Reducing Arc Flash Hazard in 3Ø Pad Mounted Transformers

and Other Safety Considerations

Presented at Western Energy InstituteOctober 12, 2010

Christian OuimetERMCO Regional Sales Manager

2009 Arc Flash Regulations

Factors affecting risk include: Proximity Duration Arc in confined space or open air

Must provide Personal Protective Equipment (PPE) to workers based on severity of arc flash energy

1.2 cal/cm2 is threshold for 2nd degree burn PPE requirements are intended to limit burns to

“just curable” 2nd degree

PPE Categories

PPE Categories Category Heat Generated PPE Required

0 ≤ 2 cal/cm2

Long sleeve shirt Long pants Safety Glasses Non-melting untreated natural fiber

1 ≤ 4 cal/cm2

FR long sleeve shirt FR pants with a minimum arc rating of 4 OR Long pants - untreated denim cotton blue jeans of 12oz/yd2 OR FR coveralls - arc rating of 4 instead of FR shirt and pants Hard Hat

2 ≤ 8 cal/cm2

In addition to items listed in Category 1, use Face shield with a minimum arc rating of 8 Wrap-around guarding for forehead, ears and neck Could use flash hood suit

3 ≤ 25 cal/cm2

Cotton undergarments Non-melting long sleeve shirt and pants FR shirt and pants FR coveralls Hearing protection Safety glasses or goggles Hand protection Foot protection

4 ≤ 40 cal/cm2

Cotton shirt and pants FR shirt and pants Flash suit and hood Hearing protection Safety glasses Hand protection Foot protection

Dangerous > 40 cal/cm2 No safe protection

The Arc Flash categories, the heat generated, and the PPE required by NESC for each category is listed in the following chart:

Typical PPE

Category 0 Category 1 Category 2

Category 3

Category 4

What Category are Distribution Transformers?

IEEE provides a resource Arc flash calculations per IEEE 1584-

2002: “Formula for Estimation of Arcing Short Circuit Current”

ERMCO engineers calculated arc flash Published a paper to show others how

to use IEEE 1584-2002 ERMCO conducted arc flash testing

Confirm IEEE 1584-2002 is a good approximation

3Ø Pads Arc Flash Summary

As a rule of thumb, most 300kVA and larger three phase padmount transformers fall into PPE Category 3 or higher.

7200V Primary - 208GrdY/120V Secondary 1" conductor gap 18" working distance Assumes infinite buss

Dual Sensing Bayonet Fuse

Dual Element Bayonet Fuse

Current Sensing Bayonet Fuse

Low Voltage Circuit Breaker HV Switch Dry Well Canister

(CL Fuse)

Fuse PPE

Category Fuse PPE

Category Fuse PPE

Category Breaker PPE

Category Switch PPE Category Fuse PPE

Category kVA %IZ

75 2.00 358C05 2 108C04 1 353C06 1 6 2 E06 2 6 3

112.5 2.00 358C08 Dangerous 108C06 3 353C06 1 7 4 E10 3 12 3

150 2.00 358C08 4 108C07 Dangerous 353C08 1 8 0 E12 3 18 3

225 2.00 358C10 Dangerous 108C09 Dangerous 353C10 4 N/A N/A E18 4 20 4

300 2.00 358C10 Dangerous 108C09 Dangerous 353C10 3 N/A N/A E25 Dangerous 25 Dangerous

500 2.00 358C12 Dangerous 108C12 108C14

Dangerous 353C12 Dangerous N/A N/A E30 Dangerous 50 Dangerous

750 5.75 358C14 Dangerous Dangerous 353C14 Dangerous N/A N/A E50 Dangerous 80 Dangerous

1000 5.75 358C14 Dangerous N/A N/A 353C16 Dangerous N/A N/A N/A N/A 100 Dangerous

1500 5.75 358C18 Dangerous N/A N/A 353C17 Dangerous N/A N/A N/A N/A N/A Dangerous

2000 5.75 361C05 Dangerous N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A

2500 5.75 361C05 Dangerous N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A

3Ø Pad Mounted Distribution Transformers

Widely used in Electric Utility Industry

Typically: Secondary conductors

are open to the air Tight working conditions

Compartment does not lend itself to working in bulky clothing

Typical Industry Standard Low Voltage Box Compartment

Three Phase Pad Mounted Distribution Transformer

ARC FLASH TESTING June 23, 2009

Ferraz Shawmut

High Power Laboratory

Newburyport, MA

Distribution TransformerArc Hazard Case Study

Distribution TransformerArc Flash Hazard Case Study

Common Industry Transformer Application

500 kVA 12470GrdY/7200 Primary 480Y/277 Secondary Most commonly specified fuse

protection for kVA size, 353C12

Distribution TransformerArc Flash Hazard Case Study

Full bolted fault limited only by transformer impedance

1 inch conductor gap per IEEE 1584 18 inch working distance per IEEE

1584 Low Voltage Terminal Arrangement per

IEEE Std. C57.12.24-2004 Figure 11(a) Minimum Dimension

Inside the Box

Inside the Box

ERMCO’s DesignOutside the Box

Made in the USA

Results

Table 3

Summary of Arc Flash Calculations and Tests

Enclosure

Configuration

Box or Open

Predicted Incident

Energy Cal/cm2

Recorded Maximum

Incident Energy

Cal/cm2

Box Configuration 11.87 12.36

Open Configuration 8.01 5.58

Percent Reduction in Incident Energy

33% energy reduction

55% energy reduction

Arc Flash and ERMCO’s Open Cabinet 3Ø Transformer

Arc flash regulations are intended to protect people from serious injury.

ERMCO is not suggesting in any way to minimize safety protection or procedures.

The ERMCO cabinet does offer enhanced safety over traditional “box” cabinets.

ERMCO COMMON SENSE Safety Features

Increased working space

Enhanced air flow helps cool workers in heavy clothing

ERMCO COMMON SENSE Safety Features

Side and top can be moved away from the bushings

No side or top for a lineman to accidentally touch a tool against

With no side or top to ground against, the surface to initiate an arc is removed

ERMCO COMMON SENSE Safety Features

Conditioned edges to prevent tears in clothing and skin

ERMCO COMMON SENSE Safety Features

Improved visibility

Tested at 35 times brighter!

0

100

200

300

400

500

600

700

Inside HV Cabinet Inside LV Cabinet

3-Phase Pad Transformer Light Density Results

ERMCO Standard Cabinet

Traditional Cabinet Painted Gray

Traditional Cabinet Painted Green

Improving Transformer Safety

ERMCO 3Ø has opening top & sides 55% reduction in arc flash energy Fewer ground planes Increased working space Enhanced air flow helps cool

workers in heavy clothing Improved visibility

Metal edges are rounded to prevent clothing tears & cuts

ERMCO’s Three Phase Pad TransformerIt’s a Good Thing!

www.ermco-eci.com

ERMCO P. O. Box 1228

Dyersburg, TN 38025-1228800-238-5587731-285-9121Made in USA

Think Think SafetySafetyThink Think

SafetySafety

Good Things Happen When You Think Outside the Box!