arc fault safety

19th Electrical Engineering Safety Seminar Nov.09

1) Fault Level: (System & Equipment)

Mechanical strength of the system (I peak =r.m.s. x 2.1)

3) Construction: (Operator safety)

Form of construction & Segregation

2) Current Rating:

Thermal Heating = I2t – Watts loss – Heat dissipation

Arc Fault containment

design of LV boards

Typical installation

LV Transformer Rating;

2000A /50kA @ Terminals

MSB

2000A / 50kA

11kV

415V

MV Cable (& cable fixing)??kA

CCT=2000A 50kA

Feeder CCT=??A 50kA

Fault Rating of LV system.

Standards

� AS3000 – Section 3 Selection and Installation of Wiring Systems

� 3.1.2 Selection and Installation.

Wiring systems shall be selected and installed to perform the following

functions associated with the safe design and construction and proper

operation of the electrical installation.

a) Protection against physical contact with live parts

b) Satisfy minimum current carrying capacity

c) Provide Reliability –connections and joints.

d) Provide adequate strength of supports, suspensions and fixings.

e) Suit intended use e.g. fire resistance, safety services etc.

f) Protection against mechanical damage…

Typical Cable Fixing

Stainless steal cable ties

220mm spacing

Single Core 33kA

3 Core 28kA

Singe Core 50kA

Applying the formula - Ft = (0.17 x ip2) / S

Ft = Maximum Force on Conductor (N/m)

ip = Peak Short Circuit Current (105kA)

S = Cable Diameter if cables in trefoil (0.0354mm dia)

How many stainless steel cable ties

do I need??

The Breaking Strength:

Heavy duty 316 Grade S/Steal cable tie = 1,112N (250lb)(This does not allow for impact strength or safety factor)

@50kA = 105kA Peak2 x 0.17 = 53,550Nm0.035mmDia

1mtr / 53,550Nm = 48/mtr

EN 50368:2003CABLE CLEATS FOR ELECTRICAL INSTALLATION

kA SPACING 20 mtr run = Qty

50kA = 20mm = Qty 1,000

40kA = 28mm = Qty 714

30kA = 49mm = Qty 408

20kA = 111mm = Qty 180

� Cable cleats @ 457mm spacing � 118kA peak short circuit current for 0.1 sec.

How many stainless steel cable ties

do I need??

Additions to AS/NZS 3439.1:2002

7.5.5.1.2

The conductors between busbars and the supply side of a single functional unit, as

well as the components in this unit, may be rated on the basis of reduced short-

circuit stresses occurring in the load side of the short-circuit protective device in this

unit provided that such conductors:

• are tested as part of the short-circuit test on the functional units;

• are substantial and not less than the rating of the functional units and,

in no case, less than 4.0mm² in cross-sectional area;

• are not more than 1M in length; and

•are provided with solid insulation (7.4.2.1) or shrouded in normal service to prevent

faults between phases or between phases and earth or neutral

Main Circuits Within an Assembly

Fault rating of Switchboard

Now in English

Additions to AS/NZS 3439.1:2002

50kA

+

ShortShort CircuitCircuit StrengthStrength TestsTestsconducted at TCA Sydney (Test Report 101740conducted at TCA Sydney (Test Report 101740--1)1)

�� GE MCCBGE MCCB’’s rated 160A, 250A, 400A & 630A at a s rated 160A, 250A, 400A & 630A at a

prospective fault level of 63kAprospective fault level of 63kA

Additions to AS3439.1:2002

Main Circuits Within an Assembly

Arcing Fault Video

50kA- Elsteel

Construction: Operator safety

Basics or Arcing Faults

•An arc fault has to be manually started by something creating the path of conduction, dropping a metal part or by a failure, such as a breakdown in insulation.

•Arc faults <120V (At 120 volts and below, the fault will normally not sustain an arc).

•The cause of the short normally burns away during the initial flash and the establishment of highly conductive plasma then sustains the arc fault.

