Advanced Protection Technologies
ITS Heartland: Overview of
Transient Overvoltage Surge
Protection in ITS/Traffic Systems
Performed by: Lou Farquhar, PE, CEM, GBE
VP Engineering Services
(800) 237-4567
Agenda - Surge Suppression
1.
2.
3.
4.
5.
History
Basics
Applying/Installing AC SPDs
Applying/Installing
Comm/Data/Coax SPDs
Grounding & Bonding
2
What Is a Surge/Transient?
• High amplitude, short duration overvoltage
• Can be positive or negative polarity
• Can be from energized or grounded conductor
Transient Overvoltage –
Can be thousands of volts
Millionths of second
3
Evolution of Surge in the
Traffic Industry
• 15 – 20 years ago, surge industry ‘sold’ traffic on line
filtering and better grounding
– Line filtering got too much credit as being part of the fix
– Other industries figured out filtering has plenty of vapor
– ‘Outside’ manufacturers faced too hard and upstream battle to
undo the hooey
– Incumbent manufacturers are happy to keep traffic in the dark
• Consequently, traffic surge suppression is about 5 – 10
years behind
4
What is Noise Filtering in SPDs?
•
•
•
•
•
•
Caution: EMI/RFI Filtering was oversold many years ago using scare tactics,
hocus-pocus & games with oscilloscopes
Utility feeds simply do not have that much noise
Most EMI/RFI noise is self-generated
Noise is relatively low amplitude and tends to dissipate
Higher frequency noise goes through the air bypassing
copper wire & SPDs
Multiple ways of filtering
– Parallel connected capacitive filters – no major side effects unless large caps
– Series connected inductive filters – Significant issues:
• Load must go through them, prone to overheating, UL regulations now
tougher, many series SPDs are no longer UL listed and pose safety
hazards
• During ground strikes, energy can attempt to leave via the service
entrance, back towards the utility. The same physics that prevents noise
from entering, prevents surge energy from leaving. The filter traps energy
in your equipment! These have fallen out of favor in other industries.
Sinewave tracking is a fancy name for modulating high frequency noise
on a 60 Hz carrier. (This is nothing new and is how radio works!)
5
SPD Operation
Load 5
Load 1
Load 2
Load 3
Load 4
MOV/SPD Acts as a momentary ‘short circuit’
‘short circuit’ ≈ no overvoltage ≈ protected load
6
Surge Current vs. Fault Current
Surge Current – Normal Operation - Momentary
MOV/SPD
Load
Fault Current – Drawn by Failed SPD - Continuous
MOV/SPD
Load
SPD fails short-circuited
and draws Fault Current
to be continued…
7
Can Anything Go Wrong?
(Good thing that will never happen to me… )
8
Typical Sequence of SPD Failure
System level Sustained Overvoltage – TOV
Voltage exceeds MCOV – as little as 2-3 cycles
MOV attempts to protect
MOV fails towards short circuit
Follow-on/fault current causes MOV to catastrophically overheat
MOV/SPD
Load
If extremely rapid
overheat, and/or faster
than OCP can clear –
can rupture
If overheats
‘slowly’ – can
catch fire
9
SPD Overcurrent Protection Flaws
Cannot assume MOV to ‘short’ to
low impedance, and draw enough
fault current to open fuse:
1.) OCP needs low enough
rating to open, and
2.) OCP needs to open
before MOV ruptures

MOV(s) can
fail short here
Then, MOV(s) can
overheat & rupture
before OCP clears

 
time
Suppose Fuse clears here
(after a few cycles)
10
Below Rating of Overcurrent Protection
Low Current Faults are Common Type of SPD Failure
(Example: 30A fuse does not clear 25A fault)
Why Thermal Protection
is Important
Line
X
Overcurrent
Protection
1.) Sustained
overvoltage
2.) MOVs try to
control
overvoltage
3.) MOVs overheat,
fail, permanently
