Singapore Industrial Automation Association

Presented by:

Eric Lim

LAC Power Solution Asia Pacific Pte Ltd

Dr Tan

SysEng Pte Ltd

2

Agenda• Introductions

• Surge 101 – The Basics of Surge Protection

– Transient Overvoltages – Causes and Effects

– How a SPD/TVSS works

– Industry Standards

• Specifying SPD’s

• Summary

• Questions

Who Needs SPDs:

• Realistically – Everyone

Hey Doc, which teeth should I floss? Just the ones you want to keep.

Surges are like termites: Either you have them now, or you’re going

to.

• Anything with electronics needs SPDs

• How can I tell if an SPD will help?

Increased run times on equipment and reduced equipment failure.

• How can I monitor for surges?

Reality: Accurately monitoring transients requires high resolution

scopes, lots of memory, high grade CTs, skilled labor, substantial

cost, and still have opportunity to not catch the problem.

Almost always less expensive to install token SPD and try it, as

opposed to bringing in test equipment

3

4

What Is a Surge/Transient?

• High amplitude, short duration overvoltage

• Can be positive or negative polarity

– Transient: > two times system’s RMS voltage

– Noise: < two times system’s RMS voltage

Transient Overvoltage –Can be thousands of volts

Millionths of second

I

5

What Causes Surges/Transients?

• Lightning

• Switching:

– Load Switching – utility & customer

• Motors, Large Loads, Faults, Fuse

Operation

– Source Switching

• Smart Grid, Gensets, PV, Wind Turbine

• Internally generated surges: ≈70%

• Externally generated surges: ≈30%

Causes of Surges• Industrial equipment

• Arcing & Flashover

• Vegetation

• Animals

• Unexpected

7

Effects of Transient Voltages?

• Microelectronics Intolerant to Surges

• Disruption

– Lockups, Downtime & Interruption costs

– Computing glitches and errors

• Degradation

– Microelectronics

– Slow & continuous damage to motor insulation

• Destruction

– Failed microelectronics, ballasts,

motors, controllers, etc.

8

Surge Suppressors• A SPD, TVSS or Surge Suppressor will Not effectively

control:

– Utility “swells” lasting several cycles

– Utility “sags”

– Harmonics

– Certain noise problems

– Not a substitute for Lightning Protection System

– Will not save energy or lower utility billing

9

SPD Building Block Technologies

• Metal Oxide Varistor (MOV) (parallel)

– Tend to be most robust

• Silicon Avalanche Diode (SAD) (parallel)

– Data/telecom – fault current limitations

• Selenium cell (parallel)

– Outdated – toxicity

• Gas discharge tube (parallel)

– Initial clamp is high

• Capacitor (parallel)

• Inductor (series)

• Hybrids (varies)

10

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

11

MOV - Metal Oxide Varistor • Overvoltage diverts through MOV as current

• Voltage is “clamped” or “equalized” as energy is transferred to other side of

MOV(s)

• MOV does not ‘absorb’ surge, however, I2R heat is retained

• Bidirectional – Operates same for positive or negative surges

• Creates a momentary short-circuit to pass transient energy to earth;

+-

+ -

12

SPD/TVSS Terminology• Let-through voltage, clamping voltage, suppressed voltage, measured

limiting voltage (measured in Vpeak)

• Surge current, peak-amp current, maximum current, (measured in

Imax)

• MCOV - Maximum Continuous Operating Voltage of the electrical

system (measured in Vrms)

Load

Surge Current

(thru SPD)

MOV/SPD

Clamping or

Let-Through

Voltage

MCOV

13

SPD/TVSS Terminology

MCOV

Most 120V SPDs use

150 MCOV MOVs

Most 277V SPDs use

320 MCOV MOVs

Most 480V SPDs use

550 MCOV MOVs

MCOV

120V

277V

480V

• MCOV - Maximum Continuous Operating Voltage of the electrical system

• Below MCOV – MOV is open (not conducting)

