Transient Overvoltage Surge
Suppression Overview for ITS
Applications
Paul Saa BSEE, MSISE, MBA
Engineering Sales Manager
Engineering Labs Quality Manager
Advanced Protection Technologies
(800) 237-4567
What Causes Surges/Transients?
• Lightning
• Switching:
– Load Switching – (Motors, Large
Reactive Loads)
– Source Switching (Smart Grid, Gensets)
•
•
•
•
•
Arcing/Flashing
Animals
Unexpected
Internally generated surges: ≈70%
Externally generated surges: ≈30%
Copyright APT 2012 – (800) 237-4567
In outdoor environment, this
ratio probably reverses
2
MOV - Metal Oxide Varistor
•
•
•
•
•
Varistor - variable resistor
Semiconductor; generally zinc oxide
Connects parallel to load (not series)
Thickness determines clamping voltage
Diameter determines current capacity
Copyright APT 2012 – (800) 237-4567
MOV symbol
SPD Operation
Load 1
Load 2
Load 3
MOV/SPD tries to:
1.) Send surge away (to ground)
2.) Acts as a momentary ‘short circuit’
‘short circuit’ ≈ voltage equalization ≈ no overvoltage ≈ protected load
Copyright APT 2012 – (800) 237-4567
4
Safety, UL 1449-3 & NEC
TVSS/SPDs 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
Copyright APT 2012 – (800) 237-4567
Typical Sequence of SPD Failure – Safety & UL
System-level Sustained Overvoltage – Not From Surges!
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
Copyright APT 2012 – (800) 237-4567
If overheats
‘slowly’ – can
catch fire
UL 1449 Safety Testing
• MOVs/SPDs have multiple failure scenarios
– UL tests at L-L voltage (i.e., 208V, 480V, 600V, etc.)
– UL limits fault current (i.e., 0.5A-200kA)
– UL tests one mode at a time
Trying to prevent these
types of failures
Individual tests at 0.5A,
2.5A, 5A, 10A, 100A,
500A, 1000A & SCCR
Copyright APT 2012 – (800) 237-4567
Fault Current Levels
7
Noise Filtering
•
•
•
•
•
•
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 (more are underground now)
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 the caps are
very large
– Series connected inductive filters – Significant issues:
• Load must go through them, prone to overheating, UL regulations became
very tough, many series SPDs are no longer UL listed and pose additional
threats beyond the filter
• 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!)
Copyright APT 2012 – (800) 237-4567
8
SPD Application
Surge Environment in Traditional
Structures is Well Defined by ANSI/IEEE
& ANSI/UL Standards
DOT & Outdoor Applications Appear to
Differ Based on Increased Likelihood of
Lightning Activity and Ground
Reference Issues
Copyright APT 2012 – (800) 237-4567
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
Copyright APT 2012 – (800) 237-4567
Cat A – 0.5kA
Panel
10m (30feet)
IEEE
Categories
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
Copyright APT 2012 – (800) 237-4567
Surge or
Transient
Overvoltage
On Ground
Conductor
11
Traffic Applications 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
Copyright APT 2012 – (800) 237-4567
??Cat C – 10kA??
Pole Ground
12
Modes of Protection
• Different ways to configure
protection within SPDs
• MOVs equalize potential
across either side of MOV
• Various ways to connect MOVs
–
–
–
–
L-N
L-G
N-G
L-L
Copyright APT 2012 – (800) 237-4567
13
Different Modes of Protection: Service
Scenario Assumes (Split Phase):
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
Copyright APT 2012 – (800) 237-4567
Could have L-G protection too, which is
functionally the same as L-N at a service entrance
because N and G are bonded together
Different Modes of Protection:
Downstream or Outdoor (Split Phase)
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
A service entrance style SPD with L-N only has almost no chance of protecting.
Modes of Protection Are Important!! (Gee, I had an SPD, but still lost my equipment.)
Copyright APT 2012 – (800) 237-4567
Consider:
There is ongoing perception that ‘downstream’ applications can
get by with modest SPDs on the presumption that the surge
environment is less hostile.
At Service Entrance: Traditional surge protection makes sense.
Because electrical system references ground at the service, L-N
protection is generally adequate (and is effectively the same as
L-G protection).
Downstream: Load is subject to reduced amplitude surges from
service. I.e., L-N protection. In addition, depending on height
and situation, load could be More vulnerable due to induced
lightning, which is poised to enter or couple via ground or
grounded enclosure. Thus, protecting G-L & G-N makes sense.
(This is more commonly referred to as L-G and N-G.)
Unfortunate reality is that ‘exposed’ downstream applications
probably need a more feature-laden SPD.
Copyright APT 2012 – (800) 237-4567
Specification Suggestions:
UL 1449-3 Listed (for ease of review)
UL 20kA I-n rating (Used by UL 96A – biggest, toughest rating)
UL VPRs of 700V or less for L-N, L-G & N-G (low clamps)
Minimum MOV size of 32mm round (more robust MOVs)
Diagnostic Monitoring for Every MOV
UL declared MCOV of 150V (prevents game-playing & early failure)
No Gas Tubes or Spark Gaps (prevents high clamps)
SCCR =>50kA (safety)
Thermal Disconnectors required for all MOVs (safety)
50kA per mode, 100kA per phase (generally adequate)
Copyright APT 2012 – (800) 237-4567
Thank you for your time
APT offers no-cost detailed training for FL PE and/or EC credits.
We also welcome tours of our facilities & labs in Clearwater
Advanced Protection Technologies
(800) 237-4567
Copyright APT 2012 – (800) 237-4567