reduce impedance
MOVs
Neutral
or
Ground
4.) MOVs draws fault
current, OCP does
NOT open
Aftermarket SPD/panel conversion
11
SPD Safety, UL 1449-3 & NEC
SPDs/TVSS arguably the most regulated electrical
product category in the 2000’s
•
•
•
•
•
•
•
UL 1449-2 (Aug 1998)
2002 NEC Article 285
2005 NEC Article 285
UL 1449-2.5 (Feb 2007)
2008 NEC Article 285
UL 1449-3 (Sept 2009)
2011 NEC Article 285
SPD
Surge
Arresters
TVSS
Safety evolved quickly as the body of knowledge grew
• UL 1449 Plays Huge Role in Surge Industry
• Much More Than a Safety Standard
• Perform Multiple Performance Tests
• UL uses for internal UL 96A Lightning Protection Master Label Eval
Appears that Traffic/DOT/ITS were left out of the loop
12
AC Power Solution: TPMOV
• TPMOV Optimizes Thermal
Protection creating Overcurrent
Protection
• TPMOVs essentially have
integral fusing
• Each MOV is individually fused
• Eliminates tolerances between
fuses, MOVs, and thermal
disconnectors
• TAC switch allows for individual
monitoring of each MOV
13
III.) Applying/Installing AC SPDs
•
•
•
•
ITS/DOT Surge Environment
Modes of Protection
Inductance and Surges
Installing AC SPDs
14
IEEE C62.41.2-2002
Categories & Surge Environment
Surge Environment based on Location within electrical
distribution system
Cat C – 10kA
Cat B – 3kA
Meter
Svc.
Disc.
Trans
Cat A – 0.5kA
Panel
10m (30feet)
IEEE
Categories
SPD & Inductive Effects
L (inductance)
limits
propagation of
lightning (good)
Load 5
Load 1
L (inductance) causes voltage
drop across conductor (bad –
need short leads)
Load 2
Load 3
Load 4
MOV/SPD Acts as a
momentary ‘short circuit’
‘short circuit’ ≈ no overvoltage
≈ protected load
16
Surges in DOT Environments
Transient overvoltages are not limited to utility or power
conductors
An Instantaneous Ground Potential Change is Also a
Surge
Lightning strike to earth-grounded pole
raises Ground Potential, also causing
Transient Overvoltage
On Power
Conductor
Surge or
Transient
Overvoltage
On Ground
Conductor
17
Traffic Applications Are Different Due to Multiple Threats:
Surge To Service Entrance:
1.) Surge Hits Power/Line
2.) Traditional Building?
3.) Inductance Limits Propagation
4.) IEEE C62.41 Categories C, B & A
Surge Near Load:
1.) Surge Hits Ground/Grounded Equip.
2.) Elevated NON-Traditional Structure
3.) Inductance Limits Propagation
4.) IEEE C62.41 Categories C, B & A?
(enter for animation 1)
(enter for animation 2)
Takeaways:
• Multiple Threats
• Plenty of Unknowns!
• Need Additional
Modes of Protection
Meter
Svc.
Cat C – 10kA
Disc.
Amber Alert
How Much to
Ground?
Cabinet
Cat 10m
B – (30feet)
3kA
Cat A – 0.5kA
How Much to
Power Lines?
Trans
Cat B – 3kA?
Power System Ground
??Cat C – 10kA??
Pole Ground
18
Different Modes of Protection: Service
Scenario Assumes:
1.) Surge Is From Outside
2.) SPD near Service Entrance or Separately Derived System
3.) Propagation, Return Paths and Ground are Ideal
4.) SPD chops off surge and sends it to Ground
(Enter for Animation)
Phase A
SPD
Transformer
Impedance
N
A-N
Ground
Earthed
A-G
19
Different Modes of Protection:
Downstream or Outdoor
1.) Surge Is From Outside to Ground, or Grounded Enclosure, or Pole
2.) Surge might go towards Ground, but inductance will limit
propagation. And/Or, there will be Ground Potential Rise. This
will have the effect of ‘trapping’ the surge near the load
3.) SPD will equalize potentials among Phases, Neutral and Ground
(Enter for Animation)
SPD
A-G
Phase A
Neutral
Ground
N-G
C-G
Assumes L-N, L-G and N-G protection
SPDs without these modes of protection will not be able to protect as
well. (Gee, I had a L-N DIN rail SPD, but still lost my equipment.)