• Above MCOV – MOV conducts – ’turns on’ or ‘clamps’

• Measured in Vrms (Vdc rating too)

– MCOV too low:

premature SPD failure

– MCOV too high:

inadequate protection

14

SPD Operation

MOV/SPD Acts as a momentary ‘short circuit’

‘short circuit’ ≈ no overvoltage ≈ protected load

Load 1

Load 2

Load 3

15

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, tie-wrapping conductors together

16

Modes of Protection

• MOVs equalize potential

across either side of MOV

• Various ways to connect MOVs

• IEEE recommends defining modes: L-N, L-G, N-G, etc. (because ‘Common Mode’ and ‘Normal Mode’ mean different things to different folks)

17

SPD/TVSS Terminology

• Surge Current

– Normal operation - Current through MOV/SPD while conducting a surge – tends to be momentary

• Fault Current

– Failure condition - Current through MOV/SPD when it has failed in a short-circuit condition – tends to be continuous

• Two totally different currents

• A transient doesn’t know if its entering 4,000A switchgear or a 100A panel.

• Fault current is based on the distribution system, not surge transient.

18

Surge Current vs. Fault Current

Load

MOV/SPD

Surge Current - Momentary

MOV/SPD

Fault Current – Drawn by Failed SPD - Continuous

SPD fails short-circuited and draws

Fault Current

Load

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Standards, Codes, Practices, and

Guidelines for Low Voltage SPDs

• IEEE Trilogy

– C62.41.1 & C62.41.2 - 2002 Best Practices

– C62.45 - 2002 Test Procedures

• Importance of UL 1449

– Safety & failure testing

– Performance testing - clamping voltage and pulse life

– Third Edition, Second Edition Revision, Second Edition

• USA National Electrical Code 2002, 2005 & 2008

• IEC EN61000-4-4 & EN61000-4-5

• CP33 ???

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Flash Density: Flashes/km2/year

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• It takes 10kV to push a 10kA surge, 10 meters• It takes 27kV to push a 10kA surge, 30 meters• It takes 45kV to push a 10kA surge, 50 meters

Voltage becomes so high

that it flashes over

upstream

10,000V

27,000V

45,000V

A B C

Panel

L - slight inductance of wire

10m

30m

50m

How Large are Surges?

IEEE Research

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IEEE C62.41.2 - 2002“Expected voltages and current surges”

Location Categorya

Peak Valuesd Effective Impedance ()

Voltage(kV)

Current(kA)

A 6 0.5 12f

B 6 3 2

Table 3 – Standard 1.2/50s – 8/20s Combination Wave

Expected voltages and current surges in Location Categoriesa A and Bb

Single-phase modesc : L-N, L-G and [L&N]-G

Polyphase modes: L-L, L-N, L-G and [L’s]-G

(See Table 5 for N-G modes)

Table 4 – Scenario I tests for SPDs intended for Location Category C3

Exposure

Standard tests Optional test

1.2/50µs Voltage generator 8/20µs Current generator

100kHz Ring Wave for front-of-wave response

evaluationMinimum open-circuit voltage

to be applied to SPDCurrent to be driven through

the SPDb

Low 6kV 3kAc 6kV

High 10kV 10kA 6kV

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IEEE C62.41.2 - 2002

Cat C High: 10kV, 10kACat B: 6kV, 3kA

Cat A: 6kV, 500A

Tidbits:

- Wallplug flashes over at about 6kV

- Incandescent light fails at about 1500A surge

Watch Outdoor Loads that might

‘convert’ to Cat C High: 10kV,

10kA

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Cascade Protection

Trans

Meter

Svc.

Disc.

