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

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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

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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

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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

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Safety, UL 1449-3 & NEC

SPD

TVSSSurge Arresters

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

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

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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 circuitFollow-on/fault current causes MOV to catastrophically overheat

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• 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 failuresTechno-babble

For Engineers,

By Engineers

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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!)

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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

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Surge Environment based on Location within electrical distribution system

IEEE C62.41.2-2002 Categories & Surge Environment

Trans

MeterSvc. Disc.

Panel10m (30feet)

Cat C – 10kA

Cat B – 3kA

Cat A – 0.5kA IEEE Categories

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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

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Amber Alert

12

Trans

MeterSvc. 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/Line2.) Traditional Building?3.) Inductance Limits Propagation4.) 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 Structure3.) Inductance Limits Propagation4.) 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?

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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

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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

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Phase A

Neutral

Ground

SPD

N-G C-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)

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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.

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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 MOVUL 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)

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Advanced Protection Technologies(800) 237-4567

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