20
SPD Connector Leads
• Need short lead lengths!
• NEC 285.12: “The conductors used to connect the SPD
(surge arrester or TVSS) to the line or bus and to
ground shall not be any longer than necessary and
shall avoid unnecessary bends”
• Industry typically states: Each foot of conductor adds
100 - 170V to clamping voltage
• No Sharp bends or kinks
• No Wire Nuts!
• Right Hand Rule – can cancel
inductive effects by bundling, tiewrapping conductors together
21
IV.) Applying/Installing
Comm/Data/Coax SPDs
•
•
•
•
•
•
•
Application
UL 497
Common Configurations
Installing Comm/Data SPDs
Coax SPDs
Cascading
Coax: Avoiding Ground Loops
22
Application of Comm, Data & Coax
•
In low voltage applications, other
SPD building block technologies
work better than MOVs
– MOVs may degrade signal quality
due to higher capacitance
•
SPDs at both ends of the signal
make sense
•
In coax applications, the pin is
protected by the shield
– Excess emphasis on protecting
the pin is misguided
•
IEEE research shows 4x more
surge current propagates on the
shield than the pin (more too
come)
23
Comm, Data & Coax SPDs
Common Configurations:
X1
Series Connected:
Parallel Connected:
Inductor, Resistor, Coaxial GDT, etc.
GDT, MOV, SAD, etc.
X1
V
Y1
L (Inductance)
Surge Operation:
High Frequency
Impedance such as
Normal Operation:
Inductance
X2
L
Unprotected
Side
GDT
SAD
Protected
Side
Load
Common (Ground)
24
Installing Comm/Data SPDs
• As a generalization: if the distance between
signal ends is greater than 15 feet, an SPD
should be installed at both ends of the cable
– Prevents surges induced into the middle of the
conductor from damaging equipment at either end
25
Concept of Cascade Protection
• UL 497 Listing Categories are often misunderstood
– Primary Protectors: intended more for life safety
protection from power line crosses & lightning, may not
clamp low enough to protect sensitive electronics
– Secondary Protectors: offer better clamping for
sensitive electronics
• Single SPDs having both properties exist
26
Coax SPDs: Avoiding Ground Loops
• Coax shields are grounded at their ‘head-end’, the
shield is not supposed to be grounded downstream
– Reason: grounded at multiple locations equals different
ground potentials and currents will loop through the shield
as ground potentials attempt to equalize
• SPDs with ground isolation is required with separate
pin-shield and shield-ground protection
27
V.) Grounding & Bonding
• Inductive Effects of Earthing/Grounding
• Bonding Systems Together
• Isolated Grounds
28
Grounding, Bonding and SPDs
•
•
•
•
Earthing/Grounding - Inductive effects are
substantial. New research is emerging.
Most ground testing is at low frequency, while
surges are high frequency
Research suggests only first 30m of ground
grid are effective at surge frequencies
(inductive affects)
Are counterpoise systems that do not
complete a loop better? (loop may be more vulnerable to
induced effects -- still emerging science)
29
Grounding, Bonding and SPDs
Examples Showing Affects of Inductance on Grounding
60Hz Grounding
Fault Current
shares approx
equally
60 Hz Grounding
During Surge
Revised 60 Hz Grounding
During Surge
Surge Current
affected by
inductance; Does
not share well
Surge Current
Less affected by
inductance
Geometry
affects sharing
Research suggesting that only first
30m of ground conductor is effective
30
Grounding/Bonding SPDs
• Bonding different systems together ensures
that all systems have the same reference to
earth ground: Common Bonding Network
– Different references to ground can
develop damaging voltages between
the systems.
– Bond different systems together.
– Be aware of inductive & di/dt effects
that tend to “unbond” bondedtogether systems
– No coils or loops in wire
31
Grounding/Bonding SPDs
• Isolated Ground Warning
– Tends to have different meanings
– Are commonly not installed as intended
or engineered
– SPDs try to ‘equalize’ voltage potential. Isolated
grounds purposely segregate. This can cause
damaging voltages.
– Reworded: SPDs with a
dedicated isolated ground
is not protecting the
‘other’ ground.
X
32
Thank you for your time
33