER CABLE
PORT
Parameters Power
Nominal Voltage Un 120 V AC
Arrester rated voltage Uc 150 V AC/ 200 V
DC
Nominal frequency fn 50/60 Hz
Discharge current to PE at Uc <0.45mA
Max. discharge surge current Imax (8/20) µs 40 kA
Nominal discharge surge current In (8/20) µs 20 kA
Lightning test current (10/350) µs, peak value Iimp 3 kA
Response time <24 ns
B. Power Input Port
The power cable to the link layer hardware would typically
use voltages in the 110-120 V AC range or 220 – 240 V AC
range. A typical product selection for this application would
be a surge protection type 2 SPD that uses a high-capacity
varistor, provides thermal fusing and a visual fault warning. It
should also be noted that Type 2 SPDs require a backup fuse,
typically with a maximum rating of 125 A. Table IV shows
the performance characteristics of a typical type 2 SPD [6].
C. Device-Mounting Technique
Many commercially available products, including SPDs,
are designed for mounting on a DIN rail inside the enclosure.
The name DIN rail is based on the Deutsches Institut für
Normung (DIN) (translation: German Institute for
Standardization), which defines the dimensions and tolerances
of the rail. This allows manufacturers to design mounting
methods for products destined for assembly onto the rail [7].
Manufacturers that use DIN mounting in their link layer
hardware find it easy to add components or customize their
designs by using other devices that mount on the DIN rail,
including terminal blocks and power distribution blocks, fuses,
relays, and power supplies.
D. Hardware Grounding Technique
In addition to providing mechanical support, the DIN rail
ideally serves as a single-point ground for SPDs and other
devices used to distribute power and signals within the
enclosure. The grounding methodology of surge protection
devices is very important to ensure proper functioning during
an overvoltage condition[8]. Surge protection devices should
be bonded to the enclosure and using either a short (i.e., low
impedance), high ampacity wire or connecting directly to a
grounded DIN rail. This ensures that the surge current is safely
and effectively routed to ground without creating voltage
differentials between components within the link layer
hardware.
E. Environmental Specifications
The ambient operating temperature is an important
environmental parameter to consider when selecting the
components, including SPDs, that will be placed into link
layer hardware enclosures. External locations must withstand
more extreme temperatures on both ends of the temperature
spectrum, so -40ºC to + 80ºC is commonly specified.
IV. CONCLUSION
Smart Grid is a term that is used to define several phases of
activities within the utility industry: from providing
communications, monitoring and control capabilities for the
energy infrastructure at the macro scale to controlling the
energy usage of home appliances at the micro scale. This
paper has addressed the segment of the Smart Grid that
distributes data during last-mile connectivity from the link
layer hardware to the home. The paper has discussed the
application of surge protection devices in protecting outdoor
link layer hardware from lightning strikes and current surges.
The paper has reviewed the definition of Lightning Protection
Zones, discussed surge protection device performance
parameter definitions, and provided selection criteria for
SPDs. In addition, typical products have been chosen as a
function of the communication network being used for both
the network and power cable inputs. Using the decision
criteria and methodologies outlined in this paper will ensure
the protection of outdoor data link layer hardware from
lightning strikes and other overvoltages.
REFERENCES
[1] Alvarion, Inc., White Paper 215135 Rev A. “Optimizing smart power
grids with WiMAX and broadband wireless connectivity solutions,”
2009. www.alvarion.com
[2] Lightning data provided by U.S. National Lightning Dection Network,
National Weather Service
www.weather.gov/om/lightning/stats/08_Vaisala_NLDN_Poster.pdf
[3] International Electrotechnical Commission, International Standard
62305-4, “Protection against lightning – Part 4: Electrical and electroinc
sysems within structures.”
[4] IEC Standard 61632-21:2000, “Low voltage surge protective devices –
Part 21: surge protective devices connected to telecommunications and
signaling networks – performance requirements and testing methods.”
[5] Phoenix Contact, specifications for the ZigBee/Wi-Fi applications for
model DT-LAN-CAT.6+ and for GSM applications Phoenix Contact
model CN-LAMBDA/4-2.0-BB, 2010.
[6] Phoenix Contact, specifications for Type 2 SPD values from Phoenix
Contact model VAL-MS 120 ST, 2010. www.phoenixcontact.com
[7] A. Offner, “DIN rail in the electrical control cabinet and junction box,”
IEEE SC2 Committee Presentation, Tucson AZ: November 2008.
[8] M. Nager, “Understanding Surge Suppression,” Plant Engineering.
November 2004, pp. 39-43.