•The plasma will conduct as much energy as is available and is only limited by the impedance of the arc and the overall electrical system impedance.

Arc BlastThe tremendous temperatures of the arc cause the explosive expansion of both the surrounding air and the metal in the arc path.

- copper expands by a factor of 67,000 times when it turns from a solid to a vapour.

The danger associated with this expansion is one of high pressures, sound, and shrapnel.

- The high pressures can easily exceed hundreds or even thousands of kg per square meter, knocking workers off ladders, rupturing ear drums, and collapsing lungs.

-The sounds associated with these pressures can exceed 160dB.

- Material and molten metal is expelled away from the arc at speeds exceeding 1600km/hr, fast

enough for shrapnel to completely penetrate the human body.

Arc FlashCan reach 35,000°F.

Exposure burns the skin directly and causes ignition of clothing, which adds to the burn injury.

The majority of hospital admissions due to electrical accidents are from arc-flash burns, not from shocks.

Each year people are admitted to burn centres with severe arc-flash burns. Arc-flashes can and do kill at distances of 3m.

Construction: Operator safety

Arcing Fault Video

50kA- Elsteel

Arcing Fault Video Unrestricted arcing Fault

Effects of an arcing fault

Arcing Fault Video -Operator

Australian Standards

- AS3000 change

- AS3439 Arc Fault containment

Operator & System Safety:

AS3000 - 2007 wiring RulesProtection against Arcing Faults

2.5.5 Protection against switchboard internal arcing fault currents

2.5.5.1 General

Protection against arcing fault currents while the equipment is in service, or is undergoing maintenance, shall be provided for heavy current switchboards.

NOTE: Heavy current circuits are regarded as those where the nominal supply current to the switchboard is 800 A or more per phase.


The supply conductors within the switchboard shall have additional insulation or segregated

In addition, the switchboard shall comply with one of the following:

(a) Clause 2.5.5.2 to reduce the probability of initiation of arcingfault.

(b) Clause 2.5.5.3. to limit the harmful effects of an arcing fault.(c) Both a) & b)


2.5.5.2 Reduction of the probability of the initiation of a switchboardinternal arcing fault

Heavy current switchboards shall be provided with internal separation in

accordance with AS/NZS 3439.1 for—

(a) busbars from functional units; and

(b) functional units from one another; and

(c) terminals provided for external conductors from the busbar; and

(d) a safety service circuit section of the switchboard,

NOTES:1. Separation

i.e. by the use of a Form 3b, Form 3bi, Form 3bh, Form 3bih, Form 4a, Form 4ah, Form 4aih, or Form 4b, Form 4bi, Form 4bh, Form 4bih constructed switchboard.

2. The required degree of protection, IP2X or IP1XB,


Test Report 29540 from TEST

SAFE Australia confirms degree of protection IP55

and

Internal Separation IP2X on Elsteel TECHNO

Switchboard System

Clause 8.1.1 of AS.NZS 3439.1:2002 “TYPE TESTS”Sub clause 8.1.1.(g) asks for Verification of the Degree of Protection &

INTERNAL SEPARATION

AS3000 - 2.5.5.2 Reduction of the probability of the initiation of a

switchboardinternal arcing fault

Heavy current switchboards shall be provided with internal separation in

accordance with AS/NZS 3439.1…

AS/NZ3000 - 2007 wiring Rules

In addition, the switchboard shall comply with one of the following:

(a) Clause 2.5.5.2 to reduce the probability of initiation of arcing fault.

(b) Clause 2.5.5.3. to limit the harmful effects of an arcing fault.

(c) Both a) & b)

2.5.5 Protection against switchboard internal arcing fault currents

•Protection against Arcing Faults

Switchgear


Protective devices shall limit, the harmful effects of a switchboard internal

arcing fault by automatic disconnection.

