ITS Heartland: Overview of Transient Overvoltage Surge Protection in ITS/Traffic Systems

Transcription

1 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)

2 Agenda - Surge Suppression 1. History 2. Basics 3. Applying/Installing AC SPDs 4. Applying/Installing Comm/Data/Coax SPDs 5. Grounding & Bonding 2

3 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

4 Evolution of Surge in the Traffic Industry 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

5 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

6 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

7 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

8 Can Anything Go Wrong? (Good thing that will never happen to me ) 8

9 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

10 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

11 Below Rating of Overcurrent Protection Low Current Faults are Common Type of SPD Failure X Overcurrent Protection (Example: 30A fuse does not clear 25A fault) Why Thermal Protection is Important Line 1.) Sustained overvoltage 2.) MOVs try to control overvoltage MOVs 3.) MOVs overheat, fail, permanently reduce impedance Neutral or Ground 4.) MOVs draws fault current, OCP does NOT open Aftermarket SPD/panel conversion 11

12 SPD Safety, UL & NEC SPDs/TVSS 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 Surge Arresters SPD 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

13 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

14 III.) Applying/Installing AC SPDs ITS/DOT Surge Environment Modes of Protection Inductance and Surges Installing AC SPDs 14

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

16 SPD & Inductive Effects L (inductance) limits propagation of lightning (good) Load 5 Load 1 Load 2 Load 3 Load 4 L (inductance) causes voltage drop across conductor (bad need short leads) MOV/SPD Acts as a momentary short circuit short circuit no overvoltage protected load 16

17 Surges in DOT Environments On Power Conductor Transient overvoltages are not limited to utility or power conductors An Instantaneous Ground Potential Change is Also a Surge Surge or Transient Overvoltage Lightning strike to earth-grounded pole raises Ground Potential, also causing Transient Overvoltage On Ground Conductor 17

18 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 (enter for animation 1) Trans Takeaways: Multiple Threats Plenty of Unknowns! Need Additional Modes of Protection Meter Cat C 10kA Svc. Disc. Cabinet 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) 10m (30feet) Amber Alert Cat A 0.5kA How Much to Ground? How Much to Power Lines? Power System Ground Cat B 3kA???Cat C 10kA?? Pole Ground 18

19 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

20 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) Phase A SPD A-G Neutral Ground Assumes L-N, L-G and N-G protection N-G C-G 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

21 SPD Connector Leads Need short lead lengths! NEC : 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 V to clamping voltage No Sharp bends or kinks No Wire Nuts! Right Hand Rule can cancel inductive effects by bundling, tiewrapping conductors together 21

22 IV.) Applying/Installing Comm/Data/Coax SPDs Application UL 497 Common Configurations Installing Comm/Data SPDs Coax SPDs Cascading Coax: Avoiding Ground Loops 22

23 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

24 Comm, Data & Coax SPDs Series Connected: Common Configurations: Inductor, Resistor, Coaxial GDT, etc. X 1 L (Inductance) Y 1 Surge Operation: High Frequency Normal Operation: L Parallel Connected: GDT, MOV, SAD, etc. Impedance such as Inductance X 1 V X 2 Unprotected Side GDT SAD Load Protected Side Common (Ground) 24

25 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

26 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

27 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

28 V.) Grounding & Bonding Inductive Effects of Earthing/Grounding Bonding Systems Together Isolated Grounds 28

29 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

30 Grounding, Bonding and SPDs Examples Showing Affects of Inductance on Grounding 60Hz Grounding Fault Current shares approx equally 60 Hz Grounding During Surge Surge Current affected by inductance; Does not share well Revised 60 Hz Grounding During Surge Surge Current Less affected by inductance Geometry affects sharing Research suggesting that only first 30m of ground conductor is effective 30

31 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

32 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

33 Thank you for your time 33