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Optical Arc Flash Protection and Installation Experience

Boris A. Vega

Regional Sales Manager, ABB Inc.

MEMSA Annual Meeting and Technical Symposium

September 4, 2008

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Discussion Topics

Arc Flash Hazards – Cause, Effect, Energy Levels and PPE.

Optical Arc flash protection.

Reducing Clearing Time and Comparison of Mitigating Options.

Optical Arc Protection Case Study and Conclusions.

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5 to 10 arc flash accidents occur daily in the United States

Capshell, Inc. - Chicago based research firm

specializes preventing workplace injuries and death

“One large utility has discovered an average of 1 arc-flash injury every 18 months for the past 54 years.”

IEEE Std 1584 – 2002, 10.3

Arcing Incidents Do Happen

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Hot gases, melt drops and thermal radiation may cause damage even farther away

A rapid temperature rise may lead to a violent explosion

Toxic chemical compounds may be formed at high temperatures

An uncontrolled arc causes

Arc Flash Hazards

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Arc Flash Hazards

Electric Arcs can reach temperatures of 34,000˚F.

The arcs can vaporize metal, burn skin, and ignite clothing.

Vaporized copper expand 67,000 times in volume.

High pressures can develop in enclosures, causing covers and molten metal to fly.

The intensity of an arc may exceed normal office lighting by 2,000 times.

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Causes of Internal Arc Faults

Failure to follow operating procedures.

Tools, foreign objects, rodents, etc.

Gradual component or insulation breakdown due to ageing.

Improper maintenance.

Operation outside the rating envelope.

Mechanical and interlock failures.

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Breaker Racking Arc Accident

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When?

With operator workingin the switchgear, 65%

Without operator,25%

With operator in front of a closed door, 10%

Arc Flash Hazards

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Arc Flash Accident

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NFPA Hazard Levels

Hazard Risk

CategoryTypical Personal Protective

Equipment (PPE)

Required Minimum Arc

Rating (cal/cm2)

0

Non-melting, flammable materials with at least 4.5 oz/yd2

N/A (1.2)

1 FR pants and FR shirt, or FR coverall 4

2 Cotton underwear, plus FR shirt and FR pants

8

3

Cotton underwear, plus FR shirt and FR pants and FR coverall 25

4

Cotton underwear, plus FR shirt and FR pants and multilayer flash suit

“Moonsuit” 40

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Typical PPE Suit Requirements

0 1 2 3 4

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Clearing Time is Critical

IEEE 1584™ Final Step in Incident Energy Calculation For applications up to 15 kV

For applications above 15 kV

x

x

nf D

tECE

610

2.0

251012.5

D

tVIxE bf

where:

t = arcing time = relay time + breaker time

cal/cm2

cal/cm2

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Clearing Time is Critical

Time Overcurrent protection can take several cycles even seconds to operate

0

5

10

15

20

25

30

35

ArcFlash

System

Diff (87)

Inst OC(50)

TOC (51)

Min (ms)

Max (ms)

Operating Time (ms)

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Optical Arc Flash Protection

Detects light flash

Supervised by current Tripping normally requires both light and fault current

First generation – Introduced in the early 1990’s Uses single-point light receptors (lens sensors)

Second generation – Introduced in 1999 Uses “long fiber” continuous optical sensors

Extremely fast – typical 2.5 ms operating time

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Typical Optical Fiber Sensor Routing

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Effect of Reduced Clearing Time

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Reducing Relay Time

Temporary instantaneous settings for faster operation (+) Fairly fast (about 2 cycles)

(+) Inexpensive to implement

(–) Activation requires operator action

(–) Normal coordination may be sacrificed

(–) Failure to deactivate could result in undesired tripping

Install high impedance bus differential protection (+) Fairly fast (about 2 cycles)

(–) Requires CTs on all circuits… expensive to implement

(–) Concerns with CT saturation

(–) Cannot protect feeder cable zone areas

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Reducing Relay Time

Install zone interlocking scheme (+) Fairly fast (5 -10 cycles); some delay required for blocking

(+) Inexpensive to implement

(–) Requires communication between devices

Install dedicated optical arc flash protection (+) Ultra fast (2.5 ms or 0.15 cycles)

(+) Fairly inexpensive to implement

(+) No coordination with downstream devices required

(+) Can support sectionalized arc flash zones and circuit breaker failure schemes

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Arc Flash Relays – Case Study

Detromovice Power Plant – Czech Republic – June 26, 2002 Closed breaker racked in (mechanical interlocks bypassed) Minimal damage

Soot damage – confined to the affected frame Breaker rosette connectors replaced, breaker cell cleaned No injuries!

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Arc Flash Relays – Case Study

Fertilizer plant – Uusikaupunki, Finland – 2003

Event occurred one day after arc flash relay installed

Event resulted from operation error Disconnect switch failed to interrupt capacitive current on an

energized, unloaded cable

Fault cleared before any significant damage occurred

Plant was restored to service in about 4 hours

No injuries!

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Optical Arc Flash Relay Applications

Ideally suited to gear with sealed interrupters (vacuum, SF6) Where no exposed arcing normally takes place

Application in air magnetic gear requires study Where arcing takes place within arc chutes

Successfully tested with 1200A, 500MVA GE Magneblast™ breakers

More tests on low voltage switchgear planned

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Conclusions

Fast response is critical to minimizing arc flash hazards

Faster clearing times yields many benefits Lower incident energy

Lower hazard levels

Lower PPE levels

Optical arc flash relaying among the fastest available protection

Actual arc flash events have proven optical arc flash protection works

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Thank You