Panel

10m (30feet)

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SPD/MOV Failures• Industry Issues – Lot of UL & NEC action

• MOV is a sacrificial element - will protect load or die trying

• Failure caused by:

Sustained Overvoltage - TOV

(Can be as few as 2-3 cycles)

Sequence: MOV protects, fails, fails short, follow-on fault current causes MOV to catastrophically overheat

Typical causes:

– Loss of neutral

– Loss of phase (ungr. wye-delta)

– Incorrect installation

– 120V SPD on 277V system

– Cross Phase with L or N

– Improper application

– Ungrounded or impedance ground

– Genset related

A-G B-G C-GA-N B-N C-N

Ground

SPD chases L-G overvoltage

A-G B-G

SPD Damage from Missing N-G Bond(Enter for Animation)

Only L-G affected,

Not L-N

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The Pin represents the system’s Neutral Bonding to Ground. If N-G Bond is made, the

electrical system has a fixed reference to ground. The system will not ‘move’, from

instability, resonance, arcing, etc.

System voltages remain stable. A ground fault

trying to short a Phase to Ground will Not skew

the system. I.e., L-G voltages do not

change. (Enter for More Animation)

If N-G Bond is NOT made, the system

becomes Ungrounded.

SPD

Ungrounded systems are inherently unstable. Nothing ‘holds’ or

‘stabilizes’ the system. If/when something happens, the system

‘moves’ and L-G voltages will fluctuate. The SPD will attempt to

control these until the SPD’s L-G mode(s) fail.

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Typical Sequence of SPD Failure

Load

MOV/SPD

If extremely rapid

overheat, and ruptureIf overheats ‘slowly’

– can catch fire

System level Sustained Overvoltage – TOV Voltage exceeds MCOV – as little as 2-3 cycles

MOV fails towards short circuit

Follow-on/fault current causes MOV to catastrophically overheat

UL 1449

• UL 1449 is the industry safety standard

• End of life testing

– Why? SPD/MOV failure

• Assigns performance ratings for comparison

• UL 1449 Second Edition effective Aug 98

• UL 1449 Second Edition Revision adds Intermediate Fault Current

testing, released and effective Feb 07

• UL 1449 Third Edition released & effective Sept 09

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UL 1449 THIRD Edition

SPD

TVSSSurge

Arresters

• New SPD Types: Types 1, 2, 3 & 4

• New Voltage Protection Ratings (VPRs) replace

old-style Suppressed Voltage Ratings (SVRs)

• New I nominal ratings

• Bid Specifications become Obsolete as product

evaluation & ratings change

(Major huge expensive big deal to manufacturers!)

Combine TVSS and Surge Arresters into one UL

Standard, UL 1449 3rd Edition renamed:

Surge Protective Devices (SPDs)

Effective: Sept 29, 2009

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UL 1449-3Nominal Discharge Current Testing – I nominal, InNew Concept to USA – Originated from IEC 61643

- Duty Cycle Testing

- 15 8x20s surges through every mode of three samples used for VPR

testing

Type 1 – 20kA or 10kA

Type 2 – 20kA, 10kA, 5kA or 3kA

Type 3 – 3kA

Type 4 – Based on intended usage as Types 1, 2 or 3

UL 96A Master Label requires 20kA In from Type 1 or Type 2

SPD

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UL 1449-3 VPR & I-nominal testing

time

VPR Benchmark

3kA clamp

voltage tests

30 minute rest

Apply

MCOV

voltage

1 minute

interval

1 minute

interval

1 minute

interval

1 minute

interval

1 minute

interval

ManufacturerDecl

ares MCOV

Record Clamp

Voltage

30 minute rest

Apply

MCOV

voltage

1 minute

interval

1 minute

interval

1 minute

interval

1 minute

interval

1 minute

interval

Apply

MCOV

voltage

1 minute

interval

1 minute

interval

1 minute

interval

1 minute

interval

VPR

Verification 3kA

clamp voltage

tests

Must be within

10%

I-nominal: 15 hits; size declared by manufacturer:

Type 1: 20kA or 10kA

Type 2: 20kA, 10kA, 5kA or 3kA

Less than 10%

EMC Directive 89/336/EC

Immunity to Fast Transients

• EN61000-4-4

• The Severity Level depends on the

environment.

