Transient Overvoltage Surge Suppression Overview for ITS Applications Paul Saa BSEE, MSISE, MBA Engineering Sales Manager Engineering Labs Quality Manager Advanced Protection Technologies (800)

Copyright APT 2012 – (800) 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% In outdoor environment, this ratio probably reverses

Copyright APT 2012 – (800) 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 MOV symbol

Copyright APT 2012 – (800) 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) Safety, UL & NEC SPD TVSS Surge Arresters TVSS/SPDs arguably the most regulated electrical product category in the 2000’s UL (Aug 1998) 2002 NEC Article NEC Article 285 UL (Feb 2007) 2008 NEC Article 285 UL (Sept 2009) 2011 NEC Article 285 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) Typical Sequence of SPD Failure – Safety & UL Load MOV/SPD If extremely rapid overheat, and/or faster than OCP can clear – can rupture If overheats ‘slowly’ – can catch fire 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

Copyright APT 2012 – (800) 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 UL 1449 Safety Testing Fault Current Levels Individual tests at 0.5A, 2.5A, 5A, 10A, 100A, 500A, 1000A & SCCR Trying to prevent these types of failures Techno-babble For Engineers, By Engineers

Copyright APT 2012 – (800) 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) 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 SPD Application

Copyright APT 2012 – (800) Surge Environment based on Location within electrical distribution system IEEE C Categories & Surge Environment Trans Meter Svc. Disc. Panel 10m (30feet) Cat C – 10kA Cat B – 3kA Cat A – 0.5kA IEEE Categories

Copyright APT 2012 – (800) Lightning strike to earth-grounded pole raises Ground Potential, also causing Transient Overvoltage Surge or Transient Overvoltage Transient overvoltages are not limited to utility or power conductors An Instantaneous Ground Potential Change is Also a Surge Surges in DOT Environments On Power Conductor On Ground Conductor

Copyright APT 2012 – (800) Amber Alert 12 Trans Meter Svc. Disc. Cabinet 10m (30feet) Cat C – 10kA Cat A – 0.5kA 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 (enter for animation 1) Cat B – 3kA 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 2) ??Cat C – 10kA?? Cat B – 3kA? Takeaways: Multiple Threats Plenty of Unknowns! Need Additional Modes of Protection Pole GroundPower System Ground How Much to Ground? How Much to Power Lines?

Copyright APT 2012 – (800) 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) A-N Phase A N Ground Earthed Transformer Impedance SPD 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) 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

Copyright APT 2012 – (800) Phase A Neutral Ground SPD N-GC-G A-G 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) 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.) Different Modes of Protection: Downstream or Outdoor (Split Phase)

Copyright APT 2012 – (800) 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) Specification Suggestions: UL 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) Advanced Protection Technologies (800) 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