2.5.5.3 Limitation of the harmful effects of a

switchboard internal arcing fault

Protection shall be initiated, i.e. pick up at a current less than 30% of the

three-phase prospective fault level.

NOTE:

Overcurrent protective devices should be set to as low an initiation

current as possible while still maintaining the correct function of the

installation,

e.g. set higher than motor-starting currents.

Earth fault protective devices shall have a maximum setting of 1200 A.

Clearing time = Maximum operating time

AS3000 2007 Wiring RulesProtection against Arcing FaultsAddresses prevention of arcing faults.

OPTIONAL - AS3439 – Internal arcing fault

containment.

Designed to limit damage to the rest of the board. To

enable the switchboard to be returned to service.

(Down time and rectification cost)

•Designed to protect the operator



• Generally ‘ARC FAULT CONTAINMENT’ refers to LIMITED Arc Fault

Containment. (Limited to the operating time of the upstream protective device. ACB / MCCB / Fuse etc)

• The protection setting of the device is important.

• It is impossible to build a board for Unlimited arc fault containment for 1 sec.

Points to NOTE:

Design Considerations for Arcing faults

1. Impact Shock of the ionised gas:

- Blows off doors bends covers and smashes

insulating barriers.

1. Volume of Gas:

- Blows open doors and bends /breaks barriers

2. Destructive effect of the arc.

- Eats through metal and copper

3. Travelling of the Arc in the conductive atmosphere of the Ionised gas.

- Arc can travel in with the volume of gas to new conductive parts ‘EARTH’.

- Into other compartments.

- On to the line side bars creating an ‘unlimited

fault’

Design concepts

Front Door

Front Door

Internal Arcing Fault Containment

FIXED TYPE COMPARTMENTS

Safety Options

US standards - NFPA-based level of PPE required

NOTE:

The switchboard will not protect the operator if…

- The doors are opened.

- The covers are not properly fitted.

Safety options

PPE

Rack Breakers remotely

RELT setting on Breakers

Use Arc Vault type device

Standards;Switchboards: AS/NZ 3439.1 2002Switchgear AS/NZ 60947-2

Temperature RiseTemperature Rise


Max. Terminals of the device - 80K on ambient

Switchboards: AS/NZ 3439.1 2002 (Cl 7.3-Table 2.)

1050C – 70K = 350C = Max. Switchroom Ambient Temp

Switchgear AS/NZ 60947-2 (Cl 8.3.3.6-Table 7.)

1050C – 80K = 250C = Max. Switchgear Ambient Temp

Busbar and conductors…. 70K temp. …..do not exceed.1050C

Switchgear is in a

Switchboard

Standards SUMMARY


Switchboards: AS/NZ 3439.1 2002

8.2.1.3 Temperature-rise test using currents on all apparatus

….For this test the incoming circuit is loaded to its rated current and each outgoing circuit is loaded with its rated

current multiplied by the rated diversity factor.

Number of Rated diversity

main circuits factor MCCB

2 & 3 0.9 125A/113A 160A/144A

250A/225A 400A/360A

4 & 5 0.8 125A/100A 160A/128A

250A/200A 400A/320A

6 to 9 0.7 125A/87.5A 160A/112A

250A/175A 400A/280A

10 & above 0.6 125A/75A 160A/96A

250A/150A 400A/240A


IDEAL RESULT= Enclosed Rated Switchboard and Switchgear

•No de-rated main bars

•No de-rated Flex or Cu bars

•No de-rated circuit breakers

FE125A

FE160A

FE250A

FG400A

MCCB LOAD

126A

160A

250A

400A

ElsteelElsteel / GE Testing/ GE Testing--Report No. TRReport No. TR--0808--0505--22

Ambient

Temp 30C

Temp Rise K

700

670

700

540

Diversity

Factor

1

1

1

1

RESULTSRESULTS

Elsteel Temp. Monitoring Software

Elsteel Temperature Vision


Monitoring productsMonitoring products

arc fault safety

Documents