• The equipment tested must not show

any change in its normal operation .

• Test levels for burst tests

Level mains supply lines I/O lines

1 500V 5kHz 250V 5kHz

2 1000V 5kHz 500V 5kHz

3 2000V 5kHz 1000V 5kHz

4 4000V 2.5kHz 2000V 5kHz

Test Levels

Immunity to Lightning Transients

• EN61000-4-5

• The Severity Level depends on the

environment.

• The equipment tested must not show

any change in its normal operation .

Immunity to Lightning Transients

Severity

Class

Test Voltage Environment

1 0,5K V Highly Protected

2 1 KV Protected

3 2 KV Normal Industry

4 4 KV Heavy Industry

X Especial Special Locations

IEC vs. UL and IEEE• Promotes the 10x350 impulse

– Evolved from a 10 Coulomb charge

– Uses ramp up or pre-conditioning test

• IEC believes 100% of lighting can enter a building and go through wire

• IEC says grounding is different and overhead lines are more vulnerable to lightning

• More concerned with protecting the switch gear not sensitive equipment

• 10x350 waves requires a different technology

– Spark gap type arrestors

– Questionable clamping and protective abilities

• Promotes the 8X20 impulse

– No pre-conditioning

– Just “whack” it with the

surge

• IEEE say natural inductance of

wire limits surges

• Lightning Protection and Surge

Protection are cousins, not

brothers

• More concerned with protection

sensitive equipment along with

the switchgear

• IEEE and UL SPDs tend to clamp

lower

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IEC vs. UL and IEEE

• There is great debate on IEC vs. IEEE

– Politics coming into play??

• IEC’s 10x350 wave is >700 times larger than IEEE experiences

– IEEE may be off by a little but not 700X!

• Spark Gap IEC units can handle a lot of energy

– Moving surge current is not the same as clamping low enough to

protect loads, ex. Clamping voltage could be 1000++ volts

– Load dies while SPD survives

• North American UL only cares about safe failure

– European surge manufacturers have difficulty passing UL

– Safety aspects are far behind UL

• The debate is not likely to end anytime soon…

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40

• Could be Biggest Myth in all of Surge Suppression

• Tends to falsely imply protection from events not demonstrated to occur

– IEEE: surge amplitude is limited

• Driven by Marketing:

– Used for spec posturing to exclude safer SPDs from specs

– Creates aura for needing larger SPDs. When LS-1 was written in 1992, a big TVSS was 30kA; now 500kA-1000kA

• Moving surge current not the same as reducing voltage to a survivable level

• Tests purposely do not show 10,000 – 20,000V clamping voltages.

– Most folks would figure out load died at least 9,000V ago

• Few grounding systems can ‘earth’ claimed ratings

• Can argue that fusing compromises associated with Single Impulse led to safety problems resulting in UL and NEC actions.

Single Impulse Testing

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Applying SPDs

• Effective Facility Protection - Factors to Consider

• Positively ID the Electrical System (480V 3phase isn’t enough)

• Proximity on Electrical Grid

• Proximity in Facility (Service is different than downstream)

• Modes of Protection

• Cascading SPDs

• Locating & Placement of Suppressors

• Grounding/Bonding SPDs

• Installed Clamping Voltage (Short Leads)

• Redundancy = Longevity (kA ratings for redundancy & longer life – to a point)

• Power + phone/data/network = Complete Protection

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Factors to Consider

• Utility Service

– Overhead or Underground

– Line Switching / Cap Banks

– End of Line (transmission line effects & reflection)

• Structure Location

– Height

– Rural / Urban

• Facility Equipment

– Expense to Repair

– Mission Critical

– Sensitive

Voltage

momentarily

doubles at

end of line

44

Thank you for your time